Coordinated post-transcriptional control of oncogene-induced senescence by UNR/CSDE1

Oncogene-induced senescence (OIS) is a form of stable cell cycle arrest elicited in cells as a response to oncogenic stimulation. OIS must be bypassed for transformation, but the mechanisms of OIS establishment and bypass remain poorly understood, especially at the post-transcriptional level. Here we show that the RNA binding protein UNR/CSDE1, previously involved in melanoma metastasis, unexpectedly enables OIS in primary mouse keratinocytes that have been challenged by over-expression of oncogenic H-Ras. Depletion of CSDE1 leads to senescence bypass, cell immortalization and tumor formation in vivo, indicating that CSDE1 behaves as a tumor suppressor. Using iCLIP-Seq, RNA-Seq and polysome profiling we have uncovered two independent molecular branches by which CSDE1 contributes to OIS. On one hand, CSDE1 enhances the senescence-associated secretory phenotype (SASP) by promoting the stability of SASP factor mRNAs. On the other hand, CSDE1 represses the synthesis of the pro-oncogenic RNA binding protein YBX1. Importantly, depletion of YBX1 from immortal keratinocytes rescues senescence and uncouples proliferation arrest from the SASP, revealing multilayered post-transcriptional mechanisms exerted by CSDE1 to control senescence. Our data uncover a novel function of CSDE1, and highlight the relevance of post-transcriptional control in the regulation of senescence.