Hypoxia Inducible Factors Regulate Hypoxia-mediated Splicing

In response to oxygen deprivation or hypoxia within a cell, HIF1A and HIF2A, hypoxia inducible transcription factors are stabilized and activate gene expression programs. Activation of HIF target genes promotes cell proliferation, apoptotic resistance, metabolic adaptation, and tissue angiogenesis in normal physiologic processes but these processes can be exploited by cancer cells to promote tumorigenesis.;Recent genome-wide studies suggest that 90% of human genes are alternatively spliced, producing RNA isoforms that encode functionally distinct proteins. Thus, effective hypoxia response requires regulation of gene transcription as well as RNA splicing. Interestingly, several reports suggest that hypoxia can regulate alternative splicing; however the mechanism was not known. Although it is well established that HIFs regulate transcription during hypoxia, it was not known if HIFs could regulate alternative splicing. We hypothesized that HIFs were responsible for regulating hypoxia-mediated splicing. The following work confirmed that hypoxia regulates alternative splicing of HIF and non-HIF target genes. Moreover, we determined that HIFs, through the activation of HIF target genes, regulates transcription and alternative splicing of a subset of HIF targets. Subsequently, we found that HIFs induced the expression of CDC-like kinases which phosphorylated and activated SR protein splicing factors and that SC35 and SRp40 SR proteins regulated hypoxia-induced splicing of HIF target genes. Importantly, our findings provide a novel molecular mechanism through which HIFs regulate gene expression programs during hypoxia by regulating alternative splicing of HIF target genes. Importantly, we determined that CDC-like kinases regulate HIF-dependent tumorigenesis by regulating splicing of HIF targets. Excitingly, these findings identify a novel HIF signaling pathway that may be exploited to inhibit HIF activity in tumorigenesis.