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© The Rockefeller University Press, 0021-9525/1997//1119 $5.00
The Journal of Cell Biology, Volume 139, Number 5, , 1997 1119-1135

Article

Involvement of the Transmembrane Protein p23 in Biosynthetic Protein Transport



Manuel Rojo*, Rainer Pepperkok{ddagger}, Gregory Emery*, Roland Kellner§, Espen Stang||, Robert G. Parton||, and Jean Gruenberg*

* Department of Biochemistry, {ddagger} Department of Cell Biology, University of Geneva, 1211 Geneva 4, Switzerland; § Institute of Physiological Chemistry and Patobiochemistry, Gutenberg Universität, 55099 Mainz, Germany; and || Centre for Microscopy and Microanalysis, Department of Physiology and Pharmacology, and Centre for Molecular and Cellular Biology, University of Queensland, Queensland 4072, Brisbane, Australia

Here, we report the localization and characterization of BHKp23, a member of the p24 family of transmembrane proteins, in mammalian cells. We find that p23 is a major component of tubulovesicular membranes at the cis side of the Golgi complex (estimated density: 12,500 copies/µm2 membrane surface area, or {approx}30% of the total protein). Our data indicate that BHKp23-containing membranes are part of the cis-Golgi network/intermediate compartment . Using the G protein of vesicular stomatitis virus as a transmembrane cargo molecule, we find that p23 membranes are an obligatory station in forward biosynthetic membrane transport, but that p23 itself is absent from transport vesicles that carry the G protein to and beyond the Golgi complex. Our data show that p23 is not present to any significant extent in coat protein (COP) I-coated vesicles generated in vitro and does not colocalize with COP I buds and vesicles. Moreover, we find that p23 cytoplasmic domain is not involved in COP I membrane recruitment. Our data demonstrate that microinjected antibodies against the cytoplasmic tail of p23 inhibit G protein transport from the cis-Golgi network/ intermediate compartment to the cell surface, suggesting that p23 function is required for the transport of transmembrane cargo molecules. These observations together with the fact that p23 is a highly abundant component in the intermediate compartment, lead us to propose that p23 contributes to membrane structure, and that this contribution is necessary for efficient segregation and transport.

Abbreviations used in this paper: BFA, brefeldin A; COP, coat protein; CT, antibodies against a peptide corresponding to the cytoplasmic tail of BHKp23; EST, expressed sequence tag; GTP{gamma}S, guanosine 5'-O-(3-thiotriphosphate); LP1 and LP2, antibodies against luminal peptides 1 and 2; NAGT I, 1,2 N-acetylglucosaminyltransferase I; PFA, paraformaldehyde; 2D, two dimensional; VSV, vesicular stomatitis virus.

Address all correspondence to J. Gruenberg, Department of Biochemistry, Sciences II, 30 quai Ernest Ansermet, 1211 Geneva 4, Switzerland. Tel. and Fax: 41-22-7042-64-64. E-mail: jean.gruenberg{at}biochem.unige.ch

R. Pepperkok's current address is ICRF 44, Lincoln's Inn Fields, London WC2A 3PX, Great Britain.


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