PLIP, a Novel Splice Variant of Tip60, Interacts with Group IV Cytosolic Phospholipase A₂, Induces Apoptosis, and Potentiates Prostaglandin Production

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 G_o 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 (62).