Evidence for proteolytic processing and stimulated organelle redistribution of iPLA(2)beta.
Over the past decade, important roles for the 84-88kDa Group VIA Ca(2+)-independent phospholipase A(2) (iPLA(2)beta) in various organs have been described. We demonstrated that iPLA(2)beta participates in insulin secretion, insulinoma cells and native pancreatic islets express full-length and truncated isoforms of iPLA(2)beta, and certain stimuli promote perinuclear localization of iPLA(2)beta. To gain a better understanding of its mobilization, iPLA(2)beta was expressed in INS-1 cells as a fusion protein with EGFP, enabling detection of subcellular localization of iPLA(2)beta by monitoring EGFP fluorescence. Cells stably-transfected with fusion protein expressed nearly 5-fold higher catalytic iPLA(2)beta activity than control cells transfected with EGFP cDNA alone, indicating that co-expression of EGFP does not interfere with manifestation of iPLA(2)beta activity. Dual fluorescence monitoring of EGFP and organelle Trackers combined with immunoblotting analyses revealed expression of truncated iPLA(2)beta isoforms in separate subcellular organelles. Exposure to secretagogues and induction of ER stress are known to activate iPLA(2)beta in beta-cells and we find here that these stimuli promote differential localization of iPLA(2)beta in subcellular organelles. Further, mass spectrometric analyses identified iPLA(2)beta variants from which N-terminal residues were removed. Collectively, these findings provide evidence for endogenous proteolytic processing of iPLA(2)beta and redistribution of iPLA(2)beta variants in subcellular compartments. It might be proposed that in vivo processing of iPLA(2)beta facilitates its participation in multiple biological processes.
Mass Spectrometry Resource, Division of Metabolism, Endocrinology, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA.
Haowei
H
Song
Shunzhong
S
Bao
Xiaoyong
X
Lei
Chun
C
Jin
Sheng
S
Zhang
John
J
Turk
Sasanka
S
Ramanadham
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism; D054522:Group VI Phospholipases A2 / Q000235:genetics / Q000378:metabolism*; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism; D013058:Mass Spectrometry; D008928:Mitochondria / Q000378:metabolism; D008969:Molecular Sequence Data; D015388:Organelles / Q000378:metabolism*; D018384:Oxidative Stress; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D054522:Group VI Phospholipases A2