SRSF5 regulates alternative splicing of DMTF1 pre-mRNA through modulating SF1 binding

Among the three DMTF1 splicing isoforms, DMTF1 alpha acts as a tumour suppressor through promoting p14ARF expression, while DMTF1 beta exhibits an oncogenic role likely through antagonizing DMTF1 alpha. However, the molecular mechanism underlying alternative splicing of DMTF1 pre-mRNA has not been delineated. In the current study, we discovered SRSF5 as a regulatory protein binding to a region located between DMTF1 beta and alpha acceptor splice sites to promote DMTF1 beta and gamma splicing. We demonstrated that SRSF5 expression positively correlated with DMTF1 beta/alpha ratio in breast cancer samples, and ectopically expressed SRSF5 promoted the splicing of DMTF1 beta and gamma, but not DMTF1 alpha, when testing endogenous DMTF1 pre-mRNA and a reporter construct. Upon SRSF5 knockdown, we observed significantly decreased DMTF1 beta and gamma ratios of endogenous transcripts. An RNA sequence just upstream of the alpha acceptor site contains two adjacent SRSF5 binding elements, one of which overlaps with an SF1 binding site. Our mechanistic studies revealed that SRSF5 binding to both elements in this region could consign SF1 to its distal-binding sites close to the beta and gamma acceptor sites, favouring splicing of their isoforms. Overall, our study revealed SRSF5 as a key regulator to promote DMTF1 beta and gamma splicing, and consequently reduce DMTF1 alpha splicing.

Automated summary

In this study, SRSF5 was identified as a key regulator promoting the splicing of DMTF1 beta and gamma, while reducing DMTF1 alpha splicing. The expression of SRSF5 was positively correlated with the DMTF1 beta/alpha ratio in breast cancer samples.