TSP‐1 Binds Thr92 Phosphorylated CD36 in a Calcium Dependent Manner and the Ligands of CD36 Regulate the Phosphorylation of Thr92 in Mouse Macrophages

CD36 is an 88 kD transmembrane glycoprotein expressed on many cell types, including platelets, macrophages and endothelial cells. Our lab and others showed that CD36 is required for the anti‐angiogenic property of Thrombospondin‐1(TSP‐1), an extracellular matrix protein. Threonine 92 (Thr92) of CD36 is an important regulator of the binding of TSP‐1. Thr92 of CD36 is within a consensus protein kinase C (PKC) phosphorylation site and can be phosphorylated by PKC in vitro . The few published studies on CD36 phosphorylation in platelets suggest that the phosphorylated form, which has low affinity to TSP‐1, may be the default state. To study the phosphorylation of Thr92 of CD36, we cloned a 111bp CD36 fragment (FP111) that encodes amino acids 81 to 117. We showed that the WT but not T92A FP111 could be phosphorylated by PKC in vitro . FP111 binds TSP‐1 in vitro in a calcium dependent manner and the phosphorylation of FP111 enhances the binding of TSP‐1. Thr92 of CD36 in both elicited and resident mouse macrophages is phosphorylated, at least in part. Moreover, the phosphorylation level of CD36 in mouse macrophages can be regulated by CD36 ligands. Ectophosphorylation of CD36 is a novel mechanism of regulation and may impact CD36‐dependent functions. Determination of the effect and the regulation of CD36 phosphorylation will improve our understanding of the regulation of CD36 dependent functions, such as angiogenesis.