Focal adhesion kinase-dependent apoptosis of melanoma induced by tyrosine and phenylalanine deficiency

We found previously that restriction of tyrosine (Tyr) and phenylalanine (P he) inhibited growth and metastasis of B16BL6 murine melanoma and arrested these cells in the G(0)-G(1) phase of the cell cycle, Here, we report that deprivation of these two amino acids in vitro induces apoptosis in B16BL6 a nd in human A375 melanoma cells but not in nontransformed, neonatal murine epidermal cells or human infant foreskin fibroblasts, Four days after depri vation of Tyr and Phe in vitro, 37% of B16BL6 and 51% of A375 melanoma cell s were undergoing apoptosis, Apoptosis was not associated with elevation in intracellular calcium or alteration in p53 or c-myc protein expression. Ex pression and Tyr phosphorylation of focal adhesion kinase (FAK) were inhibi ted in both melanoma cell lines by deprivation of Tyr and Phe but not by de privation of glutamine or serum. Tyr phosphorylation of FAK in Tyr- and Phe -deprived melanoma cells was enhanced within 30 min of refeeding with compl ete DMEM. FAK protein expression recovered within 60 min, and cell viabilit y recovered within 24 h. Genistein, a tyrosine kinase inhibitor that specif ically inhibits Tyr phosphorylation of FAK, did not induce apoptosis in A37 5 melanoma cells at a concentration of 50 mu M. Genistein prevented the rec overy of cell viability upon refeeding with Tyr and Phe to previously depri ved A375 melanoma cells. These data collectively indicate that apoptosis in duced by Tyr and Phe deprivation is FAK-dependent.