537 Functional melanoma cell heterogeneity is regulated by MITF-dependent cell-matrix interactions

Abstract

The melanoma microenvironment is important for tumor progression, but the role of neighboring keratinocytes (KC) in the tumor niche remains poorly understood. We previously showed that loss of the KC-specific desmosomal cadherin, desmoglein 1 (Dsg1), results in release of KC cytokines to alter melanocyte pigmentation and dendricity. This led us to address whether KC Dsg1 plays a role in the melanoma microenvironment. Here, we show that Dsg1 is reduced in regions surrounding melanoma lesions but is unchanged in KCs adjacent to benign nevi. To address whether melanoma cells contribute to Dsg1 loss, we cultured KCs in melanoma cell conditioned media and measured Dsg1 protein and mRNA levels. Melanoma cell, but not melanocyte, conditioned media reduced KC Dsg1 expression downstream of decreased Grhl1, a transcriptional activator of Dsg1. As we showed that Dsg1 loss stimulates expression of promigratory cytokines, we carried out transwell assays to compare behavior of melanoma cells treated with conditioned media from control, Dsg1-deficient and Dsg1-deficient KCs rescued with exogenous Dsg1. Media from Dsg1-deficient KCs increased melanoma cell migration compared to media from control KCs or KCs with Dsg1 rescue. Consistent with these data, staining of melanoma tumors revealed a negative correlation between KC Dsg1 expression and melanoma cell movement in the tumor niche. ERK1/2-dependent expression of CXCL1 increased in KCs exposed to melanoma cell conditioned media downstream of Dsg1 loss, and inhibition of the CXCL1 receptor CXCR2 abrogated Dsg1 loss driven melanoma cell migration, confirming the contribution of KC CXCL1 to the observed cell migration. Taken together, these data point to Dsg1 loss as a key regulator KC-melanoma cell cross talk in the tumor niche and a possible contributor to melanoma progression.