Keratinocyte desmosomal cadherin Desmoglein 1 as a mediator and target of paracrine signaling in the melanoma niche

Abstract Melanoma is an aggressive cancer arising from the transformation of melanocytes residing in the basal layer of the epidermis, where they are in direct contact with surrounding keratinocytes. The role of keratinocytes in shaping the melanoma tumor microenvironment, however, remains understudied. We previously showed that the keratinocyte-specific desmosomal cadherin, desmoglein 1 (Dsg1) is reduced in response to acute UV exposure. Here, we show that Dsg1 protein is reduced in keratinocytes surrounding melanoma lesions but is unchanged in keratinocytes adjacent to benign nevi. As Dsg1 reduction by UV exposure is transient, we hypothesized that the persistent loss of Dsg1 observed in the melanoma tumor niche is due to melanoma-keratinocyte paracrine crosstalk. To address this idea, keratinocytes were cultured in conditioned media from melanocytes or melanoma cells. Melanoma conditioned media reduced keratinocyte Dsg1 mRNA and protein levels, suggesting that Dsg1 downregulation in keratinocytes is maintained by melanoma cells post-transformation. Keratinocytes in melanoma conditioned media exhibited reduced Grhl1 (Grainyhead like 1), a transcriptional activator of Dsg1, and increased Snai2, a repressor of Grhl1 expression and epidermal differentiation. These data support the idea that increased Snai2 stimulated by factors secreted by melanoma cells reduces keratinocyte Dsg1 mRNA expression by repressing Grhl1. To determine the impact of keratinocyte Dsg1 loss on melanoma cell behavior, melanoma cells were grown in conditioned media from control or Dsg1-deficient keratinocytes. Melanoma cell migration increased in a trans-well assay when melanoma cells were grown in conditioned media from Dsg1-deficient keratinocytes compared to from control keratinocytes. Supporting the in vivo importance of this finding, we found a significant, negative correlation between keratinocyte Dsg1 expression and melanoma cell movement within the melanoma tumor niche in patient samples. Downregulation of keratinocyte Dsg1 by melanoma cell conditioned media increased Erk1/2 signaling upstream of pro-migratory CXCL1 production, while pharmacological inhibition of keratinocyte Erk1/2 abrogated this effect. Furthermore, inhibition of the CXCL1 receptor, CXCR2 on melanoma cells decreased migration in melanoma cells grown in Dsg1-depleted keratinocyte conditioned media. Together, these data support the idea that paracrine crosstalk between melanoma cells and keratinocytes resulting in chronic keratinocyte Dsg1 reduction is important for melanoma progression and melanoma cell movement in the early stages of metastasis. Citation Format: Hope E. Burks, Christopher Arnette, Jennifer Koetsier, Joshua Broussard, Quinn Roth-Carter, Pedram Gerami, Jodi Johnson, Kathleen Green. Keratinocyte desmosomal cadherin Desmoglein 1 as a mediator and target of paracrine signaling in the melanoma niche [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3186.