mTOR inhibitor temsirolimus and MEK1/2 inhibitor U0126 promote chromosomal instability and cell type-dependent phenotype changes of glioblastoma cells.

The phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) and the RAF/mitogen-activated and extracellular signal-regulated kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathways are frequently deregulated in cancer. Temsirolimus (TEM) and its primary active metabolite rapamycin allosterically block mTOR complex 1 substrate recruitment. The context-/experimental setup-dependent opposite effects of rapamycin on the multiple centrosome formation, aneuploidy, DNA damage/repair, proliferation, and invasion were reported. Similarly, the context-dependent either tumor-promoting or suppressing effects of RAF-MEK-ERK pathway and its inhibitors were demonstrated. Drug treatment-mediated stress may promote chromosomal instability (CIN), accelerating changes in the genomic landscape and phenotype diversity. Here, we characterized the genomic and phenotypic changes of U251 and T98G glioblastoma cell lines long-term treated with TEM or U0126, an inhibitor of MEK1/2. TEM significantly increased clonal and non-clonal chromosome aberrations. Both TEM and U0126 affected copy number alterations (CNAs) pattern. A proliferation rate of U251TEM and U251U0126 cells was lower and higher, respectively, than control cells. Colony formation efficiency of U251TEM significantly decreased, whereas U251U0126 did not change. U251TEM and U251U0126 cells decreased migration. In contrast, T98GTEM and T98GU0126 cells did not change proliferation, colony formation efficiency, and migration. Changes in the sensitivity of inhibitor-treated cells to the reduction of the glucose concentration were observed. Our results suggest that CIN and adaptive reprogramming of signal transduction pathways may be responsible for the cell type-dependent phenotype changes of long-term TEM- or U0126-treated tumor cells.

A case of prenatal detection of a de novo unbalanced complex chromosomal rearrangement involving four chromosomes.

Complex chromosomal rearrangements are rarely observed prenatally. Genetic counceling of CCR carriers is complicated, especially in cases of de novo origin of the rearrangement. Here we present a new case of a de novo CCR involving four chromosomes observed in amniotic fluid cells of the fetus at 17 weeks of gestation. The rearrangement was characterized as an apparently balanced four-way translocation t(1;11;7;13)(~p21;~q13.5;~q32;~q22)dn by conventional cytogenetic studies. However, array-based comparative genomic hybridization revealed 5 submicroscopic heterozygous interstitial deletions on chromosome 1, 11, 7, 13 with a total loss of 21.1 Mb of genetic material in regions close to those, designated as breakpoints by conventional cytogenetic analysis. The described case clearly illustrates that high-resolution molecular genetic analysis should be combined with conventional cytogenetic techniques to exclude subtle chromosomal abnormalities in CCR cases detected prenatally.

Chromosomal DNA balance in human stem cell line 4BL.

In the previous cytogenetic study of new human stem cell line 4BL at the 205th passage we observed the ploidy of chromosomal set and regular aberrations. To investigate the nature of monosomy of certain chromosomes the array CGH and FISH analyses have been used. The aberrations of chromosomes have been identified in all the cases of monosomies previously revealed by G-banding. The largest changes of the DNA balance have been detected in the chromosomes 2, 4, 10, 13 and 17. The probable cause of the monosomies of chromosomes 4, 10, 13 and 17 is massive loss of the genetic material. The monosomy of the second chromosome pair is caused by significant transformation one of the homologs in a type of numerous duplications and formation of der(2)t(2;?)(q21;?). Due to application of array CGH the regions of the structural aberrations of the chromosomes 2, 4, 10, 13 and 17 have been concretized, what permitted to perform their clarifying identification by multicolored FISH method. The results obtained by us confirm the hypothesis about coordinated appearance of the deletions and duplications and their stabilization impact on the transformed chromosomes.

[Comparative analysis of a new human cell line 4BL karyotype at long-term cultivation. Ploidy of chromosomal set].

Long-term cultivation of human cells, including stem cells, can lead to substantial transformation of the karyotype and occurrence of genetic instability. The aim of this research was a comparative cytogenetic study of the karyotype of a new human stem cell line 4BL at 160 and 205 passages. The absence of 10 and 13 pairs of chromosomes and the monosomy of chromosomes 4, 8, 10, 11, 13, 15, 17, 21, X were observed; also six regular marker chromosomes were detected. Chromosomes 1, 15 and 21 are involved in translocations t(l;11), t(5;15), t(12; 15), t(16;21). Modal class of the karyotype is within 41-43 chromosomes at both 160 and 205 passages. The frequency of polyploid cells have been increased from 2.8% at 160 passage up to 36% at 205 passage. Cells with a near-haploid karyotype were not detected at 205 passage (in contrast to 24.6% at 160 passages) and a decline of the level of premature separation of chromatids was observed. We assume stabilization of karyotype of the cell line 4BL at 205 passage and consider that further research is needed to predict the direction of karyotypic evolution of these cells in vitro.

[Correction of DNA methylation disorder as a possible way to modulation of malignant cells drug resistance].

The role of DNA methylation in functioning of a normal and cancer cell is shown in this review. The value of methylation in functioning of the systems which are involved in the process of formation of malignant cells drug resistance phenotype (regulator proteins of cellular cycle, DNA-adducts reparation, transport systems, systems of detoxication and adhesion) is explicated. The prospects of the antineoplastic therapy directed to regulation of DNA methylation by means of homocysteine and demethylation agents are analyzed.