BRAFV600E melanoma cells secrete factors that activate stromal fibroblasts and enhance tumourigenicity

Abstract

Background:Melanoma, the most lethal form of skin cancer, is responsible for over 80% of all skin cancer deaths and is highly metastatic, readily spreading to the lymph nodes or metastasising to other organs. The frequent genetic mutation found in metastatic melanoma, BRAFV600E, results in constitutive activation of the mitogen-activated protein kinase pathway.Methods:In this study, we utilised genetically engineered melanoma cell lines and xenograft mouse models to investigate how BRAFV600E affected cytokine (IL-1β, IL-6, and IL-8) and matrix metalloproteinase-1 (MMP-1) expression in tumour cells and in human dermal fibroblasts.Results:We found that BRAFV600E melanoma cells expressed higher levels of these cytokines and of MMP-1 than wild-type counterparts. Further, conditioned medium from the BRAFV600E melanoma cells promoted the activation of stromal fibroblasts, inducing expression of SDF-1 and its receptor CXCR4. This increase was mitigated when the conditioned medium was taken from melanoma cells treated with the BRAFV600E specific inhibitor, vemurafenib.Conclusions:Our findings highlight the role of BRAFV600E in activating the stroma and suggest a mechanistic link between BRAFV600E and MMP-1 in mediating melanoma progression and in activating adjacent fibroblasts in the tumour microenvironment.

The mitogen-activated protein kinase pathway plays a critical role in regulating immunological properties of BRAF mutant cutaneous melanoma cells

“…Our data support previous studies showing that in BRAF V600E melanoma cells, inhibition of either BRAF or MEK results in a decrease in the release of immunosuppressive soluble factors IL-6, IL-8, IL-10, and VEGF [18,22,25,26]. These cytokines inhibit the T-cell-stimulatory function of DCs and play various roles in tumor progression through modulation of the TME [12,25].…”

“…PLX-4032 treatment did not result in a significant change in any of the protein levels. In addition, similar to what has been shown in the literature [22][23][24], several cell lines in the BRAF WT group showed a paradoxical increase in secreted proteins upon MAPK pathway inhibition (Fig. 3).…”

Mutant B-Raf(V600E) Promotes Melanoma Paracellular Transmigration by Inducing Thrombin-mediated Endothelial Junction Breakdown

“…Targeting B-Raf(V600E) reduces tumor lung entrapment by decreasing the secretion of tumor IL-8 and interrupting ICAM-1-␤ 2 integrin binding of tumor cells to the endothelium, which is mediated by neutrophils in circulation (16). Furthermore, the roles of B-Raf(V600E) in inducing MMP-1 secretion and activating adjacent fibroblasts in the tumor microenvironment have been demonstrated (51). In this study, we showed a mechanistic link between B-Raf(V600E), TF expression, thrombin production, and endothelial junction breakdown.…”

Potential therapeutic targets of epithelial–mesenchymal transition in melanoma

“…BRAF pathway activation has been linked to increased expression of Twist1 and Zeb1 resulting in greater melanoma invasion [24]. In addition, BRAF mutation potentiates the NFκB pathway; NFκB promotes MMP expression, increasing migratory capacity, and induces expression of Snail, a known driver of metastasis [12,37]. Further downstream, BRAF mutation has been linked to compensatory increases in ERK and subsequent overexpression of MITF [38].…”

“…Further downstream, BRAF mutation has been linked to compensatory increases in ERK and subsequent overexpression of MITF [38]. In addition, melanocytes expressing BRAF V600E synthesize more MMP-1 and promote greater stromal fibroblast activation than wild-type BRAF melanoma thus promoting greater cell motility [37]. …”