Fibronectin induction abrogates the BRAF inhibitor response of BRAF V600E/PTEN-null melanoma cells

Abstract

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.

RMEL3, a novel BRAFV600E-associated long noncoding RNA, is required for MAPK and PI3K signaling in melanoma

“…Shared molecular signatures between RMEL3 knockdown and BRAF suppression also highlights the association of RMEL3 with BRAF. Common alterations are the upregulation of FOXD3 transcription factor [11]; WNT5A [12]; JUN, STAT3 [13]; fibronectin [14]; and other molecules involved in energy metabolism [15]. …”

Fibroblast-derived Neuregulin 1 Promotes Compensatory ErbB3 Receptor Signaling in Mutant BRAF Melanoma

“…The tumor microenvironment plays a key role in these adaptive responses to targeted inhibitors. For example, stromal fibroblasts may be subverted to phenotypically distinct CAFs, which promote supportive conditions for cancer cell growth through the production of soluble growth factors and the extracellular matrix (13)(14)(15)(16), induction of angiogenesis, and recruitment of inflammatory cells (14). The extent to which stromally derived factors are required for resistance to targeted inhibitors remains to be fully understood.…”

The role of phenotypic plasticity in the escape of cancer cells from targeted therapy

“…Further evidence for melanoma cells experiencing an EMT-like switch following BRAF inhibitor treatment came from proteomic studies [64]. It was found that acute treatment with the BRAF inhibitor vemurafenib led to an increase in EMT associated proteins including FAK, integrin α5β1, vimentin and fibronectin [64].…”

“…It was found that acute treatment with the BRAF inhibitor vemurafenib led to an increase in EMT associated proteins including FAK, integrin α5β1, vimentin and fibronectin [64]. The induction of fibronectin within the melanoma cells was important for therapeutic escape, with knockdown of either fibronectin or integrin α5β1 found to increase BRAF-inhibitor mediated apoptosis.…”

“…The induction of fibronectin within the melanoma cells was important for therapeutic escape, with knockdown of either fibronectin or integrin α5β1 found to increase BRAF-inhibitor mediated apoptosis. Mechanistically, it was found that melanoma cells created their own protective ECM-derived niche that led to increased signaling through AKT and the maintenance of expression of the anti-apoptotic protein Mcl-1 [64]. …”