Fig 2: The knockdown of USP4 expression promotes melanoma cell apoptosis under cisplatin treatment. A and B, Representative flow cytometry images of cell apoptosis in A2058 cell with indicated treatment. The lower panel is the knockdown efficiency of USP4 expression. The lower panel is a densitometry analysis of 3 individual experiments. C and D, Representative flow cytometry images of cell apoptosis in 451Lu cell with indicated treatment. The lower panel is a densitometry analysis of 3 individual experiments. Data are presented as the mean ± SD, ns, non-significant, *P < .05; Student's t test

Fig 3: USP4 is dispensable for melanoma cell proliferation. A and B, Cell proliferation of A2058 and 451Lu cells was measured by CCK-8 assay at 0, 24, 48 and 72 h. The lower panel is the knockdown efficiency of USP4 expression. C and D, Cell colony formation of A2058 and 451Lu cells was measured by colony formation assay. Data are presented as the mean ± SD, ns, non-significant; Student's t test

Fig 4: USP4 promotes invasion and migration of melanoma cell through the induction of EMT. A and B, A2058 cells with indicated treatment were subjected to the invasion and migration assay. Representative fields of invaded and migrated cells are shown. Scale bar = 100 μm. The invaded and migrated cells were also quantified on the right. Data represent the mean ± SD of triplicates. C, A2058 cells with indicated treatment were subjected to wound‐healing assay. Experiments were repeated 3 times with similar results. Scale bar = 100 μm. D and E, 451Lu cells with indicated treatment were subjected to the invasion and migration assay. Representative fields of invaded and migrated cells are shown. Scale bar = 100 μm. The invaded and migrated cells were also quantified on the right. Data represent the mean ± SD of triplicates. F, 451Lu cells with indicated treatment were subjected to wound‐healing assay. Experiments were repeated 3 times with similar results. Scale bar = 100 μm. G, Expressions of N‐cadherin and E‐cadherin were analysed by immunoblotting. The right panel is a densitometry analysis of 3 individual experiments. Data are presented as the mean ± SD, *P < .05, **P < .01; Student's t test

Fig 5: Proposed model of the oncogenic role of USP4 in melanoma. USP4 is significantly up‐regulated in melanoma. On the one hand, through the suppression of p53 signalling and DNA damage, USP4 is able to attenuate cell apoptotic rate in response to stress. On the other hand, though the induction of EMT, up‐regulated USP4 contributes to invasion and migration of melanoma cells