Unraveling YAP/TAZ's cytoplasmic role in cancer mechanotransduction

• Applicant: Dr. Björn von Eyss
• Subject Area: Hematology, Oncology ; Cell Biology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 546323575

A high matrix stiffness of tumors has been associated with more aggressive behavior and resistance to chemotherapy. In recent years, the Hippo signaling pathway, along with its downstream transcriptional effectors YAP and TAZ, has emerged as a key mediator of these mechanical cues such as substrate stiffness and stretching. Involved in transmitting these signals to YAP/TAZ are the kinases of the Hippo pathway, LATS1/2, as well as F-Actin and the GTPase RAP2. Through our interactomics analyses, we identified RAPGEF2 and RAPGEF6 (R2/6), also known as PDZ-GEF1 and PDZ-GEF2, as interaction partners of YAP - a direct interaction that takes place in the cytoplasm. R2/6 play an essential role as upstream regulators of mechanotransduction via the GTPase RAP2, which then acts on YAP/TAZ. Thus, it is reasonable to conclude that this cytoplasmic interaction is part of a negative feedback loop that precisely controls the interplay between mechanosignaling and YAP/TAZ activity/localization. Consistent with this hypothesis, we uncovered a differential mechanosensitive gene expression profile in cells carrying RAPGEF6 point mutations with deficient YAP/TAZ binding. This suggests a cytoplasmic role of YAP/TAZ in modulating gene expression through RAPGEF6 in response to mechanical stimuli. The focus of this proposal is to investigate the cytoplasmic interaction between RAPGEF2/6 and YAP/TAZ, with an emphasis on deciphering control mechanisms, clarifying their role in mechanotransduction, and exploring their function in vivo in development, tissue homeostasis, and cancer. One objective is to identify potential upstream regulators and downstream signaling pathways influencing the interaction of R2/6 and YAP/TAZ. These interactors will be examined for their function in relation to mechanotransduction by analyzing their functional role in cells grown under different stiffness conditions. To analyze the role of the R2/6 <-> YAP/TAZ interaction in vivo, we have generated genetically modified Rapgef2/6 mouse lines in which the interaction of R2/6 with YAP/TAZ cannot occur. These lines will be used to analyze the role of this interaction in development, tissue homeostasis, and cancer. This proposal takes a holistic approach, integrating cell biology, biochemistry, and in vivo experiments to decipher the function of the YAP/TAZ <-> R2/6 interaction. Understanding YAP/TAZ regulation in mechanoresponsive processes is valuable for gaining insights into various pathological conditions, including atherosclerosis, fibrosis, and cancer, where disrupted mechanosignaling plays a role.

• DFG Programme: Research Grants