Concanavalin A induced alterations in 125I-labeled prolactin binding.

Department of Biochemistry, St. Jude Children's Research Hospital 332 North Lauderdale, Memphis, Tennessee 38101 Received June 23,1977 SUMMARY 1251-1abeled ovine prolact in binding to receptors in the l i ve r of female rats is markedly inh ib i ted by Concanavalin A (Con A). Lens ou~ina~s agglut i n i n and succinyl-Con A i nh ib i t binding to a much lesser extent and wheat germ agglut in in and phytohemagglutinin-P are without af fect . Con A inh ib i t i on is dose related and saturable; however, 30% of prolact in receptors are unaffected by Con A. ~-Methylmannoside or ~-methylglucoside, both potent inh ib i to rs of Con A binding, reverse the inh ib i t ion . Con A also inh ib i t s prolact in binding in other normal target tissues and in neoplastic rat mammary t issue. In cont ras t , 1251-1abeled Con A binding to rat l i v e r is unaltered by pro lact in . These results suggest that Con A binding si tes may not be ident ical to the prolact in receptor and that prolact in receptors may ex is t in two domains on the cel l surface one of which is in close proximity to Con A binding si tes and another which is more distant. The plant lec t in Concanavalin A (Con A) binds to speci f ic carbohydrate determinants on the cel l surface of a var iety of mammalian cel ls . This in ter action can cause a number of diverse biological ef fects including cel l agglutination ( I ) , mi tot ic induction (2, 3), restorat ion of contact inh ib i t ion of growth (4), and mimicking the e f fec t of polypeptide hormones (5, 6). The mechanism by which Con A causes a l terat ions in cel l function and behavior is not well understood; however, i t is believed that some of i t s ef fects may be mediated through modifications of cel l surface topography (7, 8). Recently, Con A has been shown to bind spec i f i ca l l y to rat l i ve r plasma membranes (9, I0) , modify the ac t i v i t y of l i v e r membrane 5'-nucleotidase (I0) and Na+-K + ATPase ( I I ) and to i nh i b i t insul in binding to l i ve r (5). To gain ins ight into the mechanism of prolact in binding to i t s receptor, we have invest igated the e f fec t of Con A on prolact in receptors in the rat l i ve r , a known prolact in target tissue (12). In this report, we show that Con A spec i f i ca l l y a l ters prolact in binding in the rat l i ve r and that the inh ib i to ry