Blocakde of Smad4 in transformed keratinocytes containing a Ras oncogene leads to hyperactivation of the Ras-dependent Erk signalling pathway associated with progression to undifferentiated carcinomas

Thumbnail Image

Publication date


Start date of the public exhibition period

End date of the public exhibition period


Frontelo, Pilar
Gamallo, Carlos
Quintanilla, Miguel


Journal Title

Journal ISSN

Volume Title


Macmillan Publishers
Google Scholar

Research Projects

Organizational Units

Journal Issue


Smad4 functions as a transcription factor TGF-β signalling. We have investigated the role of Smad4 in the TGF-β1 cell responses of transformed PDV keratinocytes, wich contain a Ras oncogene, and of nontumorigenic MCA3D keratinocytes, by transfecting both cell lines with a dominant-negative Smad4 construct. Smad4 mediates TGF-β1-induced p21cip1 as growth factor. TGF-β1 activates Ras/Erk signalling activity in both cell lines. PD098059, as a specific inhibitor of MEK, disminishes TGF-β1-induced p21cip1 levels in PDV cells. PDV dominant-negative Smad4 cell transfectants, but not MCA3D transfectants, showed constitutive hyperactivation of the Ras/Erk signalling pathway, increased secretion of urokinase, higher motility properties, and a change to a fibroblastoid cell morphology associated in vivo with teh transition from a well differentiated to a pooly differentiated tumour phenotype. Infection of MCA3D control and dominant negative Smad4 cell transfectants with retroviruses carying a Ras oncogene led to enhaced p21cip1 and urokinase secreted levels, independently of TGF-β1 stimulation, that where reduced by PD098059. These results suggest that Smad4 acts inhibiting Ras-dependent Erk signalling activity in Ras-transformed Keratinocytes. Loss of Smad4 function in these cells results in hyperactivation of Erk signalling and progression to undifferentiated carcinomas.

Doctoral program



TGF-β1, Smad4, Ras, Erk, Urokinase, Carcinoma