A Synthetic Approach to Understanding Signal Processing in MAPK Cascades

The mitogen-activated protein kinase (MAPK) cascade is a ubiquitous and versatile signaling module found in all eukaryotic cells. MAPK cascades consist of three-tiered phosphorylation events and are essential to various biological processes such as differentiation, proliferation, motility, and apoptosis. They exhibit a broad array of system dynamics and these dynamics are often crucial in determining the biological outcome of activation. However, analysis of signal processing in endogenous mammalian MAPK cascades can be complicated by signal crosstalk and by difficulties in perturbing or rewiring the network topology in a mammalian cell. We have employed a synthetic biology approach to build an insulated mammalian MAPK cascade in yeast, and we have explored how variations in topology can influence the response of this signaling module. We will describe how the dynamics of a basic synthetic MAPK cascade can be modulated by incorporating scaffold proteins, by adding negative regulation, or by varying the concentration of the cascade. Our results indicate that the MAPK cascade is an inherently flexible signal-processing module and also elucidate mechanisms of signal tuning that may be more generally useful for probing and engineering system dynamics.