UV-induced mutations in epidermal cells of mice defective in DNA polymerase η and/or ι.

Xeroderma pigmentosum variant (XP-V) is a human rare inherited recessive disease, predisposed to sunlight-induced skin cancer, which is caused by deficiency in DNA polymerase η (Polη). Polη catalyzes accurate translesion synthesis (TLS) past pyrimidine dimers, the most prominent UV-induced lesions. DNA polymerase ι (Polι) is a paralog of Polη that has been suggested to participate in TLS past UV-induced lesions, but its function in vivo remains uncertain. We have previously reported that Polη-deficient and Polη/Polι double-deficient mice showed increased susceptibility to UV-induced carcinogenesis. Here, we investigated UV-induced mutation frequencies and spectra in the epidermal cells of Polη- and/or Polι-deficient mice. While Polη-deficient mice showed significantly higher UV-induced mutation frequencies than wild-type mice, Polι deficiency did not influence the frequencies in the presence of Polη. Interestingly, the frequencies in Polη/Polι double-deficient mice were statistically lower than those in Polη-deficient mice, although they were still higher than those of wild-type mice. Sequence analysis revealed that most of the UV-induced mutations in Polη-deficient and Polη/Polι double-deficient mice were base substitutions at dipyrimidine sites. An increase in UV-induced mutations at both G:C and A:T pairs associated with Polη deficiency suggests that Polη contributes to accurate TLS past both thymine- and cytosine-containing dimers in vivo. A significant decrease in G:C to A:T transition in Polη/Polι double-deficient mice when compared with Polη-deficient mice suggests that Polι is involved in error-prone TLS past cytosine-containing dimers when Polη is inactivated.

MUTYH-null mice are susceptible to spontaneous and oxidative stress induced intestinal tumorigenesis.

MUTYH is a mammalian DNA glycosylase that initiates base excision repair by excising adenine opposite 8-oxoguanine and 2-hydroxyadenine opposite guanine, thereby preventing G:C to T:A transversion caused by oxidative stress. Recently, biallelic germ-line mutations of MUTYH have been found in patients predisposed to a recessive form of hereditary multiple colorectal adenoma and carcinoma with an increased incidence of G:C to T:A somatic mutations in the APC gene. In the present study, a systematic histologic examination revealed that more spontaneous tumors had developed in MUTYH-null mice (72 of 121; 59.5%) than in the wild type (38 of 109; 34.9%). The increased incidence of intestinal tumors in MUTYH-null mice (11 tumors in 10 of 121 mice) was statistically significant compared with the wild type (no intestinal tumors in 109 mice). Two adenomas and seven adenocarcinomas were observed in the small intestines, and two adenomas but no carcinomas were found in the colons. In MUTYH-null mice treated with KBrO(3), the occurrence of small intestinal tumors dramatically increased. The mean number of polyps induced in the small intestines of these mice was 61.88 (males, 72.75; females, 51.00), whereas it was 0.85 (males, 0.50; females, 1.00) in wild-type mice. The tumors developed predominantly in the duodenum and in the upper region of the (jejunum) small intestines. We conclude that MUTYH suppresses spontaneous tumorigenesis in mammals, thus providing experimental evidence for the association between biallelic germ-line MUTYH mutations and a recessive form of human hereditary colorectal adenoma and carcinoma.

Measles virus infection of SLAM (CD150) knockin mice reproduces tropism and immunosuppression in human infection.

The human signaling lymphocyte activation molecule (SLAM, also called CD150), a regulator of antigen-driven T-cell responses and macrophage functions, acts as a cellular receptor for measles virus (MV), and its V domain is necessary and sufficient for receptor function. We report here the generation of SLAM knockin mice in which the V domain of mouse SLAM was replaced by that of human SLAM. The chimeric SLAM had an expected distribution and normal function in the knockin mice. Splenocytes from the SLAM knockin mice permitted the in vitro growth of a virulent MV strain but not that of the Edmonston vaccine strain. Unlike in vitro infection, MV could grow only in SLAM knockin mice that also lacked the type I interferon receptor (IFNAR). After intraperitoneal or intranasal inoculation, MV was detected in the spleen and lymph nodes throughout the body but not in the thymus. Notably, the virus appeared first in the mediastinal lymph node after intranasal inoculation. Splenocytes from MV-infected IFNAR(-/-) SLAM knockin mice showed suppression of proliferative responses to concanavalin A. Thus, MV infection of SLAM knockin mice reproduces lymphotropism and immunosuppression in human infection, serving as a useful small animal model for measles.

Bone marrow-derived monocyte chemoattractant protein-1 receptor CCR2 is critical in angiotensin II-induced acceleration of atherosclerosis and aneurysm formation in hypercholesterolemic mice.

UNLABELLED: Angiotensin II (Ang II) is implicated in atherogenesis by activating inflammatory responses in arterial wall cells. Ang II accelerates the atherosclerotic process in hyperlipidemic apoE-/- mice by recruiting and activating monocytes. Monocyte chemoattractant protein-1 (MCP-1) controls monocyte-mediated inflammation through its receptor, CCR2. The roles of leukocyte-derived CCR2 in the Ang II-induced acceleration of the atherosclerotic process, however, are not known. We hypothesized that deficiency of leukocyte-derived CCR2 suppresses Ang II-induced atherosclerosis. METHODS AND RESULTS: A bone marrow transplantation technique (BMT) was used to develop apoE-/- mice with and without deficiency of CCR2 in leukocytes (BMT-apoE-/-CCR2+/+ and BMT-apoE-/-CCR2-/- mice). Compared with BMT-apoE-/-CCR2+/+ mice, Ang II-induced increases in atherosclerosis plaque size and abdominal aortic aneurysm formation were suppressed in BMT-apoE-/-CCR2-/- mice. This suppression was associated with a marked decrease in monocyte-mediated inflammation and inflammatory cytokine expression. CONCLUSIONS: Leukocyte-derived CCR2 is critical in Ang II-induced atherosclerosis and abdominal aneurysm formation. The present data suggest that vascular inflammation mediated by CCR2 in leukocytes is a reasonable target of therapy for treatment of atherosclerosis.

Targeted disruption of one allele of the Y-box binding protein-1 (YB-1) gene in mouse embryonic stem cells and increased sensitivity to cisplatin and mitomycin C.

The eukaryotic Y-box binding protein-1 (YB-1) functions in various biological processes, including transcriptional and translational control, DNA repair, drug resistance, and cell proliferation. To elucidate the physiological role of the YB-1 protein, we disrupted one allele of mouse YB-1 in embryonic stem (ES) cells. Northern blot analysis revealed that YB-1(+/-) ES cells with one intact allele contain approximately one-half the amount of mRNA detected in wild-type (YB-1(+/+)) cells. We further found that the protein level of YB-1(+/-) cells was reduced to approximately 50-60% compared with that of YB-1(+/+) cells. However, no apparent growth difference was found between YB-1(+/-) and YB-1(+/+) cells. YB-1(+/-) cells showed increased sensitivity to cisplatin and mitomycin C, but not to etoposide, X-ray or UV irradiation, as compared to YB-1(+/+) cells. YB-1 may have the capacity to exert a protective role against cytotoxic effects of DNA damaging agents, and may be involved in certain aspects of drug resistance.

Critical role of monocyte chemoattractant protein-1 receptor CCR2 on monocytes in hypertension-induced vascular inflammation and remodeling.

Activated monocytes are present in the arterial walls of hypertensive patients and animals. Monocyte chemoattractant protein-1 (MCP-1), which controls monocyte function through its receptor (CCR2), is implicated in hypertensive inflammatory changes in the arterial wall. The role of CCR2 expression on monocytes in hypertension-induced vascular remodeling, however, has not been addressed. We hypothesized that CCR2 on monocytes is critical in hypertension-induced vascular inflammation and remodeling. Hypertension was induced by infusion of angiotensin II (Ang II) into wild-type mice, CCR2-deficient (CCR2-/-) mice, and bone marrow-transferred mice with a leukocyte-selective CCR2 deficiency (BMT-CCR2-/-). In wild-type mice, Ang II increased CCR2 intensity in circulating monocytes, which was prevented by an Ang II type-1 (AT1) receptor blocker or blunted in AT1 receptor-deficient mice. Enhanced CCR2 intensity on monocytes was observed in hypertensive patients and rats, and was reduced by treatment with the Ang II receptor blocker, supporting the clinical relevance of the observation in mice. In CCR2-/- and BMT-CCR2-/- mice, Ang II-induced vascular inflammation and vascular remodeling (aortic wall thickening and fibrosis) were blunted as compared with control mice. In contrast, Ang II-induced left ventricular hypertrophy developed in CCR2-/- and BMT-CCR2-/- mice. The present study suggests that CCR2 expression in monocytes has a critical role in vascular inflammation and remodeling in Ang II-induced hypertension, and possibly in other forms of hypertension.

Clearance of apoptotic photoreceptors: elimination of apoptotic debris into the subretinal space and macrophage-mediated phagocytosis via phosphatidylserine receptor and integrin alphavbeta3.

The effective phagocytotic clearance of apoptotic debris is fundamental to the maintenance of neural tissues during apoptosis. Retinal photoreceptors undergo apoptosis after retinal detachment. Although their induction phase of apoptosis has been well discussed, their phagocytotic process remains quite unclear. We herein demonstrate that apoptotic photoreceptors are selectively eliminated from their physiological localization, the outer nuclear layer, to the subretinal space, and then phagocytosed by monocyte-derived macrophages. This could be shown by an ultrastructural and immunophenotypic analysis. Moreover, in chimera mice expressing transgenic green fluorescent protein in bone marrow-derived cells, the local infiltration of macrophages could be detected after retinal detachment-induced photoreceptor apoptosis. The local injection of an antibody blocking the phosphatidylserine receptor (PSR) or a peptide (GRGDSP)-blocking integrin alphavbeta3 revealed that phagocytotic clearance involves the PSR as well as integrin alphavbeta3 in vivo. Importantly, the level of blockade obtained with these reagents was different. Although anti-PSR increased the frequency of apoptotic cells that fail to bind to macrophages, GRGDSP prevented the engulfment (but not the recognition) of apoptotic photoreceptor cells by macrophages. To our knowledge, this is the first report describing the mechanisms through which apoptotic photoreceptors are selectively eliminated via a directional process in the subretinal space.

Effects of single low dose irradiation on subventricular zone cells in juvenile rat brain.

Although the juvenile human brain is relatively radioresistant, irradiation can result in brain growth retardation, progressive mental disturbance, and neurologic abnormalities. As neural stem cells or progenitor cells may be a target of radiation injury and may play an important role in the brain's functional recovery, we examined the effects of whole brain irradiation on these cells in juvenile rat. Six-week-old Wistar rats, where the brain is still growing, were irradiated with single doses of 1, 2, or 3 Gy X-ray. We measured their body and brain weights at 30 or 60 days after irradiation. The chronological changes of the subventricular zone (SVZ) were examined at 6 h, 2, 7, 14, 30, or 60 days after irradiation by immunohistochemistry, specifically looking at the neural stem cells or progenitor cells using anti-nestin antibodies specific for these cells. The rate of brain weight gain of irradiated rats significantly decreased in comparison to controls, although that of body weight gain was similar among them. Multiple apoptotic cells appeared in the SVZ at 6 h after irradiation with simultaneous reduction in nestin-positive cells (69% of the control). The cell levels recovered within a week, with the nestin-positive cells reaching maximal numbers (182%) on Day 14. Nestin-positive cells returned to baseline levels within 30 days (96%) and remained unchanged for the subsequent 60 days. The X-ray dosage did not affect these findings. Our findings revealed that single low dose X-ray administration reversibly affected the levels of neural stem and progenitor cells in the SVZ region. These results suggest that continuous multiple administrations of X-rays in clinical treatment may affect irreversible changes on neural stem or progenitor cells, causing brain growth retardation, or dysfunction.

A nitroimidazole derivative, PR-350, enhances the killing of pancreatic cancer cells exposed to high-dose irradiation under hypoxia.

The radiosensitizing effects of PR-350, a nitroimidazole derivative, were examined concerning the cell killing of human pancreatic cancer cell lines exposed to high doses of gamma-ray irradiation in vitro. The percentages of dead cells were analyzed with a multiwell plate reader to measure the fluorescence intensity of propidium iodide before and after a digitonin treatment. The sensitizing effect of PR-350 on cell killing by high-dose irradiation was confirmed by time-course, dose-dependency, and microscopic observations. In five of seven pancreatic cancer cell lines in which the number of dead cells was determined 5 days after 30 Gy irradiation in the presence of PR-350, the number was significantly increased under hypoxic conditions, but not under aerobic conditions. The selective radiosensitive effect of PR-350 on hypoxic cells was also confirmed by flow cytometry. The results indicate that PR-350 can enhance the killing of pancreatic cancer cells by high-dose irradiation under hypoxia, which supports its clinical radiosensitizing effects when administered during intraoperative irradiation to pancreatic cancer.