Related Dictyostelium G protein subunits Gα1 and Gα2 have different roles in chemotaxis and transcription factor regulation

Gα subunits provide important contributions to the specificity of signaling pathways that are regulated by G protein-coupled receptors. The Dictyostelium discoideum Gα2 subunit mediates chemotactic responses to cAMP including the activation of the atypical MAPK, Erk2, and translocation of the transcription factor GtaC but some of these responses partially occur in the absence of the Gα2 subunit suggesting a Gα2 subunit-independent mechanism. The Gα1 subunit is the most closely related paralog of the Gα2 subunit making it a possible candidate for overlapping functions. Heterologous expression of Gα1 in gα2− cells did not rescue cAMP chemotaxis or other gα2− phenotypes suggesting no functional overlap between these subunits. Loss of the Gα1 subunit resulted in a slight delay in multicellular development on nonnutrient agar and a growth increase on bacterial lawns in both the parental and gα2− strains. Both gα1− and gα2− cells grew to stationary phase in axenic medium earlier than their parental strain suggesting both subunits might mediate responses to nutrient limitations. The loss of Gα1 function resulted in a marginal impact on the translocation of GtaC but in gα2− cells the absence of Gα1 enhanced the translocation of GtaC. These results indicate that the Gα1 and Gα2 subunits are not functionally redundant but could possibly interact with other proteins common to both signaling pathways. This study also suggests the presence of another cAMP stimulated pathway that can mediate the translocation of GtaC.