Heterogeneous ribonucleoprotein F regulates YAP expression via a G-tract in 3'UTR

The Yes-associated protein (YAP) is a transcription coactivator that plays crucial roles in organ size control and tumorigenesis, and was demonstrated to be inhibited by the Hippo signaling pathway. To date, the molecular mechanisms regulating the expression of YAP in human cells remain unknown. In the present study, we found that hnRNP F and hnRNP U negatively regulate YAP expression. We also showed that downregulation of YAP expression by hnRNP F and hnRNP U was not at the transcriptional level. Knockdown of hnRNP F or hnRNP U increased YAP mRNA stability, suggesting the downregulation of YAP expression was by a post-transcriptional mechanism. A putative hnRNP F binding site was identified in the YAP 3'UTR at 685 to 698, and deletion of this putative hnRNP F element abolished the down-regulation effect of YAP mRNA stability by hnRNP F. Binding of the hnRNP F to the YAP 3'UTR was demonstrated by Cross-linked RNA Immunoprecipitation. mRNA stability is a possible secondary effect of alternative splicing or other nuclear process. Understanding the regulation of YAP expression would provide insights into the mechanisms underlying the maintenance of tissue size homeostasis and tumorigenesis.