Sec15 is an effector for the Rab11 GTPase in mammalian cells.
Rab/Ypt GTPases play key roles in the regulation of vesicular trafficking. They perform most of their functions in a GTP-bound form by interacting with specific downstream effectors. The exocyst is a complex of eight polypeptides involved in constitutive secretion and functions as an effector for multiple Ras-related small GTPases, including the Rab protein Sec4p in yeast. In this study, we have examined the localization and function of the Sec15 exocyst subunit in mammalian cells. Overexpressed Sec15 associated with clusters of tubular/vesicular elements that were concentrated in the perinuclear region. The tubular/vesicular clusters were dispersed throughout the cytoplasm upon treatment with the microtubule-depolymerizing agent nocodazole and were accessible to endocytosed transferrin, but not exocytic cargo (vesicular stomatitis virus glycoprotein). Consistent with these observations, Sec15 colocalized selectively with the recycling endosome marker Rab11 and exhibited a GTP-dependent interaction with the Rab11 GTPase, but not with Rab4, Rab6, or Rab7. These findings provide the first evidence that the exocyst functions as a Rab effector complex in mammalian cells.
Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia.
Xiang-Ming
XM
Zhang
Sarah
S
Ellis
Absorn
A
Sriratana
Christina A
CA
Mitchell
Tony
T
Rowe
D000818:Animals; D001692:Biological Transport; D016466:CHO Cells; D019556:COS Cells; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D008854:Microscopy, Electron; D008870:Microtubules / Q000378:metabolism; D015739:Nocodazole / Q000494:pharmacology; D010455:Peptides / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D013696:Temperature; D014162:Transfection; D014168:Transferrin / Q000378:metabolism; D020798:Two-Hybrid System Techniques; D020691:rab GTP-Binding Proteins / Q000378:metabolism* / Q000502:physiology; D020695:rab4 GTP-Binding Proteins / Q000378:metabolism; D000090802:rab7 GTP-Binding Proteins; D000099193:rab11 GTP-Binding Proteins
D019204:GTP-Binding Proteins; D015739:Nocodazole; D010455:Peptides; D014168:Transferrin; D020691:rab GTP-Binding Proteins; D020695:rab4 GTP-Binding Proteins; D000090802:rab7 GTP-Binding Proteins; D000099193:rab11 GTP-Binding Proteins; C489222:EXOC6B protein, human; C094135:Rab6 protein; C000716463:rab7 GTP-binding proteins, human