Fighting the storm: could novel anti-TNFα and anti-IL-6 C. sativa cultivars tame cytokine storm in COVID-19?

The main aspects of severe COVID-19 disease pathogenesis include hyper-induction of proinflammatory cytokines, also known as 'cytokine storm', that precedes acute respiratory distress syndrome (ARDS) and often leads to death. COVID-19 patients often suffer from lung fibrosis, a serious and untreatable condition. There remains no effective treatment for these complications. Out of all cytokines, TNFα and IL-6 play crucial roles in cytokine storm pathogenesis and are likely responsible for the escalation in disease severity. These cytokines also partake in the molecular pathogenesis of fibrosis. Therefore, new approaches are urgently needed, that can efficiently and swiftly downregulate TNFα, IL-6, and the inflammatory cytokine cascade, in order to curb inflammation and prevent fibrosis, and lead to disease remission. Cannabis sativa has been proposed to modulate gene expression and inflammation and is under investigation for several potential therapeutic applications against autoinflammatory diseases and cancer. Here, we hypothesized that the extracts of novel C. sativa cultivars may be used to downregulate the expression of pro-inflammatory cytokines and pathways involved in inflammation and fibrosis. Initially, to analyze the anti-inflammatory effects of novel C. sativa cultivars, we used a well-established full thickness human 3D skin artificial EpiDermFTTM tissue model, whereby tissues were exposed to UV to induce inflammation and then treated with extracts of seven new cannabis cultivars. We noted that out of seven studied extracts of novel C. sativa cultivars, three (#4, #8 and #14) were the most effective, causing profound and concerted down-regulation of COX2, TNFα, IL-6, CCL2, and other cytokines and pathways related to inflammation and fibrosis. These data were further confirmed in the WI-38 lung fibroblast cell line model. Most importantly, one of the tested extracts had no effect at all, and one exerted effect that may be deleterious, signifying that careful cannabis cultivar selection must be based on thorough pre-clinical studies. The observed pronounced inhibition of TNFα and IL-6 is the most important finding, because these molecules are currently considered to be the main targets in COVID-19 cytokine storm and ARDS pathogenesis. Novel anti-TNFα and anti-IL-6 cannabis extracts can be useful additions to the current anti-inflammatory regimens to treat COVID-19, as well as various rheumatological diseases and conditions, and 'inflammaging' - the inflammatory underpinning of aging and frailty.

In search of preventive strategies: novel high-CBD Cannabis sativa extracts modulate ACE2 expression in COVID-19 gateway tissues

With the current COVID-19 pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), there is an urgent need for new therapies and prevention strategies that can help curtail disease spread and reduce mortality. The inhibition of viral entry and thus spread is a plausible therapeutic avenue. SARS-CoV-2 uses receptor-mediated entry into a human host via the angiotensin-converting enzyme 2 (ACE2), which is expressed in lung tissue as well as the oral and nasal mucosa, kidney, testes and gastrointestinal tract. The modulation of ACE2 levels in these gateway tissues may be an effective strategy for decreasing disease susceptibility. Cannabis sativa, especially those high in the anti-inflammatory cannabinoid cannabidiol (CBD), has been found to alter gene expression and inflammation and harbour anti-cancer and anti-inflammatory properties. However, its effects on ACE2 expression remain unknown. Working under a Health Canada research license, we developed over 800 new C. sativa cultivars and hypothesized that high-CBD C. sativa extracts may be used to down-regulate ACE2 expression in target COVID-19 tissues. Using artificial 3D human models of oral, airway and intestinal tissues, we identified 13 high-CBD C. sativa extracts that decrease ACE2 protein levels. Some C. sativa extracts down-regulate serine protease TMPRSS2, another critical protein required for SARS-CoV-2 entry into host cells. While our most effective extracts require further large-scale validation, our study is important for future analyses of the effects of medical cannabis on COVID-19. The extracts of our most successful novel high-CBD C. sativa lines, pending further investigation, may become a useful and safe addition to the prevention/treatment of COVID-19 as an adjunct therapy.

The crucial role of DNA-dependent protein kinase and myelin transcription factor 1-like protein in the miR-141 tumor suppressor network

Glioblastoma is the most aggressive brain tumor. Although miR-141 has been demonstrated to primarily function as a tumor suppressor in numerous malignancies, including glioblastoma, the mechanisms involved remain poorly understood. Here, it is shown that miR-141 is downregulated in glioblastoma cell lines and tissues and may exert its biological function via directly targeting myelin transcription factor 1-like (MYT1L). Using two glioblastoma cell lines that differ from each other by the functionality of DNA-dependent protein kinase (DNAPK), a functional involvement of DNAPK in the miR-141 tumor suppression network was observed. In M059K cells with a normal function of DNAPK, the enforced expression of miR-141 attenuated MYT1L expression and suppressed cell proliferation. Conversely, the inhibition of miR-141 expression promoted cell proliferation; however, in M059J cells with a loss-of-function DNAPK, miR-141 constitutively inhibited cell proliferation upon ectopic overexpression or inhibition. An overexpression of miR-141 suppressed M059J cell migration, while it had no effect on M059K. Furthermore, the ectopic expression of miR-141 induced an S-phase arrest in both cell lines, whereas the inhibition of miR-141 caused a G1 arrest in M059J and accelerated the S phase in M059K. An overexpression and suppression of miR-141 resulted in an aberrant expression of cell-cycle proteins, including p21. Moreover, MYT1L may be a transcription factor of p21 in p53-mutant cells, whereas DNAPK may function as a repressor of MYT1L. The findings revealed the crucial role of DNAPK in miR-141-mediated suppression of gliomagenesis and demonstrated that it may be a target molecule in miR-141-associated therapeutic interventions for glioblastoma.

A suppressive role of guanine nucleotide-binding protein subunit beta-4 inhibited by DNA methylation in the growth of anti-estrogen resistant breast cancer cells

BACKGROUND

Breast cancer is the most common malignancy in women worldwide. Although the endocrine therapy that targets estrogen receptor α (ERα) signaling has been well established as an effective adjuvant treatment for patients with ERα-positive breast cancers, long-term exposure may eventually lead to the development of acquired resistance to the anti-estrogen drugs, such as fulvestrant and tamoxifen. A better understanding of the mechanisms underlying antiestrogen resistance and identification of the key molecules involved may help in overcoming antiestrogen resistance in breast cancer.

METHODS

The whole-genome gene expression and DNA methylation profilings were performed using fulvestrant-resistant cell line 182R-6 and tamoxifen-resistant cell line TAMR-1 as a model system. In addition, qRT-PCR and Western blot analysis were performed to determine the levels of mRNA and protein molecules. MTT, apoptosis and cell cycle analyses were performed to examine the effect of either guanine nucleotide-binding protein beta-4 (GNB4) overexpression or knockdown on cell proliferation, apoptosis and cell cycle.

RESULTS

Among 9 candidate genes, GNB4 was identified and validated by qRT-PCR as a potential target silenced by DNA methylation via DNA methyltransferase 3B (DNMT3B). We generated stable 182R-6 and TAMR-1 cell lines that are constantly expressing GNB4 and determined the effect of the ectopic GNB4 on cell proliferation, cell cycle, and apoptosis of the antiestrogen-resistant cells in response to either fulvestrant or tamoxifen. Ectopic expression of GNB4 in two antiestrogen resistant cell lines significantly promoted cell growth and shortened cell cycle in the presence of either fulvestrant or tamoxifen. The ectopic GNB4 induced apoptosis in 182R-6 cells, whereas it inhibited apoptosis in TAMR-1 cells. Many regulators controlling cell cycle and apoptosis were aberrantly expressed in two resistant cell lines in response to the enforced GNB4 expression, which may contribute to GNB4-mediated biologic and/or pathologic processes. Furthermore, knockdown of GNB4 decreased growth of both antiestrogen resistant and sensitive breast cancer cells.

CONCLUSION

GNB4 is important for growth of breast cancer cells and a potential target for treatment.

Chemo brain or tumor brain - that is the question: the presence of extracranial tumors profoundly affects molecular processes in the prefrontal cortex of TumorGraft mice

Cancer chemotherapy causes numerous persistent central nervous system complications. This condition is known as chemo brain. Cognitive impairments occur even before treatment, and hence are referred to as cancer associated cognitive changes, or tumor brain. There is much yet to be learned about the mechanisms of both chemo brain and tumor brain. The frequency and timing of chemo brain and tumor brain occurrence and persistence strongly suggest they may be epigenetic in nature and associated with altered gene expression. Here we used TumorGraft^TM models wherein part of a patient's tumor is removed and grafted into immune-deficient mice and conducted global gene expression and DNA methylation analysis. We show that malignant non-central nervous system tumor growth causes profound molecular alterations in the brain. Mice harbouring triple negative or progesterone positive breast cancer TumorGrafts exhibited altered gene expression, decreased levels of DNA methylation, increased levels of DNA hydroxymethylation, and oxidative stress in the prefrontal cortex. Interestingly, chemotherapy did not have any additional synergistic effects on the analyzed processes. The molecular changes observed in this study are known signs of neurodegeneration and brain aging. This study provides an important roadmap for future large-scale analysis of the molecular and cellular mechanisms of tumor brain.

Growth of Triple Negative and Progesterone Positive Breast Cancer Causes Oxidative Stress and Down-Regulates Neuroprotective Transcription Factor NPAS4 and NPAS4-Regulated Genes in Hippocampal Tissues of TumorGraft Mice-an Aging Connection

While the refinement of existing and the development of new chemotherapeutic regimens has significantly improved cancer treatment outcomes and patient survival, chemotherapy still causes many persistent side effects. Central nervous system (CNS) toxicity is of particular concern, as cancer patients experience significant deficits in memory, learning, cognition, and decision-making. These chemotherapy-induced cognitive changes are termed chemo brain, and manifest in more than half of cancer survivors. Moreover, recent studies have emerged suggesting that neurocognitive deficits manifest prior to cancer diagnosis and treatment, and thus may be associated with tumor presence, a phenomenon recently termed “tumor brain.” To dissect the molecular mechanisms of tumor brain, we used TumorGraft^TM models, wherein part of a patient's tumor is grafted into immune-deficient mice. Here, we analyzed molecular changes in the hippocampal tissues of mice carrying triple negative (TNBC) or progesterone receptor positive (PR+BC) xenografts. TNBC growth led to increased oxidative damage, as detected by elevated levels of 4-hydroxy-2-nonenal, a product of lipid peroxidation. Furthermore, the growth of TNBC and PR+BC tumors altered global gene expression in the murine hippocampus and affected multiple pathways implicated in PI3K-Akt and MAPK signaling, as well as other pathways crucial for the proper functioning of hippocampal neurons. TNBC and PR+BC tumor growth also led to a significant decrease in the levels of neuronal transcription factor NPAS4, a regulator that governs the expression of brain-derived neurotrophic factor (BDNF), and several other key brain neurotrophic factors and pro-survival molecules. The decreased expression of ERK1/2, NPAS4, and BDNF are also seen in neurodegenerative conditions and aging, and may constitute an important tumor brain mechanism.

Adverse effects of paternal chemotherapy exposure on the progeny brain: intergenerational chemobrain

Recent advances in cancer treatments have led to significant increases in cure rates. Most cancer patients are treated with various cytotoxic chemotherapy regimens. These treatment modalities are mutagenic and genotoxic and cause a wide array of late-occurring health problems, and even exert a deleterious influence on future offspring. The adverse effects from exposed parents on offspring are referred to as transgenerational effects, and currently little is known about chemotherapy-induced transgenerational effects. Furthermore, transgenerational effects have not been studied in the brains of progeny of exposed parents. In this study, we analyzed the existence and molecular nature of transgenerational effects in the brains of progeny of animals exposed to three common chemotherapy agents: cyclophosphamide (CPP), procarbazine (PCB) and mitomycin C (MMC). For the first time, our results show that paternal exposure to chemotherapy drugs causes transgenerational changes in the brain of unexposed progeny. Although no DNA damage was observed in terms of γH2AX levels, some alterations were found in levels of PCNA, protein involved in DNA repair, replication and profileration. Furthermore, there were changes in proliferation and apoptosis proteins BCL2 and AKT1, the proteins associated with DNA methylation, DNMT1 and MeCP2. Some altered expression trends were noted in proteins involved in myelin biogenesis, MBP and MYT1L. Moreover, global transcriptome profiling revealed changes in over 200 genes in the whole brains of progeny of animals exposed to CPP, and the changes in the levels of FOXP2 and ELK1proteins were confirmed by western blot analysis. These findings suggest that paternal chemotherapy significantly affects offspring brain development and may affect brain functioning. This research provides a key roadmap for future investigations of the novel phenomenon of transgenerational effects of chemotherapy in the brain of progeny of exposed parents.

Sex-specific effects of cytotoxic chemotherapy agents cyclophosphamide and mitomycin C on gene expression, oxidative DNA damage, and epigenetic alterations in the prefrontal cortex and hippocampus - an aging connection

Recent research shows that chemotherapy agents can be more toxic to healthy brain cells than to the target cancer cells. They cause a range of side effects, including memory loss and cognitive dysfunction that can persist long after the completion of treatment. This condition is known as chemo brain. The molecular and cellular mechanisms of chemo brain remain obscure. Here, we analyzed the effects of two cytotoxic chemotherapy drugs—cyclophosphamide (CPP) and mitomycin C (MMC) - on transcriptomic and epigenetic changes in the murine prefrontal cortex (PFC) and hippocampal regions. We for the first time showed that CPP and MMC treatments led to profound sex- and brain region-specific alterations in gene expression profiles. Gene expression changes were most prominent in the PFC tissues of female mice 3 weeks after MMC treatment, and the gene expression response was much greater for MCC than CPP exposure. MMC exposure resulted in oxidative DNA damage, evidenced by accumulation of 8-oxo-2′-deoxyguanosine (8-oxodG) and a decrease in the level of 8-oxodG repair protein OGG1 in the PFC of female animals 3 weeks after treatment. MMC treatment decreased global DNA methylation and increased DNA hydroxymethylation in the PFC tissues of female mice. The majority of the changes induced by chemotherapy in the PFC tissues of female mice resembled those that occur during the brain's aging processes. Therefore, our study suggests a link between chemotherapy-induced chemo brain and brain aging, and provides an important roadmap for future analysis.

Growth of malignant extracranial tumors alters microRNAome in the prefrontal cortex of TumorGraft mice

A wide array of central nervous system complications, neurological deficits, and cognitive impairments occur and persist as a result of systemic cancer and cancer treatments. This condition is known as chemo brain and it affects over half of cancer survivors. Recent studies reported that cognitive impairments manifest before chemotherapy and are much broader than chemo brain alone, thereby adding in tumor brain as a component. The molecular mechanisms of chemo brain are under-investigated, and the mechanisms of tumor brain have not been analyzed at all. The frequency and timing, as well as the long-term persistence, of chemo brain and tumor brain suggest they may be epigenetic in nature. MicroRNAs, small, single-stranded non-coding RNAs, constitute an important part of the cellular epigenome and are potent regulators of gene expression. miRNAs are crucial for brain development and function, and are affected by a variety of different stresses, diseases and conditions. However, nothing is known about the effects of extracranial tumor growth or chemotherapy agents on the brain microRNAome. We used the well-established TumorGraft ™ mouse models of triple negative (TNBC) and progesterone receptor positive (PR+BC) breast cancer, and profiled global microRNAome changes in tumor-bearing mice upon chemotherapy, as compared to untreated tumor-bearing mice and intact mice. Our analysis focused on the prefrontal cortex (PFC), based on its roles in memory, learning, and executive functions, and on published data showing the PFC is a target in chemo brain. This is the first study showing that tumor presence alone significantly impacted the small RNAome of PFC tissues. Both tumor growth and chemotherapy treatment affected the small RNAome and altered levels of miRNAs, piRNAs, tRNAs, tRNA fragments and other molecules involved in post-transcriptional regulation of gene expression. Amongst those, miRNA changes were the most pronounced, involving several miRNA families, such as the miR-200 family and miR-183/96/182 cluster; both were deregulated in tumor-bearing and chemotherapy-treated animals. We saw that miRNA deregulation was associated with altered levels of brain-derived neurotrophic factor (BDNF), which plays an important role in cognition and memory and is one of the known miRNA targets. BDNF downregulation has been associated with an array of neurological conditions and could be one of the mechanisms underlying tumor brain and chemo brain. In the future our study could serve as a roadmap for further analysis of cancer and chemotherapy's neural side effects, and differentially expressed miRNAs should be explored as potential tumor brain and chemo brain biomarkers.

Fractionated low-dose exposure to ionizing radiation leads to DNA damage, epigenetic dysregulation, and behavioral impairment

Studies of Fractionated Exposure to Low Doses of Ionizing Radiation (FELDIR) has become of increasing importance to clinical interventions. Its consequences on DNA damage, physical, and mental health have been insufficiently investigated, however. The goal of this study was to determine the effects of FELDIR on the brain using a mouse model. We addressed the levels of DNA damage, global genomic methylation, and DNA methylation machinery in cerebellum, frontal lobe, olfactory bulb and hippocampal tissues, as well as behavioral changes linked to FELDIR exposure. The results reveal increased levels of DNA damage, as reflected by increased occurrence of DNA Strand Breaks (SBs) and dysregulation of stress-response kinase p38. FELDIR also resulted in initial loss of global genomic methylation and altered expression of methyltransferases DNMT1 (down-regulation) and DNMT3a (up-regulation), as well as methyl-binding protein MeCP2 (up-regulation). FELDIR-associated behavioral changes included impaired skilled limb placement on a ladder rung task, increased rearing activity in an open field, and elevated anxiety-like behaviors. The said alterations showed significant dose and tissue specificity. Thus, FELDIR represents a critical impact on DNA integrity and behavioral outcomes that need to be considered in the design of clinical intervention studies.

A suppressive role of ionizing radiation-responsive miR-29c in the development of liver carcinoma via targeting WIP1

Hepatocellular carcinoma (HCC) is the third most common cause of cancer-related deaths worldwide, and it has been linked to radiation exposure. As a well-defined oncogene, wild-type p53-induced phosphatase 1 (WIP1) plays an inhibitory role in several tumor suppressor pathways, including p53. WIP1 is amplified and overexpressed in many malignancies, including HCC. However, the underlying mechanisms remain largely unknown. Here, we show that low-dose ionizing radiation (IR) induces miR-29c expression in female mouse liver, while inhibiting its expression in HepG2, a human hepatocellular carcinoma cell line which is used as a model system in this study. miR-29c expression is downregulated in human hepatocellular carcinoma cells, which is inversely correlated with WIP1 expression. miR-29c attenuates luciferase activity of a reporter harboring the 3'UTR binding motif of WIP1 mRNA. Ectopic expression of miR-29c significantly represses cell proliferation and induces apoptosis and G1 arrest in HepG2. In contrast, the knockdown of miR-29c greatly enhances HepG2 cell proliferation and suppresses apoptosis. The biological effects of miR-29c may be mediated by its target WIP1 which regulates p53 activity via dephosphorylation at Ser-15. Finally, fluorescence in situ hybridization (FISH) and immunohistochemical analyses indicate that miR-29c is downregulated in 50.6% of liver carcinoma tissues examined, whereas WIP1 is upregulated in 45.4% of these tissues. The expression of miR-29c inversely correlates with that of WIP1 in HCC. Our results suggest that the IR-responsive miR-29c may function as a tumor suppressor that plays a crucial role in the development of liver carcinoma via targeting WIP1, therefore possibly representing a target molecule for therapeutic intervention for this disease.

Novel antioxidants are not toxic to normal tissues but effectively kill cancer cells

Free radicals are formed as a result of cellular processes and play a key role in predisposition to and development of numerous diseases and of premature aging. Recently, we reported the syntheses of a number of novel phenolic antioxidants for possible application in food industry. In the present study, analyses of the cellular processes and molecular gene expression effects of some of the novel antioxidants in normal human tissues and in cancer cells were undertaken. Results indicated that whereas the examined antioxidants showed no effects on morphology and gene expression of normal human oral and gingival epithelial tissues, they exerted a profound cell killing effect on breast cancer cells, including on chemotherapy-resistant breast cancer cells and on oral squamous carcinoma cells. Among the tested antioxidants, N-decyl-N-(3-methoxy-4-hydroxybenzyl)-3-(3,4-dihydroxyphenyl) propanamide and N-decyl-N-(3,5-dimethoxy-4-hydroxybenzyl)-3-(3,4-dihydroxyphenyl) propanamide were the most promising, with excellent potential for cancer treatment. Moreover, our gene expression databases can be used as a roadmap for future analysis of mechanisms of antioxidant action.

Intense THz pulses cause H2AX phosphorylation and activate DNA damage response in human skin tissue

Recent emergence and growing use of terahertz (THz) radiation for medical imaging and public security screening raise questions on reasonable levels of exposure and health consequences of this form of electromagnetic radiation. In particular, picosecond-duration THz pulses have shown promise for novel diagnostic imaging techniques. However, the effects of THz pulses on human cells and tissues thus far remain largely unknown. We report on the investigation of the biological effects of pulsed THz radiation on artificial human skin tissues. We observe that exposure to intense THz pulses for ten minutes leads to a significant induction of H2AX phosphorylation, indicating that THz pulse irradiation may cause DNA damage in exposed skin tissue. At the same time, we find a THz-pulse-induced increase in the levels of several proteins responsible for cell-cycle regulation and tumor suppression, suggesting that DNA damage repair mechanisms are quickly activated. Furthermore, we find that the cellular response to pulsed THz radiation is significantly different from that induced by exposure to UVA (400 nm).

Epigenetic bystander-like effects of stroke in somatic organs

Clinical evidence suggests that stroke may lead to damage of somatic organs. This communication of damage is well- established in the case of exposure to genotoxic agents is termed a bystander effect. Genotoxic stress-induced bystander effects are epigenetically mediated. Here we investigated whether stroke causes epigenetic bystander-like effects in the liver, kidney and heart. We found a significant increase in the levels of H3K3 acetylation and H3K4 trimethylation, as well as a decrease in the H3K9 trimethylation in the kidney tissue of stroked rats. Furthermore, here we for the first time show changes in the gene and microRNA expression profile in the kidney tissues of stroked rats, as compared to intact control animals. Interestingly, the observed changes were somewhat similar to those reported earlier in kidney injury, inflammation, and acute renal failure. Our data explain the recent epidemiological evidence for the increased incidence of acute kidney injury post-stroke and provide an important roadmap for the future analysis of the mechanisms and cellular repercussions of the stroke-induced bystander-like effects in distal somatic organs.

Radiation-induced bystander effects in vivo are sex specific

Ionizing radiation (IR) effects span beyond the area of direct exposure and can be observed in neighboring and distant naïve cells and organs. This phenomenon is termed a 'bystander effect'. IR effects in directly exposed tissue in vivo are epigenetically mediated and distinct in males and females. Yet, IR-induced bystander effects have never been explored in a sex-specificity domain. We used an in vivo mouse model, whereby the bystander effects are studied in spleen of male and female animals subjected to head exposure when the rest of the body is protected by a medical-grade lead shield. We analyzed the induction of DNA damage and alterations in global DNA methylation. Molecular parameters were correlated with cellular proliferation and apoptosis levels. The changes observed in bystander organs are compared to the changes in unexposed animals and animals exposed to predicted and measured scatter doses. We have found the selective induction of DNA damage levels, global DNA methylation, cell proliferation and apoptosis in exposed and bystander spleen tissue of male and female mice. Sex differences were significantly diminished in animals subjected to a surgical removal of gonads. These data constitute the first evidence of sex differences in radiation-induced bystander effects in mouse spleen in vivo. We show the role of sex hormones in spleen bystander responses and discuss implications of the observed changes.

Gene expression profiling reveals underlying molecular mechanisms of the early stages of tamoxifen-induced rat hepatocarcinogenesis☆

Tamoxifen is a widely used anti-estrogenic drug for chemotherapy and, more recently, for the chemoprevention of breast cancer. Despite the indisputable benefits of tamoxifen in preventing the occurrence and re-occurrence of breast cancer, the use of tamoxifen has been shown to induce non-alcoholic steatohepatitis, which is a life-threatening fatty liver disease with a risk of progression to cirrhosis and hepatocellular carcinoma. In recent years, the high-throughput microarray technology for large-scale analysis of gene expression has become a powerful tool for increasing the understanding of the molecular mechanisms of carcinogenesis and for identifying new biomarkers with diagnostic and predictive values. In the present study, we used the high-throughput microarray technology to determine the gene expression profiles in the liver during early stages of tamoxifen-induced rat hepatocarcinogenesis. Female Fisher 344 rats were fed a 420 ppm tamoxifen containing diet for 12 or 24 weeks, and gene expression profiles were determined in liver of control and tamoxifen-exposed rats. The results indicate that early stages of tamoxifen-induced liver carcinogenesis are characterized by alterations in several major cellular pathways, specifically those involved in the tamoxifen metabolism, lipid metabolism, cell cycle signaling, and apoptosis/cell proliferation control. One of the most prominent changes during early stages of tamoxifen-induced hepatocarcinogenesis is dysregulation of signaling pathways in cell cycle progression from the G(1) to S phase, evidenced by the progressive and sustained increase in expression of the Pdgfc, Calb3, Ets1, and Ccnd1 genes accompanied by the elevated level of the PI3K, p-PI3K, Akt1/2, Akt3, and cyclin B, D1, and D3 proteins. The early appearance of these alterations suggests their importance in the mechanism of neoplastic cell transformation induced by tamoxifen.

Role of epigenetic effectors in maintenance of the long-term persistent bystander effect in spleen in vivo

Radiation therapy is a primary treatment modality for brain tumors, yet it has been linked to the increased incidence of secondary, post-radiation therapy cancers. These cancers are thought to be linked to indirect radiation-induced bystander effect. Bystander effect occurs when irradiated cells communicate damage to nearby, non-irradiated 'bystander' cells, ultimately contributing to genome destabilization in the non-exposed cells. Recent evidence suggests that bystander effect may be epigenetic in nature; however, characterization of epigenetic mechanisms involved in bystander effect generation and its long-term persistence has yet to be defined. To investigate the possibility that localized X-ray irradiation induces persistent bystander effects in distant tissue, we monitored the induction of epigenetic changes (i.e. alterations in DNA methylation, histone methylation and microRNA (miRNA) expression) in the rat spleen tissue 24 h and 7 months after localized cranial exposure to 20 Gy of X-rays. We found that localized cranial radiation exposure led to the induction of bystander effect in lead-shielded, distant spleen tissue. Specifically, this exposure caused the profound epigenetic dysregulation in the bystander spleen tissue that manifested as a significant loss of global DNA methylation, alterations in methylation of long interspersed nucleotide element-1 (LINE-1) retrotransposable elements and down-regulation of DNA methyltransferases and methyl-binding protein methyl CpG binding protein 2 (MeCP2). Further, irradiation significantly altered expression of miR-194, a miRNA putatively targeting both DNA methyltransferase-3a and MeCP2. This study is the first to report conclusive evidence of the long-term persistence of bystander effects in radiation carcinogenesis target organ (spleen) upon localized distant exposure using the doses comparable with those used for clinical brain tumor treatments.

Epigenetic reprogramming of liver cells in tamoxifen-induced rat hepatocarcinogenesis

Tamoxifen, a nonsteroidal anti-estrogen, is a potent genotoxic hepatocarcinogen in rats, with both tumor initiating and promoting properties. Recently it has been demonstrated that genotoxic carcinogens, in addition to exerting genotoxic effects, often cause epigenetic alterations and these induced epigenetic changes may play important mechanistic role in carcinogenesis. In the present study, we investigated the role of tamoxifen-induced epigenetic changes in hepatocarcinogenic process. The results of the study showed that exposure of female F344 rats to tamoxifen resulted in progressive loss of CpG methylation in regulatory sequences of long interspersed nucleotide elements (LINE-1) and prominent increase in expression of LINE-1 elements and c-myc proto-oncogene. The accumulation of tamoxifen-induced DNA lesions was accompanied by the decreased level of Rad51, Ku70, and DNA polymerase beta (Polbeta) proteins that play a crucial role in maintenance of genomic stability. Furthermore, feeding rats with tamoxifen-containing diet led to increased regenerative cell proliferation, as indicated by the increased level of Ki-67 and proliferating cell nuclear antigen (PCNA) proteins. These data indicate that exposure of animals to genotoxic hepatocarcinogen tamoxifen led to early phenotypical alterations in livers characterized by emergence of epigenetically reprogrammed cells with a specific cancer-related epigenetic phenotype prior to tumor formation.

Effect of long-term tamoxifen exposure on genotoxic and epigenetic changes in rat liver: implications for tamoxifen-induced hepatocarcinogenesis

Tamoxifen is a non-steroidal anti-estrogen used for the treatment of breast cancer and, more recently, as a chemopreventive agent in healthy women at high risk of developing breast cancer. On the other hand, tamoxifen is a potent hepatocarcinogen in rats, with both tumor-initiating and tumor-promoting properties. There is substantial evidence that hepatic tumors in rats are initiated as a result of formation of tamoxifen-DNA adducts; however, events subsequent to DNA adduct formation are not clear. Recently, it has been demonstrated that genotoxic carcinogens, in addition to exerting genotoxic effects, often cause epigenetic alterations. In the current study, we investigated whether or not the mechanism of tamoxifen-induced hepatocarcinogenesis includes both genotoxic and epigenetic components. Female Fisher 344 rats were fed a 420 p.p.m. tamoxifen diet for 6, 12, 18 or 24 weeks. Hepatic tamoxifen-DNA adduct levels, as assessed by high-performance liquid chromatography and electrospray tandem mass spectrometry, were 580 adducts/10(8) nt at 6 weeks, and increased to approximately 1700 adducts/10(8) nt by 18 weeks. Global liver DNA hypomethylation, as determined by an HpaII-based cytosine extension assay, was increased at all time points, with the maximum increase (approximately 200%) occurring at 6 weeks. Protein expressions of maintenance (DNMT1) DNA methyltransferase and de novo DNA methyltransferases DNMT3a and DNMT3b were decreased at all time points. Likewise, trimethylation of histone H4 lysine 20 was significantly decreased at all time points. In contrast, non-target tissues (i.e. mammary gland, pancreas and spleen) did not show any changes in global DNA methylation or DNA methyltransferase activity. These data indicate the importance of genotoxic and epigenetic alterations in the etiology of tamoxifen-induced hepatocarcinogenesis.

Novel retinoblastoma binding protein RBBP9 modulates sex-specific radiation responses in vivo

Retinoblastoma (RB) tumor suppressor is a key regulator of apoptosis, a central mediator of the proliferative block induced by ionizing radiation (IR) and a binding target for a variety of proteins that regulate its activity. One of the recently discovered and the least investigated of these is the novel Rb-binding protein RBBP9/BOG. We studied the effects of acute and chronic low dose radiation (LDR) exposure on the induction of RBBP9 and RB signaling pathway in vivo in mouse spleen and found that RBBP9 played a pivotal role in IR responses in vivo. We observed that chronic LDR exposure led to a significant increase of RBBP9 expression in males and a significant decrease in females. Elevated RBBP9 expression in males was paralleled by a pronounced dephosphorylation of RB and a significant drop of PCNA and cyclin A expression. On the contrary, chronic exposure in females led to decreased levels of RBBP9 and increased levels of hyperphosphorylated RB (ppRB) in spleen. Decreased levels of ppRB in spleen of chronically exposed males were correlated with strongly elevated apoptotic rates. In females, the radiation-induced increase of apoptotic index was much less pronounced. Quite surprisingly, the observed sex-specific signaling changes did not result in the sex-specificity of cellular proliferation. The molecular mechanisms and possible repercussions of the radiation-induced sex differences in cellular proliferation and apoptosis are discussed.

Sex- and tissue-specific expression of maintenance and de novo DNA methyltransferases upon low dose X-irradiation in mice

DNA methylation is crucial for normal development, proliferation, and proper maintenance of genome stability for a given organism. A variety of DNA damaging agents that are known to affect genome stability were also shown to alter DNA methylation patterns. We have recently pioneered the studies in the area of the radiation effects on DNA methylation, and found that radiation exposure led to substantial dose-dependent and tissue-specific DNA hypomethylation, which was much more pronounced in spleen and liver of female animals. The exact mechanisms of radiation-induced DNA hypomethylation are still to be uncovered. We have previously shown that one of those mechanisms may potentially be DNA repair related. Another possible mechanism may be linked to changes in the expression of DNA methyltransferases (DNMTs). In the current study, we examined the radiation-induced changes in expression of maintenance DNMT1, and de novo methyltransferases DNMT3a and DNMT3b in spleen and liver of irradiated animals. This was paralleled by the studies of acute and chronic IR-induced methylation changes in spleen and liver of intact animals, as well as in animals with altered sex hormone status. Here we report that radiation-induced DNA methylation changes correlated with radiation-induced alterations in expression of DNA methyltransferases. We present the data on tissue-specificity in radiation-induced expression of DNA methyltransferases, and prove that changes in the expression of de novo methyltransferases DNMT3a and DNMT3b are the most important in radiation-induced DNA methylation alterations. We also discuss the role of sex hormones, especially estrogen, in the generation of the sex-specific radiation-induced methylation changes.

Selective brain responses to acute and chronic low-dose X-ray irradiation in males and females

Radiation exposure is known to have profound effects on the brain, leading to precursor cell dysfunction and debilitating cognitive declines [Nat. Med. 8 (2002) 955]. Although a plethora of data exist on the effects of high radiation doses, the effects of low-dose irradiation, such as ones received during repetitive diagnostic and therapeutic exposures, are still under-investigated [Am. J. Otolaryngol. 23 (2002) 215; Proc. Natl. Acad. Sci. USA 97 (2000) 889; Curr. Opin. Neurol. 16 (2003) 129]. Furthermore, most studies of the biological effects of ionizing radiation have been performed using a single acute dose, while clinically and environmentally relevant exposures occur predominantly under chronic/repetitive conditions. Here, we have used a mouse model to compare the effects of chronic/repetitive and acute low-dose radiation (LDR) exposure (0.5Gy) to ionizing radiation on the brain in vivo. We examined the LDR effects on p42/44 MAPK (ERK1/ERK2), CaMKII, and AKT signaling-the interconnected pathways that have been previously shown to be crucial for neuronal survival upon irradiation. We report perturbations in ERK1/2, AKT, and CREB upon acute and chronic/repetitive low-dose exposure in the hippocampus and frontal cortex of mice. These studies were paralleled by the analysis of radiation effects on neurogenesis and cellular proliferation. Repetitive exposure had a much more pronounced effect on cellular signaling and neurogenesis than acute exposure. These results suggest that studies of single acute exposures might be limited in terms of their predictive value. We also present the first evidence of sex differences in radiation-induced signaling in the hippocampus and frontal cortex. We show the role of estrogens in brain radiation responses and discuss the implications of the observed changes.