Melanoma cells repress Desmoglein 1 in keratinocytes to promote tumor cell migration

Melanoma is an aggressive cancer typically arising from 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 remains understudied. We previously showed that temporary loss of the keratinocyte-specific cadherin, Desmoglein 1 (Dsg1) controls paracrine signaling between normal melanocytes and keratinocytes to stimulate the protective tanning response. Here, we provide evidence that melanoma cells hijack this intercellular communication by secreting factors that keep Dsg1 expression low in surrounding keratinocytes, which in turn generate their own paracrine signals that enhance melanoma spread through CXCL1/CXCR2 signaling. Evidence suggests a model whereby paracrine signaling from melanoma cells increases levels of the transcriptional repressor Slug, and consequently decreases expression of the Dsg1 transcriptional activator Grhl1. Together, these data support the idea that paracrine crosstalk between melanoma cells and keratinocytes resulting in chronic keratinocyte Dsg1 reduction contributes to melanoma cell movement associated with tumor progression. Overall design: Melanoma cell lines treated with conditioned media from keratinocytes expressing shNT or shDsg1. Keratinocytes and melanocytes were isolated from discarded neonatal foreskin provided by the Northwestern University Skin Biology and Diseases Research-Based Center (NUSBDRC) as previously described (Roth-Carter et al., 2022). Keratinocytes were grown in M154 medium (Life Technologies) supplemented with human keratinocyte growth supplement (Life Technologies), 1,000 x gentamycin/amphotericin B solution (Life Technologies), and 0.07mM CaCl2. Keratinocytes were treated with conditioned media from melanoma cells for 48 hours and melanoma cells were cultured with conditioned media from keratinocytes expressing shNT or shDsg1 for 24 hours. Total RNA was extracted from cells using the Quick-RNA miniprep kit (Zymo Research) following the manufacturer's protocol. Novogene Co., LTD conducted preparation of the mRNA library and transcriptome sequencing. Differential expression analysis was performed using DESeq2, with a batch correction to account for keratinocyte clonal variation. Genes with p-value??1 were considered to be differentially expressed.