LIPOPROTEIN-LIPASE BINDING TO ADIPOCYTES - EVIDENCE FOR THE PRESENCE OF A HEPARIN-SENSITIVE BINDING-PROTEIN

Lipoprotein lipase (LPL) is synthesized by adipocytes, associated with the cell surface, and released from the cells when they are treated w ith heparin. Release of LPL from the adipocyte is required for LPL to migrate to its physiological site of action on the luminal surface of capillary endothelial cells. To better understand this process, we stu died the interaction of LPL with adipocyte cell membrane proteins. Wit h the use of a ligand blot method, LPL specifically bound to a heparin -releasable, 116-kDa protein on mouse-derived brown fat adipose cell ( BFC-1beta) and rat adipocyte membranes. A 116-kDa cell surface protein was metabolically labeled with [S-35]methionine and bound to LPL-Seph arose. This suggested that the LPL-binding protein was synthesized by the cells. When BFC-1beta were treated with heparin to eliminate hepar in-sensitive cell surface binding sites, LPL binding to the cells decr eased and release of newly synthesized LPL activity increased. I-125-l abeled LPL binding to control cells was reduced (>70%) by a 50-fold ex cess of unlabeled LPL. The residual LPL binding to heparin-treated cel ls was, however, not decreased by the addition of unlabeled LPL. These data imply that specific adipocyte surface LPL binding involves hepar in-sensitive sites. We hypothesize that the heparin-releasable, 116-kD a LPL-binding protein mediates specific LPL binding to adipocytes and that LPL activity within adipose tissue is regulated, in part, by the interaction of LPL with this binding protein.