Spontaneous overexpression of heat-shock proteins in Ehrlich ascites carcinoma cells during in vivo growth.

Ehrlich carcinoma (EC) cells isolated from mice at different phases of ascites growth were exposed to hyperthermia (44 degrees C), or oxidative stress (hydrogen peroxide or vikasol), or ATP depletion induced by rotenone. These exposures caused protein aggregation and rapid necrotic death in exponentially growing EC cells. On the contrary, the same cell culture at stationary phase of growth became considerably more resistant to all the above cytotoxic treatments, and the level of aggregated protein was significantly lower in stressed stationary EC cells than that in exponential ones. Comparative immunoblotting has revealed the unexpected expression of inducible 70 kDa heat-shock protein form (HSP68), as well as accumulation of HSP27 and HSP90 in the thermo- and drug-resistant stationary EC cells. It is suggested that the in vivo occurring HSP overexpression in stationary EC cells is an adaptive modulation of the tumor cell phenotype to maintain the viability of ascites EC cells under chronic deficiency of oxygen and nutrients.