Chondroitin sulfate proteoglycan 4 increases invasion of recessive dystrophic epidermolysis bullosa-associated cutaneous squamous cell carcinoma by modifying transforming growth factor-β signalling

BACKGROUND: Recessive dystrophic epidermolysis bullosa (RDEB) is a rare genetic skin-blistering disorder that often progresses to metastatic cutaneous squamous cell carcinoma (cSCC) at chronic wound sites. Chondroitin sulfate proteoglycan 4 (CSPG4) is a cell-surface proteoglycan that is an oncoantigen in multiple malignancies, where it modulates oncogenic signalling, drives epithelial-to-mesenchymal transition (EMT) and enables cell motility. OBJECTIVES: To evaluate CSPG4 expression and function in RDEB cSCC. METHODS: RDEB cSCC cell lines were used to assess CSPG4-dependent changes in invasive potential, transforming growth factor (TGF)-β1-stimulated signal activation and clinically relevant cytopathology metrics in an in vitro full-thickness tumour model. CSPG4 expression in RDEB cSCC and non-RDEB cSCC tumours was analysed via immunohistochemistry and single-cell RNA sequencing (scRNA-Seq), respectively. RESULTS: Inhibiting CSPG4 expression reduced invasive potential in multiple RDEB cSCC cell lines and altered membrane-proximal TGF-β signal activation via changes in SMAD3 phosphorylation. CSPG4 expression was uniformly localized to basal layer keratinocytes in fibrotic RDEB skin and tumour cells at the tumour-stroma interface at the invasive front in RDEB cSCC tumours in vivo. Analysis of published scRNA-Seq data revealed that CSPG4 expression was correlated with an enhanced EMT transcriptomic signature in cells at the tumour-stroma interface of non-RDEB cSCC tumours. Cytopathological metrics, for example nucleus : cell area ratio, were influenced by CSPG4 expression in in vitro tumour models. CONCLUSIONS: We determined that CSPG4 expression in RDEB cSCC cell lines enhanced the invasive potential of tumours. Mechanistically, CSPG4 was found to enhance membrane-proximal TGF-β-stimulated signalling via SMAD3, which is a key mediator of EMT in RDEB cSCC. The implication of these studies is that CSPG4 may represent a therapeutic target that can be leveraged for the clinical management of patients with RDEB cSCC.