Annexin VI stimulates endocytosis and is involved in the trafficking of low density lipoprotein to the prelysosomal compartment.
Annexins are calcium-binding proteins with a wide distribution in most polarized and nonpolarized cells that participate in a variety of membrane-membrane interactions. At the cell surface, annexin VI is thought to remodel the spectrin cytoskeleton to facilitate budding of coated pits. However, annexin VI is also found in late endocytic compartments in a number of cell types, indicating an additional important role at later stages of the endocytic pathway. Therefore overexpression of annexin VI in Chinese hamster ovary cells was used to investigate its possible role in endocytosis and intracellular trafficking of low density lipoprotein (LDL) and transferrin. While overexpression of annexin VI alone did not alter endocytosis and degradation of LDL, coexpression of annexin VI and LDL receptor resulted in an increase in LDL uptake with a concomitant increase of its degradation. Whereas annexin VI showed a wide intracellular distribution in resting Chinese hamster ovary cells, it was mainly found in the endocytic compartment and remained associated with LDL-containing vesicles even at later stages of the endocytic pathway. Thus, data presented in this study suggest that after stimulating endocytosis at the cell surface, annexin VI remains bound to endocytic vesicles to regulate entry of ligands into the prelysosomal compartment.
Grewal
T
T
Medizinische Kernklinik und Poliklinik, Universitäts Krankenhaus Eppendorf, Martinistr. 52, 20246 Hamburg, Germany. grewal@uke.uni-hamburg.de
Heeren
J
J
Mewawala
D
D
Schnitgerhans
T
T
Wendt
D
D
Salomon
G
G
Enrich
C
C
Beisiegel
U
U
Jäckle
S
S
D000818:Animals; D017317:Annexin A6 / Q000494:pharmacology*; D001692:Biological Transport; D016466:CHO Cells; D006224:Cricetinae; D004705:Endocytosis / Q000187:drug effects*; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism*; D011973:Receptors, LDL / Q000378:metabolism; D014168:Transferrin / Q000378:metabolism
D017317:Annexin A6; D008077:Lipoproteins, LDL; D011973:Receptors, LDL; D014168:Transferrin