C-Myc-Driven and PRMT5-Dependent Regulation of Multiple Myeloma Cell Proliferation through TNRC6B Gene

Objective: The protein arginine methyltransferase 5 (PRMT5) catalyzes the symmetrical bimethylation of arginine residues, which plays an important regulatory role in the life process. Transcription factor c-Myc is widely proved involved in the alteration and development of tumors, while the regulatory mechanism of c-Myc-mediated gene expression has not been fully understood. In this article we try to investigate the functional role of PRMT5 and c-Myc in regulating multiple myeloma cell proliferation.

Methods: The protein and mRNA expression levels of PRMT5 in myeloma cells and normal cells were detected by Western Blot and qPCR. Lentivirally transduced shRNAs targeting PRMT5 (sh-PRMT5) was constructed using lentivirus mediated RNAi technology, and was packaged to infect MM cells to select positive colonies. The effect of PRMT5 on the proliferation of MM cells was detected by cck-8 assay. Annexin V/7-AAD double staining flow cytometry was used to detect cell survival and apoptosis rate. The expression of apoptotic suppressor gene c-Myc in sh-PRMT5 cell lines was detected by Western Blot and qPCR. Finally, double-knockdown of PRMT5 and c-myc was performed and gene expression differentiation were identified by RNA sequencing (RNA-seq).

Results: PRMT5 expression in MM cell lines (RPMI8226 and U266) was relatively high compared with peripheral blood mononuclear cells (PBMCs), which was correlated with progression-free survival (PFS) and overall survival (OS) in MM patients. After sh-PRMT5 infection to MM cell lines, puromycin selection was performed and efficient gene knockdown was evaluated by Western Blot and qPCR. After targeted silencing of PRMT5 expression, the proliferation of MM cells was decreased and apoptosis was significantly increased (P < 0.05). C-Myc protein and mRNA levels were significantly downregulated after PRMT5 gene silencing. The results showed that PRMT5 promoted the proliferation of MM cells and inhibited the apoptosis of MM cells by regulating the expression of apoptotic suppressor gene c-Myc. Subsequently, RNA-seq confirmed SMCHD1 as the common candidate target gene of c-myc and PRMT5. Therefore, we speculated that PRMT5 and c-Myc may jointly regulate TNRC6B gene to promote the proliferation of MM cells.

Conclusion: Altogether, our study not only proposed the mechanism PRMT5 and c-myc in regulating multiple myeloma related gene expression, but also provided a new strategy and theoretical basis for clinical treatment of multiple myeloma.