TP53 and melanoma: Indeed, as shown in Fig. 1b, siRNA-mediated depletion of VPRBP significantly increased both the mRNA and protein levels of PD-L1 in cell lines that do (human osteosarcoma U2OS and human melanoma A375) or do not (human lung carcinoma H1299), express wild-type p53, suggesting that VPRBP can regulate PD-L1 expression regardless of p53 status.