The Rab27 effector Rabphilin, unlike Granuphilin and Noc2, rapidly exchanges between secretory granules and cytosol in PC12 cells.
Rab proteins are GTPases that transit between GTP- and GDP-bound states. In the GTP-bound form they can recruit specific effector to membrane domains. It is possible that the exchange of Rab effectors between membranes and cytosol would be determined by the exchange of the particular Rab partner. We have compared the cycling of three Rab3/27 effectors, Granuphilin, Noc2, and Rabphilin, in PC12 cells using fluorescence recovery after photobleaching of EGFP-tagged proteins. All three effectors become localised to secretory granules. Granuphilin and Noc2 showed little or no exchange between secretory granules and cytosol whereas Rabphilin showed rapid and complete exchange. Both Noc2 and Rabphilin were found to be recruited to granules by Rab27 but the data suggest that Rabphilin did not form stable complexes with Rab27 on secretory granules and so Rab effector cycling between membranes and cytosol can be independent of that of the Rab protein.
The Physiological Laboratory, School of Biomedical Sciences, University of Liverpool, Crown Street, Liverpool L693BX, UK.
Mark T W
MT
Handley
Robert D
RD
Burgoyne
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D003600:Cytosol / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D016716:PC12 Cells; D021381:Protein Transport; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D022142:Secretory Vesicles / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000075745:rab27 GTP-Binding Proteins; D020826:rab3A GTP-Binding Protein / Q000235:genetics / Q000378:metabolism; D000097624:Rabphilin-3A
D048868:Adaptor Proteins, Signal Transducing; D047908:Intracellular Signaling Peptides and Proteins; D009419:Nerve Tissue Proteins; D011506:Proteins; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins; D000075745:rab27 GTP-Binding Proteins; D020826:rab3A GTP-Binding Protein; D000097624:Rabphilin-3A; C109307:Rph3al protein, rat; C512778:Sytl4 protein, rat; C512961:Rab27a protein, rat