CD36 MEDIATES BINDING OF SOLUBLE THROMBOSPONDIN-1 BUT NOT CELL-ADHESION AND HAPTOTAXIS ON IMMOBILIZED THROMBOSPONDIN-1

In this study, we examined the binding of soluble TSP1 (and ox-LDL) to CD36-transfected cells and the mechanisms by which immobilized TSP1 m ediated attachment and haptotaxis (cell migration towards a substratum -bound ligand) of these transfected cells. CD36 cDNA transfection of N IH 3T3 cells clearly induced a dramatic increase in binding of both so luble [I-125]-TSP1 and [I-125]-ox-LDL to the surface of CD36-transfect ed cells, indicating that there was a gain of function with CD36 trans fection in NIH 3T3 cells. Despite this gain of function, mock- and CD3 6-transfected NIH 3T3 cells attached and migrated to a similar extent on immobilized TSP1. An anti-TSP1 oligoclonal antibody inhibited CD36- transfected cell attachment to TSP1 while function blocking anti-CD36 antibodies, alone or in combination with heparin, did not. A series of fusion proteins encompassing cell-recognition domains of TSP1 was the n used to delineate mechanisms by which NIH 3T3 cells adhere to TSP1. Although CD36 binds soluble TSP1 through a CSVTCG sequence located wit hin type 1 repeats, (18-19) CD36-transfected NIH 3T3 cells did not att ach to immobilized type 1 repeats while they did adhere to the N-termi nal, type 3 repeats (in an RGD-dependent manner) and the C-terminal do main of TSP1. Conversely, Bowes melanoma cells attached to type 1 repe ats and the N- and C-terminal domains of TSP1. However, CD36 cDNA tran sfection of Bowes cells did not increase cell attachment to type 1 rep eats compared to that observed with mock-transfected Bowes cells. More over, a function blocking anti-CSVTCG peptide antibody did not inhibit the attachment of mock- and CD36-transfected Bowes cells to type 1 re peats. It is suggested that CD36/TSP1 interaction does not occur upon cell-matrix adhesion and haptotaxis because TSP1 undergoes conformatio nal changes that do not allow the exposure of the CD36 binding site. ( C) 1998 John Wiley & Sons, Ltd.