Temporal Control of NF-κB Activation by ERK Differentially Regulates Interleukin-1β-induced Gene Expression*

In cultured rat vascular smooth muscle cells, sustained activation of ERK is required for interleukin-1β to persistently activate NF-κB. Without ERK activation, interleukin-1β induces only acute and transient NF-κB activation. The present study examined whether the temporal control of NF-κB activation by ERK could differentially regulate the expression of NF-κB-dependent genes, including inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), vascular cell adhesion molecule-1 (VCAM-1), and manganese-containing superoxide dismutase (Mn-SOD). Treatment of vascular smooth muscle cells with interleukin-1β induced the expression of iNOS, COX-2, VCAM-1, and Mn-SOD in a time-dependent manner, but with different patterns. Either PD98059 or U0126, selective inhibitors of MEK, or overexpression of a dominant negative MEK-1 inhibited interleukin-1β- induced ERK activation and the expression of iNOS and COX-2 but had essentially no effect on the expression of VCAM-1 and Mn-SOD. The expression of these genes was inhibited when NF-κB activation was down-regulated by MG132, a proteasome inhibitor, or by overexpression of an I-κBα mutant that prevented both the transient and the persistent activation of NF-κB. Inhibition of ERK did not affect interleukin-1β-induced I-κBα phosphorylation and degradation but attenuated I-κBβ degradation. Thus, although NF-κB activation was essential for interleukin-1β induction of each of the proteins studied, gene expression was differentially regulated by ERK and by the duration of NF-κB activation. These results reveal a novel functional role for ERK as an important temporal regulator of NF-κB activation and NF-κB-dependent gene expression.