CD36 ectodomain phosphorylation blocks thrombospondin-1 binding: structure-function relationships and regulation by...

Area of Science:

• Molecular biology
• Cell signaling
• Biochemistry

Background:

• CD36 protein interactions are modulated by extracellular domain phosphorylation.
• The mechanisms regulating CD36 phosphorylation and its functional consequences remain largely unknown.

Purpose of the Study:

• To investigate the structure-function relationships of CD36 phosphorylation concerning thrombospondin-1 (TSP-1) binding.
• To explore the regulatory mechanisms of CD36 phosphorylation by protein kinase C (PKC) in melanoma cells.

Main Methods:

• In vitro analysis of CD36 peptide phosphorylation and TSP-1 binding.
• In vivo assessment of basal CD36 phosphorylation in various cell types using immunoprecipitation and immunoblot.
• PKC activation in CD36-transfected melanoma cells with phorbol 12-myristate 13-acetate (PMA) and analysis of downstream effects.

Main Results:

• PKCα-mediated phosphorylation of CD36 at Thr92 inhibited TSP-1 peptide binding in vitro, with inhibition proportional to phosphorylation levels.
• Basal CD36 phosphorylation in platelets, endothelial cells, and melanoma cells was minimal.
• PMA treatment induced significant CD36 phosphorylation in melanoma cells, reduced Src-family protein recruitment, and did not involve extracellular kinase activity.

Conclusions:

• PMA-induced CD36 phosphorylation requires new protein synthesis and Golgi trafficking, indicating an intracellular phosphorylation site.
• A novel in vivo pathway for CD36 phosphorylation modulates affinity for TSP-1, potentially impacting vascular cell signaling.