ACID SPHINGOMYELINASE AND MITOCHONDRIA: A NEW LINKIN CHEMOTHERAPEUTIC DRUGS INDUCED APOPTOSIS

Melanoma is the most aggressive form of skin cancer and is notoriously resistant to all current modalities of cancer therapy. Malignant melanomas are composed of subpopulations of cells characterized by highly heterogeneity. This clonal heterogeneity of tumor cells accounts for the existence or appearance of tumor cell populations showing invasive and metastatic phenotype heterogeneity, different drug resistance and immunogenicity. Over the past twenty years, sphingolipids have emerged as bioeffector molecules, controlling various aspects of cell growth and proliferation in cancer and in particular A-SMase is known to be involved in the apoptotic process and, moreover, to be activated by many chemotherapeutic drugs. In this work we focused our attention on the investigation of the role of ASMase in regulation of chemoresistance. To this end we used the B16-W6 clone that was isolated from a murine melanoma cells lines, B16-F1, and that showed high A-SMase expression and the B16-W6_pSiL10 clone generated from the A-SMase highly expressing clone B16-W6. In particular, here it has been demonstrated a pivotal role of A-SMase in the regulation of the balance between apoptosis and autophagy. In our previous work we have found that the downregulation of A-SMase is correlated with high Microphtalmia-associated transcription factor (Mitf) expression. Since it is establish that Mitf regulates Hypoxia-inducible factor-1α (HIF-1α), an important transcription factor involved in chemoresistance of solid tumor, we decided to examine the possible connection between A-SMase and HIF-1α through the regulation of Mitf and what is its biological significance. We demonstrated, for the first time, that the decrease in expression of A-SMase correlates with an increased amount of HIF-1α in normoxia and this increase is responsible for the induction of autophagy. Investigating the mechanism by which A-SMase resulates the autophagic process, we found that A-SMase was able to regulate BNIP3 through the modulation of HIF-1α expression. The A-SMase/Mitf/HIF-1α axis is also responsible for the modification of mitochondrial morphology and functionality. Of particular interest, we demonstrated that the induction of autophagy is in part responsible for the resistance of chemotherapy due to the A-SMase downregulation. Indeed, we found that the inhibition of autophagy in B16-W6_pSiL10 clone restored the sensitivity to the chemotherapy. From all these results A-SMase results to be fundamental for the response of melanoma cells to the chemotherapeutic treatment and a protein to be further investigated in perspective of new and more effective anticancer strategies.