title: An AGEF-1/Arf GTPase/AP-1 ensemble antagonizes LET-23 EGFR basolateral localization and signaling during C. elegans vulva induction.
abstract: LET-23 Epidermal Growth Factor Receptor (EGFR) signaling specifies the vulval cell fates during C. elegans larval development. LET-23 EGFR localization on the basolateral membrane of the vulval precursor cells (VPCs) is required to engage the LIN-3 EGF-like inductive signal. The LIN-2 Cask/LIN-7 Veli/LIN-10 Mint (LIN-2/7/10) complex binds LET-23 EGFR, is required for its basolateral membrane localization, and therefore, vulva induction. Besides the LIN-2/7/10 complex, the trafficking pathways that regulate LET-23 EGFR localization have not been defined. Here we identify vh4, a hypomorphic allele of agef-1, as a strong suppressor of the lin-2 mutant Vulvaless (Vul) phenotype. AGEF-1 is homologous to the mammalian BIG1 and BIG2 Arf GTPase guanine nucleotide exchange factors (GEFs), which regulate secretory traffic between the Trans-Golgi network, endosomes and the plasma membrane via activation of Arf GTPases and recruitment of the AP-1 clathrin adaptor complex. Consistent with a role in trafficking we show that AGEF-1 is required for protein secretion and that AGEF-1 and the AP-1 complex regulate endosome size in coelomocytes. The AP-1 complex has previously been implicated in negative regulation of LET-23 EGFR, however the mechanism was not known. Our genetic data indicate that AGEF-1 is a strong negative regulator of LET-23 EGFR signaling that functions in the VPCs at the level of the receptor. In line with AGEF-1 being an Arf GEF, we identify the ARF-1.2 and ARF-3 GTPases as also negatively regulating signaling. We find that the agef-1(vh4) mutation results in increased LET-23 EGFR on the basolateral membrane in both wild-type and lin-2 mutant animals. Furthermore, unc-101(RNAi), a component of the AP-1 complex, increased LET-23 EGFR on the basolateral membrane in lin-2 and agef-1(vh4); lin-2 mutant animals. Thus, an AGEF-1/Arf GTPase/AP-1 ensemble functions opposite the LIN-2/7/10 complex to antagonize LET-23 EGFR basolateral membrane localization and signaling.
authors.affiliation: Division of Endocrinology and Metabolism, Department of Medicine, Research Institute of the McGill University Health Centre, McGill University, Montreal, Quebec, Canada; Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada.
authors.forename: Olga
authors.initials: O
authors.lastname: Skorobogata
authors.affiliation: Institute of Molecular Life Sciences, University of Zürich, Zürich, Switzerland.
authors.forename: Juan M
authors.initials: JM
authors.lastname: Escobar-Restrepo
authors.affiliation: Division of Endocrinology and Metabolism, Department of Medicine, Research Institute of the McGill University Health Centre, McGill University, Montreal, Quebec, Canada; Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada.
authors.forename: Christian E
authors.initials: CE
authors.lastname: Rocheleau
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D017173:Caenorhabditis elegans / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D005260:Female; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism; D016153:Genes, Suppressor; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007814:Larva / Q000378:metabolism; D008247:Lysosomes / Q000235:genetics / Q000473:pathology; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014844:Vulva / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism
chemical_list: C000607009:AGEF-1 protein, C elegans; D029742:Caenorhabditis elegans Proteins; D020662:Guanine Nucleotide Exchange Factors; D046912:Multiprotein Complexes; C085440:UNC-101 protein, C elegans; D066246:ErbB Receptors; C085873:let-23 protein, C elegans; C000607011:ARF-1.2 protein, C elegans; C000607010:ARF-3 protein, C elegans; D020558:GTP Phosphohydrolases