The mitogen-activated protein kinase kinase 1 (MAP2K1, also known as MEK1) and the highly homologous MEK2 are members of the dual specificity protein kinase family (1). MAP kinases, also known as extracellular signal-regulated kinases (ERKs), act as an integration point for multiple biochemical signals (2). MEK1 lies upstream of MAP kinases and stimulates the enzymatic activity of MAP kinases upon wide variety of extra- and intracellular signals. As an essential component of MAP kinase signal transduction pathway, MEK1 is involved in many cellular processes such as proliferation, differentiation, transcription regulation and development (2).