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

Abstract

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.

Disruption of G1-phase phospholipid turnover by inhibition of Ca2+-independent phospholipase A2 induces a p53-dependent cell-cycle arrest in G1 phase

“…Moreover, we showed that forced expression of ARD-iPLA 2 enhances p53 levels and G1-phase arrest in a concentration-dependent manner. Interestingly, the endogenous expression of an ankyrin-repeat domain of iPLA 2 has recently been described by another group of researchers, who postulate that this expression serves as a way to regulate iPLA 2 activity throughout the cell cycle (Manguikian and Barbour, 2004). It remains to be seen whether alternative splicing of iPLA 2 represents a way for the protein to be involved in cell-cycle control by interaction with p53.…”

“…We next overexpressed the ARD-iPLA 2 -GFP [ankyrinrepeat domain of iPLA 2 fused to green fluorescent protein (GFP)], an alternatively spliced form of the iPLA 2 gene known to function as a negative regulator of iPLA 2 (Larsson et al, 1998;Manguikian and Barbour, 2004), in INS-1 cells. Transient expression suppressed cell proliferation in these cells, which was reversed when ARD-iPLA 2 -GFP expression decreased (Fig.…”

Lipid Droplet Biogenesis Induced by Stress Involves Triacylglycerol Synthesis That Depends on Group VIA Phospholipase A2

“…These two variants work similarly in our hands, because iPLA 2 -VIA-1 is the main form expressed in CHO cells, and transfection of iPLA 2 -VIA-2 has the same effect regarding TAG synthesis for the biogenesis of LD. Another two variants lack enzymatic activity but may act as dominant-negative inhibitors by precluding association of the active variants (41). It would be interesting to determine whether differential expression of active and inactive variants may account for LD generation during stress.…”

Analysis of Two Major Intracellular Phospholipases A2 (PLA2) in Mast Cells Reveals Crucial Contribution of Cytosolic PLA2α, Not Ca2+-independent PLA2β, to Lipid Mobilization in Proximal Mast Cells and Distal Fibroblasts

“…This would suggest that, in addition to transcriptional control of iPLA 2 ␤ (Fig. 1A), its expression is regulated by proteolytic processing (48,49,59,60) or by alternative splicing (82,85). It has been reported that proteolytic cleavage of the N-terminal ankyrin repeats of iPLA 2 ␤ by caspase-3 or unknown proteases occurs in apoptotic cells (48,49) or even in nonapoptotic migrating cells (60) and agonist-treated islet ␤-cells (59), leading to activation of this enzyme.…”