UVB-induced Ca2+ signaling orchestrates PPP3CA-AFF4 axis to promote cancer stem cell plasticity in melanoma

Cutaneous melanoma, known for metastasis and therapy resistance, has limited treatment against cancer stem cells (CSCs). Ultraviolet B (UVB) radiation, an environmental carcinogen, is related to melanoma progression, but its impact on CSC plasticity is unclear. This study aims to explore how UVB-induced Ca 2+ (Ca 2+ ) signaling modulates the PPP3CA-AFF4 axis for CSC maintenance in melanoma. Enriched melanoma CSC models (A375/A2058) were used. UVB irradiation was applied, and Ca 2+ influx, AFF4, and PPP3CA levels were examined. Co-immunoprecipitation (IP), gene silencing, pharmacological inhibition, and in vivo tumor growth assays were conducted. UVB exposure induced a Ca 2+ influx, which led to the upregulation of AFF4 and PPP3CA, and these two proteins subsequently engaged in a physical interaction. UVB enhanced CSC markers, clonogenicity, and migration, which were blocked by AFF4 silencing or Ca 2+ pathway inhibition. In vivo, AFF4 knockdown suppressed UVB-accelerated tumor growth and reduced intratumoral Ca 2+ . Mechanistically, UVB-activated PPP3CA dephosphorylated NFAT, working with AFF4 for pluripotency gene transcription. The Ca 2+ -dependent PPP3CA-AFF4 axis is crucial for UVB-induced CSC plasticity, suggesting new melanoma therapeutic strategies.