The relationship between the stress protein response and the acute phase response (APPR) was studied in human hepatoma cells to investigate the hierarchy of regulation of these survival responses. Huh-7 cells were subjected to heat treatment (febrile-range temperature 40°C or heat shock 43°C) followed by recovery at 37°C in the presence or absence of IL-6 given either before or after heat treatment. The effects on total, fractional, and acute phase protein synthesis were then analyzed by metabolic labeling, ELISA, real-time PCR, Northern blot analysis, and activation of an α1-antitrypsin reporter plasmid. Cell energetics were studied under the same conditions using an index of mitochondrial activity and measurement of cellular ATP levels. Febrile-range temperature (40°C) augmented acute phase protein production when cells had been pretreated with IL-6. Pretreatment of cells with IL-6 also prevented heat shock-induced suppression of α1-antichymotrypsin (ACT) but not transferrin. mRNA expression of ACT and α1-antitrypsin reporter activation studies was consistent with transcriptional regulation of these proteins. Expression of mRNA transcripts for transferrin was increased despite protein expression being reduced by heat shock. The effects of heat shock on acute phase protein synthesis can be modified by preincubation with IL-6, whereas addition of this ligand after heat treatment has no effect on the suppressive effect of heat on the APPR. The mechanism of this action appears to be transcriptionally regulated in the case of ACT, but in the case of transferrin, it may be mediated by another process such as posttranslational modification.
Modeling the Dynamics of Acute Phase Protein Expression in Human Hepatoma Cells Stimulated by IL-6