Fatty acid regulation of liver X receptors (LXR) and peroxisome proliferator-activated receptor alpha (PPARalpha ) in HEK293 cells.
Fatty acids bind to and regulate the activity of peroxisome proliferator-activated (PPAR) and liver X receptors (LXR). However, the role lipid metabolism plays in the control of intracellular fatty acid ligands is poorly understood. We have identified two strains of HEK293 cells that display differences in fatty acid regulation of nuclear receptors. Using full-length and Gal4-LBD chimeric receptors in functional assays, 20:4,n6 induced PPARalpha activity approximately 2.2-fold and suppressed LXRalpha activity by 80% (ED50 approximately 25-50 microm) in HEK293-E (early passage) cells but had no effect on PPARalpha or LXRalpha receptor activity in HEK293-L (late passage) cells. LXRbeta was insensitive to fatty acid regulation in both HEK293 strains. Metabolic labeling studies using [14C]20:4,n6 (at 100 microm) indicated that the uptake of 20:4,n6 and its assimilation into triacylglycerol, diacylglycerol, and polar lipids revealed no difference between the two strains. Such treatment increased total cellular 20:4,n6 ( approximately 11-fold) and its elongation product, 22:4,n6 ( approximately 3.6-fold), within 6 h. Non-esterified 20:4,n6 and 22:4,n6 represented <or=3% of the total cellular 20:4,n6 and 22:4,n6. In HEK293-E cells, non-esterified 20:4,n6 and 22:4,n6 increased 8- and 18-fold, respectively, by 6 h and was sustained at that level for 24 h. In HEK293-L cells, non-esterified 20:4,n6 also increased (5-fold) at 6 h but fell by 70% within 24 h. In contrast to HEK293-E cells, non-esterified 22:4,n6 did not accumulate in HEK293-L cells. Functional assays showed that 22:4,n6 was approximately 2-fold more effective than 20:4,n6 at inhibiting oxysterol-induced LXRalpha activity in HEK293-E cells, but had no effect on LXRalpha activity in HEK293-L cells. Taken together, these findings demonstrate that the rate of assimilation of exogenously added fatty acids and their metabolites into complex lipids plays an important role in regulating PPARalpha and LXRalpha activity.
Pawar
Anjali
A
Department of Physiology, Michigan State University, East Lansing, Michigan 48824, USA.
Xu
Jinghua
J
Jerks
Erik
E
Mangelsdorf
David J
DJ
Jump
Donald B
DB
D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002474:Cell-Free System; D002851:Chromatography, High Pressure Liquid; D004268:DNA-Binding Proteins; D004305:Dose-Response Relationship, Drug; D005227:Fatty Acids / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D005822:Genetic Vectors; D006801:Humans; D050356:Lipid Metabolism; D000071518:Liver X Receptors; D057093:Orphan Nuclear Receptors; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection
D004268:DNA-Binding Proteins; D005227:Fatty Acids; D005231:Fatty Acids, Unsaturated; D000071518:Liver X Receptors; C000605213:NR1H3 protein, human; D057093:Orphan Nuclear Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors