Transcriptional regulation of lipid synthesis in bovine mammary epithelial cells by sterol regulatory element binding protein-1.
The objective of this study was to investigate the transcriptional regulation of lipid synthesis by sterol regulatory element binding protein-1 (SREBP-1) in bovine mammary epithelial cells. In the current study, bovine mammary epithelial (MAC-T) cells cultured in insulin- and prolactin-containing medium were treated with a transfection reagent as control, a nontargeting small interfering (si)RNA sequence (100 nM) as a negative control, or an SREBP-1-specific siRNA (100 nM) for 48 h. The mRNA expression of SREBP-1 was decreased more than 90% by siRNA. Precursor and mature forms of SREBP-1 protein were undetectable in cells treated with SREBP-1 siRNA. Fatty acid synthesis and fatty acid uptake, measured using isotope incorporation, were reduced significantly in cells treated with SREBP-1 siRNA compared with controls. Transcript abundance of acyl-CoA synthetase short-chain family member 2, acetyl-CoA carboxylase, fatty acid synthetase, and isocitrate dehydrogenase 1 (key enzymes of de novo lipogenesis) was decreased by 40 to 65% with SREBP-1 siRNA, in agreement with acetate incorporation data. The mRNA levels of fatty acid binding protein 3 and stearyl-CoA desaturase 1 (proteins responsible for intracellular fatty acid trafficking and long-chain fatty acid modification) were decreased 76 and 60%, respectively, by SREBP-1 siRNA treatment compared with controls. The mRNA expression of mitochondrial glycerol-3-phosphate acyltransferase and lipin 1 (involved in triglyceride synthesis) was significantly decreased in cells treated with SREBP-1 siRNA compared with control cells. However, the expression of milk fat globule membrane proteins measured did not differ among treatments. In conclusion, SREBP-1 plays an important role in integrated regulation of lipid synthesis in bovine mammary epithelial cells through regulation of key enzymes.
Department of Dairy Science, Virginia Tech, Blacksburg 24061, USA.
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D000103:Acetyl-CoA Carboxylase / Q000502:physiology; D000818:Animals; D002417:Cattle; D003066:Coenzyme A Ligases / Q000502:physiology; D004848:Epithelium / Q000378:metabolism / Q000502:physiology; D064429:Fatty Acid Synthases / Q000502:physiology; D005260:Female; D005786:Gene Expression Regulation / Q000502:physiology; D007521:Isocitrate Dehydrogenase / Q000502:physiology; D008055:Lipids / Q000096:biosynthesis*; D008321:Mammary Glands, Animal / Q000378:metabolism / Q000502:physiology*; D051780:Sterol Regulatory Element Binding Protein 1 / Q000502:physiology*
D008055:Lipids; D051780:Sterol Regulatory Element Binding Protein 1; D007521:Isocitrate Dehydrogenase; D064429:Fatty Acid Synthases; D003066:Coenzyme A Ligases; D000103:Acetyl-CoA Carboxylase