The levels of expression of some genes of the HSP 70 family have been assessed in rat liver and in a series of transplantable hepatomas with different growth rates, subjected to heat shock in vivo. For this purpose, the mRNAs for the constitutive cognate HSC 73, the heat-inducible HSP 70 and the glucose-regulated GRP 78 have been analyzed by: (i) translation in reticulocyte lysates; (ii) hybrid-selected translation, and (iii) Northern blot analysis. In comparison with the liver, the fastgrowing 3924A hepatoma has an increased constitutive amount of HSC 73 mRNA and a lower induction of HSP 70 mRNA after heat shock. The behavior of the 9618A slow-growing hepatoma is more similar to that of the liver, indicating that the changes detected in the fastgrowing hepatoma are correlated to the high growth rate of the tumor rather than to carcinogenesis. This conclusion is reinforced by the results obtained with Yoshida AH-130 cells, growing at two different rates imposed by the environment in which they develop. When the Yoshida hepatoma grows rapidly in the peritoneal cavity, constitutive expression of HSC 73 mRNA is high and the inducibility of HSP 70 mRNA is poor: the opposite occurs when the tumor grows slowly in the subcutaneous compartment.
The amount of GRP 78 mRNA increases progressively from the liver to the fast-growing hepatoma.
The level of HSC 73 mRNA seems to correlate with the methylation state of the corresponding gene.