Cloning and Sequencing of Human Oncodevelopmental Soluble Placental Tissue Protein 17 (PP17): Homology with Adipophilin and the Mouse Adipose Differentiation-Related Protein

Using a monospecific anti-PP17 antiserum, we detected 4 different molecular-weight PP17 immunoreactive proteins (31,500 kD PP17a, 48,000 kD PP17b, 60,900 kD PP17c and 74,000 kD PP17d) in different normal adult and fetal human tissues, and in term placenta, by chemiluminescence Western blot analysis. These proteins are overexpressed in cervix carcinoma tissue. Furthermore, increased amounts of PP17b are secreted into the circulation in cervix carcinoma patients; after radical surgery, PP17b serum levels are decreased, and the protein probably has an oncodevelopmental significance. cDNAs were isolated from a human placental cDNA library with the monospecific anti-PP17 antiserum. Sequence analysis of the clones showed that they encode for the 251 residue long PP17a variant, which is identical to the previously isolated and characterized PP17 antigen described in 1983. An alignment search of the protein databank showed that PP17a is homologous to human adipophilin and mouse adipose differentiation-related protein. PP17c turned out to be a dimer of PP17a, while PP17b and PP17d immunoreactive proteins recently detected on Western blots require further investigations.