Concerted action of TGF-β1 and its type II receptor in control of epidermal homeostasis in transgenic mice

Abstract

Transforming growth factor-β1 (TGF-β1) is a modulator of cellular proliferation, differentiation, and extracellular matrix deposition. It is a potent epithelial growth inhibitor and can alter the differentiative properties of keratinocytes, in vitro, but little is known about its normal physiological function in the epidermis in vivo. Transgenic mice were generated using a keratin 10 (K10) gene promoter to drive constitutive expression of TGF-β1 in the suprabasal keratinocyte compartment. Surprisingly, these mice showed a two- to threefold increase in epidermal DNA labeling index over control mice, in the absence of hyperplasia. The transgene, however, acted in the expected fashion, as a negative regulator of cell growth, when hyperplasia was induced by treatment by 12-tetradecanoyl- phorbol-13-acetate (TPA). Epidermal TGF-β1 type I and II receptor (TβRI and TβRII) levels were examined in control and transgenic mice during induction of hyperplasia by TPA. Whereas TβRI levels remained relatively constant, TβRII expression was strongly induced in TPA-treated skins, prior to the induction of the growth inhibitory response to TGF-β1, and its level of expression correlated with growth sensitivity to TGF-β1 in vivo and in vitro. These results suggest that TGF-β1 and its type II receptor are part of the endogenous homeostatic regulatory machinery of the epidermis.