Scatter factor/hepatocyte growth factor stimulation of glioblastoma cell cycle progression through G(1) is c-Myc dependent and independent of p27 suppression, Cdk2 activation, or E2F1-dependent transcription.
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 G(1)/G(0) 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 G(1)/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 G(1)/G(0) arrest in the absence of SF/HGF. Transient overexpression of MadMyc, a dominant-negative chimera for c-Myc, caused G(1)/G(0) arrest in logarithmically growing cells and blocked SF/HGF-mediated G(1)/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 G(1)/G(0) arrest in glioma cell lines by a c-myc-dependent mechanism that is independent of p27, Cdk2, or E2F1.
Walter
Kevin A
KA
Department of Neurosurgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Hossain
Mir Ahamed
MA
Luddy
Carey
C
Goel
Nidhi
N
Reznik
Thomas E
TE
Laterra
John
J
D021581:Active Transport, Cell Nucleus; D042846:CDC2-CDC28 Kinases; D002453:Cell Cycle / Q000187:drug effects* / Q000502:physiology; D018797:Cell Cycle Proteins / Q000378:metabolism; D003260:Contact Inhibition; D003470:Culture Media; D051357:Cyclin-Dependent Kinase 2; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D016193:G1 Phase / Q000187:drug effects / Q000502:physiology; D005909:Glioblastoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D017228:Hepatocyte Growth Factor / Q000494:pharmacology* / Q000502:physiology; D006801:Humans; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016196:S Phase / Q000187:drug effects / Q000502:physiology; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins / Q000378:metabolism
D018797:Cell Cycle Proteins; D003470:Culture Media; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D016271:Proto-Oncogene Proteins c-myc; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017228:Hepatocyte Growth Factor; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases