HEAT-SHOCK RESPONSE INHIBITS CYTOKINE-INDUCIBLE NITRIC-OXIDE SYNTHASEEXPRESSION IN RAT HEPATOCYTES

During sepsis or inflammation, the liver expresses various protective phenotypes such as the acute phase response or the heat shock response (HSR). Inducible nitric oxide synthase (NOS2) is also expressed in th e liver in these conditions and may protect the liver under some circu mstances and promote injury in others. We have previously reported tha t the acute phase response and NOS2 expression are differentially regu lated, though both can be expressed simultaneously. The HSR is known t o prevent expression of other genes, but its effects on NOS2 expressio n in the liver is unknown. Therefore, we examined how the HSR influenc es NOS2 expression in primary rat hepatocytes. Sodium arsenite (Ars) o r hyperthermia (43 degrees C) induced the synthesis of hsp72 messenger RNA (mRNA) and protein in hepatocytes, indicating activation of the H SR. In the absence of the HSR, combinations of interleukin-1 beta (IL- 1 beta), tumor necrosis factor alpha (TNF-alpha), and interferon gamma (IFN-gamma) stimulated high levels of NOS2 mRNA and nitric oxide (NO) synthesis, Hoowever, treatment with Ars or heat shock significantly a ttenuated cytokine-induced NOS2 mRNA and NO production. The addition o f the nuclear factor kappa B (NF-kappa B) inhibitor pyrrolidine dithio carbamate also inhibited NOS2 expression, suggesting a role for NF-kap pa B in the cytokine induction of NOS2 in hepatocytes. Cytokines induc ed the appearance of an NF-kappa B complex as shown in gel retardation assays; however, induction of the HSR by Ars partially prevented cyto kine-induced formation of this band while hyperthermia had a more comp lete inhibition, Furthermore, preinduction of the HSR prevented the ac tivation of the NOS2 promoter construct in hepatocytes transfected wit h a 1.6 kilobase NOS2 promoter linked to luciferase. These findings sh ow that NO production in stressed cells can be modulated by the HSR, p ossibly through repression of NOS2 gene transcription via the inhibiti on of NF-kappa B.