Endocytosis of adiponectin receptor 1 through a clathrin- and Rab5-dependent pathway

Abstract

In eukaryotic cells, receptor endocytosis is a key event regulating signaling transduction. Adiponectin receptors belong to a new receptor family that is distinct from G-protein-coupled receptors and has critical roles in the pathogenesis of diabetes and metabolic syndrome. Here, we analyzed the endocytosis of adiponectin and adiponectin receptor 1 (AdipoR1) and found that they are both internalized into transferrin-positive compartments that follow similar traffic routes. Blocking clathrin-mediated endocytosis by expressing Eps15 mutants or depleting K + trapped AdipoR1 at the plasma membrane, and K + depletion abolished adiponectin internalization, indicating that the endocytosis of AdipoR1 and adiponectin is clathrin-dependent. Depletion of K + and overexpression of Eps15 mutants enhance adiponectinstimulated AMP-activated protein kinase phosphorylation, suggesting that the endocytosis of AdipoR1 might downregulate adiponectin signaling. In addition, AdipoR1 colocalizes with the small GTPase Rab5, and a dominant negative Rab5 abrogates AdipoR1 endocytosis. These data indicate that AdipoR1 is internalized through a clathrin-and Rab5-dependent pathway and that endocytosis may play a role in the regulation of adiponectin signaling.

Molecular characterisation of the adiponectin receptors, AdipoR1 and AdipoR2

“…Indeed, several lines of evidence suggest that increased transduction of the adiponectin signal from the PM leads to enhanced coupling to AMPK 70,72,168 , which itself represents a major target for therapeutic intervention 194 .…”

“…An important role for β-arrestin 1 and 2 in mediating internalisation of some GPCRs has been established 177,179 . In 2008, overexpressed tagged AdipoR1 and AdipoR2 was used to demonstrate the endocytosis of adiponectin receptors 168 .…”

“…It was identified that Rab5, a member of GTPase large family that regulate vesicle transport in cell 180 , is involved in the endocytosis of AdipoR1 168 .…”

“…Some groups reported that AdipoR2 is not expressing at the cell-surface and therefore AdipoR1 was the main focus of most of the studies 168,169 . In contrast, a group demonstrated that both receptors were expressed at the cell-surface to same extent 152 .…”

“…Molecular and cellular studies have revealed differences between AdipoR1 and AdipoR2 that include different binding properties 48 , cell surface expression 168,200,206 and temporal signaling profiles 152,207 . Furthermore, investigations in mice have demonstrated contrasting expression profiles, with AdipoR1 expressed relatively ubiquitously compared with AdipoR2 48 , and activation of alternate signaling pathways 90 .…”