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J. Cell Biol., Volume 140, Number 2, January 26, 1998 305-313

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

Giulia Baldini,* Giovanna Baldini,Dagger Guangyi Wang,* Mattew Weber,* Marina Zweyer,Dagger Renato Bareggi,Dagger Joan W. Witkin,* and Alberto M. MartelliDagger

* Department of Anatomy and Cell Biology, Columbia University, College of Physicians and Surgeons, New York, 10032; and Dagger  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.


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