Inhibitory and stimulatory effects of lactacystin on expression of nitric oxide synthase type 2 in brain glial cells - The role of I kappa B-beta

Expression of inflammatory nitric oxide synthase (NOS2) is mediated by tran scription factor NF kappa B. By using the specific proteasome inhibitor lac tacystin to examine I kappa B degradation, we observed a paradoxical increa se in lipopolysaccharide- and cytokine-dependent NOS2 expression at low con centrations or when lactacystin was added subsequent to cytokines. Lactacys tin reduced the initial accumulation of NOS2 mRNA but reduced its subsequen t decrease. Lactacystin increased NOS2 promoter activation after 24 h, but not after 4 h, and similarly prevented initial NF kappa B activation and at later times caused NF kappa B reactivation. Lactacystin reduced initial de gradation of I kappa B-alpha and I kappa B-beta, however, at later times se lectively increased I kappa B-beta, which was predominantly non-phosphoryla ted. Expression of full-length rat I kappa B-beta, but not a carboxyl-termi nal truncated form, inhibited NOS2 induction and potentiation by lactacysti n, Lactacystin increased I kappa B-beta expression in the absence of NOS2 i nducers, as well as expression of heat shock protein 70, and the heat shock response due to hyperthermia increased I kappa B-beta expression. These re sults suggest that I kappa B-beta contributes to persistent NF kappa B acti vation and NOS2 expression in glial cells, that I kappa B-beta is a stress protein inducible by hyperthermia or proteasome inhibitors, and that delaye d addition of proteasome inhibitors can have stimulatory rather than inhibi tory actions.