Poly-ADP-Ribosylation and Chromatin Organization

Althaus, Felix R.; Richter, Christoph

doi:10.1007/978-3-642-83077-8_5

Molecular Biology Biochemistry and Biophysics

1987

DOI: 10.1007/978-3-642-83077-8_5

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Poly-ADP-Ribosylation and Chromatin Organization

Felix R. Althaus

Christoph Richter²

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1990

1993

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Cited by 3 publications

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“…Two distinct subunits of G proteins [18, 191. Cholera toxin, an exotoxin produced by Vibrio cholerae, catalyzes the transfer of ADP-ribose from NAD' to the ct subunits of G,. ADP-ribosylated G, activates adenylate cyclase independently of stimulatory receptors and lacks receptor-mediated stimulation of GTPase activity (for review see [20]). Cholera toxin is an oligomeric protein and consists of two functional units.…”

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Cholera toxin differentially decreases membrane levels of α and β subunits of G proteins in NG108‐15 cells

Klinz

Costa

1990

European Journal of Biochemistry

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Treatment of NG108-15 neuroblastoma x glioma cells (24 h) with cholera toxin (0.1 -10 pg/ml) resulted in a concentration-dependent reduction of the membrane levels of subunits of GTP-binding regulatory proteins (G proteins), as determined by quantitative immunoblot procedures. The extent of reduction differed for different types of subunits: the levels of Go, and G,, were reduced by 40 -So%, whereas those of Gncommon immunoreactivity and Gi2& were only reduced by 10-20% following treatment with 10 pg/ml cholera toxin. This effect of the toxin could not be mimicked by incubation with the resolved B oligomer of cholera toxin, nor by exposure of cells to agents able to raise the intracellular levels of CAMP. Basal adenylate cyclase was stimulated in a biphasic manner by cholera toxin, being stimulated at low concentrations (0.01 -10 ng/ml) and then decreased at high (0.1 -10 pg/ ml) concentrations. Thus, the down regulation of G-protein subunits produced by cholera toxin requires its (ADPribosy1)trdnsferase activity but does not result from a CAMP-mediated mechanism. The toxin-mediated decrease of Go, in the membrane was correlated with a diminution of opioid-receptor-mediated stimulation of high-affinity GTPase activity, suggesting that opioid receptors interact with Go in native membranes of NG108-15 cells.Northern-blot analysis of cytoplasmic RNA prepared from cells treated with cholera toxin showed that the levels of mRNA coding for G,, did not change. Thus, the cholera-toxin-induced decrease of G-protein subunits may not result from an alteration in mRNA levels, but may involve a direct effect of the toxin on the process of insertion and/or clearance of G proteins into and/or from the membrane. These data indicate that cholera toxin, besides catalyzing the ADP-ribosylation of G, and Gi/Go types of G proteins, can also reduce the steady state levels of Go, and Go, subunits in the membrane and thus alter by an additional mechanism the function of inhibitory receptor systems.Guanine-nucleotide-binding proteins (G proteins) couple hormone and neurotransmitter receptors to intracellular effector systems (for review see [l]). These proteins are heterotrimers in which the ct subunit binds GTP and exhibits a GTPase activity, whereas the p and y subunits are tightly associated and may serve as a membrane anchor at the inner side of the plasma membrane. The types of G proteins identified so far differ mostly in the peptide sequence of ct subunits but possess highly similar p subunits. The ct subunits vary in size over the range 39 -52 kDa and can be ADP-ribosylated by cholera toxin and/or pertussis toxin.Molecular cloning has been extensively used to identify different subunits of G proteins and to predict their aminoacid sequence. Among the a subunits studied this way, there are four forms of G,, the stimulator of adenylate cyclase [2-71, three forms of G,-type proteins putatively related to Gi, the inhibitory regulatory component of adenylate cyclase [4, 5, 7-1 I], Go, a G protein abundant in brain [4, 7, 121 and G,...

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confidence: 99%

Cholera toxin differentially decreases membrane levels of α and β subunits of G proteins in NG108‐15 cells

Klinz

Costa

1990

European Journal of Biochemistry

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Cell culture of tumors alters endogenous poly(ADPR)polymerase expression and activity

Chabert¹,

Kopp²,

Bischoff³

et al. 1993

Intl Journal of Cancer

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Poly(ADP-ribose)polymerase, a chromatin-bound enzyme, actively participates in processes such as cell proliferation, differentiation, and DNA repair and replication. This enzyme is also implicated in cell transformation, and its inhibition has been proposed to potentiate anti-cancer drug activity. Since cells prepared from tumor biopsies and established tumor cell lines are commonly used to evaluate the efficiency of anticancer therapies, we have compared poly(ADP-ribose)polymerase activity in animal tumor cells growing in vivo and in cell culture. Three tumor types were tested: a mastocytoma (P815), a lymphoma (RDM4), and a glioma (C6). Our results show that cell culture alters poly(ADP-ribose)polymerase levels and activity. Endogenous poly(ADP-ribose) activity was several fold higher in exponentially growing cells than in cells freshly recovered from solid or ascitic tumors. Moreover, polymerase activity increased with culture time, reaching a maximum when cells became confluent. Measurements of poly(ADP-ribose)polymerase gene expression and protein amount indicate that lower enzyme activity in tumors grown in vivo are sustained by decreases in poly(ADP-ribose)polymerase mRNA and protein amount. In contrast, the increase in endogenous poly(ADP-ribose)polymerase activity observed in cultured cells was due to enzyme activation and not to de novo protein synthesis. Such differences must be considered when assessing the applicability of cell-culture results to in vivo situations.

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Ethanol increases ADP-ribosylation of histones in rat hepatocyte nuclei

Akinshola

Potter

Mezey

1993

Alcohol

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Poly-ADP-Ribosylation and Chromatin Organization

Cited by 3 publications

References 41 publications

Cholera toxin differentially decreases membrane levels of α and β subunits of G proteins in NG108‐15 cells

Cholera toxin differentially decreases membrane levels of α and β subunits of G proteins in NG108‐15 cells

Cell culture of tumors alters endogenous poly(ADPR)polymerase expression and activity

Ethanol increases ADP-ribosylation of histones in rat hepatocyte nuclei

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