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Molecular and Cellular Biology, September 2005, p. 8251-8258, Vol. 25, No. 18
0270-7306/05/$08.00+0 doi:10.1128/MCB.25.18.8251-8258.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Institute for Biochemistry II, Cardiovascular Biochemistry, University of Frankfurt, Medical School, Theodor-Stern-Kai 7, 60590 Frankfurt, Germany
Received 10 February 2005/ Returned for modification 7 April 2005/ Accepted 21 June 2005
Nitric oxide (NO) plays a key role in vascular function, cell proliferation, and apoptosis. Proper subcellular localization of endothelial NO synthase (eNOS) is crucial for its activity; however, the role of eNOS trafficking for NO biosynthesis remains to be defined. Overexpression of NOS-interacting protein (NOSIP) induces translocation of eNOS from the plasma membrane to intracellular compartments, thereby impairing NO production. Here we report that endogenous NOSIP reduces the enzymatic capacity of eNOS, specifically in the G2 phase of the cell cycle by targeting eNOS to the actin cytoskeleton. This regulation is critically dependent on the nucleocytoplasmic shuttling of NOSIP and its cytoplasmic accumulation in the G2 phase. The predominant nuclear localization of NOSIP depends on a bipartite nuclear localization sequence (NLS) mediating interaction with importin
. Mutational destruction of the NLS abolishes nuclear import and interaction with importin
. Nuclear export is insensitive to leptomycin B and hence different from the CRM1-dependent default mechanism. Inhibition of NOSIP expression by RNA interference completely abolishes G2-specific cytoskeletal association and inhibition of eNOS. These findings describe a novel cell cycle-dependent modulation of endogenous NO levels that are critical to the cell cycle-related actions of NO such as apoptosis or cell proliferation.
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