Osmotic regulation of the heat shock response in H4IIE rat hepatoma cells

The influence of cell hydration on the heat shock response was investigated in H4IIE hepatoma cells at the levels of HSP70 expression, MAP kinase activation, induction of c-jun and the RAP kinase phosphatase MKP-1, heat resistance, and development of tolerance/sensitization to arsenite after a priming heat treatment. Induction of HSP70, MKP-1, and c-jun by heat was delayed, but more pronounced or sustained, under hyperosmotic conditions compared with normo- and hypo-osmotically exposed cells. Anisosmolarity per sc was ineffective to induce HSP70; some expression of the mRNAs for MKP-1 and c-jun in response to hyperosmolarity nas found, but was small compared with the response to heat. Heat-induced activation of JNK-1 was increased under hyperosmotic conditions and more sustained than the JNK-activity induced by hyperosmolarity at 37 degrees C, A prominent Erk-2 activation was found immediately after heat shock under hypo- and normo-osmotic conditions, but Erk-2 activation was weak in hyperosmolarity-exposed cells. Despite anisosmotic alterations of the heat shock response at the molecular level, the heat resistance of H4IIE cells toward heat shock was not affected by ambient osmolarity, However, an osmolarity-dependent sensitization to arsenite was: induced by a priming heat shock. The osmodependence of the H4IIE cell response to heat differs from that recently found in primary rat hepatocytes, The data are discussed in terms of cellular adaption mechanisms and their physiological relevance.