Abstract
We have recently reported that mammalian pancreatic group I phospholipase A2 (PLA2-I) has its specific receptor (PLA2 receptor) on a variety of mammalian cells and that various biological responses are elicited by PLA2-I via this receptor. In this study, we cloned cDNAs encoding a protein corresponding to the bovine PLA2 receptor purified from the corpora lutea on the basis of its partial amino acid sequences. The identity of a protein encoded by the cloned cDNA with the bovine PLA2 receptor was verified by a transient expression experiment using COS-7 cells. Interestingly, the deduced primary structure of the PLA2 receptor (1,463 amino acid residues) exhibits a close relatedness throughout the molecule to that of the macrophage mannose receptor, a unique member of Ca(2+)-dependent (C-type) animal lectin family, in spite of their functional diversity. Based on this sequence similarity between these two receptors, the domain organization of the PLA2 receptor could be tentatively assigned as follows; 10 extracellular domains including 8 tandem repeats homologous to C-type carbohydrate-recognition domains (CRDs) and a single transmembrane region followed by a short cytoplasmic tail. The results of transient expression experiments for mutant PLA2 receptors supported this assignment and furthermore suggested the region responsible for PLA2-I binding corresponds to CRDs in the mannose receptor.
Highlights
We have recently reported that mammalian pancre- mation
The findintghsat PLA2-I is present in various atic group I phospholipase A, (PLA,I) has its specific kinds of nondigestive organs have raised the possibility that receptor (PLA, receptor)onavariety ofmammalian this protein might have some unknownphysiological functions cells and that various biological responses are elicited besides nutrient digestion [2, 3] and led us to search for byPLA,I via this receptor
We discovered the existence of specific bindcDNAs encoding a protein correspondingto the bovine ing sites for a mature form of PLA2-I on a wide range of cell
Summary
(Received for publication, September 7, 1993, and in revised form, November 9, 1993). Screening a n d Isolation of Clones Encodingthe Bovine PLAz Receptor-Using the 62-bp cDNA fragment encoding the NH,-terminal region of the PLA, receptorlabeledwith 32Pby PCR [13], we first screened A phage bovine genomic library (Clontech). Expressions of the PLAz Receptor and Its Mutants-A cDNA clone which carries the full-length coding region of the PLA, receptor was reconstructed from pPL-1 and pMD-11 by connecting t h e 5'-portion of pPL-1 and the3"portion of pMD-11 at the NcoI site (at the nucleotide residue 799, Fig. 2 4 ). The resulting full-length cDNAinsert was placed under the control of a strong eukaryotic promoter, SRa This PLA, receptor expression plasmid(2 pg) was introduced into COS-7 cells (2 x lo5cells in a 9.6-em2plastic dish) withlipofectin reagent (Life Technologies,Inc.). Forty min after the temperatureshift, radioactivities internalized into the cells were measured, anda percentage of internalized PLA,-I to the initially bound one was calculated
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