Modulation of growth and differentiation in normal human keratinocytes by transforming growth factor-beta.
The effect of transforming growth factor-type beta 1(TGF-beta) on the growth and differentiation of normal human skin keratinocytes cultured in serum-free medium was investigated. TGF-beta markedly inhibited the growth of keratinocytes at the concentrations greater than 2 ng/ml under low Ca2+ conditions (0.1 mM). Growth inhibition was accompanied by changes in cell functions related to proliferation. Remarkable inhibition of DNA synthesis was demonstrated by the decrease of [3H]thymidine incorporation. The decrease of [3H]thymidine incorporation was observed as early as 3 hr after addition of TGF-beta. TGF-beta also decreased c-myc messenger RNA (mRNA) expression 30 min after addition of TGF-beta. This rapid reduction of c-myc mRNA expression by TGF-beta treatment is possibly one of the main factors in the process of TGF-beta-induced growth inhibition of human keratinocytes. Since growth inhibition and induction of differentiation are closely related in human keratinocytes, the growth-inhibitory effect of TGF-beta under high Ca2+ conditions (1.8 mM Ca2+, differentiation-promoting culture environment) was examined. TGF-beta inhibited the growth of keratinocytes under high Ca2+ conditions in the same manner as under low Ca2+ conditions, suggesting that it is a strong growth inhibitor in both low and high Ca2+ environments. The induction of keratinocyte differentiation was evaluated by measuring involucrin expression and cornified envelope formation: TGF-beta at 20 ng/ml increased involucrin expression from 9.3% to 18.8% under high Ca2+ conditions, while it decreased involucrin expression from 7.0% to 3.3% under low Ca2+ conditions. Cornified envelope formation was modulated in a similar way by addition of TGF-beta: TGF-beta at 20 ng/ml decreased cornified envelope formation by 53% under low Ca2+ conditions, while it enhanced cornified envelope formation by 30.7% under high Ca2+ conditions. Thus, the effect of TGF-beta on keratinocyte differentiation is Ca2+ dependent. It enhances differentiation of human keratinocytes under high Ca2+ conditions, but inhibits differentiation under low Ca2+ conditions. Taken together, there is a clear discrepancy between TGF-beta effects on growth inhibition and induction of differentiation in human keratinocytes. These data indicate that growth inhibition of human keratinocytes by TGF-beta is direct and not induced by differentiation.
Department of Dermatology, Osaka University School of Medicine, Japan.
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Matsumoto
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Hashimoto
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Hashiro
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Yoshimasa
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Yoshikawa
D002118:Calcium / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D016259:Genes, myc; D006801:Humans; D066298:In Vitro Techniques; D015603:Keratinocytes / Q000166:cytology*; D012333:RNA, Messenger / Q000096:biosynthesis; D013936:Thymidine / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000502:physiology*; D014316:Tritium
D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D014316:Tritium; D002118:Calcium; D013936:Thymidine