The p38 MAPK PMK-1 shows heat-induced nuclear translocation, supports chaperone expression, and affects the heat tolerance of Caenorhabditis elegan s

The p38 mitogen-activated protein kinase PMK-1 of Caenorhabditis elegan s has been associated with heavy metal, oxidative and pathogen stress. Pmk-1 is part of an operon comprising three p38 homologues, with pmk-1 expression suggested to be regulated by the operon promoter. There are contradictory reports about the cellular localization of PMK-1. We were interested to study principles of pmk-1 expression and to analyze the role of PMK-1 under heat stress. Using a translational GFP reporter, we found pmk-1 expression to be driven by a promoter in front of pmk-1 . PMK-1 was detected in intestinal cells and neurons, with a cytoplasmic localization at moderate temperature. Increasing temperature above 32 °C, however, induced a nuclear translocation of PMK-1 as well as PMK-1 accumulation near to apical membranes. Testing survival rates revealed 34–35 °C as critical temperature range, where short-term survival severely decreased. Mutants of the PMK-1 pathway ( pmk-1 Δ, sek-1 Δ, mek-1 Δ) as well as a mutant of JNK pathway ( jnk-1 Δ) showed significantly lower survival rates than wild-type or mutants of other pathways ( kgb-1 Δ, daf-2 Δ). Rescue and overexpression experiments verified the negative effects of pmk-1 Δ on heat tolerance. Studying gene expression by RNA-seq and semi-quantitative reverse transcriptase polymerase chain reaction revealed positive effects of the PMK-1 pathway on the expression of genes for chaperones, protein biosynthesis, protein degradation, and other functional categories. Thus, the PMK-1 pathway is involved in the heat stress responses of C. elegans , possibly by a PMK-1-mediated activation of the transcription factor SKN-1 and/or an indirect or direct PMK-1-dependent activation (hyperphosphorylation) of heat-shock factor 1.