Krebs II ascites cells

Hamza, M., Lloveras,J., Ribbes, G., Soula, G. and Douste-Blazy, L. (1983) An in vitro study of hemicholinium-3 on phospholipid metabolism of Krebs II ascites cells. Biochemical Pharmacology 32, 1893—1897. 

Another way in which picomaviruses could inhibit cellular protein synthesis would be to inactivate an initiation factor needed for cellular, but not viral, mENA translation. If this were the case one might expect to find a decreased capacity of extracts from infected cells to initiate translation of cellular mENAs compared to extracts from uninfected cells. Such studies have yielded a variety of results. In some laboratories no differences in activity were detected between extracts from xininfected cells and from EMC infected plasmacytoma cells or mengovirus infected Ehrlich ascites tumor cells (26, 44) In one laboratory the ability of extracts from infected cells to translate exogenously added encephalomyocarditis (EMC) virus ENA and total Krebs II ascites cell mENA was markedly diminished, but no evidence for the selective inhibition of translation of host cell mENA was obtained (52). 

MATHEWS, M.B. and OSBORE, M. The rate of polypeptide chain elongation in a cell-free system from Krebs II ascites cells. Biochem. Biophys. Acta. (1974)> 340t 147-152. 

Robertson, H. D., and Mathews, M. B., 1973, Double-stranded RNA as an inhibitor of protein synthesis and as a substrate for a nuclease in extracts of Krebs II ascites cells, Proc. Natl. Acad. Sci. USA 70 225. 

Trachsel, H., Erni, B., Schreier, M. H., Braun, L., and Staehelin, T., 1979, Purification of seven protein synthesis initiation factors from Krebs II ascites cells, Biochim. Biophys. Acta 561 484. 

It was shown that the polyribosomal form of mRNP complexes is actively translated, whereas the free form is not. One mi t expect that a covalent chemical modification of some of the mRNA proteins, such as ADP-ribosylation, will render the mRNA available for translation. We characterized the mRNA-associated ADP-iibosyl transferase in plasmac) oma, in Krebs II, ascite tumor cells, and in liver. Several auto(ADP-ribosylated) proteins could be obtained when mRNP particles were incubated with NAD. It is unlikely that we are dealing with a contamination of chromatin since in plasmocytoma the enzymatic activity in mRNP represent 34% of the total cellular activity, while the maximum DNA contamination is only 4%. Moreover, after DNAse hydrolysis the enzymatic activity remains unchanged and addition of DNA is without effect [31]. More information on these mRNP particles will be given by Thomassin et al. (this volume). 

Recently, we have demonstrated the existence of a poly(ADPR) polymerase activity associated with cytoplasmic free messenger ribonucleoprotein particles (mRNP) isolated from mouse plasmacytoma cells [4]. The enzyme does not require DNA for activity and is able to produce an ADP-ribosylation of some of the mRNP proteins. We have extended our observations to Krebs II ascites-tumor cells and to rat liver. In the present report, we will discuss some properties of this enzyme, particularly the activation by RNase A. 

Table 1 summarizes the poly(ADPR) polymerase activities measured in free mRNP isolated from mouse plasmacytoma, Krebs II ascites-tumor cells or rat liver. In contrast to the tumoral cells, the activity associated to rat liver free mRNP is very low nevertheless, it is twelvefold higher than the activity associated with the microsomal-ribosomal fraction reported by Burzio et al. [3]. The addition of calf thymus DNA induces only an increase of about 20% in enzymatic activity. 

Martin, E. M., Malec, J., Sved, S., and Work, T. S., 1961, Studies on protein and nucleic acid metabolism in virus-infected mammalian cells. I. Encephalomyocar-ditis virus in Krebs-II mouse ascites tumour cells, Biochem. J. 80 585. 

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