Histone modifications are involved in the DNA damage response (DDR). Here, by utilizing an ELISA immunoassay we assessed the methylation at H3K9 (H3K9me2 and H3K9me3) in two cell lines with differential sensitivity to radiation-induced apoptosis, HeLa (sensitive) and MCF-7 (resistant). We found that DNA damage induction by γ-irradiation leads to considerable accumulation (up to 5-fold) of H3K9me2 and H3K9me3, but not of H4K20me3 (control modification) in MCF-7 cells (p<0.05). Interestingly, a lower dose (2 Gy) was more effective than 5 Gy. In HeLa cells a smaller effect (approx. 1.5-1.8-fold) was evident only at 5 Gy. In conclusion, our findings reveal that DNA damage leads to specific accumulation of H3K9me2 and H3K9me3 in a cell-type specific manner.
Previously we have shown that aldolase (ALD; EC 4.1.2.13) is present in cardiomyocyte nuclei. Now, we focused our attention on ALD localization in smooth muscle cells. Immunocytochemical methods were used to study the subcellular localization of ALD. Aldolase was localized in the cytoplasm as well as in the nuclei. Within the nuclei ALD was located in the heterochromatin region. Native polyacrylamide gel electrophoresis followed by aldolase activity staining in gel was used to study the ALD isoenzyme pattern in porcine smooth muscle cells. Two ALD isoenzymes, A and C, were found in these cells but in the nuclei only the muscle isoenzyme was detected. To support the nuclear localization of ALD, measurement of aldolase activity in the smooth muscle cell nuclei isolated from porcine stomach was performed. The ALD activity in the isolated nuclei was detectable only after preincubation of the nuclear fraction with Triton X-100 and high concentration of KCl.
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