An investigation into the regulation of transcription of the splice factor kinase gene SRPK1 in prostate and leukaemia cancer cell lines

Abstract

The SRPK1 gene encodes a protein kinase that phosphorylates a class of splice factors called serine/arginine-rich proteins (SR proteins) modifying their ability to regulate alternative pre-mRNA splicing. Studies have linked high SRPK1 levels to tumour proliferation, growth and metastatic ability but little is known about how its expression is regulated. Different transcription factors including WT1 and ERG are thought to have some level of involvement in the regulation of SRPK1 transcription. The aim of this project was to study the transcriptional regulation of the splice factor kinase gene SRPK1. In this study, the regulation of SRPK1 expression was investigated in cancer cells and the results suggest that both the transcription factor WT1 and the co-repressor BASP1 are present on the SRPK1 promoter region. SRPK1 transcription is activated by WT1, but not when the WT1 binding site is mutated. Consistent with these findings, the knock- down of WT1 with siRNAs also resulted in decreased expression of endogenous SRPK1. The activity of the SRPK1 promoter in BASP1-expressing K562 cells or in PC3 cells transfected with a BASP1-expressing vector was repressed, consistent with BASP1 turning WT1 into a transcriptional repressor rather an activator. The effect of SRPK1 chemical inhibition via SPHINX and the overexpression of BASP1 on the alternative splicing of the vascular endothelial growth factor (VEGF) was also examined in this study; both SRPK1 inhibition and BASP1 expression promoted the expression of anti- angiogenic VEGF. The transcription factor ERG, on the other hand, was also shown to bind to the SRPK1 promoter but it repressed its transcription. The overexpression of ERG isoforms reduced endogenous SRPK1 expression, whereas ERG knockdown increased SRPK1 expression. Finally, following manipulation of the expression of SRPK1, WT1, BASP1 and ERG in K562, PC3 and MG63 cell lines, changes in apoptosis, cell proliferation and migration were observed, suggesting that this regulatory axis could present a valid cancer therapy target