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Y E Yegorov

Publications and source records attributed to Y E Yegorov.

10 recordsLinked to original sources
PubMed2002

Telomerase-dependent reactivation of DNA synthesis in macrophages implies alteration of telomeres.

In previous work we demonstrated that various types of cultured cells with a limited life span could not reactivate DNA synthesis in the nuclei of mouse peritoneal macrophages in heterokaryons. We now investigate the role of telomerase in the process of the macrophage nucleus reactivation in heterokaryons with immortal telomerase-positive 3T3 Swiss mouse fibroblasts and human fibroblasts with introduced hTERT gene. We report that introduction of the hTERT gene into human diploid fibroblasts results in emergence of telomerase activity in these cells and the ability to induce the reactivation of DNA synthesis in the macrophage nuclei in heterokaryons. Inhibition of telomerase activity in heterokaryons by reverse transcriptase inhibitors (azidothymidine and guanosine polyphosphonate analogues) and by a 2'-O-methyl-RNA oligonucleotide anti-sense to the template region of telomerase RNA, block reactivation of DNA synthesis in macrophage nuclei without inhibiting DNA synthesis in the nuclei of fibroblasts. Our results suggest alterations (shortening or damage) in the macrophage telomere structure. As far as we know, heterokaryons with macrophages are the first cellular model for rapid investigation of the effects of telomerase inhibitors.

3T3 Cells↗
PubMed1999

Telomerase activity of cells during alterations of their proliferative states.

We showed that the telomerase activity (TAC) of human promyelocytic leukemic cells U-937 and HL-60 sharply decreased after induction of macrophagal differentiation. Dedifferentiation which occurred several days after removing the inductor was accompanied by the resumption of proliferation and increase of TAC. Telomerase activity significantly decreased also when U-937 cells ceased to proliferate in response to long-term inhibition of the telomerase function by azidothymidine. TAC was observed to decrease slowly for 6-8 days in the course of transition of mouse fibroblasts 3T3 Swiss to the quiescent state. TAC decreased both in serum-deprived cells and in slowly proliferating high-density inhibited cells. During the exit from quiescence and in dedifferentiation, the increase in TAC preceded the resumption of proliferation. In all the cases described the alterations of TAC correlated with alterations in the nonspecific polymerase activity which we had found earlier (D. N. Chernov, Y. E. Yegorov, and S. S. Akimov, DokL Biochemistry 349:55-58 (1996)). The problems of TAC regulation are discussed.

3T3 Cells↗
PubMed1999

Blockade of telomerase function in various cells.

The reverse transcriptase inhibitors (RTI) azidothymidine and carbovir can block telomerase function in various cells, whereas dideoxycytidine does not exhibit such activity. RTI induce senescence in 3T3 Swiss, NIH 3T3 cell cultures and in the clones of immortal spontaneously transformed mouse fibroblasts. The RTI-induced senescence of L6 rat myoblasts in culture resembles the senescence of fibroblasts, but the resulting cells acquire sharp morphological peculiarities. The artificial senescence of fibroblasts and myoblasts resulted in both the appearance of corresponding senescent cells and a small portion of cells with the signs of another type of differentiation. The blockade of telomerase function by RTI in the human tumour cell lines U-937 and MeWo leads to the shortening of telomeres, but does not result in senescence. These cells may undergo crisis and after a while the proliferation resumes and resistant cells appear. RTI inhibit spontaneous reactivation of telomerase in the process of spontaneous transformation of mouse embryonic fibroblasts, which leads to the formation of telomerase-free clones. A fraction of these clones may overcome the senescence via the acquisition of telomerase activity. Cells with a very high level of telomerase activity become resistant to RTI. Thus, the blockade of telomerase function in different cells can induce senescence, partial differentiation or crisis. In human tumour cells it induces mainly crisis.

3T3 Cells↗
PubMed1998

Endogenous beta-galactosidase activity in continuously nonproliferating cells.

Cytochemically detectable activity of endogenous beta-galactosidase was found at pH 6.0 in Swiss 3T3 cells after long-term incubation in low serum or in the presence of heparin concentrations known to reversibly inhibit cell proliferation. A high percentage of beta-galactosidase-positive cells were detected in U937 and HL60 cultures at the late stage of macrophage-like differentiation induced by TPA. Interestingly, a small number of beta-galactosidase-positive cells were found even in the growing Swiss 3T3 cultures. These positive cells expressed morphological features similar to those of senescent cells. Thus, the activity of beta-galactosidase at pH 6.0 cannot be considered an exclusive marker of senescent cells since it is expressed in other types of nonproliferating cells.

3T3 Cells↗
PubMed1997

Blockade of telomerase function by nucleoside analogs.

Two types of spontaneously transformed cells appear in the culture of senescent mouse embryonic fibroblasts. The first type are cells with restricted proliferative potential (up to 30 population doublings); the other type are immortalized cells. Cells of the first type, unlike those of the second, have no telomerase activity and undergo two rounds of senescence. Spontaneous transformation of mouse embryonic fibroblasts in the presence of the reverse transcriptase inhibitors azidothymidine and carbovir led to the formation of telomerase-free clones. A fraction of these clones have the ability to overcome senescence via the acquisition of high telomerase activity. Cells with a very high level of telomerase activity become resistant to azidothymidine and carbovir. Azidothymidine-induced artificial senescence of rat myoblasts in culture resembles the senescence of fibroblasts, but the resulting cells acquire sharp morphological peculiarities. The blockade of telomerase function by azidothymidine in human U-937 and MeWo cells leads to the shortening of telomeres, but does not result in senescence. A hypothesis of the generation of the signal that induces senescence is proposed. This hypothesis suggests a change in DNA conformation during telomere shortening as a result of a change of loop structure of telomeric chromatin.

Animals↗
PubMed1996

Reverse transcriptase inhibitors suppress telomerase function and induce senescence-like processes in cultured mouse fibroblasts.

Spontaneous transformation of mouse embryonic fibroblasts in the presence of the reverse transcriptase inhibitors azidothymidine and carbovir led to the formation of telomerase-free clones. After prolonged cultivation of fibroblasts in the presence of carbovir, resistant cells with a very high level of telomerase activity were obtained. Azidothymidine and carbovir, but not dideoxycytidine, induced senescence-like processes in cultures of immortal mouse fibroblasts. After long-term incubation, cell proliferation gradually decreased, their morphology becoming similar to that of the senescent ones. The process was reversible: after inhibitor removal, the cells, including the giant ones, entered mitoses. All these data suggest that reverse transcriptase inhibitors block telomerase function in mouse cells.

3T3 Cells↗
PubMed1993

The comparison of DNA synthesis inducibility by high potassium treatment in various nonproliferating cells.

Previous studies have demonstrated that treatment of fibroblasts from confluent, density-inhibited cultures with 50 mM KCl solution led to the onset of DNA replication. In the present study we show that such treatment can induce aphidicolin-sensitive DNA replication in differentiated nondividing cells: dorsal root ganglia neurons and in vitro differentiated myotubes formed by L6 myoblasts. Murine peritoneal macrophages and macrophages/granulocytes derived from human promyelocytic leukemia cells HL60 are refractory to high potassium treatment. These results confirm the nonuniformity of the nonproliferative state of various differentiated cells.

Animals↗
PubMed1992

The short-term increase in extracellular potassium concentration causes DNA replication onset in density-inhibited cells.

The high potassium concentration effect on the human diploid fibroblasts (HDF) and 3T3 cells was investigated. The incubation of confluent cultures of HDF or 3T3 Swiss cells in the medium with 50 mM K+ for 35 min induced, 12 h later, the onset of DNA replication in a significant proportion of culture cell population. The same treatment had no effect upon the sparce cell cultures. No stimulation of DNA replication was observed in the absence of serum in culture medium.

3T3 Cells↗
PubMed1989

Resident macrophages specifically inhibit DNA synthesis in the nuclei of transformed cells in heterokaryons.

DNA synthesis in heterokaryons of mouse peritoneal macrophages and various proliferating cultured cells was analyzed. Macrophages did not inhibit replication in the nuclei of non-immortalized and spontaneously immortalized cells (rat fibroblasts and macrophages, mouse pre-macrophages, NIH3T3 cells). On the contrary, the percentage of DNA-synthesizing nuclei of malignant HeLa cells was drastically reduced in heterokaryons. The transformation of NIH3T3 cells with c-Ki-ras oncogene and that of rat chondrocytes with p53 oncogene made these cells sensitive to the replication-inhibiting activity of macrophages in heterokaryons. Our observation represents a kind of "intracellular" cytotoxic activity of macrophages directed against transformed cells.

Animals↗