Figure 1

MAP kinase signalling pathways. Major pathways that transfer extracellular signals to the nucleus are the MAP kinase signalling pathways. The extracellular stimuli may be heterogeneous, deriving from exposure of cells to growth factors, phorbol esters, cytokines, or cellular stresses, such as osmotic shock and γ-irradiation. In principal, the Ras-Raf-MEK-ERK pathway transduces mitogenic signals involved in cellular proliferation or differentiation. The JNK/SAPK and p38 pathways regulate the cellular inflammatory or stress response. There are interactions between both pathways on MAPK kinase kinase (MAPKKK) levels immediately upstream of MEK (not indicated in the presented scheme). The downstream targets of the MAP kinase signalling pathways are the MAP kinases, ERK, JNK/SAPK and p38, which directly or indirectly interfere with transcription factors, such as Elk-1, ATF2 or cJun for activation of gene transcription. Upstream signalling components include the family of Rho GTPases such as Rho, Rac and Cdc42 which interfere with MAPKKK. Cellular stresses such as hypoxia may activate JNK/SAPK and p38 pathways which exert influence on cJun and ATF-2 activation.