Abstract 3492: The small GTPase ARF6 augments BRAFV600E-MAPK signaling in melanomagenesis

Abstract ARF6 is a member of the Ras superfamily of small GTPases and has critical functions in endo-membrane trafficking pathways. We previously reported that ARF6 is aberrantly activated in metastatic melanoma and that activation of ARF6 stimulates WNT5A/beta-catenin and PI3K/AKT signaling to promote invasion and accelerate metastasis. Herein, we discovered an ARF6 activation signature in primary melanomas that is associated with inferior overall survival, supporting a novel role for ARF6 in early-stage progression. Conversely, melanocyte-specific deletion of Arf6 in Dct;TVA::BrafV600E;Cdkn2aNull murine melanoma significantly reduced tumorigenesis and progression, and improved survival. Importantly, bulk tumor transcriptome analysis showed reduced expression of ERK-induced genes in these BRAFV600E tumors. Likewise, immunofluorescent staining of tumor sections showed a significant reduction of cytoplasmic and nuclear p-ERK levels. Together these data demonstrate that loss of ARF6 reduces BRAFV600E-MAPK signaling output in vivo. This is a provocative finding because it implies that endomembrane trafficking has a major role in promoting BRAFV600E-driven tumorigenesis. More specifically, ARF6 may be critical for augmenting BRAFV600E signaling. Consistent with this hypothesis, expression of activated ARF6(ARF6Q67L) in our murine BRAFV600E melanoma cells was associated with upregulation of BRAFV600E, p-MEK, and p-ERK levels, detected by Reverse Phase Protein Array analysis. In addition, ARF6Q67L tumor cells showed an increase in anti-apoptotic proteins with a reciprocal decrease in pro-apoptotic proteins. Knockdown of Arf6 in BRAFV600E human melanoma cells significantly reduced proliferation and sensitized cells to vemurafenib-induced apoptosis. Overall, our data reveal that ARF6 augments MAPK signaling in BRAFV600E-driven tumorigenesis. Further work is needed to understand if ARF6 mediates endomembrane-dependent signaling of the BRAFV600E-MAPK pathway. Citation Format: Junhua Wang, Aaron Rogers, Coulson Rich, Lise Sorensen, Sheri Holmen, Roger Wolff, Allie Grossmann. The small GTPase ARF6 augments BRAFV600E-MAPK signaling in melanomagenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3492.