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




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