Titolo della tesi: Characterization of the transcriptional complexes enrolled by Yes-associated protein (YAP) in hepatoma cells and their regulation by ERK5/MAPK
The transcriptional cofactor Yes-Associated Protein (YAP) is known to be a master regulator of gene expression able to induce cellular reprogramming towards different cellular states. There is increasing evidence that the composition and genomic occupancy of YAP-recruiting transcriptional complexes may depend on tissue and cellular context, thus driving specific gene expression and different functional outcomes. Moreover, the formation of these complexes may be regulated by the phosphorylation status of the components, which depends on the activity of enzymes belonging to different signaling pathways.
Based on our recent work identifying STAT3 as a new interactor of YAP in liver cells and ERK5 as a new regulator of YAP activity, and on recent literature data showing lncRNAs as functional components of transcriptional molecular platforms, this PhD project aimed to the structural and functional characterization of YAP-enrolled transcriptional complexes also focusing on their regulation. Specifically, I have i) investigated the role of STAT3 in the YAP-dependent gene expression, ii) analyzed the mechanistic and functional role of ERK5/MAPK in the control of the assembly/activity of YAP/STAT3 and YAP/TEAD complexes and of their recruitment on DNA, and iii) evaluated lncRNAs as potential functional members of YAP-dependent molecular platforms.
Provided data demonstrated that, in hepatoma cells, i) STAT3 regulates YAP transcriptional activity by cooperating with TEAD on previously characterized YAP/TEAD target genes (i.e. Ctgf and Cyr61) ; ii) YAP/STAT3/TEAD DNA binding is dependent on ERK5 kinase activity; iii) ERK5 drives a multilevel regulation of YAP-enrolled transcriptional complex, including YAP phosphorylation. Furthermore, we gathered evidence that lncRNA Malat1 is bound by YAP and is required for YAP-target gene expression.
On the basis of these results, a model for the dynamic formation and activation of YAP/STAT3/TEAD transcriptional complex has been proposed for CTGF promoter, extendable to other YAP target genes and possibly involving other components, including lncRNAs.
Overall, our findings provided a possible paradigm of how specific partners of YAP in transcriptional complexes and their regulation by signaling pathways, can drive YAP-dependent gene expression to specific cellular outcomes. In perspective, these studies may pave the way to new translational approaches, aimed at interfering with YAP activity in pathologies where it has been found deregulated.