Regulation of eIF2α by RNF4 Promotes Melanoma Tumorigenesis and Therapy Resistance

Among the hallmarks of melanoma are impaired proteostasis and rapid development of resistance to targeted therapy that represent a major clinical challenge. However, the molecular machinery that links these processes is unknown. Here we describe that by stabilizing key melanoma oncoproteins, the ubiquitin ligase RNF4 promotes tumorigenesis and confers resistance to targeted therapy in melanoma cells, xenograft mouse models, and patient samples. In patients, RNF4 protein and mRNA levels correlate with poor prognosis and with resistance to MAPK inhibitors. Remarkably, RNF4 tumorigenic properties, including therapy resistance, require the translation initiation factor initiation elongation factor alpha (eIF2 alpha). RNF4 binds, ubiquitinates, and stabilizes the phosphorylated eIF2 alpha (p-eIF2 alpha) but not activating transcription factor 4 or C/EBP homologous protein that mediates the eIF2 alpha-dependent integrated stress response. In accordance, p-eIF2 alpha levels were significantly elevated in high-RNF4 patient-derived melanomas. Thus, RNF4 and p-eIF2 alpha establish a positive feed-forward loop connecting oncogenic translation and ubiquitin-dependent protein stabilization in melanoma.