Characterization of the hnRNP RALY in RNA transcription and metabolism

The heterogeneous nuclear ribonucleoproteins (hnRNPs) form a large family of RNA-binding proteins (RBPs) that exert numerous functions in RNA metabolism. For example, soluble hnRNPs bind to RNAs to mediate their maturation, processing, and shuttling from the nuclear compartment to the cytoplasm. Additionally, hnRNPs might interact with chromatin to regulate the transcription and the post-transcriptional modification of nascent transcripts. RALY is a member of the hnRNP family that binds poly-U rich elements within several RNAs and regulates the expression of specific transcripts. RALY is upregulated in different types of cancer and its downregulation has been shown to impair cell proliferation. In my PhD project, I characterized RALY to interact with transcriptionally active chromatin in a transcription-dependent manner and to cause a global decrease of RNA Polymerase II (RNAPII)-mediated transcription when downregulated, without affecting RNAPII elongation rate. Through microarray analysis of RALY-downregulated HeLa cells, I detected an altered expression of numerous genes involved in transcription promotion and cell cycle regulation, including the E2F transcription factors family. Due to its relevant role in regulating the cell cycle, I focused on the proliferation-promoting factor E2F1. I demonstrated that the stability of E2F1 mRNA is reduced in cells lacking RALY expression, with a resulting reduction of E2F1 protein levels. As a consequence of RALY knock-out, HeLa cells present a slower cell proliferation compared to control cells. Finally, by crossing the list of RALY targets with the list of genes affected by RALY downregulation, I propose a positive role of RALY in regulating the fate of specific transcripts. Taken together, my results highlight the importance of RALY expression for transcription and cell proliferation.