Previously we have demonstrated that both plasminogen (Pig) and plasmin (Pla) regulate the expression of the transcription factors c-FOS and EGR-1 [L.P. De Sousa. B.S. Brasil, B.M. Silva, M.H. Freitas, S.V. Nogueira, P.C. Ferreira, E.G. Kroon, C.A. Borijardim, Plasminogen/plasmin regulates c-fos and egr-1 expression via the MEK/ERK pathway, Biochem. Biophys. Res. Commun. 329 (2005) 237-245]. Here we show that Pig activates the mitogen-activated protein kinases MEK and ERK which leads to alpha-enolase (alpha-ENO) gene expression not only in fibroblasts, but also in peripheral blood mononuclear cells. The a-ENO mRNA accumulation was apparent three hours post-Plg treatment and remained elevated out to 28 h, a process that seems to require both de novo protein synthesis and active gene transcription. Pla mimics Pig-stimulated alpha-ENO expression through its serine protease activity, suggesting that con,version of Pla to active Pla is required. Pharmacological and genetic blockade of MEK Caused inhibition of a-ENO mRNA accumulation, implicating MEK/ERK as the transduction pathway that leads to a-ENO expression Upon Pig stimulation. Furthermore, Pig stimulated DNA binding activity of the transcription factors activator-protein I and early growth response gene-1 to their cognate regulatory sequences at alpha-ENO promoter. Altogether, our data show that Plg/Pla regulates alpha-ENO expression through the MEK/ERK pathway. (c) 2005 Elsevier Inc. All rights reserved.