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The activation of transcriptional coactivators YAP and its paralog TAZ has been shown to promote resistance to anti-cancer therapies. YAP/TAZ activity is tightly coupled to actin cytoskeleton architecture. However, the influence of actin remodeling on cancer drug resistance remains largely unexplored. Here, we report a pivotal role of actin remodeling in YAP/TAZ-dependent BRAF inhibitor resistance in BRAF V600E mutant melanoma cells. Melanoma cells resistant to the BRAF inhibitor PLX4032 exhibit an increase in actin stress fiber formation, which appears to promote the nuclear accumulation of YAP/TAZ. Knockdown of YAP/TAZ reduces the viability of resistant melanoma cells, whereas overexpression of constitutively active YAP induces resistance. Moreover, inhibition of actin polymerization and actomyosin tension in melanoma cells suppresses both YAP/TAZ activation and PLX4032 resistance. Our siRNA library screening identifies actin dynamics regulator TESK1 as a novel vulnerable point of the YAP/TAZ-dependent resistance pathway. These results suggest that inhibition of actin remodeling is a potential strategy to suppress resistance in BRAF inhibitor therapies.

Primary cilia exert a profound impact on cell signalling and cell cycle progression. Recently, actin cytoskeleton destabilization has been recognized as a dominant inducer of ciliogenesis, but the exact mechanisms regulating ciliogenesis remain poorly understood. Here we show that the actin cytoskeleton remodelling controls ciliogenesis by regulating transcriptional coactivator YAP/TAZ as well as ciliary vesicle trafficking. Cytoplasmic retention of YAP/TAZ correlates with active ciliogenesis either in spatially confined cells or in cells treated with an actin filament destabilizer. Moreover, knockdown of YAP/TAZ is sufficient to induce ciliogenesis, whereas YAP/TAZ hyperactivation suppresses serum starvation-mediated ciliogenesis. We also identify actin remodelling factors LIMK2 and TESK1 as key players in the ciliogenesis control network in which YAP/TAZ and directional vesicle trafficking are integral components. Our work provides new insights for understanding the link between actin dynamics and ciliogenesis.

Activation of YAP, a Hippo pathway effector, is an important resistance mechanism to BRAF inhibitor (BRAFi) in melanoma. Emerging evidence also suggests that YAP is involved in suppression of the antitumor immune response. However, the potential direct impact of YAP activity on cytotoxic T-cell immune responses has not been explored yet. Here, we show that BRAFi-resistant melanoma cells evade CD8 T-cell immune responses in a PD-L1-dependent manner by activating YAP, which synchronously supports melanoma cell survival upon BRAF inhibition. PD-L1 expression is elevated in BRAFi-resistant melanoma cells, in which YAP is robustly activated, and YAP knockdown decreases PD-L1 expression. In addition, constitutively active YAP (YAP-5SA) increases PD-L1 expression by binding to an upstream enhancer of the PD-L1 gene and potentiating its transcription. Both BRAFi-resistant and YAP-5SA-expressing melanoma cells suppress the cytotoxic function and cytokine production of Melan-A-specific CD8 T cells, whereas anti-PD-1 antibody reverses the YAP-mediated T-cell suppression. Moreover, nuclear enrichment of YAP in clinical melanoma samples correlates with increased PD-L1 expression. Our findings show that YAP directly mediates evasion of cytotoxic T-cell immune responses in BRAFi-resistant melanoma cells by upregulating PD-L1, and targeting of YAP-mediated immune evasion may improve prognosis of melanoma patients.