title: The primate-specific protein TBC1D3 is required for optimal macropinocytosis in a novel ARF6-dependent pathway.
abstract: The generation of novel genes and proteins throughout evolution has been proposed to occur as a result of whole genome and gene duplications, exon shuffling, and retrotransposition events. The analysis of such genes might thus shed light into the functional complexity associated with highly evolved species. One such case is represented by TBC1D3, a primate-specific gene, harboring a TBC domain. Because TBC domains encode Rab-specific GAP activities, TBC-containing proteins are predicted to play a major role in endocytosis and intracellular traffic. Here, we show that the TBC1D3 gene originated late in evolution, likely through a duplication of the RNTRE locus, and underwent gene amplification during primate speciation. Despite possessing a TBC domain, TBC1D3 is apparently devoid of Rab-GAP activity. However, TBC1D3 regulates the optimal rate of epidermal growth factor-mediated macropinocytosis by participating in a novel pathway involving ARF6 and RAB5. In addition, TBC1D3 binds and colocalize to GGA3, an ARF6-effector, in an ARF6-dependent manner, and synergize with it in promoting macropinocytosis, suggesting that the two proteins act together in this process. Accordingly, GGA3 siRNA-mediated ablation impaired TBC1D3-induced macropinocytosis. We thus uncover a novel signaling pathway that appeared after primate speciation. Within this pathway, a TBC1D3:GGA3 complex contributes to optimal propagation of signals, ultimately facilitating the macropinocytic process.
authors.affiliation: IFOM, the FIRC Institute of Molecular Oncology Foundation, 20139 Milan, Italy.
authors.forename: Emanuela
authors.initials: E
authors.lastname: Frittoli
authors.forename: Andrea
authors.initials: A
authors.lastname: Palamidessi
authors.forename: Alessandro
authors.initials: A
authors.lastname: Pizzigoni
authors.forename: Letizia
authors.initials: L
authors.lastname: Lanzetti
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Garrè
authors.forename: Flavia
authors.initials: F
authors.lastname: Troglio
authors.forename: Albino
authors.initials: A
authors.lastname: Troilo
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Fukuda
authors.forename: Pier Paolo
authors.initials: PP
authors.lastname: Di Fiore
authors.forename: Giorgio
authors.initials: G
authors.lastname: Scita
authors.forename: Stefano
authors.initials: S
authors.lastname: Confalonieri
mesh_terms: D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000235:genetics / Q000502:physiology*; D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000502:physiology; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D019143:Evolution, Molecular; D020690:GTPase-Activating Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D020440:Gene Duplication; D020868:Gene Silencing; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D015513:Oncogene Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D010802:Phylogeny; D010873:Pinocytosis / Q000235:genetics / Q000502:physiology*; D011323:Primates; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D020696:rab5 GTP-Binding Proteins / Q000235:genetics / Q000502:physiology
chemical_list: D000089982:ADP-Ribosylation Factor 6; D033942:Adaptor Proteins, Vesicular Transport; C407306:GGA adaptor proteins; D020690:GTPase-Activating Proteins; D015513:Oncogene Proteins; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; C467563:TBC1D3 protein, human; D020727:ADP-Ribosylation Factors; C000715348:ARF6 protein, human; D020696:rab5 GTP-Binding Proteins