title: Berberine up-regulates hepatic low-density lipoprotein receptor through Ras-independent but AMP-activated protein kinase-dependent Raf-1 activation.
abstract: Our previous studies showed that berberine (BBR) increases liver low-density lipoprotein (LDL) receptor expression in an extracellular signal-regulated kinase (ERK)-dependent manner. This study was designed to explore the upstream cellular signaling molecules recruited by BBR to activate the ERK mitogen-activated protein kinase (MAPK) cascade. Chemical inhibitors such as GW5074, manumycin A, and compound C or specific small interfering RNAs (siRNAs) were used in the blocking experiments; Western blot was used to determine the phosphorylation of kinases; real-time reverse transcriptase polymerase chain reaction (RT-PCR) was used to determine the expression level of LDL receptor mRNA. Our results indicate that BBR increases p-Raf-1 (ser338) level time and dose dependently in HL-7702 cells, but has no influence on Ras activity; the stimulating activities of BBR on Raf-1 signaling and LDL receptor expression can be blocked by GW5074 completely, but not by manumycin A, a Ras inhibitor. BBR activates hepatic Raf-1 signaling and up-regulates LDL receptor expression in a rat model of hyperlipidemia with no impact on liver Ras activity. Importantly, our results show that the stimulating activities of BBR on hepatic Raf-1 signaling and LDL receptor expression are totally blocked by compound C, a selective inhibitor of AMP-activated protein kinase (AMPK), and also by silencing its expression with siRNA. Taken together, our results demonstrate for the first time that BBR up-regulates LDL receptor expression through Ras-independent, but AMPK-dependent Raf-1 activation in liver cells. Our study will help to elucidate the molecular pharmacology of BBR and provide new scientific evidence for its clinical application.
authors.affiliation: Department of Pharmacology, Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical College.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Li
authors.forename: Jian-Dong
authors.initials: JD
authors.lastname: Jiang
authors.forename: Wei-Jia
authors.initials: WJ
authors.lastname: Kong
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000818:Animals; D001599:Berberine / Q000494:pharmacology*; D002460:Cell Line; D006801:Humans; D006949:Hyperlipidemias / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D011090:Polyenes / Q000494:pharmacology; D053284:Polyunsaturated Alkamides / Q000494:pharmacology; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D017207:Rats, Sprague-Dawley; D011973:Receptors, LDL / Q000096:biosynthesis* / Q000235:genetics; D015854:Up-Regulation / Q000187:drug effects; D018631:ras Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D011090:Polyenes; D053284:Polyunsaturated Alkamides; D011973:Receptors, LDL; D001599:Berberine; D019908:Proto-Oncogene Proteins c-raf; D055372:AMP-Activated Protein Kinases; D018631:ras Proteins; C054474:manumycin