CASP9 and melanoma: To further understand the mechanisms used by hydroxytyrosol to induce the death of treated melanoma cells, we analysed the expression of several pro-apoptotic and survival proteins such as p53 signalling protein, pro-caspases-9 and -3, PARP-1, the serine-139-phosphorylated form of histone variant H2AX (γH2AX), and the signalling protein AKT.