Heparin-binding property of human prolactin: A novel aspect of prolactin biology

Prolactin (PRL) shares several characteristics with growth factors and cyto kines, many of which are known to bind to heparan sulfate proteoglycans. In this study we examined the heparin-binding properties of selected members of the PRL/GH family, using heparin affinity columns followed by gel electr ophoresis/Westem blotting. Purified human PRL and its cleaved 16K fragment, but not human GH or placental lactogen, were retained on the heparin colum n and were displaced by 0.5M NaCl. Native PRL in human pituitary extracts a nd amniotic fluid showed a similar binding affinity to heparin as the purif ied hormone. None of the other hormones tested, e.g., rat, ovine and bovine PRL, glycosylated ovine PRL or rat GH, bound to heparin. Two consensus hep arin-binding sequences are present in human PRL but not in the other hormon es included in this study. We postulate that the heparin-binding capability of PRL affects its biological activity as a growth factor and the angiosta tic actions of its 16K fragment.