Andrew E. Aplin

Immune checkpoint inhibitors have improved patient survival in melanoma, but the innate resistance of many patients necessitates the investigation of alternative immune targets. Many immune checkpoint proteins lack proper characterization, including V-domain Ig suppressor of T cell activation (VISTA). VISTA expression on immune cells can suppress T cell activity; however, few studies have investigated its expression and regulation in cancer cells. In this study, we observe that VISTA is expressed in melanoma patient samples and cell lines. Tumor cell-specific expression of VISTA promotes tumor onset in vivo, associated with increased intratumoral T regulatory cells, and enhanced PDL-1 expression on tumor-infiltrating macrophages. VISTA transcript levels are regulated by the stemness factor Forkhead box D3 (FOXD3). BRAF inhibition upregulates FOXD3 and reduces VISTA expression. Overall, this study demonstrates melanoma cell expression of VISTA and its regulation by FOXD3, contributing to the rationale for therapeutic strategies that combine targeted inhibitors with immune checkpoint blockade.

In the original version of this article (1), an error in Fig. 6C was introduced by the compositor during the production of the paper. Specifically, the Raptor Western blot was improperly shifted. The figure has been corrected in the latest online HTML and PDF versions of the article. The publisher regrets the error.

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Abstract Melanoma is the deadliest form of skin cancer; however, with early detection prior to metastatic dissemination, patients generally have a good prognosis. Recently, our lab has implicated the transcription factor TWIST1 in the progression of melanoma towards metastasis. In melanoma cells, we found that RAS-RAF-MEK-ERK (ERK1/2 pathway) signaling increases TWIST1 expression, which promotes invasive properties in the dermal microenvironment at least in part by enhancing levels of the matrix metalloproteinase, MMP1. Other TWIST1 regulated targets are poorly described. In this study, we compared expression profiling data from cells expressing shRNA against TWIST1 or cells overexpressing TWIST1 in order to determine TWIST1 regulated genes. KEGG and GO analysis revealed that TWIST1 is responsible for regulating a number of genes involved in cellular adhesion. We found that TWIST1 levels inversely correlate with levels of cell adhesion molecule 1 (CADM1) (NECL-2, IGSF4, TSLC1, SynCAM). Chromatin immunoprecipitation (ChIP) studies and promoter assays demonstrate that TWIST1 physically interacts with CADM1 promoter and this is associated with reduced CADM1 levels. Additionally, CADM1 expression is inversely associated ERK1/2 signaling and TWIST1 expression. Modulation of cellular CADM1 levels does not seem to affect proliferations rates however, overexpression of CADM1 augments cell-cell interaction, and cell aggregation. Furthermore, exogenous CADM1 inhibited serum directed migration and invasion through matrigel coated boyden chambers, while knockdown of CADM1 was associated with an enhancement in the migratory and invasion properties. Taken together, these data provide evidence that CADM1 is negatively regulated by TWIST1, and may act as a suppressor of melanoma invasion. Citation Format: Edward J. Hartsough, Michele B. Weiss, Curtis H. Kugel, Sheera R. Rosenbaum, Andrew E. Aplin. CADM1 is a TWIST1 regulated suppressor of melanoma invasion. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4089. doi:10.1158/1538-7445.AM2015-4089