Abstract
Control of the stability of protein is thought to be involved in various biological processes, such as cell cycle and circadian clock. Endogenous ubiquitinated (Ub-) BMAL1 accumulated with MG132, a reversible inhibitor for proteolysis of Ub-proteins during Dexamethazone (Dex)-pulse treatment-induced cellular clock synchronization. This might be due to inhibition of BMAL1 degradation via Ub-proteasome. BMAL1 ubiqutination was suppressed by U0126, a phosphorylation inhibitor via ERK pathway. Inhibition of Ub-Proteasome during Dex-pulse significantly damped out-put circadian rhythm of luciferase-reporting Per2 gene expression (Per2-luc rhythm). BMAL1 contains conserved ERK phosphorylation sites in its PEST-like sequence, which is thought to be involved in the controlling protein stability. Transient transfection of GFP-BMAL1/PEST protein, which is expected to be a competitive inhibitor for ERK phosphorylation during Dex-pulse resulted in dramatically damped Per2-luc rhythm. We propose that controlling stability of BMAL1 via ERK phohorylation-dependent ubiquitination in its PEST-like sequence that has essential role in generating circadian clock oscillation. [J Physiol Sci. 2007;57 Suppl:S137]
