Higher sensitivity of LEC strain rat in radiation-induced acute intestinal death

Response of Fibroblasts from Menkes' and Wilson's Copper Metabolism-Related Disorders to Ionizing Radiation: Influence of the Nucleo-Shuttling of the ATM Protein Kinase

Menkes' disease (MD) and Wilson's disease (WD) are two major copper (Cu) metabolism-related disorders caused by mutations of the ATP7A and ATP7B ATPase gene, respectively. While Cu is involved in DNA strand breaks signaling and repair, the response of cells from both diseases to ionizing radiation, a common DNA strand breaks inducer, has not been investigated yet. To this aim, three MD and two WD skin fibroblasts lines were irradiated at two Gy X-rays and clonogenic cell survival, micronuclei, anti-γH2AX, -pATM, and -MRE11 immunofluorescence assays were applied to evaluate the DNA double-strand breaks (DSB) recognition and repair. MD and WD cells appeared moderately radiosensitive with a delay in the radiation-induced ATM nucleo-shuttling (RIANS) associated with impairments in the DSB recognition. Such delayed RIANS was notably caused in both MD and WD cells by a highly expressed ATP7B protein that forms complexes with ATM monomers in cytoplasm. Interestingly, a Cu pre-treatment of cells may influence the activity of the MRE11 nuclease and modulate the radiobiological phenotype. Lastly, some high-passage MD cells cultured in routine may transform spontaneously becoming immortalized. Altogether, our findings suggest that exposure to ionizing radiation may impact on clinical features of MD and WD, which requires cautiousness when affected patients are submitted to radiodiagnosis and, eventually, radiotherapy.

Synchrotron microbeam irradiation induces neutrophil infiltration, thrombocyte attachment and selective vascular damage in vivo

Our goal was the visualizing the vascular damage and acute inflammatory response to micro- and minibeam irradiation in vivo. Microbeam (MRT) and minibeam radiation therapies (MBRT) are tumor treatment approaches of potential clinical relevance, both consisting of parallel X-ray beams and allowing the delivery of thousands of Grays within tumors. We compared the effects of microbeams (25–100 μm wide) and minibeams (200–800 μm wide) on vasculature, inflammation and surrounding tissue changes during zebrafish caudal fin regeneration in vivo. Microbeam irradiation triggered an acute inflammatory response restricted to the regenerating tissue. Six hours post irradiation (6 hpi), it was infiltrated by neutrophils and fli1a⁺ thrombocytes adhered to the cell wall locally in the beam path. The mature tissue was not affected by microbeam irradiation. In contrast, minibeam irradiation efficiently damaged the immature tissue at 6 hpi and damaged both the mature and immature tissue at 48 hpi. We demonstrate that vascular damage, inflammatory processes and cellular toxicity depend on the beam width and the stage of tissue maturation. Minibeam irradiation did not differentiate between mature and immature tissue. In contrast, all irradiation-induced effects of the microbeams were restricted to the rapidly growing immature tissue, indicating that microbeam irradiation could be a promising tumor treatment tool.

Defective repair of radiation-induced DNA damage is complemented by a CHORI-230-65K18 BAC clone on rat chromosome 4

The Long Evans cinnamon (LEC) rat is highly susceptible to X-irradiation due to defective DNA repair and is thus a model for hepatocellular carcinogenesis. We constructed a bacterial artificial chromosome (BAC) contig of rat chromosome 4 completely covering the region associated with radiation susceptibility. We used transient and stable transfections to demonstrate that defective DNA repair in LEC cells is fully complemented by a 200-kb BAC, CHORI-230-65K18. Further analysis showed that the region associated with radiation susceptibility is located in a 128,543-bp region of 65K18 that includes the known gene Rpn1. However, neither knockdown nor overexpression of Rpn1 indicated that this gene is associated with radiation susceptibility. We also mapped three ESTs (TC523872, TC533727, and CB607546) in the 128,543-bp region, suggesting that 65K18 contains an unknown gene associated with X-ray susceptibility in the LEC rat.

Fine mapping of radiation susceptibility and gene expression analysis of LEC congenic rat lines

LEC rats constitute an animal model of high susceptibility to X-rays. We developed congenic LEC rat lines (recipient strain, Fischer 344 (F344)) and performed genome-wide genotyping to identify radiation susceptibility genes. We mapped seven positional candidate genes, Bmp10, Gpr73, Gp9, Cnbp, Copg, Rab7, and Rpn1, to an approximately 1.2-Mb region located between loci D4Got85 and D4Got148 on chromosome 4. None of the seven genes has been reported to be associated with radiation susceptibility. Comparison of the coding sequences for these seven genes in F344 and LEC rats showed no changes in deduced amino acid sequences. We determined gene expression differences in Gp73, Gp9, and Cnbp as well as strain-specific variations in upstream sequences of these genes. Our results suggest that radiation susceptibility in the LEC rat is primarily attributable to one of the genes within this approximately 1.2-Mb region; however, expression analysis gave no clear indication as to which gene is responsible.

Deficiency in nuclear accumulation of G22p1 and Xrcc5 proteins in hyper-radiosensitive Long-Evans Cinnamon (LEC) rat cells after X irradiation

The DNA-dependent protein kinase (DNA-PK) complex has been implicated in the repair of DNA double-strand breaks (DSBs). DNA-PK is a heterotrimeric protein complex comprised of two components: a large catalytic subunit, Prkdc, with serine/threonine kinase activity and a DNA-targeting component, G22p1 and Xrcc5. In previous report, we showed that approximately 80% of the G22p1 and Xrcc5 proteins were observed in the cytoplasm of rat fibroblasts, and that nuclear translocation of the proteins from the cytoplasm is important for the repair of DNA DSBs. In the present study, we showed that nuclear accumulation of the G22p1 and Xrcc5 proteins was not observed in fibroblasts from a mutant strain of Long-Evans Cinnamon (LEC) rat that has an enhanced radiosensitivity and a reduced level of repair of DSBs after X irradiation. Nuclear translocation of the proteins was observed in both LEC rat cells and control rat cells with normal radiosensitivity at 5 min after X irradiation. Although high levels of G22p1 and Xrcc5 proteins were observed in the nuclei of control rat cells until 60 min postirradiation, the amounts of the proteins decreased rapidly in the nuclei of LEC rat cells in the first 10 min after X irradiation. These findings suggest that there are some defects in maintaining the levels of G22p1 and Xrcc5 proteins in the nuclei of LEC rat cells. An analysis of fibroblasts from backcross rats showed that the deficiency in nuclear accumulation of G22p1 and Xrcc5 proteins is genetically linked to enhanced radiosensitivity. Since the nucleotide sequences of the G22p1 and Xrcc5 genes of the LEC rats coincided with those of the control rats, the deficiency in nuclear accumulation may not be caused by mutations of the G22p1 and Xrcc5 proteins.

Hepatic iron accumulation is not directly associated with induction of DNA strand breaks in the liver cells of Long-Evans Cinnamon (LEC) rats

Effects of accumulation of copper and iron on induction of DNA strand breaks were investigated in Long-Evans Cinnamon (LEC) rats that spontaneously develop fulminant hepatitis. Copper and iron accumulated in the liver of LEC rats in an age-dependent manner from 4 to 15 weeks. Low-iron diet prevented the accumulation of iron in the liver, but did not prevent accumulation of copper. The amounts of DNA strand breaks that were estimated by comet assay in the liver cells of rats fed standard diet increased with age from 4 to 15 weeks. No significant differences were observed in the proportions of LEC rat liver cells without tail and the average lengths of tail momentum in the comet images between LEC rats that had been fed standard MF diet and low-iron diet. These results support the idea that accumulation of iron is not directly associated with the induction of DNA damage in the liver cells of LEC rats.

No significant differences were observed in the amounts of DNA strand breaks produced by copper between male and female liver cells of long-evans cinnamon (LEC) strain rats

The amounts of DNA single strand breaks that are oxidative damage produced by copper were examined by comet assay in the liver cells of an inbred strain of Long-Evans Cinnamon (LEC) rats that spontaneously develops fulminant hepatitis. At 4 weeks of age, copper contents in the liver of LEC rats were approximately 30-fold higher than those of WKAH rats that are control rats used in the present study. Copper accumulated in the liver of LEC rats in an age-dependent manner and no significant differences were observed between copper contents in the livers of males and females at each week of age from 4 to 15 weeks. No significant amounts of DNA strand breaks were found in the liver cells of both male and female WKAH rats from 4 to 15 weeks of age. DNA strand breaks were produced in the substantial population of LEC rat liver cells at 10 weeks of age and induced in an age-dependent manner from 10 to 15 weeks of age. The amounts of DNA strand breaks produced by copper accumulation in the liver cells of female LEC rats are not more abundant than those in the cells of male rats, although it has been reported that hepatitis in female rats is more serious than that in male rats.

Hypertonic treatment inhibits radiation-induced nuclear translocation of the Ku proteins G22p1 (Ku70) and Xrcc5 (Ku80) in rat fibroblasts

The effects of X irradiation and hypertonic treatment with 0.5 M NaCl on the subcellular localization of the Ku proteins G22p1 (also known as Ku70) and Xrcc5 (also known as Ku80) in rat fibroblasts with normal radiosensitivity were examined using confocal laser microscopy and immunoblotting. Although these proteins were observed mainly in the nuclei of human fibroblasts, approximately 80% of the intensities of immunofluorescence from both G22p1 and Xrcc5 was observed in the cytoplasm of rat fibroblasts. When the rat cells were X-irradiated with 4 Gy, the intensities of the fluorescence derived from G22p1 and Xrcc5 in the nuclei increased from 20% to 50% of the total cellular fluorescence intensity at 20 min postirradiation. No significant differences were observed between the total intensities of the cellular fluorescence from the proteins in unirradiated and irradiated rat fibroblasts. The results showed that the proteins were translocated from the cytoplasm to the nucleus in the rat cells after X irradiation. The nuclear translocation of the proteins from the cytoplasm was inhibited by hypertonic treatment of the cells with 0.5 M NaCl for 20 min, which inhibits the fast repair process of potentially lethal damage (PLD). When the rat cells were treated with 0.5 M NaCl immediately after X irradiation, the repair of DNA DSBs was inhibited. The surviving fraction was approximately 60% of that of irradiated cells that were not treated with 0.5 M NaCl. The surviving fraction increased with incubation time in the growth medium before treatment with NaCl. The proportions of the intensities of fluorescence from G22p1 in the nuclei of X-irradiated cells also increased from 20% to 50% with increasing interval between X irradiation and treatment with NaCl. These results suggest that nuclear translocation of G22p1 and Xrcc5 is important for the fast repair process of PLD in rat cells.

Hepatic copper accumulation induces DNA strand breaks in the liver cells of Long-Evans Cinnamon strain rats

Effects of accumulation of copper and iron on the production of DNA strand breaks were investigated in Long-Evans Cinnamon (LEC) strain rats that spontaneously develop fulminant hepatitis. Copper and iron accumulated in the liver of LEC rats in an age-dependent manner from 4 to 15 weeks. Low-copper food prevented the accumulation of copper in the liver, but did not prevent accumulation of iron. When the amounts of DNA single strand breaks were estimated by comet assay, the number of DNA strand breaks in the liver cells of rats fed standard food increased with age from 4 to 15 weeks. The number of DNA strand breaks in the liver cells from rats fed low-copper food were the same as those of rats at 4 weeks of age. Thus, the copper accumulation in the liver of LEC rats induced DNA strand breaks, but accumulation of iron did not.

Wortmannin, a radiation sensitizer, enhances the radiosensitivity of WKAH rat cells but not that of LEC rat cells

No significant cytotoxic effect was observed in WKAH rat cells by the treatment of wortmannin, a radiation sensitizer, at concentrations lower than 30 microM for 24 hr. The relative surviving fractions of LEC rat cells were slightly, but significantly, lower than those of WKAH rat cells at each concentration of wortmannin. When the wortmannin-treated WKAH rat cells were X-irradiated, the relative surviving fractions decreased in a wortmannin concentration-dependent manner. On the contrary, no significant difference was observed between the survival curves of untreated and wortmannin-treated LEC rat cells after X-irradiation.

Deficiency in fast repair process of potentially lethal damage induced by X-irradiation in fibroblasts derived from LEC strain rats

The time course for the repair of PLD in LEC and WKAH rat cells irradiated at 5 Gy was examined. In the case of WKAH rat cells, the surviving fraction increased with increasing incubation times after X-irradiation. When hypertonic treatment was performed at each incubation time with 0.5 M NaCl for 20 min, increase in the surviving fractions was not shown. In contrast, no significant recovery of the surviving fraction in LEC rat cells was observed after incubation of irradiated cells with or without 0.5 M NaCl for 20 min. On dose-survival curves, hypertonic treatment with 0.5 M NaCl enhanced radiosensitivity of WKAH rat cells, but not LEC rat cells. Although the surviving fraction of the cells from backcross mice with normal radiosensitivity reduced by treatment with 0.5 M NaCl, the survival fraction was not affected in the cells from backcross mice with higher radiosensitivity by treatment with 0.5 M NaCl. When the cells were X-irradiated and incubated with or without 0.225 M NaCl, the radiosensitivities of LEC and WKAH rat cells treated with 0.225 M NaCl for 4 h were approximately two-fold higher than those of untreated cells. Treatment with caffeine also reduced the surviving fractions of both X-irradiated LEC and WKAH rat cells, compared with those of untreated cells. These results indicated that the slow repair of PLD occurred in LEC rat cells but not the fast repair of PLD.

Abnormal accumulation of G2/M-phase cells from LEC strain rats after X-irradiation at S phase

The effect of X-irradiation on the progression of the cell cycle in cell lines from LEC and WKAH rats was investigated by a flow cytometer. When the cells were exposed to 5 Gy of X-rays at S phase, the proportion of S-phase cells in both cell populations decreased with incubation time and that of G2/M-phase cells was approximately 80% at 6 hr post-irradiation. At 12 hr post-irradiation, approximately 45% of the WKAH rat cells appeared in the G1 phase. However, 80-90% of LEC rat cells remained in the G2/M phase and less than 5% in the G1 phase during 6-12 hr post-irradiation. Thus, the LEC rat cells irradiated at S phase remained in the G2/M phase for at least 6 hr longer than did the WKAH rat cells.

Higher sensitivity in LEC rat cells to a topoisomerase II inhibitor, ellipticine

A concentration of ellipticine, an inhibitor of topoisomerase II, required to reduce cell survival to 37% (D37) is used as an index to compare the cellular sensitivity. D37 values of LEC and WKAH rat cells were 1.2 and 2.2 microM, respectively. Thus, LEC rat cells were approximately 1.8-fold more sensitive than WKAH rat cells to ellipticine. There was no significant difference between the topoisomerase II activities in nuclear extracts of LEC and WKAH rat cells. These results suggested that the high sensitivity of LEC rat cells to ellipticine is not associated with the level of topoisomerase II activity.

Higher sensitivity in induction of apoptosis in fibroblast cell lines derived from LEC strain rats to UV-irradiation

The proportion of S-phase cells in a WKAH rat cell population decreased and that of G1-phase cells increased at 8 and 18 hr post-incubation following UV-irradiation, although no significant change was observed in the ratio of the proportion of S-phase to G1-phase cells in a LEC rat cell population. Thus, UV-radiation-induced delay in the progression from the G1 to S phase was observed in WKAH rat cells but was not apparent in LEC rat cells. The fraction of LEC rat cells containing a sub-G0 DNA content increased with post-incubation time after UV-irradiation, but not that of WKAH rat cells. The proportion of the sub-G0 fraction in LEC rat cells increased with increasing doses of UV-rays. Low molecular weight DNAs extracted from UV-irradiated LEC rat cells exhibited an intense DNA ladder pattern at 18 and 24 hr post-irradiation by electrophoretic analysis, but not those from UV-irradiated WKAH rat cells. These results showed a higher sensitivity of LEC rat cells in induction of apoptosis than that of WKAH rat cells to UV-irradiation, although there was no difference in the survival curves among the cell lines from LEC and WKAH rats after UV-irradiation.

Abnormal G1 arrest in the cell lines from LEC strain rats after X-irradiation

The effect of X-irradiation of cell lines from LEC and WKAH strain rats on a progression of cell cycle was investigated. When WKAH rat cells were exposed to 5 Gy of X-rays and their cell cycle distribution was determined by a flow cytometer, the proportion of S-phase cells decreased and that of G2/M-phase cells increased at 8 hr post-irradiation. At 18 and 24 hr post-irradiation, approximately 80% of the cells appeared in the G1 phase. On the contrary, the proportion of S-phase cells increased and that G1-phase cells decreased in LEC rats during 8-24 hr post-irradiation, compared with that at 0 hr post-irradiation. Thus, radiation-induced delay in the progression from the G1 phase to S phase (G1 arrest) was observed in WKAH rat cells but not in LEC rat cells. In the case of WKAH rat cells, the intensities of the bands of p53 protein increased at 1 and 2 hr after X-irradiation at 5 Gy, compared with those of unirradiated cells and at 0 hr post-irradiation. In contrast, the intensities of the bands were faint and did not significantly increase in LEC rat cells during 0-6 hr incubation after X-irradiation. Present results suggested that the radioresistant DNA synthesis in LEC rat cells is thought to be due to the abnormal G1 arrest following X-irradiation.

Resistance to UV-irradiation of DNA synthesis in fibroblast cell lines derived from LEC strain rats

After UV-irradiation, no difference in the survival curves was observed among cell lines derived from LEC strain (LEC) rats and WKAH strain (WKAH) rats. The dose-response curves for inhibition of DNA synthesis in WKAH-derived cells showed a sharp decline at lower doses and a mild decline at higher doses of UV-rays. In contrast, the dose-response curves in LEC-derived cell lines had no sharp component, and were almost identical to the mild component of the curves in WKAH-derived cells. These results show that DNA synthesis in the cell lines of LEC rats was more resistant to UV-irradiation than that of WKAH rats.

Radioresistant DNA synthesis in fibroblast cell lines derived from LEC strain rats

Immortalized cell lines from LEC strain (LEC) rats by SV40 large T antigen were more sensitive to X-irradiation than the cell lines from WKAH strain (WKAH) rats. The dose-response curves for inhibition of DNA synthesis in WKAH-derived cells showed a steep decline at low doses and a shallow decline at high doses. On the contrary, the dose-response curves for LEC-derived cell lines showed no steep component; they were almost identical to the shallow component of the curves for WKAH-derived cells.

A high frequency of induction of chromosome aberrations in the bone marrow cells of LEC strain rats by X-irradiation

LEC strain rats, which have been known to develop hereditarily spontaneous fulminant hepatitis 4 to 5 months after birth, are highly sensitive to whole-body X-irradiation when compared to WKAH strain rats. The present results showed that the frequencies of all types of chromosome aberrations induced by X-irradiation in the bone marrow cells of LEC rats were approximately 2- to 3-fold higher than those of WKAH rats, though no significant difference was observed in the frequency of spontaneous chromosome aberrations between LEC and WKAH rats.

Radiation hypersensitivity of LEC strain rats controlled by a single autosomal recessive gene

LEC strain rats (LEC rats), which are known to develop hereditarily spontaneous fulminant hepatitis 4-5 months after birth, were highly sensitive to whole-body X-irradiation when compared to WKAH strain rats. The radiosensitivity of F1 hybrids of LEC and WKAH rats was similar to that of WKAH rats and significantly lower than that of LEC rats. Segregation data of backcross hybrids (F1 x LEC and LEC x F1) suggested that the hypersensitivity of LEC rats to whole-body irradiation is controlled by a single autosomal recessive gene. The radiosensitivity of fibroblasts from LEC rats was higher than that of fibroblasts from WKAH rats. The repair process of DNA double-strand breaks in LEC cells was slower than that in WKAH cells. LEC rats could provide a useful animal model to assist in understanding the mechanism of radiation-induced DNA damage and repair.