EXTRACELLULAR SIGNAL-REGULATED KINASE AND THE SMALL GTP-BINDING PROTEIN, RAC, CONTRIBUTE TO THE EFFECTS OF TRANSFORMING GROWTH-FACTOR-BETA-1 ON GENE-EXPRESSION

The kinases and regulatory proteins that convey signals initiated by t ransforming growth factor-beta (TGF-beta) to the nucleus are poorly ch aracterized. To study the role of the extracellular signal-regulated k inase (ERK) pathway in this process, we transiently transfected NIH 3T 3 fibroblasts with TGF-beta-responsive luciferase re porter genes and expression vectors designed to interrupt this kinase cascade. Mitogen- activated protein (MAP) kinase phosphatase-1 and a dominant negative M AP/ERK kinase 1 mutant reduced stimulation of plasminogen activator in hibitor-1 (PAI-1) promoter activity by TGF-beta 1 from 11.5 to 4-fold and 4.9-fold, respectively. Similar results were observed with the typ e I collagen promoters. TGF-beta 1 increased ERK1 activity 4.5 fold at 5 min and 3.1-fold at 3 h, while Jun kinase and p38 activity were not affected. Cotransfection of a dominant negative mutant of the small G protein, Rac, but not dominant negative Ras, Cdc42, or Rho mutants, r educed the effects of TGF-beta 1 on the PAI-1 promoter by approximatel y half. In support of a role for Rac in signaling by TGF-beta, GTP bin ding to Pac was increased 3.7-fold following exposure of NIH 3T3 cells to TGF-beta 1 for 3 min. These findings indicate that TGF-beta 1 modu lates gene expression partly through ERK and Rac in NIH 3T3 cells.