Role of Circular RNA MMP9 in Glioblastoma Progression: From Interaction With hnRNPC and hnRNPA1 to Affecting the Expression of BIRC5 by Sequestering miR-149.

Glioblastoma multiforme (GBM) presents a significant challenge in neuro-oncology due to its aggressive behavior and self-renewal capacity. Circular RNAs (circRNAs), a subset of non-coding RNAs (ncRNAs) generated through mRNA back-splicing, are gaining attention as potential targets for GBM research. In our study, we sought to explore the functional role of circMMP9 (circular form of matrix metalloproteinase-9) as a promising therapeutic target for GBM through bioinformatic predictions and human data analysis. Our results suggest that circMMP9 functions as a sponge for miR-149 and miR-542, both upregulated in GBM based on microarray data. Kaplan-Meier analysis indicated that reduced levels of miR-149 and miR-542 correlate with worse survival outcomes in GBM, suggesting their role as tumor suppressors. Importantly, miR-149 has been demonstrated to inhibit the expression of BIRC5 (baculoviral inhibitor of apoptosis repeat-containing 5 or survivin), a significant promoter of proliferation in GBM. BIRC5 is not only upregulated in GBM but also in various other cancers, including neuroblastoma and other brain cancers. Our protein-protein interaction analysis highlights the significance of BIRC5 as a central hub gene in GBM. CircMMP9 seems to influence this complex relationship by suppressing miR-149 and miR-542, despite their increased expression in GBM. Additionally, we found that circMMP9 directly interacts with heterogeneous nuclear ribonucleoproteins C and A1 (hnRNPC and A1), although not within their protein-binding domains. This suggests that hnRNPC/A1 may play a role in transporting circMMP9. Moreover, RNA-seq data from GBM patient samples confirmed the increased expression of BIRC5, PIK3CB, and hnRNPC/A1, further emphasizing the potential therapeutic significance of circMMP9 in GBM. In this study, we propose for the first time a new epigenetic regulatory role for circMMP9, highlighting a novel aspect of its oncogenic function. circMMP9 may regulate BIRC5 expression in GBM by sponging miR-149 and miR-542. BIRC5, in turn, suppresses apoptosis and enhances proliferation in GBM. Nonetheless, more extensive studies are advised to delve deeper into the roles of circMMP9, especially in the context of glioma.