| Popis: |
The Hippo pathway is an evolutionarily conserved signaling network that integrates diverse cues to regulate cell fate and organ homeostasis. The central downstream pathway protein is the transcriptional co-activator Yes-associated protein (YAP). Although capable of inducing gene transcription, YAP cannot bind DNA directly. Instead, it mediates transcriptional activity through interaction with distinct DNA-binding transcriptional factors (TFs), including TEAD, SMAD, and p73, to form active and functionally opposing transcriptional complexes. Growing evidence in mammals demonstrates that YAP has a dual role and can either promote cell proliferation or apoptosis, which underpin its ability to function as both an oncogene or a tumour suppressor depending on the specific context. However, the mechanisms by which YAP coordinates its distinct transcriptional complexes and mediates context-dependent function remain poorly defined. This is in part due to the lack of systems-level studies that can decrypt the complexities of upstream signalling pathways and their crosstalk, which together dictate the transcriptional regulation at the YAP level. Here, we undertake an integrative systems-based approach combining computational network modelling and experimental studies to interrogate the dynamic formation of and transition between the YAP-SMAD and YAP-p73 transcriptional complexes, which control proliferative and apoptotic gene expression, respectively. We developed a new experimentally-validated mathematical model of the TGF-β/Hippo signalling crosstalk and used this model to elucidate dynamic network behaviour. Our integrative studies uncovered previously unknown molecular switches that control the YAP-SMAD/p73 complexes in an on/off, switch-like manner. RASSF1A and ITCH were identified as major regulators of the switches, whereby a graded increase in ITCH expression can trigger YAP to abruptly switch from binding p73 to SMAD, swiftly promoting proliferative gene expression. Further, adjusting the model to reflect cell type-specific protein expression profiles using both in-house and publicly available experimental data enabled us to study the YAP switches under diverse and varied cellular contexts. Overall, our studies provide a new quantitative and systems-level understanding of the dynamic regulation of functionally opposing YAP transcriptional complexes in mammalian cells. |
