title: Redox-regulated signaling by lactosylceramide in the proliferation of human aortic smooth muscle cells.
abstract: Previously, our laboratory reported that lactosylceramide (LacCer) stimulated human aortic smooth muscle cell proliferation via specific activation of p44 mitogen-activated protein kinase (MAPK) in the p21(ras)/Raf-1/MEK2 pathway and induced expression of the transcription factor c-fos downstream to the p44 MAPK signaling cascade (Bhunia A. K., Han, H., Snowden, A., and Chatterjee S. (1996) J. Biol. Chem. 271, 10660-10666). In the present study, we explored the role of free oxygen radicals in LacCer-mediated induction of cell proliferation. Superoxide levels were measured by the lucigenin chemiluminescence method, MAPK activity was measured by immunocomplex kinase assays, and Western blot analysis and c-fos expression were measured by Northern blot assay. We found that LacCer (10 microM) stimulates endogenous superoxide production (7-fold compared with control) in human aortic smooth muscle cells specifically by activating membrane-associated NADPH oxidase, but not NADH or xanthine oxidase. This process was inhibited by an inhibitor of NADPH oxidase, diphenylene iodonium (DPI), and by antioxidants, N-acetyl-L-cysteine (NAC) or pyrrolidine dithiocarbamate. NAC and DPI both abrogated individual steps in the signaling pathway leading to cell proliferation. For example, the p21(ras).GTP loading, p44 MAPK activity, and induction of transcription factor c-fos all were inhibited by NAC and DPI as well as an antioxidant pyrrolidine dithiocarbamate or reduced glutathione (GSH). In contrast, depletion of GSH by L-buthionine (S, R)-sulfoximine up-regulated the above described signaling cascade. In sum, LacCer, by virtue of activating NADPH oxidase, produces superoxide (a redox stress signaling molecule), which mediates cell proliferation via activation of the kinase cascade. Our findings may explain the potential role of LacCer in the pathogenesis of atherosclerosis involving the proliferation of aortic smooth muscle cells.
authors.affiliation: The Johns Hopkins University School of Medicine, Lipid Research Atherosclerosis Unit, Department of Pediatrics, Baltimore, Maryland 21287-3654, USA.
authors.forename: A K
authors.initials: AK
authors.lastname: Bhunia
authors.forename: H
authors.initials: H
authors.lastname: Han
authors.forename: A
authors.initials: A
authors.lastname: Snowden
authors.forename: S
authors.initials: S
authors.lastname: Chatterjee
mesh_terms: D000111:Acetylcysteine / Q000378:metabolism; D015703:Antigens, CD; D000975:Antioxidants / Q000494:pharmacology; D019328:Buthionine Sulfoximine / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002455:Cell Division; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D007790:Lactosylceramides / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D009097:Multienzyme Complexes / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D019255:NADPH Oxidases / Q000378:metabolism; D009861:Onium Compounds / Q000378:metabolism; D010084:Oxidation-Reduction; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D015398:Signal Transduction; D013482:Superoxide Dismutase / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism; D014969:Xanthine Oxidase / Q000378:metabolism
chemical_list: D015703:Antigens, CD; D000975:Antioxidants; D004791:Enzyme Inhibitors; D007790:Lactosylceramides; D009097:Multienzyme Complexes; D009861:Onium Compounds; D016760:Proto-Oncogene Proteins c-fos; D013481:Superoxides; C009744:CDw17 antigen; D019328:Buthionine Sulfoximine; C007517:diphenyleneiodonium; D006160:Guanosine Triphosphate; D013482:Superoxide Dismutase; D014969:Xanthine Oxidase; C023107:NADH oxidase; D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D005978:Glutathione; D000111:Acetylcysteine