Previous Article | Next Article ![]()
Molecular and Cellular Biology, April 2002, p. 2703-2715, Vol. 22, No. 8
0270-7306/02/$04.00+0 DOI: 10.1128/MCB.22.8.2703-2715.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Departments of Neurosurgery,1 Neurology,3 Neuroscience,4 Oncology, The Johns Hopkins University School of Medicine,5 The Kennedy Krieger Institute, Baltimore, Maryland 212052
Received 12 June 2001/ Returned for modification 23 July 2001/ Accepted 3 January 2002
Scatter factor/hepatocyte growth factor (SF/HGF) expression has been linked to malignant progression in glial neoplasms. Using two glioma cell lines, U373MG and SNB-19, we have demonstrated that SF/HGF stimulation allows cells to escape G1/G0 arrest induced by contact inhibition or serum withdrawal. SF/HGF induced effects on two mechanisms of cell cycle regulation: suppression of the cyclin-dependent kinase inhibitor p27 and induction of the transcription factor c-Myc. Regulation of p27 by SF/HGF was posttranslational and is associated with p27 nuclear export. Transient transfections of U373MG and SNB-19 with wild-type p27 and a degradation-resistant p27T187A mutant were insufficient to induce cell cycle arrest, and SF/HGF downregulation of p27 was not necessary for cell cycle reentry. Analysis of Cdk2 kinase activity and p27 binding to cyclin E complexes in the presence of exogenous wild-type p27 or p27T187A demonstrated that Cdk2 activity was not necessary for SF/HGF-mediated G1/S transition. Similarly, overexpression of dominant-negative forms of Cdk2 did not block SF/HGF-triggered cell cycle progression. In contrast, SF/HGF transcriptionally upregulated c-Myc, and overexpression of c-Myc was able to prevent G1/G0 arrest in the absence of SF/HGF. Transient overexpression of MadMyc, a dominant-negative chimera for c-Myc, caused G1/G0 arrest in logarithmically growing cells and blocked SF/HGF-mediated G1/S transition. c-Myc did not exert its effects through p27 downregulation in these cell lines. SF/HGF induced E2F1-dependent transcription, the inhibition of which did not block SF/HGF-induced cell cycle progression. We conclude that SF/HGF prevents G1/G0 arrest in glioma cell lines by a c-myc-dependent mechanism that is independent of p27, Cdk2, or E2F1.
This article has been cited by other articles:
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»