Transforming growth factor beta1 treatment of keratinocytes results in a su
ppression of differentiation, an induction of extracellular matrix producti
on, 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-beta1-induced activities. In the
first instance, we found that the induction of extracellular matrix produc
tion (characterized by 3TP-Lux reporter activity) was induced in both kerat
inocytes and a keratinocyte-derived carcinoma cell line, SCC25, in a dose-d
ependent manner. Furthermore, transforming growth factor beta1 also suppres
sed the differentiation-specific marker gene, transglutaminase type 1, in b
oth keratinocytes and SCC25 cells. In contrast, transforming growth factor
beta1 inhibited proliferation of keratinocytes but did not cause growth inh
ibition in the SCC25 cells. Transforming-growth-factor-beta1-induced growth
inhibition of keratinocytes was characterized by decreases in DNA synthesi
s, accumulation of hypophosphorylated Rb, and the inhibition of the E2F:Rb-
responsive promoter, cdc2, and an induction of the p21 promoter. When the n
egative regulator of transforming growth factor beta1 signaling, SMAD7, was
overexpressed in keratinocytes it could prevent transforming-growth-factor
-beta1-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 beta1 but it could not inhibit the repression of the cdc2 pr
omoter. These data indicate that the induction of 3TP-Lux and p21 and the s
uppression of transglutaminase type 1 are mediated by a different proximate
signaling pathway to that regulating the suppression of the cdc2 gene. Com
bined, these data indicate that the regulation of transforming growth facto
r beta1 actions are complex and involve multiple signaling pathways.