1. Epithelial Pathobiology Group, Center for Immunology and Cancer Research, Princess Alexandra Hospital, Queensland, Australia
2. ^*University of Queensland Department of Medicine, Princess Alexandra Hospital, Queensland, Australia

Correspondence: Dr Nicholas Saunders, University of Queensland Department of Medicine, Princess Alexandra Hospital, Ipswich Road, Brisbane, Queensland, Australia 4102. Email: NSaunders@medicine.pa.uq.edu.au

Received 10 January 2000; Revised 15 May 2000; Accepted 16 November 2000.

Abstract

Transforming growth factor 1 treatment of keratinocytes results in a suppression of differentiation, an induction of extracellular matrix production, and a suppression of growth. In this study we utilized markers specific for each of these functions to explore the signaling pathways involved in mediating these transforming-growth-factor-1-induced activities. In the first instance, we found that the induction of extracellular matrix production (characterized by 3TP-Lux reporter activity) was induced in both keratinocytes and a keratinocyte-derived carcinoma cell line, SCC25, in a dose-dependent manner. Furthermore, transforming growth factor 1 also suppressed the differentiation-specific marker gene, transglutaminase type 1, in both keratinocytes and SCC25 cells. In contrast, transforming growth factor 1 inhibited proliferation of keratinocytes but did not cause growth inhibition in the SCC25 cells. Transforming-growth-factor-1-induced growth inhibition of keratinocytes was characterized by decreases in DNA synthesis, accumulation of hypophosphorylated Rb, and the inhibition of the E2F:Rb-responsive promoter, cdc2, and an induction of the p21 promoter. When the negative regulator of transforming growth factor 1 signaling, SMAD7, was overexpressed in keratinocytes it could prevent transforming-growth-factor-1-induced activation of the 3TP-Lux and the p21 promoter. SMAD7 could also prevent the suppression of the transglutaminase type 1 by transforming growth factor 1 but it could not inhibit the repression of the cdc2 promoter. These data indicate that the induction of 3TP-Lux and p21 and the suppression of transglutaminase type 1 are mediated by a different proximate signaling pathway to that regulating the suppression of the cdc2 gene. Combined, these data indicate that the regulation of transforming growth factor 1 actions are complex and involve multiple signaling pathways.