Biological, immunological, and binding properties of recombinant mouse placental lactogen-I

Mouse placental lactogen-I (mPL-I) cDNA was inserted into a eukaryotic expression vector and introduced into Chinese hamster ovary cells. Cell lines that secrete high concentrations of mPL-I were isolated, and this glycoprotein was purified from the cell culture-conditioned medium. Recombinant mPL-I (mPL-I^r) is very similar to placental mPL-I (mPL-I^P) in its recognition by polyclonal antisera raised against either mPLP I^p or mPL-I^r, in displacing [¹²⁵I]iodo-mPL-II from binding sites on mouse liver microsomal membranes, and in stimulating the synthesis of α-lactalbumin in primary cultures of mouse mammary epithelial cells. Structural comparison of mPL-I^r and mPL-I^P by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that mPL-I^r comprises several proteins with mol wt ranging from 34.5-38K, while mPL-I^P consists of a similar set of proteins with mol wt ranging from 36.5-42K. Treatment of the two proteins with neuraminidase resulted in similar 2-4K decreases in mol wt. Treatment of mPL-I^P with peptide:N-glycosidase-F to remove asparagine-linked oligosaccharide chains resulted in the formation of 28K and 29K mol wt species, while treatment of mPL-I^r with the same enzyme yielded 28K and 28.5K mol wt products.