Cell Signaling and Cell Decisions

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PROJECT SUMMARY/ABSTRACT Mammalian cells must move and proliferate to maintain and regenerate tissues and defend themselves against pathogens, but mutations that increase movement or proliferation can also cause cancer. Stem, progenitor, and differentiated cells are often non-motile and quiescent but keep integrating cell-cell contacts, cell-matrix contacts, and receptor inputs, and make two distinct decisions (that are often connected) whether they should start to move and start to proliferate if needed. Several challenges have prevented an understanding of these two decision processes. Genetic approaches in animals cannot readily tackle the co-regulation of large numbers of signaling processes while biochemical analysis of cultured cells often leads to inconclusive results due to the difficulty to synchronize cells and resolve when and where in a cell signaling occurs. Only single cell analysis can resolve the spatial and temporal signaling feedbacks controlling these complex decisions. Our laboratory has developed critically needed fluorescent single-cell activity reporters, rapid perturbation strategies, and automated microscopy and analysis methods to investigate these two fundamental decision processes. To understand the decision to polarize and move, we will use the new tools we developed to explore how external receptor tyrosine kinase signals and cell-cell and cell-matrix contacts synergistically control the initiation and maintenance of gradients in cell signaling and actin organization, and how cells locally direct the signaling gradients and movement. To understand the decision to proliferate, we will investigate the competition mechanism that determines how these same signal inputs at the plasma membrane control the activation of two cyclin-Cdk kinase activities in the nucleus, explore how cells control a proliferation decision process that can still be reversed for many hours before cells commit to proliferate much later, and resolve how this same decision process coordinates the licensing of origins of replication and DNA replication to prevent genome instability and cell death. The outcome of our work will be a quantitative, molecular, and mechanistic understanding of how mammalian cells integrate signals to make decisions to start to move and proliferate, and how mutations that dysregulate these proliferation and migration decisions can cause cancer and other diseases.