Phospholipase C in Dictyostelium discoideum. Identification of stimulatory and inhibitory surface receptors and G-proteins

A combined biochemical and genetic approach was used to show that phospholipase C in the cellular slime mould Dictyostelium is under dual regulation by the chemoattractant cyclic AMP (cAMP). This dual regulation involves stimulatory and inhibitory surface receptors and G-proteins. In wild-type cells both cAMP and guanosine 5′-[gamma-thio]triphosphate (GTP[S]) stimulated phospholipase C. In contrast, mutant fgd A, lacking the G-protein alpha-subunit G alpha 2, showed no stimulation by either cAMP or GTP[S], indicating that G alpha 2 is the stimulatory G-protein. In mutant fgd C cAMP did not stimulate phospholipase C, but stimulation by GTP[S] was normal, suggesting that the defect in this mutant is upstream of the stimulatory G alpha 2. Inhibition of phospholipase C was achieved in wild-type cells by the partial antagonist 3′-deoxy-3′-aminoadenosine 3′,5′-phosphate (3′NH-cAMP). This inhibition was no longer observed in transformed cell lines lacking either the surface cAMP receptor cAR1 or the G-protein alpha-subunit G alpha 1; in these cells the agonist cAMP still activated phospholipase C. These results indicate that Dictyostelium phospholipase C is regulated via a stimulatory and an inhibitory pathway. The inhibitory pathway is composed of the surface receptor cAR1 and the G-protein G1. The stimulatory pathway consists of an unknown cAMP receptor (possibly the fgd C gene product) and the G-protein G2.

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G alpha 3 regulates the cAMP signaling system in Dictyostelium.

Molecular Biology of the Cell ◽

10.1091/mbc.8.9.1677 ◽

1997 ◽

Vol 8 (9) ◽

pp. 1677-1685 ◽

Cited By ~ 11

Author(s):

M A Brandon ◽

G J Podgorski

Keyword(s):

Mrna Expression ◽

Adenylyl Cyclase ◽

G Protein ◽

Phosphodiesterase Inhibitor ◽

Transmembrane Signaling ◽

Wild Type ◽

Signaling System ◽

G Protein Alpha Subunit ◽

Camp Receptor ◽

Protein Alpha Subunit

The Dictyostelium discoideum developmental program is initiated by starvation and its progress depends on G-protein-regulated transmembrane signaling. Disruption of the Dictyostelium G-protein alpha-subunit G alpha 3 (g alpha 3-) blocks development unless the mutant is starved in the presence of artificial cAMP pulses. The function of G alpha 3 was investigated by examining the expression of several components of the cAMP transmembrane signaling system in the g alpha 3- mutant. cAMP receptor 1 protein, cyclic nucleotide phosphodiesterase, phosphodiesterase inhibitor, and aggregation-stage adenylyl cyclase mRNA expression were absent or greatly reduced when cells were starved without exogenously applied pulses of cAMP. However, cAMP receptor 1 protein and aggregation-stage adenylyl cyclase mRNA expression were restored by starving the g alpha 3- cells in the presence of exogenous cAMP pulses. Adenylyl cyclase activity was also reduced in g alpha 3- cells starved without exogenous cAMP pulses compared with similarly treated wild-type cells but was elevated to a level twofold greater than wild-type cells in g alpha 3- cells starved in the presence of exogenous cAMP pulses. These results suggest that G alpha 3 is essential in early development because it controls the expression of components of the transmembrane signaling system.

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Purification from bovine liver membranes of a guanine nucleotide-dependent activator of phosphoinositide-specific phospholipase C. Immunologic identification as a novel G-protein alpha subunit.

Journal of Biological Chemistry ◽

10.1016/s0021-9258(17)44881-2 ◽

1990 ◽

Vol 265 (28) ◽

pp. 17150-17156 ◽

Cited By ~ 26

Author(s):

S J Taylor ◽

J A Smith ◽

J H Exton

Keyword(s):

Phospholipase C ◽

G Protein ◽

Bovine Liver ◽

Alpha Subunit ◽

Guanine Nucleotide ◽

Liver Membranes ◽

G Protein Alpha Subunit ◽

Protein Alpha Subunit

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Homologous and unique G protein alpha subunits in the nematode Caenorhabditis elegans.

Cell Regulation ◽

10.1091/mbc.2.2.135 ◽

1991 ◽

Vol 2 (2) ◽

pp. 135-154 ◽

Cited By ~ 57

Author(s):

M A Lochrie ◽

J E Mendel ◽

P W Sternberg ◽

M I Simon

Keyword(s):

Amino Acid ◽

G Protein ◽

G Proteins ◽

Amino Acid Sequences ◽

Alpha Subunit ◽

Predicted Amino Acid Sequence ◽

C Elegans ◽

Alpha Subunits ◽

G Protein Alpha Subunit ◽

Protein Alpha Subunit

A cDNA corresponding to a known G protein alpha subunit, the alpha subunit of Go (Go alpha), was isolated and sequenced. The predicted amino acid sequence of C. elegans Go alpha is 80-87% identical to other Go alpha sequences. An mRNA that hybridizes to the C. elegans Go alpha cDNA can be detected on Northern blots. A C. elegans protein that crossreacts with antibovine Go alpha antibody can be detected on immunoblots. A cosmid clone containing the C. elegans Go alpha gene (goa-1) was isolated and mapped to chromosome I. The genomic fragments of three other C. elegans G protein alpha subunit genes (gpa-1, gpa-2, and gpa-3) have been isolated using the polymerase chain reaction. The corresponding cosmid clones were isolated and mapped to disperse locations on chromosome V. The sequences of two of the genes, gpa-1 and gpa-3, were determined. The predicted amino acid sequences of gpa-1 and gpa-3 are only 48% identical to each other. Therefore, they are likely to have distinct functions. In addition they are not homologous enough to G protein alpha subunits in other organisms to be classified. Thus C. elegans has G proteins that are identifiable homologues of mammalian G proteins as well as G proteins that appear to be unique to C. elegans. Study of identifiable G proteins in C. elegans may result in a further understanding of their function in other organisms, whereas study of the novel G proteins may provide an understanding of unique aspects of nematode physiology.

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