THE STRESS-ACTIVATED PROTEIN-KINASE PATHWAY MEDIATES CELL-DEATH FOLLOWING INJURY-INDUCED BY CISPLATINUM, UV IRRADIATION OR HEAT

Background: Stimuli that stress cells, including inflammatory cytokine s, ultraviolet irradiation, DNA-damaging chemotherapeutic drugs and he at shock, stimulate a recently identified cytoplasmic signaling system that is structurally related to the mitogen-activated protein kinase pathway, This pathway consists of a cascade of protein kinases includi ng stress-activated protein kinase (SAPK), also termed Jun N-terminal kinase (JNK), and two kinases that activate it, MEKK and SEK/MKK4, Des pite rapid progress in delineating the components of this pathway, the cellular consequence of its activation remains to be defined. Results : We have screened cells for defects in SAPK signaling and identified a cell line, previously characterized for its thermotolerance properti es, as being more refractive to SAPK activation induced by heat stress than its thermosensitive parental line, Stable expression of dominant inhibiting SEK mutants in thermosensitive parental cells specifically and effectively blocked SAPK activation after heat shock, These lines also became markedly resistant to the cytocidal effects of thermal st ress, confirming the phenotype of the thermotolerant line, These cell lines defective in SAPK activation were also resistant to the lethal e ffects of the DNA-damaging drug cis-platinum. Conclusions: Experimenta lly induced stable blockade of SAPK activation in cells with normal th ermosensitivity is sufficient to confer resistance to cell death induc ed by diverse stimuli including heat and the chemotherapeutic agent ci splatinum. These results suggest that activation of the SAPK pathway b y diverse cell stressors plays a critical part in mediating the toxici ty of these treatments and inducing cell death. SAPK activation in thi s context could broadly influence cellular response to stress, modulat e apoptosis during development or determine the clinical response of t umor cells to cytotoxic therapies.