title: Phosphorylation regulates mitochondrial glycerol-3-phosphate-1 acyltransferase activity in T-lymphocytes.
abstract: Recently, we have shown that stimulation and recombinant ACBP increase mitochondrial glycerol-3-phosphate acyltransferase (mtGPAT) activity in rat splenic T-lymphocytes and that this effect is blunted in aged T-lymphocytes. In addition to decreased mtGPAT activity, aged T-lymphocytes also have altered membrane lipid composition and decreased proliferation in response to antigen. Therefore, we wanted to determine the mechanism by which mtGPAT activity is regulated in aged T-lymphocytes. We show that aged T-lymphocyte mtGPAT activity is not increased by ex vivo stimulation or in vitro phosphorylation with casein kinase II and protein kinase C theta as is seen in young T-lymphocytes. However, other factors that might impact mtGPAT activity such as reduced mtGPAT protein levels, gene expression or alterations in the soluble acyl-CoA pool were not affected by age or stimulation. The age effect was also not compensated for by increased acyl-CoA binding protein expression in aged T-lymphocytes. Currently, two mitochondrial GPAT (mtGPAT) isoforms (mtGPAT1 and mtGPAT2) have been identified. We found that T-lymphocytes express mtGPAT1, but not mtGPAT2, suggesting that at least mtGPAT1 is sensitive to phosphorylation in vitro. Support for direct phosphorylation of mtGPAT1 in young T-lymphocytes is shown by mtGPAT1 immunoprecipitation where a phosphoprotein band was detected migrating at the same molecular weight (85 kDa) as mtGPAT1. This is significant because we also show that T-lymphocytes from mtGPAT1 KO mice have reduced proliferation ex vivo as is seen in aged T-lymphocytes. These data provide evidence for a novel mechanism by which T-lymphocyte proliferation may be regulated and, for the first time, give a potential mechanistic explanation for the correlation between reduced proliferation and membrane lipid changes seen in aged T-lymphocytes.
authors.affiliation: Division of Nutritional Sciences and the Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, TX 78712, USA.
authors.forename: Lauren W
authors.initials: LW
authors.lastname: Collison
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Jolly
mesh_terms: D000818:Animals; D017931:DNA Primers; D005227:Fatty Acids / Q000032:analysis; D005992:Glycerol-3-Phosphate O-Acyltransferase / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D006706:Homeostasis; D008213:Lymphocyte Activation; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008928:Mitochondria / Q000201:enzymology*; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D051381:Rats; D017207:Rats, Sprague-Dawley; D013601:T-Lymphocytes / Q000201:enzymology*
chemical_list: D017931:DNA Primers; D005227:Fatty Acids; D005992:Glycerol-3-Phosphate O-Acyltransferase