A Gα-dependent pathway that antagonizes multiple chemoattractant responses that regulate directional cell movement

Abstract

Chemotactic cells, including neutrophils and Dictyostelium discoideum, orient and move directionally in very shallow chemical gradients. As cells polarize, distinct structural and signaling components become spatially constrained to the leading edge or rear of the cell. It has been suggested that complex feedback loops that function downstream of receptor signaling integrate activating and inhibiting pathways to establish cell polarity within such gradients. Much effort has focused on defining activating pathways, whereas inhibitory networks have remained largely unexplored. We have identified a novel signaling function in Dictyostelium involving a Gα subunit (Gα9) that antagonizes broad chemotactic response. Mechanistically, Gα9 functions rapidly following receptor stimulation to negatively regulate PI3K/PTEN, adenylyl cyclase, and guanylyl cyclase pathways. The coordinated activation of these pathways is required to establish the asymmetric mobilization of actin and myosin that typifies polarity and ultimately directs chemotaxis. Most dramatically, cells lacking Gα9 have extended PI(3,4,5)P3, cAMP, and cGMP responses and are hyperpolarized. In contrast, cells expressing constitutively activated Gα9 exhibit a reciprocal phenotype. Their second message pathways are attenuated, and they have lost the ability to suppress lateral pseudopod formation. Potentially, functionally similar Gα-mediated inhibitory signaling may exist in other eukaryotic cells to regulate chemoattractant response.