title: A direct inhibitory role for the Rab3-specific effector, Noc2, in Ca2+-regulated exocytosis in neuroendocrine cells.
abstract: Rab proteins comprise a family of GTPases, conserved from yeast to mammals, which are integral components of membrane trafficking pathways. Rab3A is a neural/neuroendocrine-specific member of the Rab family involved in Ca(2+) -regulated exocytosis, where it functions in an inhibitory capacity controlling recruitment of secretory vesicles into a releasable pool at the plasma membrane. The effector by which Rab3A exerts its inhibitory effect is unclear as the Rab3A effectors Rabphilin and RIM have been excluded from for this role. One putative Rab3A effector in dense-core granule exocytosis is the cytosolic zinc finger protein, Noc2. We have established that overexpression of Noc2 in PC12 cells has a direct inhibitory effect upon Ca(2+)-triggered exocytosis in permeabilized cells. We demonstrate specific nucleotide-dependent binding of Noc2 to Rab3A and show that the inhibition of exocytosis is dependent upon this interaction since Rab3A binding-deficient mutants of Noc2 do not inhibit exocytosis. We propose that Noc2 may be a negative effector for Rab3A in regulated exocytosis of dense-core granules from endocrine cells.
authors.affiliation: Physiological Laboratory, University of Liverpool, Crown Street, Liverpool L69 3BX, United Kingdom.
authors.forename: L P
authors.initials: LP
authors.lastname: Haynes
authors.forename: G J
authors.initials: GJ
authors.lastname: Evans
authors.forename: A
authors.initials: A
authors.lastname: Morgan
authors.forename: R D
authors.initials: RD
authors.lastname: Burgoyne
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003001:Cloning, Molecular; D003600:Cytosol / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005089:Exocytosis; D019204:GTP-Binding Proteins; D005982:Glutathione Transferase / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D016716:PC12 Cells; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D033921:Vesicular Transport Proteins; D016335:Zinc Fingers; D020691:rab GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D020826:rab3A GTP-Binding Protein / Q000737:chemistry / Q000378:metabolism; D000097624:Rabphilin-3A
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002118:Calcium; D018076:DNA, Complementary; D019204:GTP-Binding Proteins; D005982:Glutathione Transferase; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006153:Guanosine Diphosphate; D047908:Intracellular Signaling Peptides and Proteins; D009419:Nerve Tissue Proteins; D011506:Proteins; D011994:Recombinant Proteins; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins; D020826:rab3A GTP-Binding Protein; D000097624:Rabphilin-3A; C491492:RIMS1 protein, human; C107293:Rim protein, mammalian; C491489:Rims1 protein, rat; C109307:Rph3al protein, rat