Alterations of constitutive pericentromeric heterochromatin in lymphocytes of cancer patients and lymphocytes exposed to 5-azacytidine is associated with DNA-hypomethylation.

BACKGROUND

DNA hypomethylation plays a key role in carcinogenesis. The malignant transformation of cells as well as tumor progression is accompanied with increasing DNA hypomethylation in cancer cells. Nevertheless, the evolution of dis-epigenetic genomic alteration in the somatic cellular malignant transformation has not yet been clear.

AIM

To study the relationship between the pattern of genomic DNA hypomethylation and DNA hyperploidy.

METHODS

The model of 5-azacytidine demethylating DNA treatment of the mitogen-stimulated lymphocytes in parallel with patients with solid cancer has been explored. DNA content was measured by quantitative DAPI and Hoechst 33258 fluorescence in situ hybridization on interphase nuclei. The conventional mitogen-stimulated blood lymphocyte culture development was performed in metaphase chromosomes and interphase nuclei assay. The light and fluorescent cytomorphological microscopy was performed.

RESULTS

The model 5-azacytidine induced DNA demethylation results in increased DNA hyperploidy accompanying major pericentromeric heterochromatin (Alu) DNA repeats amplification similar to those during DNA hypomethylation-associated cancer events, and both contributed to nuclear heteropycnosis development. The constitutive pericentromeric heterochromatin consequent morphological disturbance to the latent polytene chromomerization and heteropycnosis development both in cancer patients and in model 5-azacytidine exposured lymphocytes are associated with DNA hypomethylation.

CONCLUSION

We have observed that the induced global DNA hypomethylation triggers dis-epigenetic morphological reprogramming of constitutive pericentromeric heterochromatin on the extrachromosomal organization pathway as seen during the heterochromatin latent polytene features development, which is of importance as one of the mechanism involving DNA hypomethylation in initiation and progression of cancer.