CDNA CLONING AND EXPRESSION OF A NOVEL FAMILY OF ENZYMES WITH CALCIUM-INDEPENDENT PHOSPHOLIPASE A(2) AND LYSOPHOSPHOLIPASE ACTIVITIES

Previous studies have suggested that activation of calcium-independent PLA(2) (CaIPLA(2)) is an early event in cell death after hypoxic inju ry in proximal tubule cells. An approximately 28-kD CaIPLA(2) with pre ferential activity toward plasmalogen phospholipids has been recently purified from rabbit kidney cortex (D. Portilla and G. Dal, J Biol Che m 271, 15451-15457, 1996). Their report describes the cloning of a ful l-length rat cDNA encoding CaIPLA(2), using sequences derived from the purified rabbit kidney cortex enzyme. In addition, cDNA from rabbit k idney that encode the rabbit homologue of the enzyme and a closely rel ated isoform were isolated. The rat cDNA is predicted to encode an app roximately 24-kD protein, and each cDNA contains the sequence G-F-S-Q- G, which fits the active site consensus sequence G-X-S-X-G of carboxyl esterases. Several lines of evidence (DNA sequence comparison, Souther n blot analysis, and examination of the expressed sequence tag databas e) show that CaIPLA(2) enzymes are encoded by a multigene family in ra ts, mice, rabbits, and humans. Northern analysis of various tissues fr om the rat indicated that the CaIPLA(2) gene is ubiquitously expressed , with highest mRNA abundance observed in the kidney and small intesti ne. The rat CaIPLA(2) cDNA, when expressed in a baculovirus expression system, and the purified rabbit kidney cortex protein exhibit both Ca IPLA(2) and lysophospholipase activities. The cloned CaIPLA(2) cDNA ar e expected to aid in understanding the role of CaIPLA(2) in cell death after hypoxic/ischemic cell injury.