The cAMP Receptor Family of Dictyostelium

This chapter discusses the current understanding of cell surface cyclic adenosine 3',5'-monophosphate (cAMP) receptors in Dictyostelium. A role for extracellular cAMP was initially suggested when it was identified as a chemoattractant for aggregation-stage cells. cAMP waves are generated by the signaling response. When stimulated, cells respond by making and secreting more cAMP, thereby relaying the cAMP signal to more distant cells. Extracellular cAMP participates in a wide variety of physiological responses during development in Dictyostelium. It serves as a chemoattractant, a cell-to-cell signaling molecule, and an inducer of cell type-specific gene expression. During development, these cells serially express a family of four cell surface cAMP receptors. All of the receptors display the characteristic seven-transmembrane domain structure and, thus, are likely to transduce extracellular signals by activating G proteins. Eight distinct G protein α-subunit genes have been cloned and sequenced. Although similar in structure, each cAMP receptor has a characteristic affinity and pharmacological specificity and may have a unique pattern of regulation by covalent modification.