Cell cortex regulation by Ca(2+) binding proteins of the S100 family

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Dynamic reorganizations in the membrane-underlying and actin-rich cell cortex control many cellular processes that include the regulation of cell shape and cell migration. Many of these reorganizations are triggered by transient elevations of intracellular Ca2+ levels that are mediated by families of Ca2+ binding proteins. S100 proteins represent the largest of these families of Ca2+ effector proteins with members being present in the cortical cytoskeleton. We developed a special affinity approach to search for physiologically relevant targets of S100 proteins and could identify two cell cortex regulators, ezrin and IQGAP1, which are controlled by interaction with Ca2+ bound S100P. Ezrin serves as a linker between plasma membrane lipids and proteins and underlying actin filaments, whereas IQGAP1 represents a cortical scaffold protein assembling different signalling intermediates in response to cell stimulation. In both cases S100P binding regulates activities of the cortical target proteins in a Ca2+ dependent manner, at least in vitro. In the case of ezrin, interaction with Ca2+/S100P releases an intramolecular autoinhibition and thereby triggers a conformational activation that exposes the membrane protein and F-actin binding sites. In the case of IQGAP1, binding of Ca2+/S100P can modulate IQGAP1-mediated signalling in response to growth factor stimulation. Thus, via S100P binding Ca2+ signalling can directly affect important regulators in the cortical cytoskeleton and thereby control cell shape changes in processes such as cell polarization and migration.The project aims at understanding the molecular mechanisms that regulate cortical cytoskeleton dynamics in response to Ca2+ signalling. Based on our previous findings a particular emphasis is on the action of Ca2+ binding proteins of the S100 family. Specifically, the following questions will be addressed:1. Is complex formation between Ca2+ bound S100P and ezrin and/or IQGAP1 observed in living cells and is it required for cortical translocation of the target protein?2. What is the role of Ca2+ dependent S100P-ezrin and S100P-IQGAP1 interactions in cell migration both, on two-dimensional surfaces and in tissues?3. Do related S100 proteins form complexes with other cortical target proteins and what is the function of these complexes?To answer these questions we will analyse the dynamics and function of Ca2+-regulated S100/target protein complexes during the migration of cultured epithelial cells and of primordial germ cells in developing zebrafish embryos.