title: The critical role of mRNA destabilizing protein heterogeneous nuclear ribonucleoprotein d in 3' untranslated region-mediated decay of low-density lipoprotein receptor mRNA in liver tissue.
abstract: OBJECTIVE
  Previous studies showed that low-density lipoprotein receptor (LDLR) mRNA 3' untranslated region (UTR) contains regulatory elements responsible for rapid mRNA turnover in hepatic cells and mediates the mRNA stabilization induced by berberine (BBR). Here, we elucidate the underlying mechanism of BBR's action by characterizing mRNA-binding proteins that modulate LDLR mRNA decay via 3'UTR in liver tissue in vivo.
  
  
  RESULTS
  We generated a transgenic mouse model (Alb-Luc-UTR) that expresses Luc-LDLR3'UTR reporter gene driven by the albumin promoter to study 3'UTR function in mediating LDLR mRNA decay in liver tissue. We show that treating Alb-Luc-UTR mice with BBR led to significant increases in hepatic bioluminescence signals, Luc-UTR mRNA, and LDLR mRNA levels as compared with control mice. These effects were accompanied by specific reductions of mRNA decay-promoting factor heterogeneous nuclear ribonucleoprotein D (hnRNP D) in liver of BBR-treated mice. Knockdown and overexpression studies further demonstrated that hnRNP D p37 isoform plays a major role in promoting hepatic LDLR mRNA degradation. In addition, we examined LDLR mRNA half-life, Luc-UTR reporter activity, and hnRNP D expression levels in cell lines derived from extrahepatic tissues. We demonstrated that strengths of 3'UTR in promoting mRNA degradation correlate with hnRNP D cellular abundances in nonhepatic cell lines, thereby suggesting its involvement in LDLR mRNA degradation beyond liver tissue.
  
  
  CONCLUSIONS
  hnRNP D is critically involved in LDLR mRNA degradation in liver tissue in vivo. The inverse relationship of hnRNP D abundance with LDLR mRNA levels after BBR treatment suggests the potential of hnRNP D of being a novel therapeutic target for LDL cholesterol lowering.
authors.affiliation: From the Veterans Affairs Palo Alto Health Care System, CA (A.B.S., H.L., C.F.K.K., B.D., M.R.N., J.L.); and Department of Medicine, Stanford University, CA (A.B.S., H.L., B.D., M.R.N.).
authors.forename: Amar Bahadur
authors.initials: AB
authors.lastname: Singh
authors.forename: Hai
authors.initials: H
authors.lastname: Li
authors.forename: Chin Fung Kelvin
authors.initials: CF
authors.lastname: Kan
authors.forename: Bin
authors.initials: B
authors.lastname: Dong
authors.forename: Mark R
authors.initials: MR
authors.lastname: Nicolls
authors.forename: Jingwen
authors.initials: J
authors.lastname: Liu
mesh_terms: D020413:3' Untranslated Regions; D000418:Albumins / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D001599:Berberine / Q000494:pharmacology; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D017930:Genes, Reporter; D006207:Half-Life; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D034502:Heterogeneous-Nuclear Ribonucleoprotein D / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D034622:RNA Interference; D020871:RNA Stability; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D011973:Receptors, LDL / Q000235:genetics* / Q000378:metabolism; D014162:Transfection
chemical_list: D020413:3' Untranslated Regions; D000418:Albumins; D034502:Heterogeneous-Nuclear Ribonucleoprotein D; C573412:LDLR protein, human; D012333:RNA, Messenger; D011973:Receptors, LDL; D001599:Berberine; D008156:Luciferases
keywords: 3' untranslated regions; AU rich elements; RNA stability; berberine; hypercholesterolemia; receptors, LDL