Characterization of MAP Kinase Regulation of Cyclic AMP Signaling in Dictyostelium

Abstract

cAMP signaling plays a critical role in cell development and chemotaxis of Dictyostelium discoideum. Regulation of the MAP kinase protein Erk2 and phosphodiesterase RegA activity eventually controls the cAMP-mediated cell activities in Dictyostelium. Previous studies suggest that Erk2 might be down regulating its substrates, including RegA, to obtain control of cAMP levels and cAMP-associated functions. Conventional MAPKs interact with its substrate via consensus docking motif found in its substrates. Mutational studies show that the putative MAPK docking motif in RegA is not essential for downregulation of RegA function by Erk2. Alteration of docking motif enhanced the Erk2-RegA interactions. Dictyostelium Erk2 is an atypical MAP kinase; therefore, it might regulate its substrates by a different mechanism. Genetic epistasis tests suggest that the MAP kinase Erk1 might positively regulate RegA function. Erk1 activation occurs as a secondary response to Erk2 activation suggesting that Erk1 might function in an adaptation response by promoting RegA function and decreasing cAMP levels. The Dictyostelium Gα2 subunit is highly expressed during the aggregation stage of development and the loss of Gα2 function results in the inability of cells to chemotax to cAMP and to aggregate. A putative MAPK docking motif in the amino terminus of the Dictyostelium Gα2 subunit suggests this subunit might interact with MAPKs in a manner similar to that observed for a Gα subunit in yeast during mating responses. Alteration of the MAPK docking motif in Gα2 impairs aggregation but enhances cell movement. These phenotypes suggest that the docking site might facilitate the interaction of Gα2 with MAPKs in the adaptation response to cAMP.