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Lack of correlation between sensitivity to growth inhibition and receptor number for transforming growth factor beta
1Systemic Toxicology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709.
Abstract:
Four human squamous carcinoma cell lines, SCC-9, SCC-12F, SCC-15G, and SCC-25, were examined for sensitivity to the growth-inhibitory and differentiation-inducing effects of transforming growth factor beta (TGF-beta). None of the four cell lines was induced to differentiate, as measured by staining for keratin and by competence of cells to form cross-linked envelopes, by concentrations of TGF-beta as high as 1000 pM. TGF-beta did not inhibit DNA synthesis or proliferation of SCC-12F cells in monolayer culture. Monolayer growth and DNA synthesis of SCC-15G and SCC-25 cells were markedly inhibited by 10 pM TGF-beta, with maximal inhibition between 10 and 100 pM. Inhibition of SCC-15G cells was apparent as early as 8 h after addition of TGF-beta, but inhibition of SCC-25 cells was not measurable until 2 days. Growth inhibition of SCC-15G cells was completely reversible, whereas inhibition of SCC-25 cells was irreversible. When growth of cells was measured in a defined medium supplemented with 0.5% fetal bovine serum, TGF-beta inhibited both the monolayer and clonal growth of SCC-15G cells. The monolayer growth, but not the clonal growth, of SCC-25 cells was inhibited. Growth of SCC-9 cells in confluent cultures was slightly inhibited by TGF-beta, while growth in subconfluent cultures was unaffected. All four cell lines, when assayed for binding of 125I-labeled TGF-beta, displayed high-affinity (KD = 2-44 pM) binding sites. These sites were present in very low numbers (less than 2000 sites/cell) in SCC-9, SCC-15G, and SCC-25 cells. SCC-12F cells contained 2000-5500 high-affinity sites/cell. Thus, a lack of sensitivity to growth inhibition by TGF-beta does not necessarily correlate with an inability to bind the growth factor to specific cell surface receptors. The possibility remains that altered sensitivity to TGF-beta may be due to loss of or changes in the relative proportions of the various TGF-beta receptor types. TGF-beta is believed to play a primary role in control of normal cellular growth and differentiation, and the study of cells with defective responses to this growth factor should help to identify some of the critical points within the growth cycle at which malignant cells may escape normal regulatory controls. The differential responses of these four human squamous carcinoma cell lines to TGF-beta should provide a useful model for studying such control mechanisms.
Insights
Transforming growth factor beta (TGF-beta) differentially affects human squamous carcinoma cell lines. While some cell lines show growth inhibition, none differentiate, indicating complex TGF-beta signaling in cancer.
Area of Science:
- Cell Biology
- Cancer Research
- Molecular Biology
Background:
- Transforming growth factor beta (TGF-beta) is crucial for regulating normal cell growth and differentiation.
- Understanding cancer cell responses to TGF-beta is vital for identifying mechanisms of uncontrolled proliferation.
Purpose of the Study:
- To investigate the differential sensitivity of four human squamous carcinoma cell lines (SCC-9, SCC-12F, SCC-15G, SCC-25) to TGF-beta's growth-inhibitory and differentiation effects.
- To explore the correlation between TGF-beta binding to cell surface receptors and cellular response.
Main Methods:
- Exposure of four human squamous carcinoma cell lines to varying concentrations of TGF-beta.
- Assessment of cellular differentiation via keratin staining and cross-linked envelope formation.
- Measurement of DNA synthesis and cell proliferation in monolayer and clonal cultures.
- Quantification of high-affinity TGF-beta binding sites using 125I-labeled TGF-beta.
Main Results:
- None of the cell lines differentiated in response to TGF-beta.
- TGF-beta inhibited monolayer growth and DNA synthesis in SCC-15G and SCC-25 cells, with varying reversibility and time courses.
- SCC-12F cells showed no inhibition of proliferation, while SCC-9 cells exhibited slight inhibition only in confluent cultures.
- All cell lines possessed high-affinity TGF-beta binding sites, but receptor number did not consistently correlate with growth inhibition response.
Conclusions:
- Differential sensitivity to TGF-beta's growth inhibitory effects exists among human squamous carcinoma cell lines.
- The inability to inhibit growth does not necessarily correlate with a lack of TGF-beta binding sites.
- Variations in TGF-beta receptor types or signaling pathways may explain the differential responses, offering a model to study cancer escape from regulatory controls.