DGAT1 participates in the effect of HNF4A on hepatic secretion of triglyceride-rich lipoproteins.
OBJECTIVE
Hepatocyte nuclear factor-4alpha (HNF4A) is a transcription factor that influences plasma triglyceride metabolism via an as of yet unknown mechanism. In this study, we searched for the critical protein that mediates this effect using different human model systems.


RESULTS
Up- and downregulation of HNF4A in human hepatoma Huh7 and HepG2 cells was associated with marked changes in the secretion of triglyceride-rich lipoproteins (TRLs). Short interfering RNA (siRNA) inhibition of HNF4A influenced the expression of several genes, including acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1). siRNA knockdown of DGAT1 reduced DGAT1 activity and decreased the secretion of TRLs. No additive effects of combined siRNA inhibition of HNF4A and DGAT1 were found on the secretion of TRLs, whereas the increase in TRL secretion induced by HNF4A overexpression was largely abolished by DGAT1 siRNA inhibition. A putative binding site for HNF4A was defined by in silico and in vitro methods. HNF4A and DGAT1 expressions were analyzed in 80 human liver samples, and significant relationships were observed between HNF4A and DGAT1 mRNA levels (r(2)=0.50, P<0.0001) and between DGAT1 mRNA levels and plasma triglyceride concentration (r(2)=0.09, P<0.01).


CONCLUSIONS
This study identified DGAT1 as an important protein that participates in the effect of HNF4A on hepatic secretion of TRLs.
Krapivner
Sergey
S
Cardiovascular Genetics Group, Center for Molecular Medicine, Karolinska University Hospital, Stockholm, Sweden.
Iglesias
Maria Jesus
MJ
Silveira
Angela
A
Tegnér
Jesper
J
Björkegren
Johan
J
Hamsten
Anders
A
van't Hooft
Ferdinand M
FM
D001665:Binding Sites; D001706:Biopsy; D051048:Diacylglycerol O-Acyltransferase / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D056945:Hep G2 Cells; D051557:Hepatocyte Nuclear Factor 4 / Q000235:genetics / Q000378:metabolism*; D022781:Hepatocytes / Q000201:enzymology* / Q000378:metabolism; D006801:Humans; D008074:Lipoproteins / Q000097:blood / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D014162:Transfection; D014280:Triglycerides / Q000097:blood / Q000378:metabolism*
C496592:HNF4A protein, human; D051557:Hepatocyte Nuclear Factor 4; D008074:Lipoproteins; D012333:RNA, Messenger; D014280:Triglycerides; C494881:DGAT1 protein, human; D051048:Diacylglycerol O-Acyltransferase