Steroid sulfatase suppresses keratinization by inducing proteasomal degradation of E-cadherin via Hakai regulation.

X-linked ichthyosis (XLI) is a genetic disorder characterized by a steroid sulfatase (STS) deficiency inducing excessive cholesterol sulfate accumulation and keratinization. Our study utilizes STS knockout mice to reproduce the hyperkeratinization typical of XLI, providing a valuable model for investigating the underlying mechanisms. From the experiment of STS-deficient keratinocytes using the CRISPR/Cas9 system, we observed upregulation of E-cadherin, which is associated with keratinocyte differentiation and stratification. This was accompanied by elevated levels of keratinization markers, including involucrin and loricrin. We also found an increased expression of SULT2B1, which converts cholesterol to cholesterol sulfate, further accelerating cholesterol sulfate accumulation. As a result, STS deficiency and cholesterol sulfate accumulation lead to decreased expression of Hakai, the ubiquitin E3 ligase for E-cadherin. With reduced Hakai, endocytosis and ubiquitin-mediated degradation of E-cadherin are inhibited, resulting in its stabilization. This stabilization of E-cadherin is accompanied by increased expression of involucrin and loricrin, which is suppressed when the N-terminal extracellular domain of E-cadherin, responsible for cell-cell adhesion, is genetically modified. We propose that inhibition of E-cadherin, genetic modification of the N-terminal extracellular domain, and treatment with miR-6766 targeting E-cadherin significantly reduce the expression of keratinization markers, suggesting a potential therapeutic approach. We further suggest that the increased expression of E-cadherin observed in keratinocytes with STS deficiency is regulated by Hakai, underscoring the central role of E-cadherin in the pathogenesis of XLI.