EXPRESSION AND CHARACTERIZATION OF RECOMBINANT RAT PLACENTAL PROLACTIN-LIKE PROTEIN-C

Prolactin-like protein C (PLP-C) is a member of the rat placental fami ly of proteins which are structurally related to pituitary prolactin ( PRL). In an effort to characterize the receptor specificity and biolog ical activity of PLP-C, we used a PLP-C cDNA to express the recombinan t protein in a bacterial system. The PLP-C cDNA was modified by oligon ucleotide mutagenesis and ligated into a human carbonic anhydrase II ( hCAII) expression vector. Following a single step affinity purificatio n, the hCAII-PLP-C fusion protein was digested with enterokinase to re lease a 25 kDa protein. N-Terminal sequence analysis of the 25 kDa ban d demonstrated identity with PLP-C. A polyclonal antiserum to the fusi on protein cross reacted with seven major proteins in rat placental cu lture media of which two were the native forms of PLP-C. Recombinant P LP-C was not mitogenic in the Nb2 lymphoma bioassay and did not exhibi t high affinity binding to rat PRL receptor. The choice of hCA-II fusi on allows for rapid purification of rPLP-C which will aid in further i nvestigation of the biological role of PLP-C.