Leukocyte DNA damage after reduced and conventional absorbed radiation doses using 3rd generation dual-source CT technology.

PURPOSE: Computed tomography (CT) scans are an important source of ionizing irradiation (IR) in medicine that can induce a variety of DNA damage in human tissues. With technological improvements CT scans at reduced absorbed doses became feasible presumably lowering genotoxic side effects. MATERIALS AND METHODS: For measuring DNA damage we performed γH2AX foci microscopy in peripheral blood mononuclear cells (PBMC) after exposure to reduced and conventional absorbed radiation doses using 3rd generation dual-source CT (DSCT) technology. RESULTS: CT scans performed at reduced absorbed doses of 3 mGy induced significant lower levels (p < 0.0001) of DNA damage (0.05 focus per cell ± 0.01 [mean ± standard error of mean]) at 5 min after IR compared to conventional absorbed doses of 15 mGy (0.30 focus per cell ± 0.03). With ongoing DNA repair background γH2AX foci levels (0.05 focus per cell) were approached at 24 h after CT with both protocols. CONCLUSION: Our results provide evidence that reduced absorbed doses mediated by adjusted tube current in 3rd generation DSCT induce lower levels of DNA damage in PBMC compared to conventional absorbed doses suggesting a lower genotoxic risk for state-of-the-art tube current reduced CT protocols.

c-MYB is a transcriptional regulator of ESPL1/Separase in BCR-ABL-positive chronic myeloid leukemia.

BACKGROUND: Genomic instability and clonal evolution are hallmarks of progressing chronic myeloid leukemia (CML). Recently, we have shown that clonal evolution and blast crisis correlate with altered expression and activity of Separase, a cysteine endopeptidase that is a mitotic key player in chromosomal segregation and centriole duplication. Hyperactivation of Separase in human hematopoietic cells has been linked to a feedback mechanism that posttranslationally stimulates Separase proteolytic activity after imatinib therapy-induced reduction of Separase protein levels. METHODS AND RESULTS: In search for potential therapy-responsive transcriptional mechanisms we have investigated the role of the transcription factor c-MYB for Separase expression in CML cell lines (LAMA-84, K562, BV-173) and in clinical samples. Quantitative RT-PCR and Western blot immunostaining experiments revealed that c-MYB expression levels are decreased in an imatinib-dependent manner and positively correlate with Separase expression levels in cell lines and in clinical CML samples. RNA silencing of c-MYB expression in CML cell lines resulted in reduced Separase protein levels. Gelshift and ChIP assays confirmed that c-MYB binds to a putative c-MYB binding sequence located within the ESPL1 promoter. CONCLUSIONS: Our data suggest that ESPL1/Separase is a regulatory target of c-MYB. Therefore, c-MYB, known to be required for BCR-ABL-dependent transformation of hematopoietic progenitors and leukemogenesis, may also control the Separase-dependent fidelity of mitotic chromosomal segregation and centriole duplication essential for maintenance of genomic stability.