Control of the eukaryotic cell cycle by MAP kinase signaling pathways

In an often rapidly changing environment, cells must adapt by monitoring an d reacting quickly to extracellular stimuli detected by membrane-bound rece ptors and proteins, Reversible phosphorylation of intracellular regulatory proteins has emerged as a crucial mechanism effecting the transmission and modulation of such signals and is determined by the relative activities of protein kinases and phosphatases within the cell, These are often arranged into complex signaling networks that may function independently or be subje ct to cross-regulation. Recently, genetic and biochemical analyses have ide ntified the universally conserved mitogen-activated protein (MAP) kinase ca scade as one of the most ubiquitous signal transduction systems. This pathw ay is activated after a variety of cellular stimuli and regulates numerous physiological processes, particularly the cell division cycle, Progression through the cell cycle is critically dependent on the presence of environme ntal growth factors and stress stimuli, and failure to correctly integrate such signals into the cell cycle machinery can lead to the accumulation of genetic damage and genomic instability characteristic of cancer cells. Here we focus on the MAP kinase cascade and discuss the molecular mechanisms by which these extensively studied signaling pathways influence cell growth a nd proliferation.