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© The Rockefeller University Press, 0021-9525/1998//305 $5.00
The Journal of Cell Biology, Volume 140, Number 2, , 1998 305-313

Article

Expression of Rab3D N135I Inhibits Regulated Secretion of ACTH in AtT-20 Cells



Giulia Baldini*, Giovanna Baldini{ddagger}, Guangyi Wang*, Mattew Weber*, Marina Zweyer{ddagger}, Renato Bareggi{ddagger}, Joan W. Witkin*, and Alberto M. Martelli{ddagger}

* Department of Anatomy and Cell Biology, Columbia University, College of Physicians and Surgeons, New York, 10032; and {ddagger} Dipartimento di Morfologia Umana Normale, University of Trieste, Trieste, Italy I-34138

Rab proteins are small molecular weight GTPases that control vesicular traffic in eucaryotic cells. A subset of Rab proteins, the Rab3 proteins are thought to play an important role in regulated exocytosis of vesicles. In transfected AtT-20 cells expressing wild-type Rab3D, we find that a fraction of the protein is associated with dense core granules. In the same cells, expression of a mutated isoform of Rab3D, Rab3D N135I, inhibits positioning of dense core granules near the plasma membrane, blocks regulated secretion of mature ACTH, and impairs association of Rab3A to membranes. Expression of Rab3D N135I does not change the levels of ACTH precursor or the efficiency with which the precursor is processed into ACTH hormone and packaged into dense core granules. We also find that cells expressing mutated Rab3D differentiate to the same extent as untransfected AtT-20 cells. We conclude that expression of Rab3D N135I specifically impairs late membrane trafficking events necessary for ACTH hormone secretion.

Abbreviations used in this paper: SNAP-25, synaptomal-associated protein of 25 kD; VAMP, vesicle-associated membrane protein.

This work has been funded in part by a grant from the American Diabetes Association and by a Grant-In-Aid from the American Heart Association, New York City Affiliate.

Address all correspondence to Giulia Baldini, Department of Anatomy and Cell Biology, Columbia University, College of Physicians and Surgeons, New York, NY 10032. Tel.: (212) 305-6405. Fax: (212) 328-3890. E-mail: gb74{at}columbia.edu


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