title: The annexin 2/S100A10 complex controls the distribution of transferrin receptor-containing recycling endosomes.
abstract: The Ca2+- and lipid-binding protein annexin 2, which resides in a tight heterotetrameric complex with the S100 protein S100A10 (p11), has been implicated in the structural organization and dynamics of endosomal membranes. To elucidate the function of annexin 2 and S100A10 in endosome organization and trafficking, we used RNA-mediated interference to specifically suppress annexin 2 and S100A10 expression. Down-regulation of both proteins perturbed the distribution of transferrin receptor- and rab11-positive recycling endosomes but did not affect uptake into sorting endosomes. The phenotype was highly specific and could be rescued by reexpression of the N-terminal annexin 2 domain or S100A10 in annexin 2- or S100A10-depleted cells, respectively. Whole-mount immunoelectron microscopy of the aberrantly localized recycling endosomes in annexin 2/S100A10 down-regulated cells revealed extensively bent tubules and an increased number of endosome-associated clathrin-positive buds. Despite these morphological alterations, the kinetics of transferrin uptake and recycling was not affected to a significant extent, indicating that the proper positioning of recycling endosomes is not a rate-limiting step in transferrin recycling. The phenotype generated by this transient loss-of-protein approach shows for the first time that the annexin 2/S100A10 complex functions in the intracellular positioning of recycling endosomes and that both subunits are required for this activity.
mesh_terms: D017306:Annexin A2 / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D002966:Clathrin / Q000378:metabolism / Q000502:physiology; D003001:Cloning, Molecular; D015536:Down-Regulation / Q000187:drug effects; D011992:Endosomes / Q000378:metabolism* / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism* / Q000502:physiology; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary / Q000235:genetics / Q000502:physiology; D034741:RNA, Small Interfering / Q000494:pharmacology; D011990:Receptors, Transferrin / Q000378:metabolism / Q000502:physiology; D009418:S100 Proteins / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D013347:Subcellular Fractions; D020691:rab GTP-Binding Proteins / Q000378:metabolism / Q000502:physiology; D000099193:rab11 GTP-Binding Proteins; D000099248:S100 Calcium Binding Protein A10
chemical_list: D017306:Annexin A2; D002966:Clathrin; D034741:RNA, Small Interfering; D011990:Receptors, Transferrin; D009418:S100 Proteins; D020691:rab GTP-Binding Proteins; D000099193:rab11 GTP-Binding Proteins; D000099248:S100 Calcium Binding Protein A10