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<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">Front. Immunol.</journal-id>
<journal-title>Frontiers in Immunology</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Immunol.</abbrev-journal-title>
<issn pub-type="epub">1664-3224</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.3389/fimmu.2024.1475206</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Immunology</subject>
<subj-group>
<subject>Original Research</subject>
</subj-group>
</subj-group>
</article-categories>
<title-group>
<article-title>Machine learning-based discovery of UPP1 as a key oncogene in tumorigenesis and immune escape in gliomas</article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname>Chen</surname>
<given-names>Zigui</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/1241142"/>
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<role content-type="https://credit.niso.org/contributor-roles/methodology/"/>
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<role content-type="https://credit.niso.org/contributor-roles/formal-analysis/"/>
<role content-type="https://credit.niso.org/contributor-roles/data-curation/"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Liu</surname>
<given-names>Chao</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<role content-type="https://credit.niso.org/contributor-roles/writing-original-draft/"/>
<role content-type="https://credit.niso.org/contributor-roles/data-curation/"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Zhang</surname>
<given-names>Chunyuan</given-names>
</name>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
<xref ref-type="aff" rid="aff4">
<sup>4</sup>
</xref>
<role content-type="https://credit.niso.org/contributor-roles/writing-original-draft/"/>
<role content-type="https://credit.niso.org/contributor-roles/formal-analysis/"/>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Xia</surname>
<given-names>Ying</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="author-notes" rid="fn001">
<sup>*</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/2282139"/>
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</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Peng</surname>
<given-names>Jun</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="author-notes" rid="fn001">
<sup>*</sup>
</xref>
<role content-type="https://credit.niso.org/contributor-roles/writing-review-editing/"/>
<role content-type="https://credit.niso.org/contributor-roles/supervision/"/>
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</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Miao</surname>
<given-names>Changfeng</given-names>
</name>
<xref ref-type="aff" rid="aff5">
<sup>5</sup>
</xref>
<xref ref-type="author-notes" rid="fn001">
<sup>*</sup>
</xref>
<role content-type="https://credit.niso.org/contributor-roles/writing-review-editing/"/>
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</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Luo</surname>
<given-names>Qisheng</given-names>
</name>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
<xref ref-type="aff" rid="aff4">
<sup>4</sup>
</xref>
<xref ref-type="author-notes" rid="fn001">
<sup>*</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/2173123"/>
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</contrib-group>
<aff id="aff1">
<sup>1</sup>
<institution>Department of Neurosurgery, Haikou Affiliated Hospital of Central South University Xiangya School of Medicine</institution>, <addr-line>Haikou</addr-line>, <country>China</country>
</aff>
<aff id="aff2">
<sup>2</sup>
<institution>Department of Neurosurgery, Central Hospital of Zhuzhou</institution>, <addr-line>Zhuzhou, Hunan</addr-line>, <country>China</country>
</aff>
<aff id="aff3">
<sup>3</sup>
<institution>Department of Neurosurgery, Affiliated Hospital of Youjiang Medical University for Nationalities</institution>, <addr-line>Baise, Guangxi</addr-line>, <country>China</country>
</aff>
<aff id="aff4">
<sup>4</sup>
<institution>Guangxi Engineering Research Center for Biomaterials in Bone and Joint Degenerative Diseases</institution>, <addr-line>Baise, Guangxi</addr-line>, <country>China</country>
</aff>
<aff id="aff5">
<sup>5</sup>
<institution>Department of Neurosurgery Second Branche, Hunan Provincial People&#x2019;s Hospital (The First Affiliated Hospital of Hunan Normal University)</institution>, <addr-line>Changsha, Hunan</addr-line>, <country>China</country>
</aff>
<author-notes>
<fn fn-type="edited-by">
<p>Edited by: Pengpeng Zhang, Nanjing Medical University, China</p>
</fn>
<fn fn-type="edited-by">
<p>Reviewed by: Dechao Feng, University College London, United Kingdom</p>
<p>Jindong Xie, Sun Yat-sen University Cancer Center (SYSUCC), China</p>
<p>Jinghao Sheng, Zhejiang University, China</p>
</fn>
<fn fn-type="corresp" id="fn001">
<p>*Correspondence: Ying Xia, <email xlink:href="mailto:xiaying008@163.com">xiaying008@163.com</email>; Jun Peng, <email xlink:href="mailto:xypengjun@126.com">xypengjun@126.com</email>; Changfeng Miao, <email xlink:href="mailto:miaochangfeng@hunnu.edu.cn">miaochangfeng@hunnu.edu.cn</email>; Qisheng Luo, <email xlink:href="mailto:1917@ymcn.edu.cn">1917@ymcn.edu.cn</email>
</p>
</fn>
</author-notes>
<pub-date pub-type="epub">
<day>24</day>
<month>09</month>
<year>2024</year>
</pub-date>
<pub-date pub-type="collection">
<year>2024</year>
</pub-date>
<volume>15</volume>
<elocation-id>1475206</elocation-id>
<history>
<date date-type="received">
<day>03</day>
<month>08</month>
<year>2024</year>
</date>
<date date-type="accepted">
<day>30</day>
<month>08</month>
<year>2024</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#xa9; 2024 Chen, Liu, Zhang, Xia, Peng, Miao and Luo</copyright-statement>
<copyright-year>2024</copyright-year>
<copyright-holder>Chen, Liu, Zhang, Xia, Peng, Miao and Luo</copyright-holder>
<license xlink:href="http://creativecommons.org/licenses/by/4.0/">
<p>This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.</p>
</license>
</permissions>
<abstract>
<sec>
<title>Introduction</title>
<p>Gliomas are the most common and aggressive type of primary brain tumor, with a poor prognosis despite current treatment approaches. Understanding the molecular mechanisms underlying glioma development and progression is critical for improving therapies and patient outcomes.</p>
</sec>
<sec>
<title>Methods</title>
<p>The current study comprehensively analyzed large-scale single-cell RNA sequencing and bulk RNA sequencing of glioma samples. By utilizing a series of advanced computational methods, this integrative approach identified the gene UPP1 (Uridine Phosphorylase 1) as a novel driver of glioma tumorigenesis and immune evasion.</p>
</sec>
<sec>
<title>Results</title>
<p>High levels of UPP1 were linked to poor survival rates in patients. Functional experiments demonstrated that UPP1 promotes tumor cell proliferation and invasion and suppresses anti-tumor immune responses. Moreover, UPP1 was found to be an effective predictor of mutation patterns, drug response, immunotherapy effectiveness, and immune characteristics. </p>
</sec>
<sec>
<title>Conclusions</title>
<p>These findings highlight the power of combining diverse machine learning methods to identify valuable clinical markers involved in glioma pathogenesis. Identifying UPP1 as a tumor growth and immune escape driver may be a promising therapeutic target for this devastating disease.</p>
</sec>
</abstract>
<kwd-group>
<kwd>UPP1</kwd>
<kwd>glioma</kwd>
<kwd>immunotherapy</kwd>
<kwd>machine learning</kwd>
<kwd>single-cell sequencing</kwd>
</kwd-group>
<counts>
<fig-count count="9"/>
<table-count count="0"/>
<equation-count count="0"/>
<ref-count count="30"/>
<page-count count="14"/>
<word-count count="3309"/>
</counts>
<custom-meta-wrap>
<custom-meta>
<meta-name>section-in-acceptance</meta-name>
<meta-value>Cancer Immunity and Immunotherapy</meta-value>
</custom-meta>
</custom-meta-wrap>
</article-meta>
</front>
<body>
<sec id="s1" sec-type="intro">
<title>Introduction</title>
<p>Gliomas are the most common and aggressive type of primary brain tumor, with a poor prognosis despite current treatment approaches. Understanding the molecular mechanisms underlying glioma development and progression is critical for improving therapies and patient outcomes (<xref ref-type="bibr" rid="B1">1</xref>). Recent advances in single-cell sequencing (scRNA-seq) have provided unprecedented resolution into the cellular heterogeneity of gliomas, revealing diverse populations of tumor, immune, and stromal cells (<xref ref-type="bibr" rid="B2">2</xref>, <xref ref-type="bibr" rid="B3">3</xref>). At the same time, bulk tumor sequencing has identified key driver mutations and signaling pathways dysregulated in gliomas (<xref ref-type="bibr" rid="B4">4</xref>, <xref ref-type="bibr" rid="B5">5</xref>). However, integrating single-cell and bulk tumor data to identify critical genes and pathways remains an important challenge.</p>
<p>Immune evasion is a key hallmark of cancer, where tumor cells are able to avoid detection and destruction by the body&#x2019;s immune system. Understanding the mechanisms of immune evasion in cancer is crucial for the development of effective immunotherapies, which aim to overcome these immune evasion strategies and reactivate the body&#x2019;s immune system to recognize and eliminate cancer cells (<xref ref-type="bibr" rid="B6">6</xref>).</p>
<p>In this study, we utilized diverse machine learning methods to comprehensively analyze scRNA-seq and bulk RNA sequencing of glioma samples (<xref ref-type="bibr" rid="B7">7</xref>). Through a series of advanced computational techniques, this integrative approach identified UPP1 (Uridine Phosphorylase 1) as a novel driver of glioma tumorigenesis and immune evasion. High UPP1 expression was linked to poor patient survival. Functional experiments revealed that UPP1 promotes tumor cell proliferation and invasion while suppressing anti-tumor immune responses. Additionally, UPP1 effectively predicted mutation characteristics, drug response, immunotherapy response, and immune features. These findings highlight the power of integrating single-cell and bulk tumor data from over 3,000 samples to identify critical genes involved in glioma pathogenesis. Identifying UPP1 as a tumor growth and immune escape driver suggests it may be a promising therapeutic target for this devastating disease.</p>
</sec>
<sec id="s2" sec-type="materials|methods">
<title>Materials and methods</title>
<sec id="s2_1">
<title>Data collection and processing</title>
<p>The scRNA-seq data of human glioblastoma (GBM) samples were obtained from the Single Cell Portal platform (SCP50 and SCP393) and processed using Smart-seq2. The bulk-sequencing data of human glioma samples were obtained from the TCGA (The Cancer Genome Atlas), CGGA (Chinese Glioma Genome Atlas), and GEO (Gene Expression Omnibus) databases. The current study included over 3,000 samples. The raw data from the GEO database was generated using the Affymetrix and Agilent platforms. The robust multichip average (RMA) technique accomplished the background correction and normalization. The RNA-sequencing data were obtained from the TCGA and CGGA data sites. Transcripts per kilobase million (TPM) values were created by converting the fragments per kilobase million (FPKM) values into values with a signal strength comparable to the RMA-processed values.</p>
</sec>
<sec id="s2_2">
<title>Computational analysis</title>
<p>Uniform Manifold Approximation and Projection (UMAP) function from the R package Seurat was used to depict the microenvironment cells in the scRNA-seq data. Differentially expressed genes (DEGs) between the immune cells and neoplastic cells were identified. 182 immune escape (IE) pathway genes were collected (<xref ref-type="bibr" rid="B8">8</xref>). Weighted Correlation Network Analysis (WGCNA) was performed on the TCGA glioma dataset to determine the IE-related genes (<xref ref-type="bibr" rid="B9">9</xref>). Soft threshold settings were established to ensure a scale-free topology network and generate a TOM matrix. A power of &#x3b2; = 10 was used as the parameter. Blue module genes were extracted for subsequent analysis. The intersected genes between IE-related genes and DEGs were identified. Univariate Cox regression analysis was performed on intersected genes. Machine learning, RSF (Random Survival Forests) analysis (<xref ref-type="bibr" rid="B10">10</xref>), was performed on prognostic intersected genes. Machine learning, LASSO (Least Absolute Shrinkage and Selection Operator) regression analysis (<xref ref-type="bibr" rid="B11">11</xref>), was further performed on prognostic intersected genes. The R package survminer was used to create the survival curves of UPP1-related groups. Gene Set Enrichment Analysis (GSEA) was performed on UPP1. The R package oncoPredict was used to predict drug responses related to UPP1 (<xref ref-type="bibr" rid="B12">12</xref>). GISTIC 2.0 analysis was performed on UPP1 (<xref ref-type="bibr" rid="B13">13</xref>). The R packages maftools was used&#xa0;to&#xa0;generate the mutation landscape (<xref ref-type="bibr" rid="B14">14</xref>). The R package ComplexHeatmap was used to generate a heatmap of the immune infiltrating cells calculated by TIMER, MCPcounter, and ssGSEA (<xref ref-type="bibr" rid="B15">15</xref>&#x2013;<xref ref-type="bibr" rid="B18">18</xref>) related to UPP1. The R package ComplexHeatmap was also to create a heatmap of the immune modulators related to UPP1.</p>
</sec>
<sec id="s2_3">
<title>
<italic>In vitro</italic> validation on UPP1</title>
<p>The glioma cell lines U251 and LN229 and microglia cell line HMC3 were purchased from iCell. Two siRNA sequences of UPP1 (Forward AGGCAGAGUUUGAGCAGAUTT; Forward UCAAGAAGAAACUGAGCAATT) were used to silence the expression of UPP1. Total RNA was extracted from siRNA-transfected glioma cells. The extracted RNA was then reverse-transcribed into cDNA using a reverse transcriptase enzyme. Next, the cDNA was used as a qPCR amplification template. Gene-specific primers were used to measure the abundance of target gene transcripts. The qPCR reaction was monitored in real-time, allowing for precise quantification of mRNA levels. Relative expression was calculated using the 2^-&#x394;&#x394;Ct method, with normalization to endogenous control genes. The EdU assay was employed to assess cell proliferation. Glioma cells were incubated with the thymidine analog EdU, which gets incorporated into the DNA of proliferating cells during S-phase. The stained cells were then analyzed by microscopy. The percentage of EdU-positive cells reflects the fraction of proliferating cells in the population, providing a quantitative measure of cell proliferation. The Transwell assay was used to evaluate the migratory capabilities of glioma cells. Cells were seeded onto the top chamber of a Transwell plate with a porous membrane. Cells that migrated through the porous membrane to the bottom chamber were quantified. The Co-culture Transwell assay was used to evaluate the migratory capabilities of macrophages. Macrophages were seeded onto the top chamber of a Transwell plate, and glioma cells were seeded onto the down chamber of a Transwell plate. Cells that migrated through the porous membrane to the bottom chamber were quantified.</p>
</sec>
<sec id="s2_4">
<title>Statistical analysis</title>
<p>All statistical analyses were conducted with R. Student&#x2019;s t-test and wilcoxon test were used to compare normally distributed variables and non-normally distributed data between the two groups, respectively. P &lt;0.05 was considered statistically significant.</p>
</sec>
</sec>
<sec id="s3" sec-type="results">
<title>Results</title>
<sec id="s3_1">
<title>The scRNA-seq analysis for malignant markers</title>
<p>The microenvironment cells (astrocyte, oligodendrocyte, macrophage, microglial cell, neoplastic, neural stem cell, neuron, T cell, etc.) in GBM are shown in <xref ref-type="fig" rid="f1">
<bold>Figure&#xa0;1A</bold>
</xref>. The major types of immune cells (macrophage, microglial cell, T cell) and neoplastic cells in GBM are shown in <xref ref-type="fig" rid="f1">
<bold>Figure&#xa0;1B</bold>
</xref>. The immune cells and neoplastic cells in GBM are shown in <xref ref-type="fig" rid="f1">
<bold>Figures&#xa0;1C, D</bold>
</xref>. DEGs between the immune cells and neoplastic cells are shown in <xref ref-type="fig" rid="f1">
<bold>Figure&#xa0;1D</bold>
</xref>.</p>
<fig id="f1" position="float">
<label>Figure&#xa0;1</label>
<caption>
<p>scRNA-seq analysis for malignant genes. <bold>(A)</bold> UMAP shows the microenvironment cells. <bold>(B)</bold> UMAP shows the major types of immune cells and neoplastic cells. <bold>(C)</bold> UMAP shows the immune cells and neoplastic cells. <bold>(D)</bold> DEGs between the immune cells and neoplastic cells.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fimmu-15-1475206-g001.tif"/>
</fig>
</sec>
<sec id="s3_2">
<title>WGCNA for IE-related markers</title>
<p>ssGSEA was performed on IE pathway genes to calculate the IE score. Scale-free topology model fit and mean connectivity are shown in <xref ref-type="fig" rid="f2">
<bold>Figure&#xa0;2A</bold>
</xref>. WGCNA-based gene models in the glioma dataset are shown in <xref ref-type="fig" rid="f2">
<bold>Figure&#xa0;2B</bold>
</xref>. Correlation between gene modules and IE score showed that the blue module was the most correlated among the nine gene modules (<xref ref-type="fig" rid="f2">
<bold>Figure&#xa0;2C</bold>
</xref>). Gene significance is significantly associated with module membership in the blue module (<xref ref-type="fig" rid="f2">
<bold>Figure&#xa0;2D</bold>
</xref>).</p>
<fig id="f2" position="float">
<label>Figure&#xa0;2</label>
<caption>
<p>WGCNA for IE-related genes. <bold>(A)</bold> Scale-free topology model fit and mean connectivity. <bold>(B)</bold> Waterfall plot shows the gene models. <bold>(C)</bold> Correlation between gene modules and immune escape. <bold>(D)</bold> Correlation between gene significance and module membership.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fimmu-15-1475206-g002.tif"/>
</fig>
</sec>
<sec id="s3_3">
<title>Machine learning for potent markers</title>
<p>The high IE group is related to worse survival (<xref ref-type="fig" rid="f3">
<bold>Figure&#xa0;3A</bold>
</xref>). 69 intersected genes between IE-related genes and malignant genes are identified (<xref ref-type="fig" rid="f3">
<bold>Figure&#xa0;3B</bold>
</xref>). Univariate Cox regression analysis on intersected genes showed that 21 genes were hazardous (<xref ref-type="fig" rid="f3">
<bold>Figure&#xa0;3C</bold>
</xref>). RSF analysis was performed for dimension reduction of prognostic intersected genes, which came to CD151, EFEMP2, PLS3, TMSB10, and UPP1 (<xref ref-type="fig" rid="f3">
<bold>Figure&#xa0;3D</bold>
</xref>). LASSO regression analysis was further performed for dimension reduction of prognostic intersected genes, which also came to CD151, EFEMP2, PLS3, TMSB10, and UPP1 (<xref ref-type="fig" rid="f3">
<bold>Figure&#xa0;3E</bold>
</xref>).</p>
<fig id="f3" position="float">
<label>Figure&#xa0;3</label>
<caption>
<p>Machine learning for potent genes. <bold>(A)</bold> Survival plot shows the survival outcomes in the high and low IE groups. <bold>(B)</bold> Intersected genes between IE-related genes and malignant genes. <bold>(C)</bold> Univariate Cox regression analysis on intersected genes. <bold>(D)</bold> RSF analysis on prognostic intersected genes. <bold>(E)</bold> LASSO regression analysis on prognostic intersected genes.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fimmu-15-1475206-g003.tif"/>
</fig>
</sec>
<sec id="s3_4">
<title>Prognostic value of UPP1</title>
<p>Univariate and multivariate Cox regression analysis on UPP1 and clinical factors (age, gender, IDH, 1p19q, MGMT) showed that UPP1 was an independent prognostic factor (<xref ref-type="fig" rid="f4">
<bold>Figure&#xa0;4A</bold>
</xref>). The high UPP1 group was related to worse survival (<xref ref-type="fig" rid="f4">
<bold>Figure&#xa0;4B</bold>
</xref>). Univariate Cox regression analysis on UPP1 in different glioma datasets showed that UPP1 was a hazardous marker (<xref ref-type="fig" rid="f4">
<bold>Figure&#xa0;4C</bold>
</xref>). The high UPP1 group was related to worse survival in different glioma datasets (<xref ref-type="fig" rid="f4">
<bold>Figure&#xa0;4D</bold>
</xref>).</p>
<fig id="f4" position="float">
<label>Figure&#xa0;4</label>
<caption>
<p>Prognostic value of UPP1. <bold>(A)</bold> Univariate and multivariate Cox regression analysis on UPP1 and clinical factors. <bold>(B)</bold> Survival plot shows the survival outcomes in the high and low UPP1 groups. <bold>(C)</bold> Univariate Cox regression analysis on UPP1 in different glioma datasets. <bold>(D)</bold> Survival plot shows the survival outcomes in the high and low UPP1 groups in different glioma datasets.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fimmu-15-1475206-g004.tif"/>
</fig>
</sec>
<sec id="s3_5">
<title>
<italic>In vitro</italic> validation on UPP1</title>
<p>Given the potential prognostic value of UPP1, experimental validation was performed. RT-qPCR assay showed that UPP1 expression was significantly suppressed in siRNA-transfected groups in U251 (<xref ref-type="fig" rid="f5">
<bold>Figure&#xa0;5A</bold>
</xref>) and LN229 (<xref ref-type="fig" rid="f5">
<bold>Figure&#xa0;5B</bold>
</xref>) cells. EdU assay showed that the proliferated glioma cells were significantly reduced in siRNA-transfected groups in U251 and LN229 cells (<xref ref-type="fig" rid="f5">
<bold>Figures&#xa0;5C, F</bold>
</xref>). Transwell assay shows the migrated glioma cells were significantly reduced in siRNA-transfected groups in U251 and LN229 cells (<xref ref-type="fig" rid="f5">
<bold>Figures&#xa0;5D, F</bold>
</xref>). Co-culture Transwell assay showed the migrated macrophages were significantly reduced in siRNA-transfected groups in U251 and LN229 cells (<xref ref-type="fig" rid="f5">
<bold>Figures&#xa0;5E, F</bold>
</xref>).</p>
<fig id="f5" position="float">
<label>Figure&#xa0;5</label>
<caption>
<p>
<italic>In vitro</italic> validation on UPP1. <bold>(A)</bold> RT-qPCR assay shows the RNA expression of UPP1 in different groups in U251 cells. <bold>(B)</bold> RT-qPCR assay shows the RNA expression of UPP1 in different groups in LN229 cells. <bold>(C)</bold> EdU assay shows the proliferated glioma cells in different groups in U251 and LN229 cells. <bold>(D)</bold> Transwell assay shows the migrated glioma cells in different groups in U251 and LN229 cells. <bold>(E)</bold> Co-culture Transwell assay shows the migrated macrophages in different groups in U251 and LN229 cells. <bold>(F)</bold> Statistical analysis of RT-qPCR, EdU, and Transwell assays in U251 cells. <bold>(G)</bold> Statistical analysis of RT-qPCR, EdU, and Transwell assays in LN229 cells. **, P &lt; 0.01; ***, P &lt; 0.001; ****, P &lt; 0.0001.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fimmu-15-1475206-g005.tif"/>
</fig>
</sec>
<sec id="s3_6">
<title>Functional annotations of UPP1</title>
<p>GSEA on UPP1 was performed, and immune pathways such as cytokine, chemokine, T cell activation, and macrophage activation were significantly enriched (<xref ref-type="fig" rid="f6">
<bold>Figure&#xa0;6A</bold>
</xref>). This indicates that UPP1 is intimately linked to the regulation of the tumor immune microenvironment. Drug prediction of UPP1 revealed that Dasatinib, Temozolomide, AZD5582, Fludarabine, AZD3759, and AZD8186 in the low UPP1 group had significantly higher drug sensitivity (<xref ref-type="fig" rid="f6">
<bold>Figure&#xa0;6B</bold>
</xref>).</p>
<fig id="f6" position="float">
<label>Figure&#xa0;6</label>
<caption>
<p>Functional annotation of UPP1. <bold>(A)</bold> GSEA on UPP1. <bold>(B)</bold> Drug prediction of UPP1. **, P &lt; 0.01; ***, P &lt; 0.001.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fimmu-15-1475206-g006.tif"/>
</fig>
</sec>
<sec id="s3_7">
<title>Immunological features of UPP1</title>
<p>UPP1 was significantly associated with immune modulators CD274, CD276, CD28, and ICOSLG (<xref ref-type="fig" rid="f7">
<bold>Figure&#xa0;7A</bold>
</xref>). This suggests that UPP1 may contribute to immune evasion by modulating the expression of these immune checkpoint molecules. Besides, UPP1 was significantly associated with immune cells DCs, B cells, T cells, MDSCs, Tregs, and macrophages (<xref ref-type="fig" rid="f7">
<bold>Figure&#xa0;7B</bold>
</xref>). This indicates that UPP1 may play a role in shaping the composition and function of the tumor immune microenvironment.</p>
<fig id="f7" position="float">
<label>Figure&#xa0;7</label>
<caption>
<p>Immune features of UPP1. <bold>(A)</bold> Correlation between UPP1 and immune modulators. <bold>(B)</bold> Correlation between UPP1 and immune cells. **, P &lt; 0.01; ***, P &lt; 0.001; ****, P &lt; 0.0001.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fimmu-15-1475206-g007.tif"/>
</fig>
</sec>
<sec id="s3_8">
<title>Immunotherapy response prediction of UPP1</title>
<p>ROC curves of UPP1 in four immunotherapy cohorts showed that UPP1 could effectively predict immunotherapy responses (<xref ref-type="fig" rid="f8">
<bold>Figure&#xa0;8A</bold>
</xref>). Besides, the high UPP1 group was associated with better survival in four immunotherapy cohorts (<xref ref-type="fig" rid="f8">
<bold>Figure&#xa0;8B</bold>
</xref>).</p>
<fig id="f8" position="float">
<label>Figure&#xa0;8</label>
<caption>
<p>Immunotherapy prediction of UPP1. <bold>(A)</bold> ROC curves of UPP1 in four immunotherapy cohorts. <bold>(B)</bold> Survival plot shows the survival outcomes in the high and low UPP1 groups in four immunotherapy cohorts.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fimmu-15-1475206-g008.tif"/>
</fig>
</sec>
<sec id="s3_9">
<title>Mutation characteristics of UPP1</title>
<p>The mutation landscape in the high UPP1 group is shown in <xref ref-type="fig" rid="f9">
<bold>Figure&#xa0;9A</bold>
</xref>, in which EGFR and PTEN were highly mutated. The mutation landscape in the low UPP1 group is shown in <xref ref-type="fig" rid="f9">
<bold>Figure&#xa0;9B</bold>
</xref>, in which TP53 and IDH were highly mutated. Differentially expressed mutation genes in the high and low UPP1 groups are shown in <xref ref-type="supplementary-material" rid="SF1">
<bold>Supplementary Figure 1A</bold>
</xref>, in which IDH was the top-ranked mutated gene in the low UPP1 group. Mutually mutated gene pairs in the high UPP1 group are shown in <xref ref-type="supplementary-material" rid="SF1">
<bold>Supplementary Figure 1B</bold>
</xref>. Mutually mutated gene pairs in the low UPP1 group are shown in <xref ref-type="supplementary-material" rid="SF1">
<bold>Supplementary Figure 1C</bold>
</xref>.</p>
<fig id="f9" position="float">
<label>Figure&#xa0;9</label>
<caption>
<p>Mutation characteristics of UPP1. <bold>(A)</bold> Mutation landscape in high UPP1 group. <bold>(B)</bold> Mutation landscape in low UPP1 group.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fimmu-15-1475206-g009.tif"/>
</fig>
</sec>
<sec id="s3_10">
<title>Pan-cancer analysis of UPP1</title>
<p>UPP1 expression was significantly higher in tumor and normal tissues in most cancer types (<xref ref-type="supplementary-material" rid="SF2">
<bold>Supplementary Figure 2A</bold>
</xref>). Univariate Cox regression analysis of UPP1 confirmed that UPP1 was a hazardous marker in most cancer types (<xref ref-type="supplementary-material" rid="SF2">
<bold>Supplementary Figure 2B</bold>
</xref>).</p>
</sec>
</sec>
<sec id="s4" sec-type="discussion">
<title>Discussion</title>
<p>The rapid advancement of high-throughput genomic and molecular profiling technologies has generated vast amounts of complex biological data in cancer research. This data deluge has necessitated the development of sophisticated computational approaches to extract meaningful insights and patterns from the data (<xref ref-type="bibr" rid="B19">19</xref>). Machine learning, a field of artificial intelligence, has emerged as a powerful tool to tackle these challenges in cancer research. Machine learning models can analyze multi-omics data, such as genomics, transcriptomics, and proteomics, to identify robust molecular biomarkers predictive of cancer risk, prognosis, or treatment response (<xref ref-type="bibr" rid="B20">20</xref>). This can help guide the development of personalized cancer diagnostics and therapeutics. Our integrative analysis of single-cell and bulk tumor sequencing data by machine learning identified the gene UPP1 as a critical driver of glioma tumorigenesis and immune evasion. UPP1 encodes the enzyme uridine phosphorylase 1, which catalyzes the reversible phosphorolysis of uridine and 2&#x2019;-deoxyuridine (<xref ref-type="bibr" rid="B21">21</xref>). It plays a significant role in the ubiquitin-proteasome system, which is essential for maintaining cellular homeostasis by regulating protein turnover. In the context of cancer, UPP1 is involved in various aspects of cancer development and progression, including regulation of protein homeostasis, cell cycle regulation, apoptosis and survival, angiogenesis and metastasis, and immune evasion (<xref ref-type="bibr" rid="B22">22</xref>).</p>
<p>Elevated expression of UPP1 was associated with significantly worse patient survival across multiple independent glioma cohorts. Functional studies demonstrated that silencing UPP1 in glioma cell lines reduced tumor cell proliferation and invasion, enhancing anti-tumor immune responses through increased cell recruitment and activation of macrophages. These results indicate that UPP1 plays a dual role in promoting intrinsic tumor growth and immunosuppression within the glioma microenvironment. UPP1 plays a significant role in modulating macrophage activity through several potential mechanisms: UPP1 is involved in the ubiquitin-proteasome pathway, where it tags dysfunctional proteins for degradation. By regulating protein turnover, UPP1 helps maintain macrophage homeostasis, ensuring that only functional proteins are present for critical immune responses. UPP1 can influence the production of pro-inflammatory cytokines. By degrading specific proteins involved in inflammatory signaling pathways, UPP1 may help fine-tune the macrophage response to pathogens and tissue damage, preventing excessive inflammation that could lead to tissue injury. Macrophages play a crucial role in antigen presentation. UPP1 may facilitate the processing of antigens by regulating the degradation of precursor proteins, thus enhancing the ability of macrophages to present antigens to T cells and initiate adaptive immune responses. UPP1 can affect the expression of surface receptors involved in phagocytosis. By regulating the turnover of these receptors, UPP1 may enhance or diminish the macrophage&#x2019;s ability to engulf and eliminate pathogens or debris. In response to environmental stress, UPP1 can help macrophages adapt by managing the levels of proteins involved in stress responses. This may enhance macrophage survival and functionality under adverse conditions, such as during infection or inflammation. UPP1 may interact with various signaling pathways, such as NF-kB and MAPK pathways, which are critical for macrophage activation and function. By modulating these pathways, UPP1 can influence macrophage differentiation, activation, and effector functions.</p>
<p>The identification of UPP1 as a driver of glioma malignancy is notable, as the role of this enzyme in cancer pathogenesis has been relatively unexplored. Previous studies have primarily focused on the potential utility of UPP1 as a target for cancer chemotherapy, given its involvement in the metabolism of nucleoside analogs (<xref ref-type="bibr" rid="B23">23</xref>, <xref ref-type="bibr" rid="B24">24</xref>). Our findings suggest a more fundamental role for UPP1 in regulating core tumorigenic processes, including cell proliferation, migration, and immune evasion.</p>
<p>Mechanistically, UPP1 may promote glioma progression through several potential pathways. At the metabolic level, UPP1-mediated catabolism of nucleosides could influence nucleotide biosynthesis, DNA repair, and other proliferation-associated processes (<xref ref-type="bibr" rid="B25">25</xref>). UPP1 has also been linked to regulating inflammatory signaling cascades, which could modulate the anti-tumor immune response (<xref ref-type="bibr" rid="B26">26</xref>, <xref ref-type="bibr" rid="B27">27</xref>). Through the PI3K/AKT/mTOR pathway, UPP1 overexpression also increases the production of PD-L1, which aids in inhibiting CD8+ T cells and shapes the immunosuppressive nature of the TME (<xref ref-type="bibr" rid="B27">27</xref>). Further investigation is needed to fully elucidate the downstream effectors of UPP1 that drive its pro-tumorigenic and immunosuppressive functions. It is hypothesized that PP1&#x2019;s role in nucleotide metabolism allows cancer cells to adapt their energy production and biosynthetic pathways, enhancing their survival and competitive advantage in nutrient-poor environments.</p>
<p>In addition to its prognostic significance, our analysis indicates that UPP1 expression levels could be a useful biomarker to predict other clinically relevant tumor characteristics. High UPP1 was associated with specific genomic alterations, drug response profiles, and immune infiltration patterns. The differential mutation patterns observed in the high UPP1 and low UPP1 groups may provide insights into the potential mechanisms by which UPP1 expression influences cancer biology. For example, the interplay between UPP1 and the deubiquitination of key oncogenic or tumor suppressor proteins, such as those encoded by EGFR, PTEN, TP53, and IDH, may be an important factor in cancer development (<xref ref-type="bibr" rid="B28">28</xref>). This suggests that UPP1 could be a versatile marker to help guide personalized treatment approaches for glioma patients. Notably, the expression level of UPP1 could be used as a biomarker to predict the sensitivity of cancer cells to certain drugs, such as Dasatinib, Temozolomide, AZD5582, Fludarabine, AZD3759, and AZD8186. Understanding the relationship between UPP1 expression and drug sensitivity could help develop personalized treatment strategies where the choice of drug therapy is based on the UPP1 status of the cancer (<xref ref-type="bibr" rid="B29">29</xref>, <xref ref-type="bibr" rid="B30">30</xref>). In addition, the ability of UPP1 to predict immunotherapy responses and its association with better survival in immunotherapy-treated patients suggest a complex interplay between UPP1 and anti-tumor immunity. While high UPP1 expression was generally associated with immune suppression, the improved outcomes in the immunotherapy cohorts indicate that the heightened immune response elicited by immunotherapy can overcome the suppressive effects of UPP1.</p>
<p>In conclusion, our study has uncovered a previously unappreciated role for the metabolic enzyme UPP1 as a driver of glioma malignancy. Targeting UPP1 or its downstream effectors may represent a promising therapeutic strategy for this devastating disease. Further research is needed to elucidate the precise molecular mechanisms by which UPP1 drives tumor progression and immune evasion. Investigating the downstream signaling pathways and regulatory networks of UPP1 could uncover additional therapeutic vulnerabilities. Besides, the role of UPP1 in tumorigenesis and immune evasion identified in this study may not be limited to glioma. Investigating the potential implications of UPP1 in other cancer types could uncover broader therapeutic applications. There are also some limitations of the study. While UPP1 shows promise as a therapeutic target, the study does not provide a detailed analysis of potential resistance mechanisms or how targeting UPP1 could interact with existing therapies. Besides, a real-world cohort is expected to confirm the prognostic roles of UPP1.</p>
</sec>
</body>
<back>
<sec id="s5" sec-type="data-availability">
<title>Data availability statement</title>
<p>The original contributions presented in the study are included in the article/<xref ref-type="supplementary-material" rid="SF1">
<bold>Supplementary Material</bold>
</xref>. Further inquiries can be directed to the corresponding authors.</p>
</sec>
<sec id="s6" sec-type="ethics-statement">
<title>Ethics statement</title>
<p>Ethical approval was not required for the studies on humans in accordance with the local legislation and institutional requirements because only commercially available established cell lines were used. Ethical approval was not required for the studies on animals in accordance with the local legislation and institutional requirements because only commercially available established cell lines were used.</p>
</sec>
<sec id="s7" sec-type="author-contributions">
<title>Author contributions</title>
<p>ZC: Writing &#x2013; original draft, Methodology, Funding acquisition, Formal analysis, Data curation. CL: Writing &#x2013; original draft, Data curation. CZ: Writing &#x2013; original draft, Formal analysis. YX: Writing &#x2013; review &amp; editing, Supervision, Funding acquisition. JP: Writing &#x2013; review &amp; editing, Supervision, Funding acquisition. CM: Writing &#x2013; review &amp; editing, Supervision, Funding acquisition. QL: Writing &#x2013; review &amp; editing, Visualization, Supervision, Investigation, Funding acquisition.</p>
</sec>
<sec id="s8" sec-type="funding-information">
<title>Funding</title>
<p>The author(s) declare financial support was received for the research, authorship, and/or publication of this article. Project supported by Hainan Province Clinical Medical Research Center (grant no. LCYX202410, LCYX202309) and the Hainan Province Clinical Medical Center (grant no. 0202068). National Natural Science Foundation of China (grant no. 82360259). Natural Science Foundation of Hunan Province (grant no. 2024JJ9290).</p>
</sec>
<sec id="s9" sec-type="COI-statement">
<title>Conflict of interest</title>
<p>The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.</p>
</sec>
<sec id="s10" sec-type="disclaimer">
<title>Publisher&#x2019;s note</title>
<p>All claims expressed in this article are solely those of the authors&#xa0;and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.</p>
</sec>
<sec id="s11" sec-type="supplementary-material">
<title>Supplementary material</title>
<p>The Supplementary Material for this article can be found online at: <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fimmu.2024.1475206/full#supplementary-material">https://www.frontiersin.org/articles/10.3389/fimmu.2024.1475206/full#supplementary-material</ext-link>
</p>
<supplementary-material xlink:href="Image1.jpeg" id="SF1" mimetype="image/jpeg">
<label>Supplementary Figure&#xa0;1</label>
<caption>
<p>Mutation characteristics of UPP1. <bold>(A)</bold> Differentially expressed mutation genes in the high and low UPP1 groups. <bold>(B)</bold> Mutually mutated gene pairs in high UPP1 group. <bold>(C)</bold> Mutually mutated gene pairs in low UPP1 group.</p>
</caption>
</supplementary-material>
<supplementary-material xlink:href="Image2.jpeg" id="SF2" mimetype="image/jpeg">
<label>Supplementary Figure&#xa0;2</label>
<caption>
<p>Pan-cancer analysis of UPP1. <bold>(A)</bold> Vlnplot shows the expression of UPP1 in tumor and normal tissues in pan-cancer. <bold>(B)</bold> Univariate Cox regression analysis of UPP1 in pan-cancer.</p>
</caption>
</supplementary-material>
</sec>
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