Abstract
The group IV cytosolic phospholipase A2(cPLA2) has been localized to the nucleus (M. R. Sierra-Honigmann, J. R. Bradley, and J. S. Pober, Lab. Investig. 74:684–695, 1996) and is known to translocate from the cytosolic compartment to the nuclear membrane (S. Glover, M. S. de Carvalho, T. Bayburt, M. Jonas, E. Chi, C. C. Leslie, and M. H. Gelb, J. Biol. Chem. 270:15359–15367, 1995; A. R. Schievella, M. K. Regier, W. L. Smith, and L. L. Lin, J. Biol. Chem. 270:30749–30754, 1995). We hypothesized that nuclear proteins interact with cPLA2 and participate in the functional effects of this translocation. We have identified a nuclear protein, cPLA2-interacting protein (PLIP), a splice variant of human Tip60, which interacts with the amino terminal region of cPLA2. Like Tip60, PLIP cDNA includes the MYST domain containing a C2HC zinc finger and well-conserved similarities to acetyltransferases. Both PLIP and Tip60 coimmunoprecipitate and colocalize with cPLA2 within the nuclei of transfected COS cells. A polyclonal antibody raised to PLIP recognizes both PLIP and Tip60. Endogenous Tip60 and/or PLIP in rat mesangial cells is localized to the nucleus in response to serum deprivation. Nuclear localization coincides temporally with apoptosis. PLIP expression, mediated by adenoviral gene transfer, potentiates serum deprivation-induced prostaglandin E2 (PGE2) production and apoptosis in mouse mesangial cells from cPLA2 +/+ mice but not in mesangial cells derived from cPLA2 −/− mice. Thus PLIP, a splice variant of Tip60, interacts with cPLA2 and potentiates cPLA2-mediated PGE2 production and apoptosis.
ACKNOWLEDGMENTS
This work was supported by National Institutes of Health grants DK02356, DK 39773, DK 38452, NS 10828, and DK 54741 and American Heart Association grant-in-aid 9950460N.
We thank R. Brent, E. Golemis, J. Gyuris, and S. Hanes for the vectors used in the two-hybrid interaction trap; C. Sardet for the fibroblast Go library and for invaluable advice on the two-hybrid system; R. Finley for the anti-LexA antibody; J. Settleman for pRc/CMV-GAP plasmid; A. Cybulsky for the anti-cPLA2antibody; and J. Clark for the pMT2-cPLA2plasmid. We also thank D. A. Dichek (Gladstone Institute for Cardiovascular Disease) for the pADRSV4-LacZ construct, James Kamine for Tip60 cDNA, and S. Breton for assistance with immunofluorescence microscopy.
ADDENDUM IN PROOF
While the manuscript was in preparation Tip60(β), which is identical to PLIP, was isolated by the laboratory of Pereira-Smith (Citation62).