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.
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