Abstract
The class B scavenger receptor CD36 has numerous ligands that include modified forms of low density lipoprotein, fibrillar amyloid, apoptotic cells, and Plasmodium falciparum-infected red blood cells, linking this molecule to atherosclerosis, Alzheimer disease, malaria, and other diseases. We studied the signaling events that follow receptor engagement and lead to CD36 and ligand internalization. We show that oxidized low density lipoprotein or antibody-induced clustering of CD36 triggers macropinocytosis and internalization of the receptor-ligand complex. Remarkably, however, CD36 internalization is independent of macropinocytosis and occurs by a novel endocytic mechanism that depends on actin, but not dynamin. This actin-driven endocytosis requires the activation Src family kinases, JNK, and Rho family GTPases, but, unlike macropinocytosis, it is not affected by inhibitors of phosphatidylinositol 3-kinase or Na/H exchange. Manipulation of this unique mode of internalization may prove helpful in the prevention and management of the wide range of diseases in which CD36 is implicated.
Highlights
OxLDL particles are recognized by a variety of receptors, including the class A scavenger receptor SR-A and the class B scavenger receptor CD36
Anti-CD36 Antibodies and OxLDL Trigger Internalization of CD36—We first examined the steady-state distribution of unstimulated CD36 in fixed and permeabilized macrophages
Conditions used, CD36 is responsible for the majority of oxidized LDL (oxLDL) Actin polymerization often follows activation of Rho family uptake and that the internalization of CD36 triggered by oxLDL GTPases, and Rac has been implicated in forming large memcan be mimicked by cross-linking the receptors with anti-CD36 brane ruffles of the type involved in macropinocytosis
Summary
Antibodies—Mouse anti-human CD36 IgG (clone 131.2) was prepared by Narendra N. Acid Wash—In most cases, antibodies bound to the noninternalized CD36 were stripped off with an acid wash protocol: Cells were treated for 2 min with ice-cold acid wash buffer (0.5 M glacial acetic acid, 150 mM sodium chloride, pH 2.5) followed by recovery in ice-cold H-RPMI for 2 min To examine PAK1 recruitment during CD36 cross-linking, cells were transfected with PAK1PBD-YFP, labeled for CD36, warmed in H-RPMI for 3 min, fixed, and imaged on a spinning disc microscope. Cells were warmed for 30 min and fixed (without acid wash), and CD36 internalization was imaged by spinning disc microscopy. Cells were incubated in H-RPMI containing 40 ng/ml mouse M-CSF (SigmaAldrich), 150 g/ml sulforhodamine B (Molecular Probes), and the appropriate inhibitor for 30 min at 37 °C without CO2. These data were normalized to the control (untreated cells), standard deviations were calculated, and the data were plotted in Excel
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call