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Altered regulation of intercellular communication by epidermal growth factor, transforming growth factor-beta and
B V Madhukar1, S Y Oh, C C Chang
1Department of Pediatrics/Human Development, Michigan State University, E. Lansing 48824.
Abstract:
Since many chemical tumor promoters and some oncogenes have been shown to inhibit gap junction-mediated intercellular communication, the effect of various growth factors on gap junctional intercellular communication on normal human keratinocytes was examined. In order to measure the effect of the growth factors on gap junctional communication, the scrape loading/dye transfer technique was used on human keratinocytes grown in a serum-free medium in vitro. At 24 h after treatment epidermal growth factor (10 ng/ml), transforming growth factor-beta (1 ng/ml), whole bovine pituitary extract (70 micrograms/ml) and 12-O-tetradecanoylphorbol-13-acetate (TPA) (100 ng/ml) inhibited intercellular communication. Treatment of these cells with transforming growth factor-beta (1 ng/ml) induced morphological changes in some of the cells and brought about selective intercellular communication within and between the nonaltered and altered cells. Epidermal growth factor and whole bovine pituitary extract, significantly enhanced [3H]thymidine uptake and also stimulated cellular proliferation under the experimental conditions used to inhibit intercellular communication. Both transforming growth factor-beta and TPA markedly inhibited [3H]thymidine uptake and induced differentiation of some of these cells. In order to study the possible mechanism by which the growth factors might inhibit intercellular communication, the effect of the growth factors on protein kinase C activation and alterations of intracellular free calcium was investigated. The results indicated that neither protein kinase C nor an increase in [Ca2+]i were involved in the modulation of gap junctional communication by epidermal growth factor or transforming growth factor-beta. The study suggests that in the human keratinocytes inhibition of intercellular communication may be involved (i) in the action of growth factors such as epidermal growth factor during cellular proliferation and (ii) in the differentiation of primary keratinocytes by transforming growth factor-beta.
Insights
Growth factors like epidermal growth factor and transforming growth factor-beta inhibit intercellular communication in human keratinocytes. This inhibition is linked to cellular proliferation and differentiation, but not protein kinase C or calcium signaling.
Area of Science:
- Cell Biology
- Dermatology
- Cancer Research
Background:
- Chemical tumor promoters and oncogenes are known to inhibit gap junction-mediated intercellular communication.
- Understanding how growth factors affect intercellular communication in normal human keratinocytes is crucial for cell biology and dermatology.
Purpose of the Study:
- To investigate the effects of various growth factors on gap junctional intercellular communication in normal human keratinocytes.
- To explore the mechanisms underlying growth factor-induced modulation of intercellular communication, including protein kinase C activation and intracellular calcium levels.
Main Methods:
- The scrape loading/dye transfer technique was employed on human keratinocytes cultured in a serum-free medium.
- Cells were treated with epidermal growth factor, transforming growth factor-beta, bovine pituitary extract, and 12-O-tetradecanoylphorbol-13-acetate (TPA).
- Protein kinase C activation and intracellular free calcium ([Ca2+]i) were assessed to investigate signaling pathways.
Main Results:
- Epidermal growth factor, transforming growth factor-beta, bovine pituitary extract, and TPA all inhibited intercellular communication at 24 hours.
- Transforming growth factor-beta induced morphological changes and selective communication patterns.
- Epidermal growth factor and bovine pituitary extract stimulated [3H]thymidine uptake and proliferation, while transforming growth factor-beta and TPA inhibited it and induced differentiation.
- Neither protein kinase C activation nor increased intracellular calcium mediated the effects of epidermal growth factor or transforming growth factor-beta on gap junctional communication.
Conclusions:
- Inhibition of intercellular communication in human keratinocytes by growth factors is implicated in cellular proliferation (epidermal growth factor) and differentiation (transforming growth factor-beta).
- The mechanisms do not involve protein kinase C or intracellular calcium signaling pathways.
- These findings provide insights into the roles of intercellular communication in keratinocyte growth and differentiation.