Uveal melanoma (UM), the most common ocular malignancy, is characterized by GNAQ/11 mutations.,Hippo/YAP and Ras/mitogen-activated protein kinase (MAPK) emerge as two important signaling pathways downstream of G protein alpha subunits of the Q class (GαQ/11)-mediated transformation, although whether and how they contribute to UM genesis in vivo remain unclear.,Here, we adapt an adeno-associated virus (AAV)-based ocular injection method to directly deliver Cre recombinase into the mouse uveal tract and demonstrate that Lats1/2 kinases suppress UM formation specifically in uveal melanocytes.,We find that genetic activation of YAP, but not Kras, is sufficient to initiate UM.,We show that YAP/TAZ activation induced by Lats1/2 deletion cooperates with Kras to promote UM progression via downstream transcriptional reinforcement.,Furthermore, dual inhibition of YAP/TAZ and Ras/MAPK synergizes to suppress oncogenic growth of human UM cells.,Our data highlight the functional significance of Lats-YAP/TAZ in UM initiation and progression in vivo and suggest combination inhibition of YAP/TAZ and Ras/MAPK as a new therapeutic strategy for UM.
The mechanisms by which some melanoma cells adapt to BRAF inhibitor therapy are incompletely understood.,In the present study, we used mass spectrometry-based phosphoproteomics to determine how BRAF inhibition remodeled the signaling network of melanoma cell lines that were BRAF-mutant and PTEN-null.,Short-term BRAF inhibition was associated with marked changes in fibronectin-based adhesion signaling that were PTEN-dependent.,These effects were recapitulated through BRAF siRNA knockdown and following treatment with chemotherapeutic drugs.,Increased fibronectin expression was also observed in mouse xenograft models as well as specimens from melanoma patients undergoing BRAF inhibitor treatment.,Analysis of a melanoma TMA showed loss of PTEN expression to predict for a lower overall survival, with a trend for even lower survival being seen when loss of fibronectin was included in the analysis.,Mechanistically, the induction of fibronectin limited the responses of these PTEN-null melanoma cell lines to vemurafenib, with enhanced cytotoxicity observed following the knockdown of either fibronectin or its receptor α5β1 integrin.,This in turn abrogated the cytotoxic response to BRAF inhibition via increased AKT signaling, which prevented the induction of cell death by maintaining the expression of the pro-survival protein Mcl-1.,The protection conveyed by the induction of fibronectin expression could be overcome through combined treatment with a BRAF and PI3K inhibitor.