G-PROTEIN SIGNALING EVENTS ARE ACTIVATED AT THE LEADING-EDGE OF CHEMOTACTIC CELLS

Directional sensing by eukaryotic cells does not require polarization of chemoattractant receptors. The translocation of the PH domain-conta ining protein CRAC in D. discoideum to binding sites on the inner face of the plasma membrane reflects activation of the G protein-linked si gnaling system. Increments in chemoattractant elicit a uniform respons e around the cell periphery. Yet when cells are exposed to a gradient, the activation occurs selectively at the stimulated edge, even in imm obilized cells. We propose that such localized activation, transmitted by the recruitment of cytosolic proteins, may be a general mechanism for gradient sensing by G protein-linked chemotactic systems including those involving chemotactic cytokines in leukocytes.