Cloning and sequence analysis of cDNAs encoding human placental tissue protein 17 (PP17) variants

Using monospecific anti-PP17 serum with chemiluminescence Western-blot analysis, we detected different molecular-mass variants of human soluble placental tissue protein 17 (PP17) in different normal adult and fetal human tissues besides term placenta. 13 cDNAs with three different insert lengths encoding PP17 variants were isolated by screening a human placental cDNA library. Sequence analysis of the shortest clones showed that the inserts contain the same open reading frame encoding PP17a variant (28,129 kDa) consisting of 251 residues, which is identical to the previously isolated and characterised PP17 antigen described in 1983. The ubiquitous PP17b variant is encoded by longer clones and contains 434 residues with a predicted molecular mass of 47,208 kDa. Compared to normal conditions, these newly discovered PP17 variants are overexpressed in cervix carcinoma tissue, as are their three different-size messenger RNAs in HeLa cell line. Increased amounts of PP17b are secreted into the circulation in cervix carcinoma patients. We also observed a typical elevation in serum levels of PP17 variants during healthy pregnancy. An alignment search of the protein databank showed that PP17a and PP17b are homologous to adipose tissue differentiation and lipid-droplet-associated proteins: human adipophilin, mouse adipose differentiation-related protein and rat perilipin A and B.