Protein-bound mono(ADP-ribose) residues in differentiating cells of Dictyostelium discoideum

An NAD+-dependent novel transcription factor controls stage conversion in Entamoeba

Developmental switching between life-cycle stages is a common feature among parasitic pathogens to facilitate disease transmission and pathogenesis. The protozoan parasite Entamoeba switches between invasive trophozoites and dormant cysts, but the encystation process remains poorly understood despite being central to amoebic biology. We identify a transcription factor, Encystation Regulatory Motif-Binding Protein (ERM-BP), that regulates encystation. Down-regulation of ERM-BP decreases encystation efficiency resulting in abnormal cysts with defective cyst walls. We demonstrate that direct binding of NAD+ to ERM-BP affects ERM-BP conformation and facilitates its binding to promoter DNA. Additionally, cellular NAD+ levels increase during encystation and exogenous NAD+ enhances encystation consistent with the role of carbon source depletion in triggering Entamoeba encystation. Furthermore, ERM-BP catalyzes conversion of nicotinamide to nicotinic acid, which might have second messenger effects on stage conversion. Our findings link the metabolic cofactors nicotinamide and NAD+ to transcriptional regulation via ERM-BP and provide the first mechanistic insights into Entamoeba encystation.

ADP-ribosyl transferase, rearrangement of DNA, and cell differentiation

Cell differentiation is the process by which genetic information is selectively expressed to produce cells with various morphologies and functions. The integrated changes necessary for this fundamentally important process have recently been the subject of intense study. This review will summarize data from several laboratories correlating differentiation with the activity of the enzyme ADP-ribosyl transferase and with changes in single-strand DNA breaks in various diverse eukaryotic systems. We will then discuss the implications of these observations for differentiation in general, including the possibility that rearrangement of genetic material is a widespread mechanism for controlling gene expression.

ADP-ribosyl-protein conjugate subclasses in various tissues. Specific influence of thyroid hormone on liver conjugates

The amounts of endogenous mono (ADP ribose)-protein conjugates and their hydroxyl-amine-sensitive and hydroxylamine-resistant subfractions in various tissues of the mouse were determined and compared with poly (ADP-ribose) conjugates. Total mono-(ADP-ribose) conjugates did not correlate with poly (ADP-ribose) residues or the cellularity of a tissue, but were related to the protein content and the amounts of NAD+ +NADH. The hydroxylamine-resistant subfraction, which in liver is mainly associated with the mitochondria [Adamietz, Wielckens, Bredehorst, Lengyel & Hilz (1981) Biochem. Biophys. Res, Commun. 101, 96-103], did not correlate with the tissue content of cytochrome c oxidase. In hypothyroid mice hydroxylamine-resistant mono (ADP-ribose) conjugates of the liver were increased by a factor of two while the hydroxylamine-sensitive conjugates did not change significantly under these conditions. Upon administration of thyroxine the hydroxylamine-resistant subfraction returned to normal.

Mono ADP-ribosylation and poly ADP-ribosylation of proteins in normal and malignant tissues

Three subclasses of (ADPR)n protein conjugates were quantified from intact tissue; proteins carrying poly(ADPR) and two types of mono(ADPR) protein conjugates, one susceptible, the other resistant to neutral hydroxylamine. Mono(ADPR) conjugates were found in all major compartments of the liver cell although the two subfractions were unevenly distributed. Poly(ADPR) protein conjugates appear to be restricted to the nucleus. Independent changes of the subclasses in normal and malignant tissues associated with cell growth and differentiation also point to independent functions. Hydroxylamine-resistant mono(ADPR) protein conjugates of various tissues changed with the degree of terminal differentiation. Formation of poly(ADPR) proteins, on the other hand, was stimulated by treatment of cells with alkylating agents which lead to DNA-fragmentation. This points to an involvement of polyADP-ribosylation in DNA excision repair.

Mono(ADP-ribosyl)ation and poly(ADP-ribosyl)ation of proteins in developing liver and in hepatomas: relation of conjugate subfractions to metabolic competence and proliferation rates

Endogenous levels of mono(ADP-ribose)-protein conjugates are low in fetal liver. They increase during development reaching 30-times higher levels in the adult stage. Undifferentiated hepatomas also exhibit low degrees of mono(ADP-ribosyl)ation compared with differentiated tumors. The observed changes cannot be explained by depolymerisation of pre-existing protein-bound poly(ADP-ribose) groups or elongation of monomeric ADP-ribose residues since the monomeric and polymeric residues change independently, the absolute levels of residues present in the form of polymers being 20--350-times lower than monomeric ADP-ribose residues. Subfractionation of the mono(ADP-ribose)-protein conjugates on the basis of their NH2OH sensitivity also showed independent changes during liver development. The level of the NH2OH-sensitive conjugates exhibit an inverse relationship to cell proliferation rates in normal and malignant hepatic tissues, while the NH2OH-resistant subfraction, which was hardly detectable in fetal liver, could be related to the degree of terminal differentiation (relative to adult liver). The ratio of NH2OH-resistant to NH2OH-sensitive mono(ADP-ribose)-protein conjugates being near unity in adult liver, fell to extremely low values in fetal and neonatal liver. In undifferentiated hepatomas (proliferating or stationary), however, the ratio was higher than in the adult normal tissue. This parameter, then, allows one to discriminate between malignant and normal hepatic tissues with similar proliferative capacity and similar metabolic competence. On the basis of the findings presented it is suggested that covalent modification of proteins by mono(ADP-ribosyl)ation and poly(ADP-ribosyl)ation serve multiple and independent functions.

Protein-bound polymeric and monomeric ADP-ribose residues in hepatic tissues. Comparative analyses using a new procedure for the quantification of poly(ADP-ribose)

Determination of poly(ADP-ribose) levels was performed by a new procedure involving covalent chromatography of released polymer, degradation to phosphoribosyl AMP and quantification of this specific derivative by a radioimmunoassay. In adult rat liver, about 85 pmol polymeric ADP-ribose residues/g tissue was found. Similar values were obtained when the determination was carried out by an independent procedure not involving boronate chromatography or sedimentation of DNA. In adult rat liver, polymeric ADP-ribose residues amounted to about 1/200 of total monomeric ADP-ribose residues. Most of the polymeric ADP-ribose residues were linked to proteins by NH2OH-sensitive bonds, while mono(ADP-ribose)-protein conjugates consisted of about equal amounts of NH2OH-sensitive and NH2OH-resistant subfractions. Poly(ADP-ribose) levels immediately after birth were similar to the adult status. They decreased, however, by a factor of three at the time of most rapid post-natal liver growth (day 17). A comparison with the protein-bound monomeric ADP-ribose residues indicated independent changes, and therefore presumably independent functions of these monomeric ADP-ribose residues.