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J. Biol. Chem., Vol. 281, Issue 24, 16615-16624, June 16, 2006

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Identification of the Expressed Form of Human Cytosolic Phospholipase A₂ (cPLA₂)

cPLA₂3 IS A NOVEL VARIANT LOCALIZED TO MITOCHONDRIA AND EARLY ENDOSOMES^*

Moumita Ghosh, Robyn Loper, Michael H. Gelb, and Christina C. Leslie^¶1

From the Program in Cell Biology, Department of Pediatrics, National Jewish Medical and Research Center, Denver, Colorado 80206, the Departments of Chemistry and Biochemistry, University of Washington, Seattle, Washington 98195, and the ^¶Departments of Pathology and Pharmacology, University of Colorado School of Medicine, Denver, Colorado 80206

In this study, we identify the principal splice variant of human cytosolic phospholipase A₂ (cPLA₂) (also known as Group IVB cPLA₂) present in cells. In human lung, spleen, and ovary and in a lung epithelial cell line (BEAS-2B), cPLA₂ is expressed as a 100-kDa protein, not the 114-kDa form originally predicted. Using RNA interference, the 100-kDa protein in BEAS-2B cells was confirmed to be cPLA₂. BEAS-2B cells contain three different RNA splice variants of cPLA₂ (1, 2, and 3). cPLA₂1 is identical to the previously cloned cPLA₂, predicted to encode a 114-kDa protein. However, cPLA₂2 and cPLA₂3 splice variants are smaller and contain internal deletions in the catalytic domain. The 100-kDa cPLA₂ in BEAS-2B cells is the translated product of cPLA₂3. cPLA₂3 exhibits calcium-dependent PLA₂ activity against palmitoyl-arachidonyl-phosphatidylethanolamine and low level lysophospholipase activity but no activity against phosphatidylcholine. Unlike Group IVA cPLA₂, cPLA₂3 is constitutively bound to membrane in unstimulated cells, localizing to mitochondria and early endosomes. cPLA₂3 is widely expressed in tissues, suggesting that it has a generalized function at these unique sites.

Received for publication, February 23, 2006 , and in revised form, April 12, 2006.

^* This work was supported by National Institutes of Health Grants HL34303 and HL61378 (to C. C. L.) and HL50040 (to M. H. G). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. The nucleotide sequence(s) reported in this paper has been submitted to the Gen-Bank^TM/EBI Data Bank with accession number(s) DQ523799 for cPLA₂2 (Group IVB2 PLA₂), and DQ523800 for cPLA₂3 (Group IVB3 PLA₂).

¹ To whom correspondence should be addressed: Dept. of Pediatrics, National Jewish Medical and Research Center, 1400 Jackson St., Denver, CO 80206. Tel.: 303-398-1214; Fax: 303-270-2155; E-mail: lesliec{at}njc.org.

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