title: RanGAP-mediated nuclear protein import in vascular smooth muscle cells is augmented by lysophosphatidylcholine.
abstract: The intracellular mechanism responsible for the mitogenic effects of lysophosphatidylcholine (LPC) is unclear. Import of proteins from the cytoplasm into the cell nucleus is integral to the regulation of gene expression and cell growth. We hypothesized that LPC exerts its intracellular effects through alterations in nuclear protein import. Rabbit aortic smooth muscle cells incubated with LPC induced a significant increase in cell proliferation in both quiescent cells (63.2+/-6.48% of control) and cells grown in 1% fetal bovine serum (FBS) (28.3+/-7.35% of control). Vascular smooth muscle cells were preincubated with LPC then microinjected with a marker protein for nuclear import. A significant stimulation of nuclear protein transport was observed. Using a conventional nuclear protein import assay in permeabilized cells, a significant stimulation of import (72.3+/-5.2% of control) was again observed when the cytosolic nuclear import cocktail was treated with LPC. This effect was not observed with other lysophosphatidyl species. LPC also activated the extracellular signal-regulated kinase (ERK) 1/2 mitogen-activated protein kinase (MAPK) pathway, and this was blocked by 2'-amino-3'-methoxyflavone (PD98059), which inhibits the activation of ERK 1/2. The stimulation of nuclear import was also blocked by PD98059. LPC-induced MAPK activation augmented GTP hydrolysis by RanGAP, a RanGTPase activating protein and a critical regulatory component of nuclear protein import, and this stimulation was again blocked by PD98059. We conclude that LPC alters gene expression and cell proliferation through striking effects on nuclear protein import via a MAP kinase-induced activation of RanGAP. This may play an important role in cancer and atherosclerosis and other disorders involving accelerated cell growth/proliferation.
authors.affiliation: Cell Biology Laboratory, Institute of Cardiovascular Sciences, St. Boniface General Hospital Research Centre, and Department of Physiology, Faculty of Medicine, University of Manitoba, 351 Tache Avenue, Winnipeg, Manitoba, Canada.
authors.forename: Randolph S
authors.initials: RS
authors.lastname: Faustino
authors.forename: Lyle N W
authors.initials: LN
authors.lastname: Stronger
authors.forename: Melanie N
authors.initials: MN
authors.lastname: Richard
authors.forename: Michael P
authors.initials: MP
authors.lastname: Czubryt
authors.forename: David A
authors.initials: DA
authors.lastname: Ford
authors.forename: Michele A
authors.initials: MA
authors.lastname: Prociuk
authors.forename: Elena
authors.initials: E
authors.lastname: Dibrov
authors.forename: Grant N
authors.initials: GN
authors.lastname: Pierce
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D001011:Aorta; D049109:Cell Proliferation / Q000187:drug effects; D020690:GTPase-Activating Proteins / Q000502:physiology*; D008244:Lysophosphatidylcholines / Q000494:pharmacology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000187:drug effects / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000187:drug effects / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000166:cytology*; D032389:Myocytes, Smooth Muscle; D009687:Nuclear Proteins / Q000378:metabolism*; D011817:Rabbits
chemical_list: D020690:GTPase-Activating Proteins; D008244:Lysophosphatidylcholines; D009687:Nuclear Proteins; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3