Transforming growth factor beta (
TGFbeta) plays a key role in maintaining tissue homeostasis by inducing cell cycle arrest, differentiation and apoptosis, and ensuring genomic integrity. Furthermore,
TGFbeta orchestrates the response to tissue injury and mediates repair by inducing epithelial to mesenchymal transition and by stimulating cell motility and invasiveness. Although loss of the homeostatic activity of
TGFbeta occurs early on in
tumor development, many advanced
cancers have coopted the tissue repair function to enhance their metastatic phenotype. How these two functions of
TGFbeta become uncoupled during
cancer development remains poorly understood. Here, we show that, in human keratinocytes,
TGFbeta induces phosphorylation of Smad2 and Smad3 as well as Smad1 and Smad5 and that both pathways are dependent on the
kinase activities of the type I and II
TGFbeta receptors (T beta R). Moreover,
cancer-associated missense mutations of the T beta RII gene (
TGFBR2) are associated with at least two different phenotypes. One type of mutant (
TGFBR2(E526Q)) is associated with loss of
kinase activity and all signaling functions. In contrast, a second mutant (
TGFBR2(R537P)) is associated with high intrinsic
kinase activity, loss of Smad2/3 activation, and constitutive activation of Smad1/5. Furthermore, this
TGFBR2 mutant endows the
carcinoma cells with a highly motile and invasive fibroblastoid phenotype. This activated phenotype is T beta RI (Alk-5) independent and can be reversed by the action of a dual T beta RI and T beta RII
kinase inhibitor. Thus, identification of such activated T beta RII receptor mutations in
tumors may have direct implications for appropriately targeting these
cancers with selective therapeutic agents.