Role of COL6A2 in malignant progression and temozolomide resistance of glioma
Introduction
Glioma in the central nervous system (CNS) is the most common primary malignant tumor with poor prognosis, with characteristics including rapid growth, strong infiltration, high morbidity rate, high case fatality rate, high relapse rate, and low cure rate. The main current treatment regimen is excision combined with postoperative chemotherapy and radiotherapy [1,2]. Chemotherapy plays an irreplaceable role in comprehensive treatment of glioma; TMZ is applied most widely. However, in the middle and later period of treatment, sensitivity to TMZ progressively decreases in some patients, and the difficulty of radical treatment progressively increases [3]. Therefore, further exploring the molecular mechanisms for glioma acquired resistance, and seeking new biomarkers to effectively reduce glioma resistance, are significant for reducing the relapse rate in glioma patients and increasing the survival rate.
Cancer stem cells (CSCs) are a subgroup of tumor tissue correlated with radiotherapy/chemotherapy resistance and high relapse rate [4,5]. Recent studies have shown that differential expression of some gene markers was correlated to stemness of GSCs and adverse prognosis. CD133 is one of the CSCs biomarkers most frequently studied [6]. Several studies have shown that CD133 knockout could attenuate GSCs tumorigenicity [7,8]. ITGA6 is expressed in various cancer stem cells, and richly expressed on the surface of GSCs; it is regarded as a biomarker for proliferation and self-renewal of GBM stem cells and oncogenesis [9]. CD9 is a new selective biomarker for GSCs highly expressed in GSCs, and it is directly correlated to survival rate of GBM patients [10]. In addition, other molecular markers related to GSCs have been reported, such as CD15, CD44, IL6 and STAT3 [[11], [12], [13], [14]].
COL6 (Collagen, type VI) is a member of the collagen family, and is extensively distributed in various tissues [15]. According to research, COL6 is the predominant protein in the matrix of tumor cells. It is located in the blood vessels and is an interesting component of brain tumors, and it plays a crucial role in glioblastoma adhesion and growth. Moreover, it is strongly associated with an adverse prognosis for glioblastoma [[16], [17], [18]]. Assembly of COL6-dependent vascular matrix membranes is a determining factor in vascular function and tumor development [19]. COL6A2 (Collagen type VI alpha 2 chain) is one of encoder genes in the three α chains of Collagen VI; the α2(VI) it encodes and the α chains of α1(VI) and α3(VI) collagen encoded by the COL6A1 and COL6A3 genes, respectively, form the most common molecular form of Collagen VI [20]. A study found that COL6A2 was correlated to the proliferation, migration and invasion of tumors. For example, COL6A2 effectively inhibits the proliferation of human BCa_EJ cells (MGH-U1), induces the stagnation of the cell cycle at the G1 stage, and inhibits wound healing and invasion by inhibiting the activity of matrix metalloproteinase MMP-2 and MMP-9 [21]. Research demonstrates that COL6A2 is a significant gene for relapse in LGG. The LncRNAHOXA-AS2/miR-184/COL6A2 axis may serve as a crucial regulator of LGG relapse [22]. In the meantime, although the expression level of COL6A2 in GBM is dramatically elevated [23,24], its function and clinical importance in GBM remain unknown.
This study identified COL6A2 as a new prognostic factor for glioma. Expression preference, prognostic significance, and biological function of the COL6A2 gene were analyzed using gene chip datasets from the Chinese Glioma Genome Atlas (CGGA). Intriguingly, we discovered that COL6A2 not only played a key role in the malignant growth of gliomas but was also tightly associated with the tumor's TMZ resistance and immune response. These findings suggest that COL6A2 may be a new biomarker for glioma treatment resistance. The aforementioned observational findings have also been confirmed in RNA sequencing datasets from The Cancer Genome Atlas (TCGA). In addition, we identified the function of COL6A2 in many glioma cell lines. According to the data, COL6A2 plays a significant role in the malignant development of brain gliomas and may serve as a possible therapeutic target for gliomas.
Section snippets
Data downloading
Separate from the CGGA, TCGA, GEO and GETx databases, data on gene expression and clinical data were downloaded. Data on 1857 glioma specimens or paracancerous specimens were downloaded from the TCGA and GETx databases. mRNAseq_693 and mRNAseq_325 datasets were downloaded from CGGA, containing data on 1018 glioma specimens. GSE16011 and GSE23806 datasets were downloaded from GEO; GSE16011 contained data on 284 glioma or paracancerous specimens, and GSE23806 contained data on 32 glioma cell
Screening of key genes
In order to screen out prognostic genes related to glioma stemness and TMZ resistance, first, the GSE23806 dataset was downloaded from the GEO database. Glioblastoma stem cell lines (n = 27) and conventional glioblastoma cell lines (n = 32) were selected; GSC-related genes were screened out through the “limma” package in R. 12,514 genes had significantly different expression (Fig. 1A). Then, glioma-related cell lines were selected from the GDSC database; according to their IC50 value of TMZ,
Discussion
Glioma is the most common intracranial primary tumor, with high mortality rate. Due to drug resistance, GBM is the glioma with the highest malignancy [27]. Despite the combined use of precise surgery, chemotherapy, and radiotherapy, GBM patients still have very poor prognosis. Their mean life expectancy is 12–18 months; <10% survive for >5 years [28]. A study has shown that cancer stem cells (CSCs) were closely correlated with radiotherapy/chemotherapy resistance and high relapse rate [4].
Conclusion
To sum up, COL6A2 plays an important role in the malignant progression of glioma; it may be correlated to TMZ resistance, GSC and immune response. In glioma patients with higher COL6A2 expression, the sensitivity to TMZ treatment may worsen. COL6A2 expression is up-regulated in glioma tissue, it is an independent prognostic factor for glioma patients, and it is significantly correlated to clinical features such as 1p19q_codeletion_status, age, Chemo_status, grade, histology, PRS_type,
Ethics approval and consent to participate
Not applicable.
Consent for publication
All authors have agreed to publish this manuscript.
Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
Authors' contributions
XP designed the research; XP and HX performed bioinformatics analysis; JMZ, SH and JJZ performed research; JO and BX contributed to manuscript discussion; HX and JJZ wrote the manuscript; PW analyzed results; XP and PW reviewed the manuscript. All authors approved the final manuscript.
Funding
This study was supported by President Foundation of The Fifth Affiliated Hospital, Southern Medical University (No. YZ2020MS04) and The Project of Hubei Provincial Department of Education, China (No. QN202107) and Medical Scientific Research Foundation of Guangdong Province of China (No. B2022213) and Project of Administration of Traditional Chinese Medicine of Guangdong Province of China (No. 20211269).
Declaration of Competing Interest
The authors declare no competing financial interests.
Acknowledgements
Not applicable.
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Xia Hong, Jingjing Zhang and Jianmin Zou should be regarded as joint first authors