CLONING AND EXPRESSION OF A RAT PLACENTAL CDNA-ENCODING A NOVEL CATHEPSIN L-RELATED PROTEIN

Cathepsin L is a major lysosomal cysteine protease produced by mouse p lacenta and fibroblasts. This study characterizes a novel cathepsin L- related mRNA expressed in rat placenta. Immunological and nucleotide s creening of a rat placental library identified six positive clones, th e largest, pCLRP-9, being 924 base pairs in length. The combined seque nces of all the clones contain an open reading frame of 711 nucleotide s, a termination codon, a polyadenylation site, and 197 nucleotides of 3' untranslated region, but lack the 5' translation initiation codon. The pCLRP nucleotide sequence showed 60-64% identity to those of mous e, rat, and human cathepsin L. The deduced amino acid sequence of pCLR P codes for 237 amino acids, which align with the carboxy-terminal seq uence of cathepsin L and has the active site residues characteristic o f the cysteine protease family. Northern blot analysis showed hybridiz ation of pCLRP with a major mRNA transcript of 1.3 kilobases expressed in placenta, but not kidney or liver. In contrast, a cDNA for mouse p ro-cathepsin L hybridized with a transcript of 1.7 kilobases expressed in rat kidney, as well as placenta. During late gestation, steady-sta te levels of rat placental pCLRP mRNA were highest on day 18, whereas those of mouse procathepsin L were greatest on day 20 of gestation. An tiserum to mouse cathepsin L cross-reacted with four proteins of molec ular weights 36,000 to 42,000 in rat placental culture medium, of whic h two were absent in the kidney. These data indicate that rat placenta expresses several species of cathepsin L-type proteins, which may be involved in placental function and nutrient supply. (C) 1995 Wiley-Lis s, Inc.