Increased Radiosensitivity of Solid Tumors Harboring ATM and BRCA1/2 Mutations.

PURPOSE: Preclinical data indicate that response to radiotherapy (RT) depends on DNA damage repair. In this study, we investigated the role of mutations in genes related to DNA damage repair in treatment outcome after RT. MATERIALS AND METHODS: Patients with solid tumor who participated in next generation sequencing panel screening using biopsied tumor tissue between October 2013 and February 2019 were reviewed and 97 patients that received RT were included in this study. Best response to RT and the cumulative local recurrence rate (LRR) were compared according to absence or presence of missense, nonsense, and frameshift mutations in ATM and/or BRCA1/2. RESULTS: Of the 97 patients, five patients harbored mutation only in ATM, 22 in only BRCA1/2, and six in both ATM and BRCA1/2 (ATMmtBRCAmt). Propensity score matching was performed to select the control group without mutations (ATMwtBRCAwt, n=33). In total, 90 RT-treated target lesions were evaluated in 66 patients. Highest objective response rate of 80% was observed in ATMmtBRCAmt lesions (p=0.007), which was mostly durable. Furthermore, the cumulative 1-year LRR was the lowest in ATMmtBRCAmt lesions and the highest in ATMwtBRCAwt lesions (0% vs. 47.9%, p=0.008). RT-associated toxicities were observed in 10 treatments with no significant difference among the subgroups (p=0.680). CONCLUSION: Tumors with ATM and BRCA1/2 mutations exhibited superior tumor response and local control after RT compared to tumors without these mutations. The results are hypothesis generating and suggest the need for integrating the tumor mutation profile of DNA repair genes during treatment planning.

E2F6 negatively regulates ultraviolet-induced apoptosis via modulation of BRCA1.

E2F6 is believed to repress E2F-responsive genes and therefore plays an important role in cell-cycle regulation. However, the role of E2F6 in the control of apoptosis remains unknown. We show here that the expression of E2F6 was downregulated with a concurrent increase in BRCA1 mRNA and cleaved protein during ultraviolet (UV)-induced apoptosis in human embryonic kidney 293 cells. Moreover, E2F6 overexpression distinctly inhibited UV-induced apoptosis as well as UV-induced increases in BRCA1 expression and cleavage, accompanied with increases of the full-length BRCA1 and BRCA1 nuclear foci. In contrast, knockdown of E2F6 by small interfering RNA had opposite effects. Furthermore, these effects of E2F6 on BRCA1 depended upon the association of E2F6 with BRCA1 via its C-terminus in a UV-triggered manner and upon the transcriptional repression by E2F6 on the BRCA1 promoter. These findings provide the first demonstration of the important role for E2F6 in the control of apoptosis via targeting of BRCA1.

[Structural and functional changing induced by exposure to adaptive doses of X-rays in the human lymphocytes both normal and defective by reparation of DNA double strands breaks]. / Strukturnye i funktsional'nye preobrazovaniia, indutsiruemye X-radiatsiei v diapazone adaptiruiushchikh doz, v normal'nykh i defektnykh do reparatsiidvoinykh razryvov DNK G0-limfotsitakh cheloveka.

In the present work it is shown that the phenomenon of interphase chromosome centromeric region displacement, earlier revealed by the authors, is not realized in G0-lymphocytes with heterozygous BRCA1/2 gene mutations. The role of these genes in DNA double strand break (DSB) reparation is known. It is concluded that chromosome locus displacement is necessary for DSB repair, at least in the process of homologous recombination. In accordance with our data, some feature (pericentromeric cluster disintegration and displacement, the nucleus size increasing) characteristic for S- and G0-lymphocytes are observed in normal G0-lymphocytes treated with 3 and 10 cGy. However, the size of nucleus in G0-lymphocytes is restored through 6 hours after irradiation in opposite to the process in dividing cells. It was proposed that some typical for resting cell functions of G0-lymphocytes after inducing by adaptive doze of radiation are stopped as similarly as after stimulation of cells. Interestingly, that the process of the induced chromosome loci displacement is correlated with the decreasing of DNA reparation possibilities under UV-irradiation. The induced apoptosis level also decreases when chromosome loci are displaced. The possible mechanisms of the revealed phenomenon are discussed. This research supported by RFBR grant (No. 01-04-49180).

Ultraviolet radiation down-regulates expression of the cell-cycle inhibitor p21WAF1/CIP1 in human cancer cells independently of p53.

PURPOSE: To investigate the regulation of G1 cyclin-dependent kinase inhibitor p21WAF1/CIP1 by ultraviolet (UV) radiation in human carcinoma cells. MATERIALS AND METHODS: Human cancer cell lines were irradiated with UV-C (254 nm) radiation, and their responses were characterized by Western blotting, Northern blotting, semi-quantitative RT-PCR analysis, trypan blue staining and flow cytometric cell cycle analysis. RESULTS: At 24 h after UV irradiation, p21 expression was down-regulated in various cancer cell types (breast, prostrate, cervix, colon, glioma, squamous cancers), independently of their p53 genetic and functional status. UV-mediated down-regulation of p21 was dose- and time-dependent, was observed at the protein and mRNA levels, and did not correlate with cytotoxicity. Reduction of p21 protein levels required about 4 and 1 h, respectively, in MCF-7 and MDA-MB-231 breast cancer cells; some of the UV-induced decreases in p21 levels in these cell lines was due to enhanced proteasomal degradation. Despite decreased p21 levels, UV-irradiated breast cancer cells with wild-type p53 (MCF-7) retained the capacity for G1 cell-cycle arrest, whereas UV-treated cells with mutant p53 (MDA-MB-231) accumulated in S phase, suggesting a p53-dependent G1 checkpoint in MCF-7. UV treatment caused other alterations in cell-cycle regulatory, DNA repair and tumour suppressor genes, as described in this report. CONCLUSIONS: In contrast to X-rays, UV causes down-regulation of the cell-cycle inhibitor p21 in tumour cells. It is postulated that this may be an adaptation to promote the growth and survival of transformed cells.