Carcinogenesis, Vol. 21, No. 4, 567-572,
April 2000
© 2000 Oxford University Press
Cancer Biology |
TGF
is required for full expression of the transformed growth phenotype of NIH 3T3 cells overexpressing ornithine decarboxylase
1 Center for Molecular Medicine and Genetics and
2 Department of Internal Medicine, Wayne State University School of Medicine and
3 John D.Dingell VA Medical Center, Detroit, MI 48201, USA
Ornithine decarboxylase (ODC) overexpressed from a heterologous promoter drives the tumorigenic transformation of NIH 3T3 cells and provides a model to investigate the underlying molecular mechanisms. These transformed cells, designated NODC cells, exhibit elevated levels of epidermal growth factor receptor (EGFR) tyrosine kinase (Tyr-k) activity relative to control transfected cells and inhibition of EGFR Tyr-k activation suppresses the transformed growth phenotype of these cells. Thus, ODC-induced transformation of NIH 3T3 cells appears to be mediated, at least in part, by enhanced signaling through the EGFR pathway. Here we extend these studies by evaluating: (i) the effects on growth regulation of overexpressing ODC in EGFR-deficient NIH 3T3 cells; (ii) the potential role of TGF
in mediating the EGFR-dependent transformation of NIH 3T3 cells by ODC. Disruption of EGFR–TGF interactions either by deleting EGFR, by treatment with anti-TGF neutralizing antibody or by transfection with a TGF antisense expression vector suppressed acquisition of the full transformed growth phenotype. Specifically, the loss of contact inhibition and the capacity for clonogenic growth appear more dependent on EGFR–TGF interactions than anchorage-independent growth in ODC-overexpressing cells. ODC overexpression does not alter the amount, localization or secretion of TGF. Thus, TGF is not the ODC-responsive component of the EGFR signaling pathway but appears to be critically involved in development of the transformed phenotype of NODC cells.
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