Seven Dictyostelium discoideum phosphodiesterases degrade three pools of cAMP and cGMP

Abstract

The Dictyostelium discoideum genome uncovers seven cyclic nucleotide PDEs (phosphodiesterases), of which six have been characterized previously and the seventh is characterized in the present paper. Three enzymes belong to the ubiquitous class I PDEs, common in all eukaryotes, whereas four enzymes belong to the rare class II PDEs that are present in bacteria and lower eukaryotes. Since all D. discoideum PDEs are now characterized we have calculated the contribution of each enzyme in the degradation of the three important pools of cyclic nucleotides: (i) extracellular cAMP that induces chemotaxis during aggregation and differentiation in slugs; (ii) intracellular cAMP that mediates development; and (iii) intracellular cGMP that mediates chemotaxis. It appears that each cyclic nucleotide pool is degraded by a combination of enzymes that have different affinities, allowing a broad range of substrate concentrations to be degraded with first-order kinetics. Extracellular cAMP is degraded predominantly by the class II high-affinity enzyme DdPDE1 and its close homologue DdPDE7, and in the multicellular stage also by the low-affinity transmembrane class I enzyme DdPDE4. Intracellular cAMP is degraded by the DdPDE2, a class I enzyme regulated by histidine kinase/phospho-relay, and by the cAMP-/cGMP-stimulated class II DdPDE6. Finally, basal intracellular cGMP is degraded predominantly by the high-affinity class I DdPDE3, while the elevated cGMP levels that arise after receptor stimulation are degraded predominantly by a cGMP-stimulated cGMP-specific class II DdPDE5. The analysis shows that the combination of enzymes is tuned to keep the concentration and lifetime of the substrate within a functional range.

New insights regarding the regulation of chemotaxis by nucleotides, adenosine, and their receptors

“…One consequence of the activation of P1 (and certain P2Y) receptors is a change in cellular levels of cAMP, which can exit cells by certain multidrug resistant proteins (MRPs 4 and 5; [20]). The conversion of extracellular cAMP to AMP by D. discoidium occurs via extracellular phosphodiesterases [21]. Although similar mechanisms are not as clearly defined in mammalian tissues, metabolism of cAMP to AMP has been demonstrated in several systems (e.g., [22], [23]).…”

The Group Migration of Dictyostelium Cells Is Regulated by Extracellular Chemoattractant Degradation

“…In this context, cells internalize the bound receptor and as part of the receptor recycling pathway the ligand is released for degradation (Minina et al, 2007;Boldajipour et al, 2008;Borroni et al, 2008;Scola et al, 2008). Alternatively, extracellular enzymes can specifically degrade the extracellular signaling molecules, allowing the sensing machinery to go back to basal levels and retain high sensitivity (Leidal et al, 2003;Bader et al, 2007;Van Lint and Libert, 2007;Leung et al, 2008).…”

“…In this context, cells internalize the bound receptor and as part of the receptor recycling pathway the ligand is released for degradation (Minina et al, 2007;Boldajipour et al, 2008;Borroni et al, 2008;Scola et al, 2008). Alternatively, extracellular enzymes can specifically degrade the extracellular signaling molecules, allowing the sensing machinery to go back to basal levels and retain high sensitivity (Leidal et al, 2003;Bader et al, 2007;Van Lint and Libert, 2007;Leung et al, 2008).Dictyostelium is an excellent model system to study chemotaxis. These social amoebae occur naturally in the soil, and they exist in two independent life stages: a growth stage and a developmental stage (Chisholm and Firtel, 2004;Manahan et al, 2004;Mahadeo and Parent, 2006;Urushihara, 2008).…”

“…We propose that the formation of head-to-tail arrays is regulated by the specific release of cAMP from vesicles at the back of cells. Cyclic nucleotide phosphodiesterases (PDEs), which catalyze the hydrolysis of the 3Ј-5Ј phosphodiester bond, are also up-regulated in early development (Lacombe et al, 1986;Bader et al, 2007). Four of the seven Dictyostelium PDEs degrade intracellular cyclic nucleotides, and the remaining three have extracellular activity (Bader et al, 2007).…”

“…Cyclic nucleotide phosphodiesterases (PDEs), which catalyze the hydrolysis of the 3Ј-5Ј phosphodiester bond, are also up-regulated in early development (Lacombe et al, 1986;Bader et al, 2007). Four of the seven Dictyostelium PDEs degrade intracellular cyclic nucleotides, and the remaining three have extracellular activity (Bader et al, 2007). PdsA (also called PDE1 or PdeA) is the main PDE that is responsible for the degradation of extracellular cAMP (Lacombe et al, 1986;Bader et al, 2007).…”