On the diversity of secreted phospholipases A(2) - Cloning, tissue distribution, and functional expression of two novel mouse group II enzymes

Over the last decade, an expanding diversity of secreted phospholipases A(2 ) (sPLA(2)s) has been identified in mammals. Here, we report the cloning in mice of three additional sPLA(2)s called mouse group IIE (mGIIE), IIF (mGI IF), and X (mGX) sPLA(2)s, thus giving rise to eight distinct sPLA(2)s in t his species. Both mGIIE and mGIIF sPLA(2)s contain the typical cysteines of group II sPLA(2)s, but have relatively low levels of identity (less than 5 1%) with other mouse sPLA(2)s, indicating that these enzymes are novel grou p II sPLA(2)s. However, a unique feature of mGIIF sPLA(2) is the presence o f a C-terminal extension of 23 amino acids containing a single cysteine. mG X sPLA(2) has 72% identity with the previously cloned human group X (hGX) s PLA(2) and displays similar structural features, making it likely that mGX sPLA(2) is the ortholog of hGX sPLA(2). Genes for mGIIE and mGrIIF sPLA(2)s are located on chromosome 4, and that of mGX sPLA(2) on chromosome 16. Nor thern and dot blot experiments with 22 tissues indicate that all eight mous e sPLA(2)s have different tissue distributions, suggesting specific functio ns for each, mGIIE sPLA(2) is highly expressed in uterus, and at lower leve ls in various other tissues. mGIIF sPLA(2) is strongly expressed during emb ryogenesis and in adult testis. mGX sPLA(2) is mostly expressed in adult te stis and stomach. When the cDNAs for the eight mouse sPLA(2)s were transien tly transfected in COS cells, sPLA(2) activity was found to accumulate in c ell medium, indicating that each enzyme is secreted and catalytically activ e. Using COS cell medium as a source of enzymes, pH rate profile and phosph olipid headgroup specificity of the novel sPLA(2)s were analyzed and compar ed with the other mouse sPLA(2)s.