Intracellular oxidative stress induced by calcium influx initiates the activation of phagocytosis in keratinocytes accumulating at S-phase of the cell cycle after UVB irradiation.

BACKGROUND: Phagocytosis is an essential process that maintains cellular homeostasis. In the epidermis, the phagocytosis of melanosomes into keratinocytes is important to protect their DNA against damage from ultraviolet B (UVB) radiation. Furthermore, it is considered that UVB activates the phagocytosis by keratinocytes but the detailed mechanism involved is not fully understood. OBJECTIVE: To clarify the mechanism of UVB-enhanced phagocytosis in keratinocytes, we investigated the relationship between the phagocytic ability of keratinocytes and the cell cycle stage of keratinocytes. METHODS: The phagocytic ability of keratinocytes was evaluated using the incorporation of fluorescent beads after exposure to UVB or oxidative stress. S-phase was evaluated by BrdU incorporation and immunostaining of cyclin D1. Intracellular calcium levels of keratinocytes were measured using the probe Fluo-4AM. RESULTS: The phagocytosis of fluorescent beads into keratinocytes was enhanced by UVB and also by oxidative stress. We found that keratinocytes exposed to UVB or oxidative stress were at S-phase of the cell cycle. Furthermore, keratinocytes synchronized to S-phase showed a higher phagocytic ability according to the increased intracellular ROS level. The UVB-enhanced phagocytosis and entrance into S-phase of keratinocytes was abolished by ascorbic acid, a typical antioxidant. Keratinocytes synchronized to S-phase and exposed to UVB or oxidative stress had increased levels of intracellular calcium and their enhanced phagocytic abilities were diminished by the calcium ion chelator BAPTA-AM. CONCLUSION: Taken together, intracellular oxidative stress induced by intracellular calcium influx mediates the UVB-enhanced phagocytic ability of keratinocytes accumulating at S-phase of the cell cycle.

Obesity-Altered Adipose Stem Cells Promote Radiation Resistance of Estrogen Receptor Positive Breast Cancer through Paracrine Signaling.

Obesity is associated with poorer responses to chemo- and radiation therapy for breast cancer, which leads to higher mortality rates for obese women who develop breast cancer. Adipose stem cells (ASCs) are an integral stromal component of the tumor microenvironment (TME). In this study, the effects of obesity-altered ASCs (obASCs) on estrogen receptor positive breast cancer cell's (ER+BCCs) response to radiotherapy (RT) were evaluated. We determined that BCCs had a decreased apoptotic index and increased surviving fraction following RT when co-cultured with obASCs compared to lnASCs or non-co-cultured cells. Further, obASCs reduced oxidative stress and induced IL-6 expression in co-cultured BCCs after radiation. obASCs produce increased levels of leptin relative to ASCs from normal-weight individuals (lnASCs). obASCs upregulate the expression of IL-6 compared to non-co-cultured BCCs, but BCCs co-cultured with leptin knockdown obASCs did not upregulate IL-6. The impact of shLeptin obASCs on radiation resistance of ER+BCCs demonstrate a decreased radioprotective ability compared to shControl obASCs. Key NOTCH signaling players were enhanced in ER+BBCs following co-culture with shCtrl obASCs but not shLep obASCs. This work demonstrates that obesity-altered ASCs, via enhanced secretion of leptin, promote IL-6 and NOTCH signaling pathways in ER+BCCs leading to radiation resistance.

Genetic aberrations in iPSCs are introduced by a transient G1/S cell cycle checkpoint deficiency.

A number of point mutations have been identified in reprogrammed pluripotent stem cells such as iPSCs and ntESCs. The molecular basis for these mutations has remained elusive however, which is a considerable impediment to their potential medical application. Here we report a specific stage at which iPSC generation is not reduced in response to ionizing radiation, i.e. radio-resistance. Quite intriguingly, a G1/S cell cycle checkpoint deficiency occurs in a transient fashion at the initial stage of the genome reprogramming process. These cancer-like phenomena, i.e. a cell cycle checkpoint deficiency resulting in the accumulation of point mutations, suggest a common developmental pathway between iPSC generation and tumorigenesis. This notion is supported by the identification of specific cancer mutational signatures in these cells. We describe efficient generation of human integration-free iPSCs using erythroblast cells, which have only a small number of point mutations and INDELs, none of which are in coding regions.

Safe and Efficacious Diphtheria Toxin-Based Treatment for Melanoma: Combination of a Light-On Gene-Expression System and Nanotechnology.

The controversy surrounding the use of diphtheria toxin (DT) as a therapeutic agent against tumor cells arises mainly from its unexpected harmfulness to healthy tissues. We encoded the cytotoxic fragment A of DT (DTA) as an objective gene in the Light-On gene-expression system to construct plasmids pGAVPO (pG) and pU5-DTA (pDTA). Meanwhile, a cRGD-modified ternary complex comprising plasmids, chitosan, and liposome (pG&pDTA@cRGD-CL) was prepared as a nanocarrier to ensure transfection efficiency. Benefiting from spatiotemporal control of this light-switchable transgene system and the superior tumor targeting of the carrier, toxins were designed to be expressed selectively in illuminated lesions. In vitro studies suggested that pG&pDTA@cRGD-CL exerted arrest of the S phase in B16F10 cells upon blue light irradiation and, ultimately, induced the apoptosis and necrosis of tumor cells. Such DTA-based treatment exerted enhanced antitumor activity in mice bearing B16F10 xenografts and displayed prolonged survival time with minimal side effects. Hence, we described novel DTA-based therapy combined with nanotechnology and the Light-On gene-expression system: such treatment could be a promising strategy against melanoma.

Scrippsiella acuminata versus Scrippsiella ramonii: A Physiological Comparison.

Scrippsiella is a cosmopolitan dinoflagellate genus that is able to form Harmful Algal Blooms in coastal waters. The large physiological, morphological, and genetic variability that characterizes this genus suggest the existence of cryptic species. In this study, flow cytometric analyses were carried out to compare the cell cycle and life cycle of two Scrippsiella strains from two different species: Scrippsiella ramonii (VGO1053) and Scrippsiella acuminata (S3V). Both species were also investigated by internally transcribed spacer rDNA sequencing and high-performance liquid chromatography-based pigment analyses. The reddish-brown color of S. acuminata and yellowish-green hue of S. ramonii were consistent with the quantitative differences determined in their pigment profiles. Our results indicate that the cell cycle is light-controlled and that it differs in the two species. S-phase was detected during the light period in both, whereas the G2/M phase occurred during the light period in S. ramonii but under dark conditions in S. acuminata. The detection of 4C stages, mobile zygotes (planozygotes), and resting cysts in S. ramonii (nonclonal) provided convincing evidence of sexuality in this species. Sexual related processes were not found in the clonal S. acuminata strain, suggesting its heterothallic behavior (i.e., the need for outcrossing). The differences in the genome size of these species were examined as well. © 2019 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry.

The Nup84 complex coordinates the DNA damage response to warrant genome integrity.

DNA lesions interfere with cellular processes such as transcription and replication and need to be adequately resolved to warrant genome integrity. Beyond their primary role in molecule transport, nuclear pore complexes (NPCs) function in other processes such as transcription, nuclear organization and DNA double strand break (DSB) repair. Here we found that the removal of UV-induced DNA lesions by nucleotide excision repair (NER) is compromised in the absence of the Nup84 nuclear pore component. Importantly, nup84Δ cells show an exacerbated sensitivity to UV in early S phase and delayed replication fork progression, suggesting that unrepaired spontaneous DNA lesions persist during S phase. In addition, nup84Δ cells are defective in the repair of replication-born DSBs by sister chromatid recombination (SCR) and rely on post-replicative repair functions for normal proliferation, indicating dysfunctions in the cellular pathways that enable replication on damaged DNA templates. Altogether, our data reveal a central role of the NPC in the DNA damage response to facilitate replication progression through damaged DNA templates by promoting efficient NER and SCR and preventing chromosomal rearrangements.

The key role of UVA-light induced oxidative stress in human Xeroderma Pigmentosum Variant cells.

The UVA component of sunlight induces DNA damage, which are basically responsible for skin cancer formation. Xeroderma Pigmentosum Variant (XP-V) patients are defective in the DNA polymerase pol eta that promotes translesion synthesis after sunlight-induced DNA damage, implying in a clinical phenotype of increased frequency of skin cancer. However, the role of UVA-light in the carcinogenesis of these patients is not completely understood. The goal of this work was to characterize UVA-induced DNA damage and the consequences to XP-V cells, compared to complemented cells. DNA damage were induced in both cells by UVA, but lesion removal was particularly affected in XP-V cells, possibly due to the oxidation of DNA repair proteins, as indicated by the increase of carbonylated proteins. Moreover, UVA irradiation promoted replication fork stalling and cell cycle arrest in the S-phase for XP-V cells. Interestingly, when cells were treated with the antioxidant N-acetylcysteine, all these deleterious effects were consistently reverted, revealing the role of oxidative stress in these processes. Together, these results strongly indicate the crucial role of oxidative stress in UVA-induced cytotoxicity and are of interest for the protection of XP-V patients.

Drosophila Caliban mediates G1-S transition and ionizing radiation induced S phase checkpoint.

Cell cycle progression is precisely regulated by diverse extrinsic and intrinsic cellular factors. Understanding the underlying mechanisms of cell cycle regulation is essential to address how normal development and tissue homeostasis are achieved. Here, we present a novel cell cycle regulator Caliban (Clbn), the Drosophila ortholog of human Serologically defined colon cancer antigen 1 (SDCCAG1) gene. We show that ionizing radiation induces expression of clbn, and over-expression of clbn blocks G1-to-S cell cycle transition in Drosophila, while flies loss of clbn have defective S phase checkpoint in response to irradiation. Mechanistically, induced expression of clbn suppressed E2F1 activity and down-regulates the DNA replication and expression of its downstream target cyclin E, a key regulator of G1-to-S transition. Meanwhile, clbn over-expression leads to upregulation of the CDK inhibitor Dacapo (Dap), and upregulated Dap is decreased when e2f1 is over-expressed. Furthermore, expression of clbn is down-regulated in cells with e2f1 over-expression or rbf1 knockdown, indicating that Clbn and E2F1 act antagonistically in mediating G1-to-S transition. Thus we provide genetic evidence that Clbn works together with E2F1 in regulating cell cycle progression, and Clbn is required for S phase cell cycle checkpoint in response to DNA damage.

Recruitment kinetics of the homologous recombination pathway in procyclic forms of Trypanosoma brucei after ionizing radiation treatment.

One of the most important mechanisms for repairing double-strand breaks (DSBs) in model eukaryotes is homologous recombination (HR). Although the genes involved in HR have been found in Trypanosoma brucei and studies have identified some of the proteins that participate in this HR pathway, the recruitment kinetics of the HR machinery onto DNA during DSB repair have not been clearly elucidated in this organism. Using immunofluorescence, protein DNA-bound assays, and DNA content analysis, we established the recruitment kinetics of the HR pathway in response to the DSBs generated by ionizing radiation (IR) in procyclic forms of T. brucei. These kinetics involved the phosphorylation of histone H2A and the sequential recruitment of the essential HR players Exo1, RPA, and Rad51. The process of DSB repair took approximately 5.5 hours. We found that DSBs led to a decline in the G2/M phase after IR treatment, concomitant with cell cycle arrest in the G1/S phase. This finding suggests that HR repairs DSBs faster than the other possible DSB repair processes that act during the G1/S transition. Taken together, these data suggest that the interplay between DNA damage detection and HR machinery recruitment is finely coordinated, allowing these parasites to repair DNA rapidly after DSBs during the late S/G2 proficient phases.

Effective intra-S checkpoint responses to UVC in primary human melanocytes and melanoma cell lines.

The objective of this study was to assess potential functional attenuation or inactivation of the intra-S checkpoint during melanoma development. Proliferating cultures of skin melanocytes, fibroblasts, and melanoma cell lines were exposed to increasing fluences of UVC and intra-S checkpoint responses were quantified. Melanocytes displayed stereotypic intra-S checkpoint responses to UVC qualitatively and quantitatively equivalent to those previously demonstrated in skin fibroblasts. In comparison with fibroblasts, primary melanocytes displayed reduced UVC-induced inhibition of DNA strand growth and enhanced degradation of p21Waf1 after UVC, suggestive of enhanced bypass of UVC-induced DNA photoproducts. All nine melanoma cell lines examined, including those with activating mutations in BRAF or NRAS oncogenes, also displayed proficiency in activation of the intra-S checkpoint in response to UVC irradiation. The results indicate that bypass of oncogene-induced senescence during melanoma development was not associated with inactivation of the intra-S checkpoint response to UVC-induced DNA replication stress.

NONO regulates the intra-S-phase checkpoint in response to UV radiation.

The main risk factor for skin cancer is ultraviolet (UV) exposure, which causes DNA damage. Cells respond to UV-induced DNA damage by activating the intra-S-phase checkpoint, which prevents replication fork collapse, late origin firing and stabilizes fragile sites. Recently, the 54-kDa multifunctional protein NONO was found to be involved in the non-homologous end-joining DNA repair process and in poly ADP-ribose polymerase 1 activation. Interestingly, NONO is mutated in several tumour types and emerged as a crucial factor underlying both melanoma development and progression. Therefore, we set out to evaluate whether NONO could be involved in the DNA-damage response to UV radiations. We generated NONO-silenced HeLa cell clones and found that lack of NONO decreased cell growth rate. Then, we challenged NONO-silenced cells with exposure to UV radiations and found that NONO-silenced cells, compared with control cells, continued to synthesize DNA, failed to block new origin firing and impaired CHK1S345 phosphorylation showing a defective checkpoint activation. Consistently, NONO is present at the sites of UV-induced DNA damage where it localizes to RAD9 foci. To position NONO in the DNA-damage response cascade, we analysed the loading onto chromatin of various intra-S-phase checkpoint mediators and found that NONO favours the loading of topoisomerase II-binding protein 1 acting upstream of the ATM and Rad3-related kinase activity. Strikingly, re-expression of NONO, through an sh-resistant mRNA, rescued CHK1S345 phosphorylation in NONO-silenced cells. Interestingly, NONO silencing affected cell response to UV radiations also in a melanoma cell line. Overall, our data uncover a new role for NONO in mediating the cellular response to UV-induced DNA damage.

Stem Cell-Specific Mechanisms Ensure Genomic Fidelity within HSCs and upon Aging of HSCs.

Whether aged hematopoietic stem and progenitor cells (HSPCs) have impaired DNA damage repair is controversial. Using a combination of DNA mutation indicator assays, we observe a 2- to 3-fold increase in the number of DNA mutations in the hematopoietic system upon aging. Young and aged hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) do not show an increase in mutation upon irradiation-induced DNA damage repair, and young and aged HSPCs respond very similarly to DNA damage with respect to cell-cycle checkpoint activation and apoptosis. Both young and aged HSPCs show impaired activation of the DNA-damage-induced G1-S checkpoint. Induction of chronic DNA double-strand breaks by zinc-finger nucleases suggests that HSPCs undergo apoptosis rather than faulty repair. These data reveal a protective mechanism in both the young and aged hematopoietic system against accumulation of mutations in response to DNA damage.

Visualisation of cell cycle modifications by X-ray irradiation of single HeLa cells using fluorescent ubiquitination-based cell cycle indicators.

To explore the effects of X-ray irradiation on mammalian cell cycle dynamics, single cells using the fluorescent ubiquitination-based cell cycle indicator (Fucci) technique were tracked. HeLa cells expressing Fucci were used to visualise cell cycle modifications induced by irradiation. After cultured HeLa-Fucci cells were exposed to 5 Gy X-rays, fluorescent cell images were captured every 20 min for 48 h using a fluorescent microscope. Time dependence of the fluorescence intensity of S/G2 cells was analysed to examine the cell cycle dynamics of irradiated and non-irradiated control cells. The results showed that irradiated cells could be divided into two populations: one with similar cell cycle dynamics to that of non-irradiated cells, and another displaying a prolonged G2 phase. Based on these findings, it is proposed in this article that an underlying switch mechanism is involved in cell cycle regulation and the G2/M checkpoint of HeLa cells.

Let-7b overexpression leads to increased radiosensitivity of uveal melanoma cells.

Uveal melanoma (UM) is an intraocular malignant tumor in adults that is characterized by rapid progression and recurrence. Irradiation has become the primary therapy for UM patients who are not candidates for surgery. However, after large-dose fraction irradiation treatment, some patients undergo subsequent enucleation because of radiotherapy-related complications. This situation has raised concerns on how to optimize the effectiveness of radiation treatment. Recent investigations of microRNAs are changing our understanding of UM tumor biology and are helping to identify novel targets for radiotherapy. The radioresistant UM cell lines OM431 and OCM1 were selected and exposed to irradiation, and let-7b was found to be downregulated after exposure. We then confirmed that let-7b mimics could inhibit UM growth both in vitro and in vivo. More specifically, transfection with let-7b mimics markedly resensitized OCM1 and OM431 cells to irradiation by reducing the population of S-phase cells. Cyclin D1 plays a vital role in cell cycle arrest, which is induced by let-7b overexpression. Cyclin D1 is also a target of let-7b and its expression is suppressed by upregulation of let-7b. Collectively, our results indicate that let-7b overexpression can in turn downregulate cyclin D1 expression and enhance the radiosensitivity of UM through cell cycle arrest. Let-7b could serve as a marker for radiosensitivity and could enhance the therapeutic benefit of UM cell irradiation.

Regulation of DNA damage responses and cell cycle progression by hMOB2.

Mps one binder proteins (MOBs) are conserved regulators of essential signalling pathways. Biochemically, human MOB2 (hMOB2) can inhibit NDR kinases by competing with hMOB1 for binding to NDRs. However, biological roles of hMOB2 have remained enigmatic. Here, we describe novel functions of hMOB2 in the DNA damage response (DDR) and cell cycle regulation. hMOB2 promotes DDR signalling, cell survival and cell cycle arrest after exogenously induced DNA damage. Under normal growth conditions in the absence of exogenously induced DNA damage hMOB2 plays a role in preventing the accumulation of endogenous DNA damage and a subsequent p53/p21-dependent G1/S cell cycle arrest. Unexpectedly, these molecular and cellular phenotypes are not observed upon NDR manipulations, indicating that hMOB2 performs these functions independent of NDR signalling. Thus, to gain mechanistic insight, we screened for novel binding partners of hMOB2, revealing that hMOB2 interacts with RAD50, facilitating the recruitment of the MRE11-RAD50-NBS1 (MRN) DNA damage sensor complex and activated ATM to DNA damaged chromatin. Taken together, we conclude that hMOB2 supports the DDR and cell cycle progression.

Assessing cell cycle progression of neural stem and progenitor cells in the mouse developing brain after genotoxic stress.

Neurons of the cerebral cortex are generated during brain development from different types of neural stem and progenitor cells (NSPC), which form a pseudostratified epithelium lining the lateral ventricles of the embryonic brain. Genotoxic stresses, such as ionizing radiation, have highly deleterious effects on the developing brain related to the high sensitivity of NSPC. Elucidation of the cellular and molecular mechanisms involved depends on the characterization of the DNA damage response of these particular types of cells, which requires an accurate method to determine NSPC progression through the cell cycle in the damaged tissue. Here is shown a method based on successive intraperitoneal injections of EdU and BrdU in pregnant mice and further detection of these two thymidine analogues in coronal sections of the embryonic brain. EdU and BrdU are both incorporated in DNA of replicating cells during S phase and are detected by two different techniques (azide or a specific antibody, respectively), which facilitate their simultaneous detection. EdU and BrdU staining are then determined for each NSPC nucleus in function of its distance from the ventricular margin in a standard region of the dorsal telencephalon. Thus this dual labeling technique allows distinguishing cells that progressed through the cell cycle from those that have activated a cell cycle checkpoint leading to cell cycle arrest in response to DNA damage. An example of experiment is presented, in which EdU was injected before irradiation and BrdU immediately after and analyzes performed within the 4 hr following irradiation. This protocol provides an accurate analysis of the acute DNA damage response of NSPC in function of the phase of the cell cycle at which they have been irradiated. This method is easily transposable to many other systems in order to determine the impact of a particular treatment on cell cycle progression in living tissues.

Nuclear accumulation of cyclin D1 following long-term fractionated exposures to low-dose ionizing radiation in normal human diploid cells.

Cyclin D1 is a mitogenic sensor that responds to growth signals from the extracellular environment and regulates the G 1-to-S cell cycle transition. When cells are acutely irradiated with a single dose of 10 Gy, cyclin D1 is degraded, causing cell cycle arrest at the G 1/S checkpoint. In contrast, cyclin D1 accumulates in human tumor cells that are exposed to long-term fractionated radiation (0.5 Gy/fraction of X-rays). In this study we investigated the effect of fractionated low-dose radiation exposure on cyclin D1 localization in 3 strains of normal human fibroblasts. To specifically examine the nuclear accumulation of cyclin D1, cells were treated with a hypotonic buffer containing detergent to remove cytoplasmic cyclin D1. Proliferating cell nuclear antigen (PCNA) immunofluorescence was used to identify cells in S phase. With this approach, we observed S-phase nuclear retention of cyclin D1 following low-dose fractionated exposures, and found that cyclin D1 nuclear retention increased with exposure time. Cells that retained nuclear cyclin D1 were more likely to have micronuclei than non-retaining cells, indicating that the accumulation of nuclear cyclin D1 was associated with genomic instability. Moreover, inhibition of the v-akt murine thymoma viral oncogene homolog (AKT) pathway facilitated cyclin D1 degradation and eliminated cyclin D1 nuclear retention in cells exposed to fractionated radiation. Thus, cyclin D1 may represent a useful marker for monitoring long-term effects associated with exposure to low levels of radiation.

High-dose irradiation induces cell cycle arrest, apoptosis, and developmental defects during Drosophila oogenesis.

Ionizing radiation (IR) treatment induces a DNA damage response, including cell cycle arrest, DNA repair, and apoptosis in metazoan somatic cells. Because little has been reported in germline cells, we performed a temporal analysis of the DNA damage response utilizing Drosophila oogenesis as a model system. Oogenesis in the adult Drosophila female begins with the generation of 16-cell cyst by four mitotic divisions of a cystoblast derived from the germline stem cells. We found that high-dose irradiation induced S and G2 arrests in these mitotically dividing germline cells in a grp/Chk1- and mnk/Chk2-dependent manner. However, the upstream kinase mei-41, Drosophila ATR ortholog, was required for the S-phase checkpoint but not for the G2 arrest. As in somatic cells, mnk/Chk2 and dp53 were required for the major cell death observed in early oogenesis when oocyte selection and meiotic recombination occurs. Similar to the unscheduled DNA double-strand breaks (DSBs) generated from defective repair during meiotic recombination, IR-induced DSBs produced developmental defects affecting the spherical morphology of meiotic chromosomes and dorsal-ventral patterning. Moreover, various morphological abnormalities in the ovary were detected after irradiation. Most of the IR-induced defects observed in oogenesis were reversible and were restored between 24 and 96 h after irradiation. These defects in oogenesis severely reduced daily egg production and the hatch rate of the embryos of irradiated female. In summary, irradiated germline cells induced DSBs, cell cycle arrest, apoptosis, and developmental defects resulting in reduction of egg production and defective embryogenesis.

The RASSF6 tumor suppressor protein regulates apoptosis and the cell cycle via MDM2 protein and p53 protein.

Ras association domain family (RASSF) 6 is a member of the C-terminal RASSF proteins such as RASSF1A and RASSF3. RASSF6 is involved in apoptosis in various cells under miscellaneous conditions, but it remains to be clarified how RASSF6 exerts tumor-suppressive roles. We reported previously that RASSF3 facilitates the degradation of MDM2, a major E3 ligase of p53, and stabilizes p53 to function as a tumor suppressor. In this study, we demonstrate that RASSF6 overexpression induces G1/S arrest in p53-positive cells. Its depletion prevents UV- and VP-16-induced apoptosis and G1/S arrest in HCT116 and U2OS cells. RASSF6-induced apoptosis partially depends on p53. RASSF6 binds MDM2 and facilitates its ubiquitination. RASSF6 depletion blocks the increase of p53 in response to UV exposure and up-regulation of p53 target genes. RASSF6 depletion delays DNA repair in UV- and VP-16-treated cells and increases polyploid cells after VP-16 treatment. These findings indicate that RASSF6 stabilizes p53, regulates apoptosis and the cell cycle, and functions as a tumor suppressor. Together with the previous reports regarding RASSF1A and RASSF3, the stabilization of p53 may be the common function of the C-terminal RASSF proteins.

Highly sensitive automated method for DNA damage assessment: gamma-H2AX foci counting and cell cycle sorting.

Phosphorylation of the H2AX protein is an early step in the double strand break (DSB) repair pathway; therefore, phosphorylated histone (γH2AX) foci scoring is widely used as a measure for DSBs. Foci scoring is performed either manually or semi-automatically using hand-operated capturing and image analysis software. In general, both techniques are laborious and prone to artifacts associated with manual scoring. While a few fully automated methods have been described in the literature, none of them have been used to quantify γH2AX foci in combination with a cell cycle phase analysis. Adding this feature to a rapid automated γH2AX foci quantification method would reduce the scoring uncertainty that arises from the variations in the background level of the γH2AX signal throughout the cell cycle. The method was set up to measure DNA damage induced in human mammary epithelial cells by irradiation under a mammogram device. We adapted a FISH (fluorescent in situ hybridization) Spot-counting system, which has a slide loader with automatic scanning and cell capture system throughout the thickness of each cell (z-stack), to meet our assay requirements. While scanning the sample, the system classifies the selected nuclei according to the signal patterns previously described by the user. For our purposes, a double staining immunofluorescence was carried out with antibodies to detect γH2AX and pericentrin, an integral component of the centrosome. We could thus distinguish both the number of γH2AX foci per cell and the cell cycle phase. Furthermore, restrictive settings of the program classifier reduced the "touching nuclei" problem described in other image analysis software. The automated scoring was faster than and as sensitive as its manually performed counterpart. This system is a reliable tool for γH2AX radio-induced foci counting and provides essential information about the cell cycle stage. It thus offers a more complete and rapid assessment of DNA damage.