Human keratinocytes respond to osmotic stress by p38 map kinase regulated induction of HSP70 and HSP27

Human skin is exposed to an environment that varies in humidity from 100 to 0%, leading to seasonal variations in the condition of the skin. Exposure to a low humidity environment creates an osmotic gradient across the stratu m corneum, which is known to modulate cutaneous barrier function. Heat shoc k proteins protect against stress-induced destabilization of proteins. We i nvestigated whether osmotic shock (sorbitol) induced a heat shock protein r esponse in normal human keratinocytes, and used heat shock as a positive co ntrol. Both heat shock and osmotic stress (200 and 300 mM sorbitol) clearly induced heat shock proteins 70 and 27 mRNA levels. The induction of heat s hock protein 70 mRNA levels by osmotic stress peaked at 16 h and persisted until 24 h, whereas upregulation of heat shock protein 70 mRNA levels by he at peaked at 2 h and returned to baseline levels by 6 h. Sorbitol also incr eased heat shock protein 70 levels in a concentration-dependent manner. The kinetics of heat shock protein 27 mRNA induction by osmotic stress and hea t were similar with peak induction at 6 h. The mitogen activated protein ki nase family of proteins plays an important part in the coordination of gene responses to various stress conditions. We have demonstrated that the p38 mitogen activated protein kinase was strongly activated by 200 mM and 300 m M sorbitol. The specific p38 mitogen activated protein kinase inhibitor PD1 69316 almost completely blocked heat shock protein 70 mRNA induction by 200 mM and 300 mM sorbitol and completely suppressed heat shock protein 27 mRN A induction with 200 mM sorbitol. PD169316 also counteracted upregulation o f heat shock protein 70 levels by sorbitol. These data indicate that kerati nocytes respond to osmotic stress by p38 mitogen activated protein kinase r egulated induction of heat shock proteins. This molecular pathway may be re levant for the mechanisms regulating the response of human skin to variatio ns in environmental humidity.