Complex transcriptional and translational regulation of iPLAgamma resulting in multiple gene products containing dual competing sites for mitochondrial or peroxisomal localization.
Membrane-associated calcium-independent phospholipase A2gamma (iPLA2gamma) contains four potential in-frame methionine start sites (Mancuso, D.J. Jenkins, C.M. & Gross, R.W. (2000) J. Biol. Chem.275, 9937-9945), but the mechanisms regulating the types, amount and subcellular localization of iPLA2gamma in cells are incompletely understood. We now: (a) demonstrate the dramatic transcriptional repression of mRNA synthesis encoding iPLA2gamma by a nucleotide sequence nested in the coding sequence itself; (b) localize the site of transcriptional repression to the most 5' sequence encoding the iPLA2gamma holoprotein; (c) identify the presence of nuclear protein constituents which bind to the repressor region by gel shift analysis; (d) demonstrate the translational regulation of distinct iPLA2gamma isoforms; (e) identify multiple novel exons, promoters, and alternative splice variants of human iPLA2gamma; (f) document the presence of dual-competing subcellular localization signals in discrete isoforms of iPLA2gamma; and (g) demonstrate the functional integrity of an N-terminal mitochondrial localization signal by fluorescence imaging and the presence of iPLA2gamma in the mitochondrial compartment of rat myocardium. The intricacy of the regulatory mechanisms of iPLA2gamma biosynthesis in rat myocardium is underscored by the identification of seven distinct protein products that utilize multiple mechanisms (transcription, translation and proteolysis) to produce discrete iPLA2gamma polypeptides containing either single or dual subcellular localization signals. This unanticipated complex interplay between peroxisomes and mitochondria mediated by competition for uptake of the nascent iPLA2gamma polypeptide identifies a new level of phospholipase-mediated metabolic regulation. Because uncoupling protein function is regulated by free fatty acids in mitochondria, these results suggest that iPLA2gamma processing contributes to integrating respiration and thermogenesis in mitochondria.
Mancuso
David J
DJ
Division of Bioorganic Chemistry and Molecular Pharmacology, Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA.
Jenkins
Christopher M
CM
Sims
Harold F
HF
Cohen
Joshua M
JM
Yang
Jingyue
J
Gross
Richard W
RW
D017398:Alternative Splicing; D001483:Base Sequence; D015152:Blotting, Northern; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D024202:Electrophoretic Mobility Shift Assay; D054522:Group VI Phospholipases A2; D006801:Humans; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000201:enzymology*; D020675:Peroxisomes / Q000201:enzymology*; D010741:Phospholipases A / Q000235:genetics*; D016133:Polymerase Chain Reaction; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
D017931:DNA Primers; D012333:RNA, Messenger; D010741:Phospholipases A; D054522:Group VI Phospholipases A2; C516475:PLA2G6 protein, human