Summary
CD36 is a cell surface receptor that has been shown to interact with a large variety
of ligands including thrombospondin, collagen, Plasmodium falciparum-infected erythrocytes,
apoptotic neutrophils, modified low density lipoproteins, anionic phospholipids and
long chain fatty acids. A number of these CD36 ligands elicit the transduction of
intracellular signals involved in cell activation and internalization of bound ligands.
The engagement of CD36 possibly activates three cytosolic protein tyrosine kinases
that are presumably associated with the C- terminal cytoplasmic tail of CD36. However,
the mechanisms by which CD36 functions in ligand binding and signal transduction are
poorly understood. In the present study, a membrane-bound and a truncated soluble
form of CD36 were expressed in HeLa cells and analyzed by velocity-gradient centrifugation
and chemical cross-linking. We show that membrane CD36 exists predominantly as a monomer
but a homo- dimeric form is also found. In contrast, soluble CD36 sedimented in sucrose
gradient as a monomer. However, when incubated with thrombospondin, the membrane form
of CD36 predominantly sedimented as a dimer whereas soluble CD36 was monomeric. This
study shows that thrombospondin has the ability to induce dimerization of CD36 and
may be implicated in the signal transduction capacity of this adhesion molecule.
