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 mediated attachment and haptotaxis (cell migration towards a substratum‐bound ligand) of these transfected cells. CD36 cDNA transfection of NIH 3T3 cells clearly induced a dramatic increase in binding of both soluble [125I]‐TSP1 and [125I]‐ox‐LDL to the surface of CD36‐transfected cells, indicating that there was a gain of function with CD36 transfection in NIH 3T3 cells. Despite this gain of function, mock‐ and CD36‐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 then used to delineate mechanisms by which NIH 3T3 cells adhere to TSP1. Although CD36 binds soluble TSP1 through a CSVTCG sequence located within type 1 repeats,18,19 CD36‐transfected NIH 3T3 cells did not attach to immobilized type 1 repeats while they did adhere to the N‐terminal, type 3 repeats (in an RGD‐dependent manner) and the C‐terminal domain of TSP1. Conversely, Bowes melanoma cells attached to type 1 repeats and the N‐ and C‐terminal domains of TSP1. However, CD36 cDNA transfection of Bowes cells did not increase cell attachment to type 1 repeats compared to that observed with mock‐transfected Bowes cells. Moreover, a function blocking anti‐CSVTCG peptide antibody did not inhibit the attachment of mock‐ and CD36‐transfected Bowes cells to type 1 repeats. It is suggested that CD36/TSP1 interaction does not occur upon cell–matrix adhesion and haptotaxis because TSP1 undergoes conformational changes that do not allow the exposure of the CD36 binding site. © 1998 John Wiley & Sons, Ltd.