Piperlongumine induces apoptosis via the MAPK pathway and ERK-mediated autophagy in human melanoma cells

Piperlongumine (PL) is an amide alkaloid with diverse pharmacological effects against cancer, bronchitis and asthma; however, research on its efficacy against melanoma is lacking. The present study investigated the anticancer effects of PL on A375SM and A375P human melanoma cells. PL decreased the survival rate of A375SM and A375P cells, as shown by MTT assay, increase of apoptotic cells by DAPI staining. And PL induced apoptosis by decreasing the expression of the anti-apoptotic protein Bcl-2 and increasing that of the pro-apoptotic proteins cleaved-PARP and Bax. PL also induced apoptosis in A375SM and A375P cells via the MAPK pathway, increasing expression of the MAPK pathway proteins, phosphorylated-(p-ERK), p-JNK p-p38. These proteins were confirmed by western blot. In addition, A375SM and A375P cells treated with PL showed an increased number of acidic vesicular organelles by acridine orange staining. Also, autophagy induced by the expression of 1A/1B-light chain 3, Beclin 1and mTOR was investigated through western blot. When PL was applied following treatment with autophagy inhibitors 3-methyladenine and hydroxychloroquine, autophagy exhibited a cytoprotective effect against apoptosis in MTT assay. Pretreatment of A375P cells with the ERK inhibitor PD98059 and the JNK inhibitor SP600125 followed by treatment with PL confirmed that apoptosis and autophagy were mediated via the MAPK/ERK pathway by western blot. In summary, the present study provided empirical evidence supporting the anticancer effects of PL on human melanoma cells and indicated the potential of PL as a treatment for melanoma.