The Rab5 effector Rabankyrin-5 regulates and coordinates different endocytic mechanisms.
The small GTPase Rab5 is a key regulator of clathrin-mediated endocytosis. On early endosomes, within a spatially restricted domain enriched in phosphatydilinositol-3-phosphate [PI(3)P], Rab5 coordinates a complex network of effectors that functionally cooperate in membrane tethering, fusion, and organelle motility. Here we discovered a novel PI(3)P-binding Rab5 effector, Rabankyrin-5, which localises to early endosomes and stimulates their fusion activity. In addition to early endosomes, however, Rabankyrin-5 localises to large vacuolar structures that correspond to macropinosomes in epithelial cells and fibroblasts. Overexpression of Rabankyrin-5 increases the number of macropinosomes and stimulates fluid-phase uptake, whereas its downregulation inhibits these processes. In polarised epithelial cells, this function is primarily restricted to the apical membrane. Rabankyrin-5 localises to large pinocytic structures underneath the apical surface of kidney proximal tubule cells, and its overexpression in polarised Madin-Darby canine kidney cells stimulates apical but not basolateral, non-clathrin-mediated pinocytosis. In demonstrating a regulatory role in endosome fusion and (macro)pinocytosis, our studies suggest that Rab5 regulates and coordinates different endocytic mechanisms through its effector Rabankyrin-5. Furthermore, its active role in apical pinocytosis in epithelial cells suggests an important function of Rabankyrin-5 in the physiology of polarised cells.
Schnatwinkel
Carsten
C
Max-Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany.
Christoforidis
Savvas
S
Lindsay
Margaret R
MR
Uttenweiler-Joseph
Sandrine
S
Wilm
Matthias
M
Parton
Robert G
RG
Zerial
Marino
M
D000256:Adenoviridae / Q000235:genetics; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D003001:Cloning, Molecular; D004285:Dogs; D015536:Down-Regulation; D004705:Endocytosis / Q000502:physiology*; D011992:Endosomes / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology; D005347:Fibroblasts / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000737:chemistry; D005786:Gene Expression Regulation; D006801:Humans; D007295:Inositol Phosphates / Q000737:chemistry; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000502:physiology*; D008081:Liposomes / Q000378:metabolism; D051379:Mice; D018613:Microscopy, Confocal; D018715:Microscopy, Video; D009068:Movement; D041681:NIH 3T3 Cells; D010873:Pinocytosis; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D011994:Recombinant Proteins / Q000737:chemistry; D013997:Time Factors; D000077191:Wortmannin; D020696:rab5 GTP-Binding Proteins / Q000502:physiology*
D000730:Androstadienes; D004791:Enzyme Inhibitors; D007295:Inositol Phosphates; D047908:Intracellular Signaling Peptides and Proteins; D008081:Liposomes; D011994:Recombinant Proteins; D020558:GTP Phosphohydrolases; D020696:rab5 GTP-Binding Proteins; D000077191:Wortmannin