ST induces the expression of LSD1 (6, 7), and our findings also add that LSD1 regulates δ-catenin isoform expression in VP-MCC cells through ESRP1, which is both necessary and sufficient for δ-catenin isoform 3 expression (Fig. S4) to promote cell proliferation in VP-MCC cells. Here, ESRP1 is linked to Merkel cell skin cancer.