title: Inhibition of PCSK9 transcription by berberine involves down-regulation of hepatic HNF1α protein expression through the ubiquitin-proteasome degradation pathway.
abstract: Our previous in vitro studies have identified hepatocyte nuclear factor 1α (HNF1α) as an obligated trans-activator for PCSK9 gene expression and demonstrated its functional involvement in the suppression of PCSK9 expression by berberine (BBR), a natural cholesterol-lowering compound. In this study, we investigated the mechanism underlying the inhibitory effect of BBR on HNF1α-mediated PCSK9 transcription. Administration of BBR to hyperlipidemic mice and hamsters lowered circulating PCSK9 concentrations and hepatic PCSK9 mRNA levels without affecting the gene expression of HNF1α. However, hepatic HNF1α protein levels were markedly reduced in BBR-treated animals as compared with the control. Using HepG2 cells as a model system, we obtained evidence that BBR treatment let to accelerated degradation of HNF1α protein. By applying inhibitors to selectively block the ubiquitin proteasome system (UPS) and autophagy-lysosomal pathway, we show that HNF1α protein content in HepG2 cells was not affected by bafilomycin A1 treatment, but it was dose-dependently increased by UPS inhibitors bortezomib and MG132. Bortezomib treatment elevated HNF1α and PCSK9 cellular levels with concomitant reductions of LDL receptor protein. Moreover, HNF1α protein displayed a multiubiquitination ladder pattern in cells treated with BBR or overexpressing ubiquitin. By expressing GFP-HNF1α fusion protein in cells, we observed that blocking UPS resulted in accumulation of GFP-HNF1α in cytoplasm. Importantly, we show that the BBR reducing effects on HNF1α protein and PCSK9 gene transcription can be eradicated by proteasome inhibitors. Altogether, our studies using BBR as a probe uncovered a new aspect of PCSK9 regulation by ubiquitin-induced proteasomal degradation of HNF1α.
authors.affiliation: From the Department of Veterans Affairs Palo Alto Health Care System, Palo Alto, California 94304.
authors.forename: Bin
authors.initials: B
authors.lastname: Dong
authors.affiliation: From the Department of Veterans Affairs Palo Alto Health Care System, Palo Alto, California 94304.
authors.forename: Hai
authors.initials: H
authors.lastname: Li
authors.affiliation: From the Department of Veterans Affairs Palo Alto Health Care System, Palo Alto, California 94304.
authors.forename: Amar Bahadur
authors.initials: AB
authors.lastname: Singh
authors.affiliation: From the Department of Veterans Affairs Palo Alto Health Care System, Palo Alto, California 94304.
authors.forename: Aiqin
authors.initials: A
authors.lastname: Cao
authors.affiliation: From the Department of Veterans Affairs Palo Alto Health Care System, Palo Alto, California 94304 Jingwen.Liu@va.gov.
authors.forename: Jingwen
authors.initials: J
authors.lastname: Liu
mesh_terms: D000818:Animals; D001599:Berberine / Q000494:pharmacology*; D015153:Blotting, Western; D002478:Cells, Cultured; D006224:Cricetinae; D005786:Gene Expression Regulation / Q000187:drug effects*; D057809:HEK293 Cells; D056945:Hep G2 Cells; D051538:Hepatocyte Nuclear Factor 1-alpha / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008647:Mesocricetus; D051379:Mice; D011401:Promoter Regions, Genetic / Q000235:genetics; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases / Q000037:antagonists & inhibitors* / Q000235:genetics* / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012697:Serine Endopeptidases / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D051538:Hepatocyte Nuclear Factor 1-alpha; D012333:RNA, Messenger; D025801:Ubiquitin; D001599:Berberine; C472126:Pcsk9 protein, mouse; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases; D012697:Serine Endopeptidases; D046988:Proteasome Endopeptidase Complex
keywords: Dyslipidemia; HNF1a; LDL Receptor; Lipid Metabolism; Nuclear Receptor; Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9); Proteasome; Ubiquitylation (Ubiquitination)