Effect of transforming growth factor-β1 on parathyroid hormone-related protein secretion and mRNA expression by normal human keratinocytes in vitro

Parathyroid hormone-related protein (PTHrP) is produced by a wide range of neoplastic and normal cells, including keratinocytes where it may regulate growth and differentiation. Transforming growth factor-β (TGF-β) is a growth factor produced by many cells, including keratinocytes where it regulates epidermal homeostasis. TGF-β has been reported to be cosecreted with PTHrP in some neoplasms and to stimulate PTHrP production by neoplastic keratinocytes. However, the effects of TGF-β on PTHrP production by normal keratinocytes are not well characterized. In this study, we investigated the effects of endogenous and exogenous TGF-β on PTHrP production by normal human foreskin keratinocytes. PTHrP secretion, mRNA expression, and mRNA transcription in vitro were determined by N-terminal radioimmunoassay, ribonuclease protection assay, and transient transfections. PTHrP production and secretion of latent TGF-β activity were greatest in proliferating keratinocytes prior to and at confluence of monolayer cultures. TGF-β1 increased PTHrP mRNA expression by normal keratinocytes in a dose-dependent manner with maximal stimulation at 6–12 h after treatment. In addition, keratinocytes treated with a monoclonal anti-TGF-β antibody expressed decreased levels of PTHrP mRNA. The increased levels of PTHrP mRNA following TGF-β1 treatment were owing, at least partly, to an increase in PTHrP mRNA stability. TGF-β1 failed to activate transcription of the luciferase reporter gene driven by either the human or mouse PTHrP promoters. In conclusion, TGF-β1 functions as a paracrine or autocrine regulator of PTHrP production in normal human keratinocytes, and this may play a role in the regulation of keratinocyte proliferation or differentiation.