Figure 4.

PD-L2 upregulation promotes tumor cell–intrinsic MAPKi resistance. A, PD-L2 surface detection in P and Rr lines with stable expression of empty vector (shVec) or shPD-L2. Error bars, SEM. B, Clonogenic growth of indicated Rr lines, with shVec or indicated shPD-L2, for 9 days. Quantifications relative to each cell line culture with shVec. C, Apoptosis (%) in Rr lines stably expressing shVec or shPD-L2 #9 + #24 on indicated days after lentiviral infection. GFP- (VEC) or PD-1–GFP-expressing HEK293T cells were added to melanoma cell cultures on day 2 of infection at a ratio of 1 to 2. D, Apoptosis on indicated days in Rr lines cocultured from the outset with GFP- (VEC) or PD-1–GFP-expressing HEK293T cells at a ratio of 2 to 1. E, Apoptosis on day 2 in Rr lines pretreated with DMSO or staurosporine (STP; 0.5 μmol/L) for 20 minutes or 3 hours, washed free of STP, and then cocultured with GFP- (VEC) or PD-1–GFP-expressing HEK293T cells at a ratio of 2 to 1. F, PCA of RNA-seq profiles of indicated Rr lines pretreated with DMSO or STP (0.5 μmol/L) for 20 minutes, washed free of DMSO/STP, and cocultured with GFP- (VEC) or PD-1–GFP-expressing HEK293T cells for 1 or 2 days. Live Rr cells were sorted as GFP-negative cells and then RNA-seq profiled. G, GO enrichment analysis of the PC3− and PC3+ driving genes from F.