Quaking Promotes the Odontoblastic Differentiation of Human Dental Pulp Stem Cells by Regulating the Expression of NUMB mRNA

The odontoblastic differentiation of dental pulp stem cells (hDPSCs) is the key to the repair of dental pulp tissue after irritation. Alternative splicing (AS) plays a crucial part in the physiological activities and pathological changes of stem cells. Quaking (QKI), as a well-known RNA-binding protein, can directly regulate AS of pre-mRNAs. In addition, our previous study found that QKI could positively promote hDPSCs to differentiate into odontoblast-like cells. In this study, we found that massive AS events of mRNA happened during this process through the analysis of RNA-sequencing, which NUMB mRNA took an active part in. Then, it was proved that QKI had binding sites on NUMB mRNA by bioinformatic analysis and RIP experiment. Downregulation of QKI led to the decrease of NUMB transcripts without exon 12 (NUMB-S), which was in line with the expression trends of genes involved in the differentiation. In contrast, NUMB transcripts with exon 12 (NUMB-L) increased. The expression levels of QKI and NUMB-S were significantly upregulated after hDPSCs were differentiated. Further knockdown of NUMB-S in vitro caused decreases of DSPP, DMP1, and ALP expression. In summary, we concluded that QKI might promote the above process by regulating the alternative splicing of NUMB mRNA.