Survival advantage of cultured human vascular endothelial cells that lost chromosome 13

The Influence of C-Ions and X-rays on Human Umbilical Vein Endothelial Cells

Damage to the endothelium of blood vessels, which may occur during radiotherapy, is discussed as a potential precursor to the development of cardiovascular disease. We thus chose human umbilical vein endothelial cells as a model system to examine the effect of low- and high-linear energy transfer (LET) radiation. Cells were exposed to 250 kV X-rays or carbon ions (C-ions) with the energies of either 9.8 MeV/u (LET = 170 keV/μm) or 91 MeV/u (LET = 28 keV/μm). Subculture of cells was performed regularly up to 46 days (~22 population doublings) post-irradiation. Immediately after exposure, cells were seeded for the colony forming assay. Additionally, at regular intervals, mitochondrial membrane potential (MMP) (JC-1 staining) and cellular senescence (senescence-associated β-galactosidase staining) were assessed. Cytogenetic damage was investigated by the micronucleus assay and the high-resolution multiplex fluorescence in situ hybridization (mFISH) technique. Analysis of radiation-induced damage shortly after exposure showed that C-ions are more effective than X-rays with respect to cell inactivation or the induction of cytogenetic damage (micronucleus assay) as observed in other cell systems. For 9.8 and 91 MeV/u C-ions, relative biological effectiveness values of 2.4 and 1.5 were obtained for cell inactivation. At the subsequent time points, the number of micronucleated cells decreased to the control level. Analysis of chromosomal damage by mFISH technique revealed aberrations frequently involving chromosome 13 irrespective of dose or radiation quality. Disruption of the MMP was seen only a few days after exposure to X-rays or C-ions. Cellular senescence was not altered by radiation at any time point investigated. Altogether, our data indicate that shortly after exposure C-ions were more effective in damaging endothelial cells than X-rays. However, late damage to endothelial cells was not found for the applied conditions and endpoints.

Aneuploidy in immortalized human mesenchymal stem cells with non-random loss of chromosome 13 in culture

Aneuploidy (an abnormal number of chromosomes) is commonly observed in most human cancer cells, highlighting the need to examine chromosomal instability in tumorigenesis. Previously, the immortalized human mesenchymal stem cell line UE6E7T-3 was shown to undergo a preferential loss of one copy of chromosome 13 after prolonged culture. Here, the loss of chromosome 13 was found to be caused by chromosome missegregation during mitosis, which involved unequal segregation, exclusion of the misaligned chromosome 13 on the metaphase plate, and trapping of chromosome 13 in the midbody region, as observed by fluorescence in situ hybridization. Near-diploid aneuploidy, not tetraploidy, was the direct result. The loss of chromosome 13 was non-random, and was detected by analysis of microsatellites and single nucleotide polymorphism-based loss of heterozygosity (LOH). Of the five microsatellite loci on chromosome 13, four loci showed microsatellite instability at an early stage in culture, and LOH was apparent at a late stage in culture. These results suggest that the microsatellite mutations cause changes in centromere integrity provoking loss of this chromosome in the UE6E7T-3 cell line. Thus, these results support the use of this cell line as a useful model for understanding the mechanism of aneuploid formation in cell cultures.

Allelic loss of 3 different tumor suppressor gene loci in benign and malignant endothelial tumors of the head and neck

CONTEXT

Angiosarcomas are rare malignancies that commonly arise in the head and neck. No definitive precursor lesion or etiological link between hemangiomas and angiosarcoma has been postulated. Evidence at the cell culture level suggests that loss of heterozygosity of 13q might be involved in tumorigenesis of endothelial cells. Although overexpression of p53 and WT-1 has been found in angiosarcoma, little is known about the molecular changes involved.

OBJECTIVE

This study compared the molecular profile of angiosarcoma with that in some benign vascular lesions.

DESIGN

Specimens from 6 cases of angiosarcoma, 5 of hemangioma, and 5 of granulation tissue were microdissected. DNA extraction and polymerase chain reaction amplification for 11 microsatellite markers on chromosomes 11p13, 13q14, and 17p13 (WT-1, RB, p53) were performed. Loss of heterozygosity of amplification products was assessed by capillary electrophoresis. Allelic loss and fractional allelic loss were calculated.

RESULTS

The mean fractional allelic loss was 43% for angiosarcomas and 29% for hemangiomas. Eighty-three percent of angiosarcomas had allelic loss at 17p13, 66% at 13q14, and 50% at 11p13. Allelic loss was seen in 60% of hemangiomas at 13q14 and 17p13, but only in 20% at 11p13. Two cases of hemangioma and all the granulation tissue cases had no allelic losses.

CONCLUSIONS

In our study, 11p13, 13q14, and 17p13 allelic losses were present in both hemangiomas and angiosarcomas. This supports the cell culture-based theories that tumorigenesis in endothelial cells likely involves these chromosomes and provides some insight into the potential pathogenesis of angiosarcomas and benign hemangiomas.