[Changes in the mechanisms controlling mRNA stability during the process of liver regeneration in rats]. / Smena mekhanizmov, kontroliruiushchikh stabil'nost' mRNK, v protsesse regeneratsii pecheni krys.

If the protein biosynthesis was inhibited by cycloheximide, an elevated degradation of total mRNA, including mRNA of membrane-bound and free polyribosomes, occurred in the liver cells at early steps of regeneration, within 48 hrs after partial hepatectomy. Simultaneously, distinct increase in activity of alkaline RNAases was observed in cytoplasm as well as of endo-RNAase--in the membrane-bound and free polyribosomes. As shown in experiments with-p-chloromercuribenzoate, the increase in activity of alkaline RNAases in treatment with cycloheximide was due to a decrease in content of short-living proteins, which are inhibitors of RNAases, in cytoplasm of 48 hr regenerating liver cells. At the later period of liver tissue regeneration within 5 days after partial hepatectomy), under conditions of inhibition of protein biosynthesis using cycloheximide, stabilization of mRNA from membrane-bound polyribosomes was observed while the mRNA from free polyribosomes was in a state of degradation. Within this period the endo-RNAase activity was markedly decreased in membrane-bound polyribosomes but the enzymatic activity was increased in free polyribosomes. The mechanisms, controlling the mRNA stability, were apparently changed during the regeneration of rat liver tissue.

[Nucleo-cytoplasmic mRNA transport in liver rat and hepatoma cells following suppression of protein synthesis by cycloheximide]. / Iaderno-tsitoplazmaticheskii transport mRNK v kletkakh pecheni i gepatomy krys pri podavlenii belkovogo sinteza tsiklogeksimidom.

Specific radioactivity of uridylic nucleotide pool was found to be 2-2.5-fold higher in rat liver cells treated with cycloheximide within 3 hrs as compared with the control liver cells. Cycloheximide did not affect the specific radioactivity of the nucleotide pool in cells of Zajhdel ascites hepatoma. Nuclear-cytoplasmic transport of mRNA was decreased by 40-60% in rat liver cells after inhibition of protein synthesis by cycloheximide within 3 hrs. In this case, synthesis of non-ribosomal RNA was also decreased by 20-30% in nuclei. Treatment with cycloheximide caused 2.5-3-fold increase in synthesis of non-ribosomal nuclear RNA in rat cells of Zajhdel ascites hepatoma; amount of mRNA, transported from nucleus into cytoplasm, was also 2-3-fold higher in the tumoral cells as compared with controls. Under conditions of cycloheximide action, mRNA, which is transported from nuclei, continued to enter the polyribosomes of Zajhdel ascites hepatoma cells at the normal rate, although the protein synthesis did not occur in these polyribosomes.

[Change in RNase activity in rat liver cells in cycloheximide protein synthesis inhibition]. / Izmenenie aktivnosti RNK-az v kletkakh pechenie krys pri ingibirovanii belkovogo sinteza tsiklogeksimidom.

Administration of cycloheximide to rats does not change the activity of acid and alkaline RNAases in the cytoplasm of hepatocytes. At the same time cycloheximide-induced inhibition of protein synthesis leads to a fall in the activity of RNAase of microsomes and membrane-bound polyribosomes. The activity of RNAase of free polyribosomes of hepatocytes rises considerably under the action of cycloheximide.

[mRNA breakdown in tumor cells in vivo under cycloheximide protein synthesis inhibition]. / Razrushenie mRNK v opukholevykh kletkakh in vivo pri ingibirovanii belkovogo sinteza tsiklogeksimidom.

Amoung of prelabelled mRNA was unaltered in Zajhdel ascites hepatoma of rat cells within 3.5-4 hrs under conditions of treatment with actinomycin D. Due to combined effect of actinomycin D and cycloheximide the content of mRNA in the hepatoma cells was rapidly decreased. Degradation of mRNA occurred in membrane-bound polyribosomes, free polyribosomes and in cytoplasmic mRNP-particles /informosomes/ as a result of the effect of cycloheximide. Simultaneously with these phenomena, distinct increase in activity of acid and alkaline RNAases was observed in cytoplasma of the hepatoma cells; activity of endoRNAase from membrane-bound and free polyribosomes of the hepatoma was also markedly increased. Cycloheximide did not affect the activity of polynucleotide phosphorylase in polyribosomes of the hepatoma cells. Labile proteins, responsible for inhibition of RNAses appeart to participate in regulation of mRNA stability in malignant cells.

[Biochemical analysis of RNA particles and nucleolar RNases in eucaryotic cells]. / Biokhimicheskaia kharakteristika RNP-chastits i RNKaz iadryshka kletok dukariotov.

Four types of rat liver nucleolar RNP particles with the sedimentation coefficients of 120S, 80S, 60S and 12--16S were analyzed and their chemical composition was established. The nucleolar RNP particles were found to contain a RNA set with the sedimentation coefficients of 43S, 33S, 20S and 7S. The nucleolar proteins were shown to contain endonucleases, one of which was isolated and partially purified by fractionation on DEAE-Sephadex A-50. In some of its properties this RNAse was found similar to an analogous enzyme from membrane-bound ribosomes.

[Nuclease activity of the cytoplasmic ribosomes of hepatocytes and several experimental hepatomas]. / Nukleaznaia aktivnost' tsitoplazmaticheskikh ribosom gepatotsitov i nekotorykh éksperimental'nykh gepatom.

The nuclease activities of proteins, constituents of cytoplasmic ribosomes obtained from normal liver rats (Wistar) and C3HA mice as well as from hepatomas (both solid and ascites forms) transplanted into the above animals, were studied. RNA in membrane-bound ribosomes of normal rat liver incubated at 37 degrees C undergoes endogeneous hydrolysis resulting in formation, apart from acid-soluble products, of 6S, 8S and 11S fragments comprising 15 to 20% of the original amount of RNA. In contrast, in hepatoma membrane-bound ribosomes RNA treated likewisely remains intact. The proteins responsible for the RNase activity isolated from ribosomes were subsequently fractionated using ammonium sulfate and chromatography on DEAE-Sephadex columns and their properties were studied. The RNase activity completely disappeared from the membrane-bound ribosomes of Zajdela, 27 rat hepatomas and Guelstein hepatoma 22A, but not from the slow growing Guelstein hepatoma 48.

[Correlation of membrane-bound and free ribosomes in normal rat liver, Zajdela hepatoma rat liver and ascite cells proper]. / Soothoshenie membranosviazannykh i svobodnykh ribosom v pecheni zdprpvulj krys, krys s astsitnoi gepatomoi zaidela i v samikh astsitnykh kletkakh

The content of membrane-bound ribosomes in normal rat liver cells is 3 times as high as compared to that of free ribosomes. (K=membrane-bound ribosome RNAs divided by free ribosome RNAs=3, the opposite effect being observed in case of ascites hepatoma cells. A considerable increase in the free ribosome fraction in the liver of hepatoma-bearing rats occurs by the sixth day due to a decrease in the content of hepatoma-bearing rats occurs by the sixth day due to a decrease in the content of membrane-bound ribosomes (K=0.6). Similar, but less-pronounced changes were observed in liver cells of control animals after 48-hour starvation (K=0.9), simulating the condition occurring during the last days of tumour animals' life. Thus, changes in the rativ of membrane-bound to free ribosomes in liver during the ascites tumour growth are probably specifics and are not only due to anorexia in Zajdela hepatoma animals.