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Selective inhibition of growth-related gene expression in murine keratinocytes by transforming growth factor beta
R J Coffey1, C C Bascom, N J Sipes
1Department of Cell Biology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
Abstract:
Transforming growth factor beta (TGF beta) is a potent inhibitor of epithelial cell proliferation. A nontumorigenic epidermal growth factor (EGF)-dependent epithelial cell line, BALB/MK, is reversibly growth arrested by TGF beta. TGF beta will also abrogate EGF-stimulated mitogenesis of quiescent BALB/MK cells. Increased levels of calcium (greater than 1.0 mM) will induce differentiation in BALB/MK cells; in contrast, TGF beta-mediated growth inhibition does not result in induction of terminal differentiation. In the present study, the effects of TGF beta and calcium on growth factor-inducible gene expression were examined. TGF beta markedly decreased c-myc and KC gene expression in rapidly growing BALB/MK cells and reduced the EGF induction of c-myc and KC in a quiescent population of cells. TGF beta exerted its control over c-myc expression at a posttranscriptional level, and this inhibitory effect was dependent on protein synthesis. TGF beta had no effect on c-fos gene expression, whereas 1.5 mM calcium attenuated EGF-induced c-fos expression in quiescent cells. Expression of beta-actin, however, was slightly increased in both rapidly growing and EGF-restimulated quiescent BALB/MK cells treated with TGF beta. Thus, in this system, TGF beta selectively reduced expression of certain genes associated with cell proliferation (c-myc and KC), and at least part of the TGF beta effect was at a posttranscriptional level.
Insights
Transforming growth factor beta (TGF-β) inhibits epithelial cell proliferation by reducing c-myc and KC gene expression. This TGF-β effect on c-myc occurs post-transcriptionally and requires protein synthesis.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Transforming growth factor beta (TGF-β) is a known inhibitor of epithelial cell proliferation.
- Epidermal growth factor (EGF) stimulates mitogenesis in BALB/MK epithelial cells.
- Calcium can induce differentiation in BALB/MK cells, but TGF-β does not.
Purpose of the Study:
- To investigate the effects of TGF-β and calcium on growth factor-inducible gene expression in BALB/MK cells.
- To determine the mechanism by which TGF-β inhibits c-myc gene expression.
Main Methods:
- Treatment of BALB/MK cells with TGF-β and/or calcium.
- Analysis of gene expression for c-myc, KC, c-fos, and beta-actin using quantitative methods.
- Investigation of the posttranscriptional regulation of c-myc by TGF-β.
Main Results:
- TGF-β significantly decreased c-myc and KC gene expression in proliferating and quiescent BALB/MK cells.
- TGF-β's inhibition of c-myc expression was post-transcriptional and protein synthesis-dependent.
- Calcium attenuated EGF-induced c-fos expression, while TGF-β had no effect on c-fos.
- TGF-β slightly increased beta-actin expression.
Conclusions:
- TGF-β selectively reduces the expression of proliferation-associated genes like c-myc and KC.
- TGF-β exerts its inhibitory control over c-myc at a post-transcriptional level.
- These findings elucidate TGF-β's role in regulating gene expression during cell growth and differentiation.