CLONING AND EXPRESSION OF RAT LUNG ACIDIC CA2-INDEPENDENT PLA(2) AND ITS ORGAN DISTRIBUTION()

A clone for a rat acidic Ca2+-independent phospholipase A(2) (aiPLA(2) ) was isolated from a cDNA library prepared from rat granular pneumocy tes with a probe based on the human aiPLA(2) sequence (T. S. Kim, C. S . Sundaresh, S. I. Feinstein, C. Dodia, W. R. Skach, M. K. Jain, T. Na gase, N. Seki, K. Ishikawa, N. Nomura, and A. B. Fisher. J. Biol. Chem . 272: 2542-2550, 1997). In addition, a consensus sequence for mouse a iPLA(2) was constructed from several mouse cDNA clones in the GenBank and dbEST databases. Each sequence codes for a 224-amino acid protein with 88% identity of the amino acids among the three species and conse rvation of a putative lipase motif (GDSWG). Translation of mRNA produc ed from the rat clone in a wheat germ system resulted in expression of PLA(2) activity with properties similar to those of the human enzyme, i.e., acidic pH optimum and Ca2+ independence. The localization of ai PLA(2) in rat tissues was studied with the human cDNA probe, polyclona l and monoclonal antibodies, and aiPLA(2) activity. aiPLA(2) is presen t in the lung as evidenced by high levels of mRNA and protein expressi on and by enzymatic activity that is inhibited by anti-PLA(2) antibody and by the transition state analog decyl-3-trifluoroethylglycero-sn-2 -phosphomethanol (MJ33). Immunocytochemistry showed the presence of ai PLA(2) in alveolar type II cells, alveolar macrophages, and bronchiola r epithelium. In the brain, heart, liver, kidney, spleen, and intestin e, aiPLA(2) mRNA content was <50% of that in the lung, immunoreactive protein was not detectable, and enzymatic activity was not inhibited b y MJ33 or aiPLA(2) antibody. These results show marked enrichment of a iPLA(2) in the lung compared with the other organs and suggest transla tional control of aiPLA(2) expression.