title: Optineurin mediates a negative regulation of Rab8 by the GTPase-activating protein TBC1D17.
abstract: Rab GTPases regulate various membrane trafficking pathways but the mechanisms by which GTPase-activating proteins recognise specific Rabs are not clear. Rab8 is involved in controlling several trafficking processes, including the trafficking of transferrin receptor from the early endosome to the recycling endosome. Here, we provide evidence to show that TBC1D17, a Rab GTPase-activating protein, through its catalytic activity, regulates Rab8-mediated endocytic trafficking of transferrin receptor. Optineurin, a Rab8-binding effector protein, mediates the interaction and colocalisation of TBC1D17 with Rab8. A non-catalytic region of TBC1D17 is required for direct interaction with optineurin. Co-expression of Rab8, but not other Rabs tested, rescues the inhibition of transferrin receptor trafficking by TBC1D17. The activated GTP-bound form of Rab8 is localised to the tubules emanating from the endocytic recycling compartment. Through its catalytic activity, TBC1D17 inhibits recruitment of Rab8 to the tubules and reduces colocalisation of transferrin receptor and Rab8. Knockdown of optineurin or TBC1D17 results in enhanced recruitment of Rab8 to the tubules. A glaucoma-associated mutant of optineurin, E50K, causes enhanced inhibition of Rab8 by TBC1D17, resulting in defective endocytic recycling of transferrin receptor. Our results show that TBC1D17, through its interaction with optineurin, regulates Rab8-mediated endocytic recycling of transferrin receptor and recruitment of Rab8 to the endocytic recycling tubules. We describe a mechanism of regulating a Rab GTPase by an effector protein (optineurin) that acts as an adaptor to bring together a Rab (Rab8) and its GTPase-activating protein (TBC1D17).
authors.affiliation: Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad 500 007, India.
authors.forename: Vipul
authors.initials: V
authors.lastname: Vaibhava
authors.forename: Ananthamurthy
authors.initials: A
authors.lastname: Nagabhushana
authors.forename: Madhavi Latha Somaraju
authors.initials: ML
authors.lastname: Chalasani
authors.forename: Cherukuri
authors.initials: C
authors.lastname: Sudhakar
authors.forename: Asha
authors.initials: A
authors.lastname: Kumari
authors.forename: Ghanshyam
authors.initials: G
authors.lastname: Swarup
mesh_terms: D001667:Binding, Competitive; D018797:Cell Cycle Proteins; D004705:Endocytosis; D025461:Feedback, Physiological; D020690:GTPase-Activating Proteins / Q000737:chemistry / Q000378:metabolism*; D005901:Glaucoma / Q000235:genetics; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D026901:Membrane Transport Proteins; D008870:Microtubules / Q000378:metabolism; D020125:Mutation, Missense; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D021381:Protein Transport; D011990:Receptors, Transferrin / Q000378:metabolism; D035582:Transcription Factor TFIIIA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D020690:GTPase-Activating Proteins; D026901:Membrane Transport Proteins; C409460:OPTN protein, human; D011990:Receptors, Transferrin; C581544:TBC1D17 protein, human; D035582:Transcription Factor TFIIIA; C082377:RAB8A protein, human; D020691:rab GTP-Binding Proteins