Extracellular signal-regulated kinase-dependent stabilization of hepatic low-density lipoprotein receptor mRNA by herbal medicine berberine

Objective - Our recent studies identified berberine (BBR) as a novel cholesterol-lowering drug that upregulates low-density lipoprotein (LDL) receptor expression through mRNA stabilization. Here, we investigated mechanisms underlying regulatory effects of BBR on LDL receptor ( LDLR) messenger. Methods and Results - We show that the extracellular signal-regulated kinase (ERK) signaling pathway is used primarily by BBR to attenuate the decay of LDLR mRNA in HepG2 cells. Using different reporter constructs, we demonstrate that BBR affects LDLR mRNA stability entirely through 3' untranslated region (UTR) in an ERK-dependent manner, and this stabilizing effect is more prominent in liver-derived cells than nonhepatic cell lines. In contrast to BBR, the mRNA stabilizing effect of bile acid chenodeoxycholic acid is mediated through the LDLR coding sequence, whereas the 5' UTR, 3'UTR, and the coding sequence of LDLR mRNA are all implicated in the action of phorbol 12-myristate 13-acetate. By performing UV cross-linking and SDS-PAGE, we identify 2 cytoplasmic proteins of 52 and 42 kDa that specifically bind to the LDLR 3' UTR in BBR-inducible and ERK-dependent manners. Conclusions - These new findings demonstrate that the BBR-induced stabilization of LDLR mRNA is mediated by the ERK signaling pathway through interactions of cis-regulatory sequences of 3'UTR and mRNA binding proteins that are downstream effectors of this signaling cascade.