The MAP kinase cascade is not essential for transcriptional stimulation of osmolyte transporter genes.

Kidney derived MDCK cells are protected from the stress of hypertonicity by accumulating compatible osmolytes. Accumulation of the compatible osmolytes myo-inositol and betaine is driven by hypertonicity-induced stimulation of transcription of the genes coding for the myo-inositol cotransporter and the betaine cotransporter. We tested the importance of the mitogen-activated protein kinase pathway in transcriptional activation of the genes for the two osmolytes cotransporters because this kinase pathway is rapidly activated when cells are exposed to hypertonicity and a mitogen-activated protein kinase pathway is essential for the osmo-protective transcriptional response of yeast to hypertonicity. Eliminating the activation of mitogen-activated protein kinase did not block the hypertonicity induced increase in accumulation of osmolyte transporter mRNA.