TY - JOUR
T1 - Seven helix cAMP receptors stimulate Ca2+ entry in the absence of functional G proteins in Dictyostelium
AU - Milne, J. L.S.
AU - Wu, L.
AU - Caterina, M. J.
AU - Devreotes, P. N.
PY - 1995
Y1 - 1995
N2 - Surface cAMP receptors (cARs) in Dictyostelium transmit a variety of signals across the plasma membrane. The best characterized cAR, cAR1, couples to the heterotrimeric guanine nucleotide-binding protein (G protein) α- subunit Gα2 to mediate activation of adenylyl and guanylyl cyclases and cell aggregation. cAR1 also elicits other cAMP-dependent responses including receptor phosphorylation, loss of ligand binding (LLB), and Ca2+ influx through a Gα2-independent pathway that may not involve G proteins. Here, we have expressed cAR1 and a related receptor, cAR3, in a gβ- strain (Lilly, P., Wu. L., Welker, D. L., and Devreotes, P. N. (1993) Genes and Dev. 7, 986- 995), which lacks G protein activity. Both cell lines failed to aggregate, a process requiring the Gα2 and Gβ-subunits. In contrast, cAR1 phosphorylation in cAR1/gβ- cells showed a time course and cAMP dose dependence indistinguishable from those of cAR1/Gβ+ controls. cAMP-induced LLB was also normal in the cAR1/gβ- cells. Finally, cAR1/gβ- cells and cAR3/gβ- cells showed a Ca2+ response with kinetics, agonist dependence, ion specificity, and sensitivity to depolarization agents that were like those of Gβ+ controls, although they accumulated fewer Ca2+ ions per cAMP receptor than the control strains. Together, these results suggest that the Gβ-subunit is not required for the activation or attenuation of cAR1 phosphorylation, LLB, or Ca2+ influx. It may, however, serve to amplify the Ca2+ response, possibly by modulating other intracellular Ca2+ signal transduction pathways.
AB - Surface cAMP receptors (cARs) in Dictyostelium transmit a variety of signals across the plasma membrane. The best characterized cAR, cAR1, couples to the heterotrimeric guanine nucleotide-binding protein (G protein) α- subunit Gα2 to mediate activation of adenylyl and guanylyl cyclases and cell aggregation. cAR1 also elicits other cAMP-dependent responses including receptor phosphorylation, loss of ligand binding (LLB), and Ca2+ influx through a Gα2-independent pathway that may not involve G proteins. Here, we have expressed cAR1 and a related receptor, cAR3, in a gβ- strain (Lilly, P., Wu. L., Welker, D. L., and Devreotes, P. N. (1993) Genes and Dev. 7, 986- 995), which lacks G protein activity. Both cell lines failed to aggregate, a process requiring the Gα2 and Gβ-subunits. In contrast, cAR1 phosphorylation in cAR1/gβ- cells showed a time course and cAMP dose dependence indistinguishable from those of cAR1/Gβ+ controls. cAMP-induced LLB was also normal in the cAR1/gβ- cells. Finally, cAR1/gβ- cells and cAR3/gβ- cells showed a Ca2+ response with kinetics, agonist dependence, ion specificity, and sensitivity to depolarization agents that were like those of Gβ+ controls, although they accumulated fewer Ca2+ ions per cAMP receptor than the control strains. Together, these results suggest that the Gβ-subunit is not required for the activation or attenuation of cAR1 phosphorylation, LLB, or Ca2+ influx. It may, however, serve to amplify the Ca2+ response, possibly by modulating other intracellular Ca2+ signal transduction pathways.
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U2 - 10.1074/jbc.270.11.5926
DO - 10.1074/jbc.270.11.5926
M3 - Article
C2 - 7534302
AN - SCOPUS:0028924615
SN - 0021-9258
VL - 270
SP - 5926
EP - 5931
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 11
ER -