SASH1 impairs melanin synthesis and metastasis by down-regulating the TGF-β signaling pathway

Dyschromatosis universalis hereditaria (DUH) is a rare genetic dermatosis characterized by widespread hyperpigmentation and depigmentation. In our previous study, we identified SH3 domain-containing protein 1 (SASH1) mutations associated with the DUH phenotype in Chinese families and predict SASH1/THBS1/TGF-{beta}1 signaling to mediate melanin production and melanocyte transport. We detected SASH1/THBS1/TGF-{beta}1 pathway genes expression and evaluated cell phenotypes and melanin synthesis in A375 and PIG1 cell lines by regulating the expression of SASH1 and THBS1 respectively. Finally, we validated the results of the cellular experiments in nude mice. Results showed that SASH1 inhibited the proliferation, migration, invasion, EMT ability and melanin synthesis via TGF-{beta}1 signaling, and THBS1 reversed the elevation of TGF-{beta}1 caused by SASH1 knockdown. We demonstrated that SASH1 further inhibits TGF-{beta}1 through its regulatory effect on THBS1, thereby inhibiting melanin synthesis and metastasis, which may advance the utilization of TGF-{beta}1 for therapeutic purposes. Plain Language SummaryDyschromatosis universalis hereditaria(DUH) is a genetic disease showing uneven pigment pattern, which greatly affects the appearance. In our previous study, we had reported a SASH1 mutation in a Chinese DUH pedigree. In this study, we mainly focus on the effect of SASH1 gene on pigment synthesis and metabolism at the cell and animal level. The results show SASH1 inhibits the melanin synthesis of melanocytes, it can also hinder cell migration, invasion, and EMT. More than that, SASH1 reduced TGF-{beta}1 mRNA, protein expression and promoter activity, and THBS1 could discharge this effect. In mice, SASH1 inhibits the tumor growth via TGF-{beta}1 signaling. We detected a novel SASH1/THBS1/TGF-{beta}1 pathway in cell phenotypes and melanin synthesis.