Glioma is the most common malignant primary brain tumor, accounting for approximately 80% of all malignant central nervous system tumors. Glioblastoma, its most prevalent and aggressive form in adults, carries a five-year survival rate of only about 5.5%, whereas patients with low-grade glioma can reach ten-year survival rates of up to 90%. Under the World Health Organization grading system, higher-grade gliomas are generally associated with poorer prognosis than lower-grade tumors, yet outcomes vary substantially even among patients with the same histological grade. This variability has motivated a continuing search for molecular markers that can refine prognosis and point toward new therapeutic targets.

PCGF1, or polycomb group ring finger 1, is a member of the polycomb group proteins, which act as regulators of gene expression. Previous work has shown that PCGF1 regulates the differentiation and self-renewal of hematopoietic cells and helps maintain the stemness of embryonic stem cells. It has also been implicated in maintaining stemness in cancers such as embryonal carcinoma and oral squamous cell carcinoma, and earlier studies found that it promotes cancer stem cell self-renewal and glioma cell proliferation, suggesting it could serve as a prognostic biomarker in glioma. CCDC34, a coiled-coil domain-containing protein involved in regulating cell movement and signal transduction, had been linked to tumor growth, apoptosis, and invasion in colorectal cancer, to proliferation and metastasis in hepatocellular carcinoma, and to poor survival in cervical, pancreatic, and esophageal cancers, but its expression and function in glioma had not been reported before this study.

To find genes downstream of PCGF1, the team analyzed RNA-sequencing data from glioma cell lines with PCGF1 knockdown, available in the GEO database under accession GSE121463. After processing, 687 genes showed differential expression between the groups, with 245 downregulated and 422 upregulated. From the top 20 most significant genes, the researchers identified four that had not previously been studied in glioma, and subsequent validation experiments showed that overexpression of PCGF1 significantly increased the mRNA levels of CCDC34.

The relationship between the two proteins was then examined across multiple datasets. Analysis of mRNA expression data from The Cancer Genome Atlas (TCGA), the Chinese Glioma Genome Atlas (CGGA), and GEO revealed a positive correlation between PCGF1 and CCDC34 expression levels, and a similar relationship was detected in clinical glioma tissue samples. In laboratory experiments, overexpression of PCGF1 significantly enhanced CCDC34 expression at both the mRNA and protein levels in U87 and U251 glioma cells, leading the authors to conclude that CCDC34 is a downstream target of PCGF1 in glioma.

CCDC34 expression itself tracked with tumor aggressiveness. Across the TCGA, CGGA, and GEO (GSE43378) databases, a positive correlation was observed between tumor grade and CCDC34 expression, with grade 2 gliomas showing lower mRNA levels. In the clinical cohort, RT-qPCR analysis of tissue samples stored at −80°C showed that CCDC34 expression was significantly higher in tumors of advanced histological grade. Western blotting in five pairs of glioma tissues and adjacent paracancerous normal tissues detected upregulation of CCDC34 in the tumor samples, and taken together, the tumor grade and CCDC34 mRNA expression showed a positive correlation.

Survival analyses supported an association between CCDC34 and patient outcomes. Kaplan–Meier plots based on the TCGA, CGGA, and GSE43378 databases showed that low CCDC34 expression was associated with prolonged survival, whereas high expression correlated with shorter survival time. In the clinical cohort of 68 glioma patients, who were followed after surgery, elevated CCDC34 expression consistently correlated with reduced overall survival, with significant differences between the high- and low-expression groups. Stratified analyses by WHO grade showed that in low-grade gliomas (grades II and III), elevated CCDC34 expression was consistently associated with reduced overall survival, but no statistically significant association was observed in high-grade glioblastoma, suggesting that CCDC34 may serve as a potential prognostic biomarker specifically in low-grade gliomas. Because IDH mutation is a key favorable prognostic biomarker in gliomas, the researchers also found that CCDC34 expression is associated with IDH mutation status and that CCDC34 expression is associated with prognosis in both IDH-mutant and IDH-wild-type patients. Multivariate Cox regression analyses using the TCGA and CGGA cohorts as well as the clinical samples demonstrated that elevated CCDC34 expression was an independent predictor of poor prognosis in glioma patients, with a p value below 0.05.

Laboratory experiments then tested whether CCDC34 functionally affects glioma cell growth. Among five glioma cell lines examined (U251, U87, HS683, SHG44, and U373), SHG44 showed the highest CCDC34 expression, and stable knockdown of CCDC34 in SHG44 cells using two separate shRNA sequences significantly inhibited cell growth in MTS assays and markedly reduced colony formation. Conversely, stable overexpression of CCDC34 in U251 and U87 cells significantly promoted cell growth. Overexpression of PCGF1 in U251 and U87 cells also significantly promoted cell proliferation and enhanced colony formation. A rescue experiment tied the two findings together: PCGF1 upregulated CCDC34 protein levels, and depletion of CCDC34 in cells stably overexpressing PCGF1 led to decreased CCDC34 expression without significantly affecting PCGF1 expression. In MTS and colony formation assays, PCGF1 promoted glioma proliferation, but this effect was inhibited when CCDC34 was depleted in the PCGF1-overexpressing cells, indicating that PCGF1 promotes glioma proliferation in a CCDC34-dependent manner.

To explore potential downstream pathways, the researchers performed Gene Set Enrichment Analysis (GSEA) on TCGA and CGGA data stratified by high and low expression of PCGF1 and CCDC34, and on RNA-sequencing data from PCGF1-knockdown glioma cell lines. PCGF1 and CCDC34 expression was significantly associated with eight key signaling pathways in the TCGA and CGGA databases, and PCGF1 expression was correlated with ten pathways in the knockdown dataset. Integrative analysis of the three datasets revealed that PCGF1 and CCDC34 expression were positively correlated with hypoxia, coagulation, and epithelial–mesenchymal transition (EMT) signaling pathways. The authors note that no studies have yet revealed the involvement of the hypoxia and coagulation pathways in regulation by PCGF1 and CCDC34, and they hypothesize that PCGF1 may upregulate CCDC34 to drive glioma progression by modulating these pathways, while emphasizing that the exact mechanisms require further investigation.

The study has important limitations acknowledged by the authors. The clinical data came from samples obtained from 68 patients, which may introduce bias into the statistical results. Direct mechanistic evidence demonstrating how PCGF1 regulates CCDC34 in glioma is lacking, the underlying molecular mechanisms were not extensively explored, and there was no in vivo validation, which the authors describe as essential for definitive confirmation. The findings are therefore associations and cell-line observations rather than proof of a therapeutic target, and additional studies are needed to elucidate the regulatory mechanisms, which could potentially be targeted to improve the prognosis of glioma patients.

Subject of Research: The role of PCGF1 and CCDC34 in glioma progression and prognosis

Article Title: PCGF1 Promotes the Tumorigenesis of Malignancies Through Upregulating CCDC34 in Glioma

Article References: Chen, Y., Xiong, J., Ou, Z., Zhao, T., Li, H., Huang, J., Tian, Z., & Cao, W. (2026). PCGF1 Promotes the Tumorigenesis of Malignancies Through Upregulating CCDC34 in Glioma. Annals of Clinical and Translational Neurology, Article acn3.70559. https://doi.org/10.1002/acn3.70559

Image Credits: AI Generated

DOI: 10.1002/acn3.70559

Keywords: glioma, glioblastoma, PCGF1, CCDC34, prognosis, biomarker, cell proliferation, TCGA, CGGA, gene expression, low-grade glioma, rescue experiment