The activation of the c-Jun N-terminal kinase and p38 mitogen-activated protein kinase signaling pathways protects HeLa cells from apoptosis following photodynamic therapy with hypericin

In this study, we elucidate signaling pathways induced by photodynamic ther apy (PDT) with hypericin. We show that PDT rapidly activates JNK1 while irr eversibly inhibiting ERK2 in several cancer cell lines. In HeLa cells, sust ained PDT-induced JNK1 and p38 mitogen-activated protein kinase (MAPK) acti vations overlap the activation of a DEVD-directed caspase activity, poly(AD P-ribose) polymerase (PARP) cleavage, and the onset of apoptosis, The caspa se inhibitors benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (zVAD-fmk) a nd benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethylketone (zDEVD-fmk) protect cells against apoptosis and inhibit DEVD-specific caspase activity and PAR P cleavage without affecting JNK1 and p38 MAPK activations, Conversely, sta ble overexpression of CrmA, the serpin-like inhibitor of caspase-1 and casp ase-8, has no effect on PDT-induced PARP cleavage, apoptosis, or JNK1/p38 a ctivations. Cell transfection with the dominant negative inhibitors of the c-Jun N-terminal kinase (JNK) pathway, SEK-AL and TAM-67, or pretreatment w ith the p38 MAPK inhibitor PD169316 enhances PDT-induced apoptosis, A simil ar increase in PDT-induced apoptosis was observed by expression of the dual specificity phosphatase MKP-1, The simultaneous inhibition of both stress kinases by pretreating cells with PD169316 after transfection with either T AM-67 or SEK-AL produces a more pronounced sensitizing effect. Cell pretrea tment with the p38 inhibitor PD169316 causes faster kinetics of DEVD-caspas e activation and PARP cleavage and strongly oversensitizes the cells to apo ptosis following PDT, These observations indicate that the JNK1 and p38 MAP K pathways play an important role in cellular resistance against PDT-induce d apoptosis with hypericin.