DISTINCT REGULATION OF OSMOPROTECTIVE GENES IN YEAST AND MAMMALS - ALDOSE REDUCTASE OSMOTIC RESPONSE ELEMENT IS INDUCED INDEPENDENT OF P38 AND STRESS-ACTIVATED PROTEIN-KINASE JUN N-TERMINAL KINASE IN RABBIT KIDNEY-CELLS

In yeast glycerol-3-phosphate dehydrogenase 1 is essential for synthes is of the osmoprotectant glycerol and is osmotically regulated via the high osmolarity glycerol (HOG1) kinase pathway. Homologous protein ki nases, p38, and stress-activated protein kinase/Jun N-terminal kinase (SAPK/JNK) are hyperosmotically activated in some mammalian cell lines and complement HOG1 in yeast, In the present study we asked whether p 38 or SAPK/JNK signal synthesis of the osmoprotectant sorbi tol in rab bit renal medullary cells (PAP-HT25), analogous to the glycerol system in yeast, Sorbitol synthesis is catalyzed by aldose reductase (AR). H yperosmolality increases AR transcription through an osmotic response element (ORE) in the 5'-flanking region of the AR gene, resulting in e levated sorbitol, We tested if AR-ORE is targeted by p38 or SAPK/JNK p athways in PAP-HT25 cells. Hyperosmolality (adding 150 nM NaCl) strong ly induces phosphorylation of p38 and of c-Jun, a specific target of S APK/JNK, Transient lipofection of a dominant negative mutant of SAPK k inase, SEK1-AL, into PAP-HT25 cells specifically inhibits hyperosmotic ally induced c-Jun phosphorylation, Transient Lipofection of a dominan t negative p38 kinase mutant, MKK3-AL, into PAP-HT25 cells specificall y suppresses hyperosmotic induction of p38 phosphorylation, We cotrans fected either one of these mutants or their empty vector with an AR OR E luciferase reporter construct and compared the hyperosmotically indu ced increase in luciferase activity with that in cells lipofected with only the AR-ORE luciferase construct, Hyperosmolality increased lucif erase activity equally (5-7-fold) under all conditions, We conclude th at hyperosmolality induces p38 and SAPK/JNK cascades in mammalian rena l cells, analogous to inducing the HOG1 cascade in yeast. However, act ivation of p38 or SAPK/JNK pathways is not necessary for transcription al regulation of AR through the ORE. This finding stands in contrast t o the requirement for the HOG1 pathway for hyperosmotically induced ac tivation of yeast GPD1.