SEMA6A/RhoA/YAP axis mediates tumor-stroma interactions and prevents response to dual BRAF/MEK inhibition in BRAF-mutant melanoma

Abstract

Background Despite the promise of dual BRAF/MEK inhibition as a therapy for BRAF-mutant (BRAF-mut) melanoma, heterogeneous responses have been observed in patients, thus predictors of benefit from therapy are needed. We have previously identified semaphorin 6A (SEMA6A) as a BRAF-mut-associated protein involved in actin cytoskeleton remodeling. The purpose of the present study is to dissect the role of SEMA6A in the biology of BRAF-mut melanoma, and to explore its predictive potential towards dual BRAF/MEK inhibition. Methods SEMA6A expression was assessed by immunohistochemistry in melanoma cohort RECI1 (N = 112) and its prognostic potential was investigated in BRAF-mut melanoma patients from DFCI and TCGA datasets (N = 258). The molecular mechanisms regulated by SEMA6A to sustain tumor aggressiveness and targeted therapy resistance were investigated in vitro by using BRAF-mut and BRAF-wt melanoma cell lines, an inducible SEMA6A silencing cell model and a microenvironment-mimicking fibroblasts-coculturing model. Finally, SEMA6A prediction of benefit from dual BRAF/MEK inhibition was investigated in melanoma cohort RECI2 (N = 14). Results Our results indicate higher protein expression of SEMA6A in BRAF-mut compared with BRAF-wt melanoma patients and show that SEMA6A is a prognostic indicator in BRAF-mut melanoma from TCGA and DFCI patients cohorts. In BRAF-mut melanoma cells, SEMA6A coordinates actin cytoskeleton remodeling by the RhoA-dependent activation of YAP and dual BRAF/MEK inhibition by dabrafenib+trametinib induces SEMA6A/RhoA/YAP axis. In microenvironment-mimicking co-culture condition, fibroblasts confer to melanoma cells a proliferative stimulus and protect them from targeted therapies, whereas SEMA6A depletion rescues the efficacy of dual BRAF/MEK inhibition. Finally, in BRAF-mut melanoma patients treated with dabrafenib+trametinib, high SEMA6A predicts shorter recurrence-free interval. Conclusions Overall, our results indicate that SEMA6A contributes to microenvironment-coordinated evasion of melanoma cells from dual BRAF/MEK inhibition and it might be a good candidate predictor of short-term benefit from dual BRAF/MEK inhibition.

The MITF/mir-579-3p regulatory axis dictates BRAF-mutated melanoma cell fate in response to MAPK inhibitors

“…1B–D ). It has to be mentioned that these cell lines are characterized by high basal levels of p-ERK activation, as demonstrated by Western Blot analyses, because they all harbor oncogenic alterations in the MAPK signaling different from BRAF mutations [ 21 – 23 ]. Altogether these results show that miR-579-3p and MITF expression levels are co-regulated in BRAF mutated melanoma and that this co-regulation is linked to activation of BRAF-MAPK signaling.…”

Recent advances in the role of Yes‐associated protein in dermatosis

“…In melanoma models, semaphorin 6A (SEMA6A) was shown to activate the RhoA/YAP axis, which remolded the actin cytoskeleton and predicted shorter recurrencefree interval in patients. 72 Upstream of RhoA/YAP, PPARG coactivator 1 alpha inhibition increased the expression of WNT5A and activated…”

“…As a classic mechanical sensor, YAP is modulated by static mechanical stimulation of the actin cytoskeleton. In melanoma models, semaphorin 6A (SEMA6A) was shown to activate the RhoA/YAP axis, which remolded the actin cytoskeleton and predicted shorter recurrence‐free interval in patients 72 . Upstream of RhoA/YAP, PPARG coactivator 1 alpha inhibition increased the expression of WNT5A and activated RhoA to increase the level of YAP, thereby increasing melanoma invasion 73 through the regulation of actin‐related protein 2/3 complex subunit 5, which is associated with melanocyte adhesion 74 …”

Extracellular Vesicles-Based Cell-Cell Communication in Melanoma: New Perspectives in Diagnostics and Therapy

“…The resistance of melanoma to targeted therapies can be driven by genetic changes [ 88 ] and adaptive epigenetic alterations supported by the plasticity of cellular signaling and tumor microenvironment [ 89 , 90 , 91 , 92 , 93 ]. The role of tumor microenvironment in mediating epigenetic escape of melanoma cells from the BRAF V600 /MEK inhibition is well proven by numerous studies as exemplified by [ 94 , 95 , 96 , 97 , 98 , 99 , 100 ]. The exosomal transfer of functional cargo is a part of the microenvironmental contribution to epigenetic changes crucial for the resistance to treatments.…”