A feed-forward loop amplifies nutritional regulation of PNPLA3.
The upsurge in prevalence of obesity has spawned an epidemic of nonalcoholic fatty liver disease (NAFLD). Previously, we identified a sequence variant (I148M) in patatin-like phospholipase domain-containing protein 3 (PNPLA3) that confers susceptibility to both hepatic triglyceride (TG) deposition and liver injury. To glean insights into the biological role of PNPLA3, we examined the molecular mechanisms by which nutrient status controls hepatic expression of PNPLA3. PNPLA3 mRNA levels, which were low in fasting animals, increased approximately 90-fold with carbohydrate feeding. The increase was mimicked by treatment with a liver X receptor (LXR) agonist and required the transcription factor SREBP-1c. The site of SREBP-1c binding was mapped to intron 1 of Pnpla3 using chromatin immunoprecipitation and electrophoretic mobility shift assays. SREBP-1c also promotes fatty acid synthesis by activating several genes encoding enzymes in the biosynthetic pathway. Addition of fatty acids (C16:0, C18:1, and C18:2) to the medium of cultured hepatocytes (HuH-7) increased PNPLA3 protein mass without altering mRNA levels. The posttranslational increase in PNPLA3 levels persisted after blocking TG synthesis with triascin C. Oleate (400 muM) treatment prolonged the half-life of PNPLA3 from 2.4 to 6.7 h. These findings are consistent with nutritional control of PNPLA3 being effected by a feed-forward loop; SREBP-1c promotes accumulation of PNPLA3 directly by activating Pnpla3 transcription and indirectly by inhibiting PNPLA3 degradation through the stimulation of fatty acid synthesis.
Huang
Yongcheng
Y
Departments of Molecular Genetics and Internal Medicine, The Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
He
Shaoqing
S
Li
John Zhong
JZ
Seo
Young-Kyo
YK
Osborne
Timothy F
TF
Cohen
Jonathan C
JC
Hobbs
Helen H
HH
D000818:Animals; D002460:Cell Line; D047369:Chromatin Immunoprecipitation; D002874:Chromosome Mapping; D004040:Dietary Carbohydrates / Q000494:pharmacology; D024202:Electrophoretic Mobility Shift Assay; D005215:Fasting / Q000502:physiology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D008049:Lipase / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009752:Nutritional Status / Q000502:physiology*; D009841:Oligonucleotides / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000217:Acyltransferases; D054512:Phospholipases A2, Calcium-Independent
D004040:Dietary Carbohydrates; D047908:Intracellular Signaling Peptides and Proteins; D008049:Lipase; D008565:Membrane Proteins; D009841:Oligonucleotides; C102196:SREBP cleavage-activating protein; C533682:PNPLA3 protein, human; D000217:Acyltransferases; D054512:Phospholipases A2, Calcium-Independent
Am J Physiol. 1994 Feb;266(2 Pt 1):E179-85
8141275
Nat Genet. 2010 Jan;42(1):21-3
19946271
Proc Natl Acad Sci U S A. 2003 Oct 14;100(21):11980-5
14530388
Biochem J. 1971 Feb;121(3):379-90
5154523
J Clin Invest. 2002 May;109(9):1125-31
11994399
Proc Natl Acad Sci U S A. 2009 Aug 18;106(33):13765-9
19666523
J Biol Chem. 2004 Nov 19;279(47):48968-75
15364929
J Biol Chem. 2004 Nov 5;279(45):47066-75
15337759
Cell. 1987 Mar 27;48(6):1061-9
3030558
J Biol Chem. 2001 Sep 7;276(36):33336-44
11431482
J Lipid Res. 2009 Apr;50 Suppl:S63-8
19029121
J Antibiot (Tokyo). 1986 Sep;39(9):1211-8
3781919
Curr Protoc Bioinformatics. 2002 Nov;Chapter 2:Unit 2.4
18792935
Proc Natl Acad Sci U S A. 1998 May 26;95(11):5987-92
9600904
Gastroenterology. 1998 Apr;114(4):842-5
9547102
Proc Natl Acad Sci U S A. 2004 Aug 3;101(31):11245-50
15266058
Hepatology. 2004 Dec;40(6):1387-95
15565570
Biochemistry. 2003 Jun 10;42(22):6696-708
12779324
J Clin Invest. 1996 Oct 1;98(7):1575-84
8833906
J Biol Chem. 1999 Oct 15;274(42):30028-32
10514488
J Lipid Res. 2009 Oct;50(10):2111-6
19738004
J Med Genet. 2010 Feb;47(2):116-9
19542081
J Clin Invest. 1997 Mar 1;99(5):838-45
9062340
J Hepatol. 2008;48 Suppl 1:S104-12
18304679
J Biol Chem. 2002 Mar 15;277(11):9520-8
11782483
J Neurochem. 2004 Feb;88(3):545-53
14720204
J Hepatol. 2010 Feb;52(2):244-51
20015565
Diabetologia. 2009 Jun;52(6):1056-60
19224197
Am J Gastroenterol. 2004 Feb;99(2):292-8
15046220
Diabetes. 2006 Jan;55(1):148-57
16380488
J Biol Chem. 2008 Nov 28;283(48):33772-83
18835813
Genes Dev. 2000 Nov 15;14(22):2819-30
11090130
J Biol Chem. 2010 Feb 26;285(9):6706-15
20034933
Nat Genet. 2008 Dec;40(12):1461-5
18820647
Cell. 1996 Nov 1;87(3):415-26
8898195
J Clin Invest. 1997 Mar 1;99(5):846-54
9062341
Mol Cell Biol. 2001 May;21(9):2991-3000
11287605
J Lipid Res. 2006 Sep;47(9):1940-9
16799181
Am J Hum Genet. 2008 Oct;83(4):520-8
18940312
J Clin Invest. 1998 Jun 1;101(11):2331-9
9616204
Genes Dev. 2001 May 15;15(10):1206-16
11358865
J Clin Invest. 2008 Mar;118(3):956-64
18292813
Science. 2004 Nov 19;306(5700):1383-6
15550674
J Lipid Res. 2005 Nov;46(11):2477-87
16150821
Genes Dev. 2000 Nov 15;14(22):2831-8
11090131
J Biol Chem. 1998 Dec 25;273(52):35299-306
9857071