The human calcium‐independent phospholipase A 2 gene

2؉ release (net loss) as well as by simple buffering of free Ca 2؉ within the stores, 2) a specific 82-kDa variant of iPLA 2 ␤ and its corresponding activity are present in membrane fraction of RBL cells, 3) exogenous CIF (extracted from other species) mimics the effects of endogenous CIF and activates iPLA 2 ␤ when applied to cell homogenates but not intact cells, 4) activation of I CRAC can be triggered in resting RBL cells by dialysis with exogenous CIF, 5) molecular or functional inhibition of iPLA 2 ␤ prevents activation of I CRAC , which could be rescued by cell dialysis with a human recombinant iPLA 2 ␤, 6) dependence of I CRAC on intracellular pH strictly follows pH dependence of iPLA 2 ␤ activity, and 7) (S)-BEL, a chiral enantiomer of suicidal substrate specific for iPLA 2 ␤, could be effectively used for pharmacological inhibition of I CRAC and store-operated Ca 2؉ entry. These findings validate and significantly advance our understanding of the CIF-iPLA 2 -dependent mechanism of activation of I CRAC and store-operated Ca 2؉ entry.

Section: From the Boston University School Of Medicine Boston Massasupporting

confidence: 85%

Activation Mechanism for CRAC Current and Store-operated Ca2+ Entry

Csutora

Zarayskiy

Peter

et al. 2006

“…Based on these observations, we predict that the truncated protein associates with full-length iPLA 2 and regulates iPLA 2 activity during the cell cycle through the mechanism proposed by Larsson et al (12,35). Indeed, our co-immunoprecipitation 2 S. Barbour, personal communication.…”

Section: Discussionmentioning

confidence: 60%

“…Although the splice variant mRNAs have been demonstrated in human B cells, testes, and myeloid cells (35,36), to date there is no conclusive evidence for the existence of the proteins encoded by these messages. Until recently, the only commercially available anti-iPLA 2 antibodies were directed against the C terminus of the enzyme and therefore could not recognize the truncated proteins.…”

Section: Discussionmentioning

confidence: 99%

Cell Cycle Dependence of Group VIA Calcium-independent Phospholipase A2 Activity

Manguikian

Barbour

2004

2 activity, suggesting that regulation of this enzyme contributes to phospholipid accumulation. The levels of 80 kDa iPLA 2 protein do not change and thus cannot account for changes in enzyme activity. Reverse transcriptase and real-time PCR experiments show that splice variant iPLA 2 mRNAs are preferentially expressed during G 2 /M. Immunoblot analyses with an antibody directed against the N terminus of iPLA 2 revealed a ϳ50 kDa protein that is of appropriate size to be the truncated protein encoded by the ankyrin-iPLA 2 -1 splice variant mRNA. The levels of truncated iPLA 2 protein were high in cells in late G 1 and S phase cells that had low iPLA 2 activity and low in G 2 /M cells that had high iPLA 2 activity. The truncated protein co-immunoprecipitated with full-length iPLA 2 , indicating a physical interaction between the two proteins. Together, these data suggest that truncated iPLA 2 proteins associate with active iPLA 2 and down-regulate its activity during G 1 . This down-regulation may contribute to phospholipid accumulation during the cell cycle.

“…The function of iPLA 2 ␤ in a given setting might depend in part on which splice variants (40,41) and proteolytic processing products (29,102,103) of iPLA 2 ␤ are expressed in a given cell and on what interacting proteins (98) are present in the cell compartment (84,101) in which the iPLA 2 ␤ isoform resides.…”

Section: Discussionmentioning

confidence: 99%

Attenuated Free Cholesterol Loading-induced Apoptosis but Preserved Phospholipid Composition of Peritoneal Macrophages from Mice That Do Not Express Group VIA Phospholipase A2

Bao

Lei

et al. 2007

Mouse macrophages undergo ER stress and apoptosis upon free cholesterol loading (FCL). We recently generated iPLA 2 ␤-null mice, and here we demonstrate that iPLA 2 ␤-null macrophages have reduced sensitivity to FCL-induced apoptosis, although they and wild-type (WT) cells exhibit similar increases in the transcriptional regulator CHOP. iPLA 2 ␤-null macrophages are also less sensitive to apoptosis induced by the sarcoplasmic reticulum Ca 2؉ -ATPase inhibitor thapsigargin and the scavenger receptor A ligand fucoidan, and restoring iPLA 2 2 ␤ modulates mitochondrial cytochrome c release, and we find that thapsigargin and fucoidan induce mitochondrial phospholipid loss and cytochrome c release into WT macrophage cytosol and that these events are blunted in iPLA 2 ␤-null cells. Immunoblotting studies indicate that iPLA 2 ␤ associates with mitochondria in macrophages subjected to ER stress. AA incorporation into glycerophosphocholine lipids is unimpaired in iPLA 2 ␤-null macrophages upon electrospray ionization-tandem mass spectrometry analyses, and their complex lipid composition is similar to WT cells. These findings suggest that iPLA 2 ␤ participates in ER stress-induced macrophage apoptosis caused by FCL or thapsigargin but that deletion of iPLA 2 ␤ does not impair macrophage arachidonate incorporation or phospholipid composition.