Oncogenic BRAF(V600E) Promotes Stromal Cell-Mediated Immunosuppression Via Induction of Interleukin-1 in Melanoma

Abstract

Purpose In this study, we assessed the specific role of BRAF(V600E) signaling in modulating the expression of immune regulatory genes in melanoma, in addition to analyzing downstream induction of immune suppression by primary human melanoma tumor-associated fibroblasts (TAFs). Experimental Design Primary human melanocytes and melanoma cell lines were transduced to express WT or V600E forms of BRAF, followed by gene expression analysis. The BRAF(V600E) inhibitor vemurafenib was used to confirm targets in BRAF(V600E)-positive melanoma cell lines and in tumors from melanoma patients undergoing inhibitor treatment. TAF lines generated from melanoma patient biopsies were tested for their ability to inhibit the function of tumor antigen-specific T-cells, prior to and following treatment with BRAF(V600E)-upregulated immune modulators. Transcriptional analysis of treated TAFs was conducted to identify potential mediators of T-cell suppression. Results Expression of BRAF(V600E) induced transcription of IL-1α and IL-1β in melanocytes and melanoma cell lines. Furthermore, vemurafenib reduced the expression of IL-1 protein in melanoma cell lines and most notably in human tumor biopsies from 11 of 12 melanoma patients undergoing inhibitor treatment. Treatment of melanoma-patient-derived TAFs with IL-1α/β significantly enhanced their ability to suppress the proliferation and function of melanoma-specific cytotoxic T cells, and this inhibition was partially attributable to upregulation by IL-1 of COX-2 and the PD-1 ligands PD-L1 and PD-L2 in TAFs. Conclusions This study reveals a novel mechanism of immune suppression sensitive to BRAF(V600E) inhibition, and suggests that clinical blockade of IL-1 may benefit patients with BRAF wild-type tumors and potentially synergize with immunotherapeutic interventions.

Expression Profiling of a Human Thyroid Cell Line Stably Expressing the BRAFV600E Mutation

“…Highdose IL-1β administration causes broad inflammation and is accompanied by tissue damage and tumor invasiveness (24). In vitro analysis of melanocytes and melanoma cell lines showed that BRAF V600E increases, while BRAF V600E inhibition reduces, the transcription of IL-1α and IL-1β (25,26). In human thyrocytes, IL-1β alters the expression and localization of junction proteins (27).…”

MEK Inhibition, Alone or in Combination with BRAF Inhibition, Affects Multiple Functions of Isolated Normal Human Lymphocytes and Dendritic Cells

“…The increase in MDA and tumor antigen expression was associated with enhanced antigen-specific T-lymphocyte recognition in vitro (21,22) and in clinical trial patients (24), providing the first evidence for combining vemurafenib treatment with T-lymphocyte-directed immunotherapy. BRAFi also enhances the levels of MHC molecules on melanoma cells, reverses immune suppression of T lymphocytes by inhibiting IL-1a and IL-1b (25), and inhibits VEGF secretion from tumor cells (26), providing an additional explanation for why T-cell recognition is enhanced.…”

“…The anticancer effects of these agents are mediated by cellular effectors of the immune system. This has provided a rationale for combining MAPK pathway inhibitors with immunotherapy, as BRAFi can sensitize BRAF-mutant melanoma cells to immune recognition and relieve immune suppression (21)(22)(23)(24)(25)(26). Amid the speculation as to the role for combined MAPK pathway inhibition and immunotherapy, the degree to which kinase inhibition, specifically dabrafenib and/or trametinib, may directly affect immune function remains poorly defined.…”

Targeting the PD1/PD-L1 axis in melanoma: Biological rationale, clinical challenges and opportunities

“…The inhibition of RAS and PI3K/AK3 pathways cooperates to inhibit lymphocytes' function and survival. [63]. Tumor-associated fibroblasts (TAFs) respond to IL-1 by upregulating an immunomodulatory transcriptional program resulting in the production of COX-2, PD-1 ligands, and chemokines, as well as in the amplification of IL-1 signaling (Fig.…”