DOMINANT-NEGATIVE SMAD-3 INTERFERES WITH TRANSCRIPTIONAL ACTIVATION BY MULTIPLE AGONISTS

Smad proteins have recently been identified as mediators of transcript ional activation by members of the transforming growth factor-beta sup erfamily. To determine if Smads might also be involved in inducing gen e transcription in response to other agonists, expression vectors for dominant-negative Smad proteins were constructed. These plasmids were transiently cotransfected with luciferase reporter genes and the effec ts of various agonists on reporter gene activity evaluated in NIH 3T3 cells. Dominant-negative Smads, but not other dominant-negative Smads, reduced stimulation of the plasminogen activator inhibitor-1 (PAI-1) and other gene promoters by phorbol ester, cAMP, and platelet-derived growth factor. Activation of the PAI-1 promoter by TGF-beta or prostag landin F2 alpha, and transactivation by c-Jun or JunB were not inhibit ed by dominant-negative Smad3, supporting the specificity of this muta nt. These results suggest that Smad3, like CREB-binding protein (CBP), may participate in transcriptional activation by multiple agonists. ( C) 1997 Academic Press.