Interactions of Annexins with the mu Subunits of the Clathrin Assembly Proteins

Abstract

A number of biochemical and genetic studies have suggested that certain annexins play important roles in the endocytic pathway, possibly involving the generation, localization, or fusion of endocytic compartments. In a yeast two-hybrid screen for proteins that interact with the N-terminal domain of annexin A2 we identified the mu2 subunit of the clathrin assembly protein complex AP-2. The interaction depended upon two copies of a YxxΦ amino acid sequence motif (Y ) tyrosine, x ) variable residue, Φ ) bulky, hydrophobic residue) in the annexin that is also characteristic of the binding site for mu2 on the cytoplasmic domains of transmembrane receptors. The interaction between mu2 and full-length annexin A2 was demonstrated in vitro to be direct, to require calcium, and to be functional in the sense that annexin A2 was able to recruit the mu2 to immobilized lipids. Examination of other annexins and mu subunits demonstrated that annexin A2 also binds the mu1 subunit of the AP-1 complex, that annexin A6 binds mu1 and mu2, and that annexin A1 binds only mu1. We propose that annexins can "masquerade" as transmembrane receptors when they are attached to membranes in the presence of calcium and that they might therefore function to initiate calcium-regulated coated pit formation at the cell surface or on intracellular organelles.

Cytosolic Dynamics of Annexin A6 Trigger Feedback Regulation of Hypertrophy via Atrial Natriuretic Peptide in Cardiomyocytes

“…8, A and B). This phosphomimic of Anxa6 reportedly exhibits a conformation resembling the Ca 2ϩ -bound state of WT and is assumed to possess a more flexible, open structure, enabling it to interact with multiple membranes simultaneously (39,40,54). Furthermore, cells stably expressing T356D were found to be superior to WT Anxa6 in defending PE-induced hypertrophy (Fig.…”

“…6E. ture that can simultaneously bind multiple membranes (39,40). We found that membrane association of Anxa6 T356D under PE treatment was more prominent than that of Anxa6 FL (Fig.…”

“…7H and supplemental Movie 7), it is possible that Anxa6 is critical for delivering Ca 2ϩ necessary for pro-ANP trafficking. It has long been known that the C terminus of Anxa6 is essential for Ca 2ϩ and phospholipid binding (39). Given that the Anxa6 ⌬C mutant exhibits partial association with pro-ANP, it is likely that Ca 2ϩ binding at the C terminus induces the conformational change in the N terminus (53) necessary to associate with pro-ANP-SG, thereby driving regulated vesicular traffic of pro-ANP.…”

Role of annexin A6 in cancer

“…The targeting of AnxA6 to membrane locations via the phospholipid is regulated by the pH and the levels of cholesterol (12)(13)(14). AnxA6 contributes to membrane organization; participates in cholesterol homeostasis (12,13,15,16); regulates the interactions of membranes and actin during endocytic transport (17,18); and regulates secretory events with S100 proteins (19) and tumor protein D52 (TPD52) (20). The interaction of AnxA6 with activated protein kinase C (PKC)-α and p120GTPase-activating protein (GAP) (21-23) may downregulate the epidermal growth factor receptor (EGFR)/Ras signaling pathway, since p120GAP is the sole GAP known to bind to EGFR and promote the hydrolysis of Ras-GTP (24).…”

Regulation of Lysosomal Degradation by CA2+And CA2+-Binding Proteins

“…It belongs to the network of membrane-cytoskeleton linkages (ChasserotGolaz et al, 1996) and is also associated to CLATHRIN coated vesicles (Creutz and Snyder, 2005) and to early and late endosomes, where it appears to be involved in intracellular vesicle movement and MVB formation (Merrifield et al, 1999;Mayran et al, 2003).…”