Differential Effects of Temperature on cAMP-induced Excitation, Adaptation, and Deadaptation of Adenylate and Guanylate Cyclase in Dictyostelium discoideum

Extracellular cAMP induces excitation of adenylate and guanylate cyclase in Dictyostelium discoideum. Continuous stimulation with cAMP leads to adaptation, while cells deadapt upon removal of the cAMP stimulus. Excitation of guanylate cyclase by cAMP has a lag time of ~oI s; excitation of adenylate cyclase is much slower with a lag time of 30 s. Excitation of both enzyme activities is less than twofold slower at 0~ than at 20~ Adaptation of guanylate cyclase is very fast (t,~ = 2.4 s at 20~ and virtually absent at 0~ Adaptation of adenylate cyclase is much slower (t,h = 110 s at 20~ but not very temperature sensitive (t,~ = 290 s at 0~ At 20~ deadaptation of adenylate cyclase is about twofold slower than deadaptation of guanylate cyclase (t,~ = 190 and 95 s, respectively). Deadaptation of adenylate cyclase is absent at 0~ while that of guanylate cyclase proceeds slowly (t,~ = 975 s). The results show that excitation, adaptation, and deadaptation of guanylate cyclase have different kinetics and temperature sensitivities than those of adenylate cyclase, and therefore are probably independent processes. A intercellular signal molecule in the cellular slime mold Dictyostelium discoideum, cAMP, is involved in chemotaxis, differentiation, and morphogenesis (18, 24, 25). The free-living amebae of this organism feed on bacteria. Food deprivation induces a social phase in the life cycle. Some cells start to secrete cAMP in a pulsatile manner. Surrounding cells detect this cyclic nucleotide by means of cell surface receptors, which lead to two responses: chemotactic reaction towards the source of cAMP secretion, and activation of adenylate cyclase followed by secretion of the newly synthesized cAMP (reviewed in 3, 10, 39). This cAMP stimulates more distally located amebae. Finally, an aggregation center is formed, which may collect up to 100,000 amebae. cAMP stimulates both adenylate and guanylate cyclase activity in D. discoideum cells (19, 21). In contrast to the synthesized cAMP, the newly formed cyclic guanosine 3',5'monophosphate (cGMP) 1 is not secreted but may bind to an intracellular receptor. It has been proposed that intracellular cGMP is a key component during the chemotactic reaction (22, 45). This suggests that the kinetics of the cAMP-induced activation of adenylate and guanylate cyclase are of major importance for chemotaxis-mediated cell aggregation in this organism. 1. Abbreviations used in this paper: dcAMP, 2' deoxyadenosine 3',5'-monophosphate; cGMP, cyclic guanosine Y,5'-monophosphate; IP3, inositol 1,4,5-trisphosphate; (Sp)-cAMPS, adenosine 3',5'-monophosphorothioate, (Sp)-isomer. The continuous stimulation of cells with cAMP leads to adaptation (i.e., adenylate and guanylate cyclase are activated transiently) and prestimulus enzyme activities are recovered even when cAMP remains present. Cells deadapt upon removal of the stimulus, and gradually regain responsiveness to cAMP. Adaptation of adenylate and guanylate cyclase have many properties in common (5-8, 32, 40, 46); (a) cells remain responsive to elevations of the cAMP concentration, (b) adaptation is complete, i.e., no residual response remains after prolonged stimulation, (c) adaptation is cAMPconcentration dependent, (d) adaptation shows additivity, (e) deadaptation follows first order kinetics with t,~ = 2-3 min. This may suggest that adaptation of adenylate and guanylate cyclase occurs at a common step in the signal transduction pathway. However, it has been shown that adaptation of guanylate cyclase of cells in suspension occurs much faster than adaptation of adenylate cyclase of cells on filters (8, 40). Adaptation is probably essential for the cAMP relay mechanism (5-7), the cGMP response (40), and for chemotaxis (31). In this study, relationships of excitation, adaptation, and deadaptation of adenylate and guanylate cyclase were investigated under identical stimulus conditions at two temperatures, 20 and 0~ The results show that these processes have widely different kinetics and temperature sensitivities. Guanylate cyclase does not adapt at 0~ while adenylate cyclase does. In contrast, adenylate cyclase does not deadapt at 0~ while guanylate cyclase deadapts slowly. This suggests that deadaptation of adenylate and guanylate cyclase may occur independently. 9 The Rockefeller University Press, 0021-9525/87/11/2301/6 $2.00 The Journal of Cell Biology, Volume 105, November 1987 2301-2306 2301 on A uust 8, 2017 jcb.rress.org D ow nladed fom Materials and Methods