METTL14 facilitates global genome repair and suppresses skin tumorigenesis.

Global genome repair (GGR), a subpathway of nucleotide excision repair, corrects bulky helix-distorting DNA lesions across the whole genome and is essential for preventing mutagenesis and skin cancer. Here, we show that METTL14 (methyltransferase-like 14), a critical component of the N6-methyladenosine (m6A) RNA methyltransferase complex, promotes GGR through regulating m6A mRNA methylation-mediated DDB2 translation and suppresses ultraviolet B (UVB) radiation-induced skin tumorigenesis. UVB irradiation down-regulates METTL14 protein through NBR1-dependent selective autophagy. METTL14 knockdown decreases GGR and DDB2 abundance. Conversely, overexpression of wild-type METTL14 but not its enzymatically inactive mutant increases GGR and DDB2 abundance. METTL14 knockdown decreases m6A methylation and translation of the DDB2 transcripts. Adding DDB2 reverses the GGR repair defect in METTL14 knockdown cells, indicating that METTL14 facilitates GGR through regulating DDB2 m6A methylation and translation. Similarly, knockdown of YTHDF1, an m6A reader promoting translation of m6A-modified transcripts, decreases DDB2 protein levels. Both METTL14 and YTHDF1 bind to the DDB2 transcript. In mice, skin-specific heterozygous METTL14 deletion increases UVB-induced skin tumorigenesis. Furthermore, METTL14 as well as DDB2 is down-regulated in human and mouse skin tumors and by chronic UVB irradiation in mouse skin, and METTL14 level is associated with the DDB2 level, suggesting a tumor-suppressive role of METTL14 in UVB-associated skin tumorigenesis in association with DDB2 regulation. Taken together, these findings demonstrate that METTL14 is a target for selective autophagy and acts as a critical epitranscriptomic mechanism to regulate GGR and suppress UVB-induced skin tumorigenesis.

Whole-Exome Sequencing of Acquired Nevi Identifies Mechanisms for Development and Maintenance of Benign Neoplasms.

The melanoma transformation rate of an individual nevus is very low despite the detection of oncogenic BRAF or NRAS mutations in 100% of nevi. Acquired melanocytic nevi do, however, mimic melanoma, and approximately 30% of all melanomas arise within pre-existing nevi. Using whole-exome sequencing of 30 matched nevi, adjacent normal skin, and saliva we sought to identify the underlying genetic mechanisms for nevus development. All nevi were clinically, dermoscopically, and histopathologically documented. In addition to identifying somatic mutations, we found mutational signatures relating to UVR mirroring those found in cutaneous melanoma. In nevi we frequently observed the presence of the UVR mutation signature compared with adjacent normal skin (97% vs. 10%, respectively). Copy number aberration analysis showed that for nevi with copy number loss of tumor suppressor genes, this loss was balanced by loss of potent oncogenes. Moreover, reticular and nonspecific patterned nevi showed an increased (P < 0.0001) number of copy number aberrations compared with globular nevi. The mutation signature data generated in this study confirms that UVR strongly contributes to nevogenesis. Copy number changes reflect at a genomic level the dermoscopic differences of acquired melanocytic nevi. Finally, we propose that the balanced loss of tumor suppressor genes and oncogenes is a protective mechanism of acquired melanocytic nevi.

Generation of Optogenetically Modified Adenovirus Vector for Spatiotemporally Controllable Gene Therapy.

Gene therapy is expected to be utilized for the treatment of various diseases. However, the spatiotemporal resolution of current gene therapy technology is not high enough. In this study, we generated a new technology for spatiotemporally controllable gene therapy. We introduced optogenetic and CRISPR/Cas9 techniques into a recombinant adenovirus (Ad) vector, which is widely used in clinical trials and exhibits high gene transfer efficiency, to generate an illumination-dependent spatiotemporally controllable gene regulation system (designated the Opt/Cas-Ad system). We generated an Opt/Cas-Ad system that could regulate a potential tumor suppressor gene, and we examined the effectiveness of this system in cancer treatment using a xenograft tumor model. With the Opt/Cas-Ad system, highly selective tumor treatment could be performed by illuminating the tumor. In addition, Opt/Cas-Ad system-mediated tumor treatment could be stopped simply by turning off the light. We believe that our Opt/Cas-Ad system can enhance both the safety and effectiveness of gene therapy.

Aberrant microRNA expression in radiation-induced rat mammary cancer: the potential role of miR-194 overexpression in cancer cell proliferation.

Aberrant expression of microRNAs (miRNAs) is frequently associated with a variety of cancers, including breast cancer. We and others have demonstrated that radiation-induced rat mammary cancer exhibits a characteristic gene expression profile and a random increase in aberrant DNA copy number; however, the role of aberrant miRNA expression is unclear. We performed a microarray analysis of frozen samples of eight mammary cancers induced by γ irradiation (2 Gy), eight spontaneous mammary cancers and seven normal mammary samples. We found that a small set of miRNAs was characteristically overexpressed in radiation-induced cancer. Quantitative RT-PCR analysis confirmed that miR-135b, miR-192, miR-194 and miR-211 were significantly up-regulated in radiation-induced mammary cancer compared with spontaneous cancer and normal mammary tissue. The expression of miR-192 and miR-194 also was up-regulated in human breast cancer cell lines compared with noncancer cells. Manipulation of the miR-194 expression level using a synthetic inhibiting RNA produced a small but significant suppression of cell proliferation and upregulation in the expression of several genes that are thought to act as tumor suppressors in MCF-7 and T47D breast cancer cells. Our data suggest that the induction of rat mammary cancer by radiation involves aberrant expression of miRNAs, which may facilitate cell proliferation.

Environmental toxicants--induced epigenetic alterations and their reversers.

Epigenetics has been emphasized in the postgenome era to clarify obscure health risks of environmental toxicants including endocrine disrupting chemicals (EDCs). In addition, mixed exposure in real life can modify health consequences of the toxicants. Particularly, some nutritional and dietary materials modify individual susceptibility through changes in the epigenome. Therefore, we focused on some environmental toxicants that induce epigenetic alterations, and introduced chemopreventive materials to reverse the toxicants-induced epigenetic alterations. Methodologically, we used global and specific DNA methylation as epigenetic end points and searched epigenetic modulators in food. We reviewed various epigenetic end points induced by environmental toxicants including alcohol, asbestos, nanomaterials, benzene, EDCs, metals, and ionizing radiation. The epigenetic end points can be summarized into global hypomethylation and specific hypermethylation at diverse tumor suppress genes. Exposure timing, dose, sex, or organ specificity should be considered to use the epigenetic end points as biomarkers for exposure to the epimutagenic toxicants. Particularly, neonatal exposure to the epimutagens can influence their future adult health because of characteristics of the epimutagens, which disrupt epigenetic regulation in imprinting, organogenesis, development, etc. Considering interaction between epimutagenic toxicants and their reversers in food, we suggest that multiple exposures to them can alleviate or mask epigenetic toxicity in real life. Our present review provides useful information to find new end points of environmental toxicants and to prevention from environment-related diseases.

Photocarcinogenesis--molecular mechanisms.

The carcinogenicity (photocarcinogenicity) of sunlight to human skin has been recognized more than a century ago. Last decades numerous experimental studies show that UV rays damage DNA, cause gene mutations leading to the development of malignant tumors such basal cell carcinomas, squamous cell carcinomas and melanomas. The tumors occur most frequently in fair skinned people, and the mutations typically are found at dipyrimidine sites with C-T or / and CC-TT tandem double mutations. The authors briefly summarize their investigation of the p53 suppressor gene, and expose their hypothesis of hTERT involvement in cancerogenesis. Also their underline the importance of UV induced immunosuppression in photocarcinogenesis. Psoriatic patients are exposed to numerous cancerogens in their treatment. A better understanding of the mechanisms of photocarcinogenesis could provide new ways in the treatment of skin tumors.

RB1 and TP53 pathways in radiation-induced sarcomas.

The tumour suppressor genes, TP53 and RB1, and four genes involved in their regulation, INK4a, ARF, MDM2 and MDMX, were analysed in a series of 36 post-radiotherapy radiation-induced sarcomas. One-third of the tumours developed in patients carrying a germline mutation of RB1 that predisposed them to retinoblastoma and radiation-induced sarcomas. The genetic inactivation of RB1 and/or TP53 genes was frequently observed in these sarcomas. These inactivations were owing to an interplay between point mutations and losses of large chromosome segments. Radiation-induced somatic mutations were observed in TP53, but not in RB1 or in the four other genes, indicating an early role of TP53 in the radio-sarcomagenesis. RB1 and TP53 genes were biallelically coinactivated in all sarcomas developing in the context of the predisposition, indicating that both genes played a major role in the formation of these sarcomas. In the absence of predisposition, TP53 was biallelically inactivated in one-third of the sarcomas, whereas at least one allele of RB1 was wild type. In both genetic contexts, the TP53 pathway was inactivated by genetic lesions and not by the activation of the ARF/MDM2/MDMX pathway, as recently shown in retinoblastomas. Together, these findings highlight the intricate tissue- and aetiology-specific relationships between TP53 and RB1 pathways in tumorigenesis.

Evidence for clustered tumour suppressor gene loci on mouse chromosomes 2 and 4 in radiation-induced acute myeloid leukaemia.

PURPOSE: To investigate the influence of genetic and epigenetic factors on allelic loss on chromosomes 2 and 4 in mouse radiation-induced acute myeloid leukaemia (r-AML). METHODS: r-AML that arose in (CBA/HxC57BL/6)F1xCBA/H and F1xC57BL/6 mice were screened for transcription factor PU1 (also known as SPI-1) gene mutations and methylation of the paired box gene 5 (Pax5) gene promoter. We have increased the statistical significance of a genetic linkage analysis of affected F1xCBA/H mice to test for linkage to loci implicated directly or indirectly with r-AML-susceptibility. RESULTS: There was a statistically significant difference ( p < 10-4) in the frequency of PU1 gene mutations in F1xCBA/H and F1xC57BL/6 r-AML, implicating a second linked but genotype-dependent myeloid leukaemia suppressor gene on chromosome 2. A suggestive CBA/H r-AML-resistance locus maps within 10 cM of the minimally deleted region on chromosome 4. The Pax5 gene promoter is subject to ongoing subclonal promoter methylation in the r-AML, evidence that Pax5 gene silencing confers a selective advantage during clonal expansion in vivo. CONCLUSIONS: Allelic loss in mouse r-AML and subsequent tumour suppressor gene mutation (PU1) or silencing (Pax5) is strongly influenced by genetic background and/or epigenetic factors, and driven by in vivo clonal selection.

Radiation carcinogenesis in mouse thymic lymphomas.

Ionizing radiation is a well-known carcinogen for various human tissues and a complete carcinogen that is able to initiate and promote neoplastic progression. Studies of radiation-induced mouse thymic lymphomas, one of the classic models in radiation carcinogenesis, demonstrated that even the unirradiated thymus is capable of developing into full malignancy when transplanted into the kidney capsule or subcutaneous tissue of irradiated mice. This suggests that radiation targets tissues other than thymocytes to allow expansion of cells with tumorigenic potential in the thymus. The idea is regarded as the 'indirect mechanism' for tumor development. This paper reviews the indirect mechanism and genes affecting the development of thymic lymphomas that we have analyzed. One is the Bcl11b/Rit1 tumor suppressor gene and the other is Mtf-1 gene affecting tumor susceptibility.

Development of a mantle cell lymphoma in an ATM heterozygous woman after occupational exposure to ionising radiation and somatic mutation of the second allele.

Predisposition to lymphomagenesis is a well-known phenomenon of ataxia-telangiectasia, a recessive disorder caused by germline inactivation of ATM. ATM encodes a protein implicated in the repair of radiation induced double-strand breaks. Biallelic ATM inactivation was described also in sporadic lymphoid malignancies, supporting a role of ATM as a tumour suppressor gene. It is, however, still unclear whether ATM heterozygotes are at higher risk of tumours. We describe an ATM heterozygous patient, who developed a mantle cell lymphoma (MCL) after occupational exposure to ionising radiation and somatic mutation of the second ATM allele supporting the contention that heterozygous germline ATM alterations in combination with irradiation exposure predisposes to sporadic MCL.

Ultraviolet radiation induces phosphorylation and ubiquitin-mediated degradation of DeltaNp63alpha.

DeltaNp63alpha, a homologue of the tumor suppressor p53, acts as a transcriptional repressor with dominant negative effects towards p53. Additionally, DeltaNp63alpha is overexpressed in a number of squamous cell carcinomas, suggesting a potential role in oncogenesis. However, the mechanisms regulating p63 have yet to be elucidated. The goal of the current study was to determine the effect of various genotoxic stresses on DeltaNp63alpha posttranslational modification and stability in normal and transformed squamous epithelial cells. We found that DeltaNp63alpha protein levels decreased after ultraviolet radiation and paclitaxel treatment of both normal and transformed cells. After UV and paclitaxel treatment, DeltaNp63alpha phosphorylation was significantly modulated. Additionally, DeltaNp63alpha protein levels were regulated in a proteasome-dependent manner in control and UV treated cells with increased DeltaNp63alpha ubiquitination after UV treatment or proteasome inhibition. Our studies provide insight to a mechanism for DeltaNp63alpha regulation during normal cell proliferation and, in particular, after stress. Further, the inverse regulation of p53 and DeltaNp63alpha protein levels after cell stress through opposing regulation of proteasome-mediated degradation may allow for rapid transcriptional changes of specific target genes that are consistent with the roles of these family members in tumor suppression and cell growth.

UVB-induced mutations in human key gatekeeper genes governing signalling pathways and consequences for skin tumourigenesis.

The UVB component of the solar spectrum induces DNA lesions that, in the absence of error-free DNA repair, may give rise during DNA replication to mutations in caretaker and gatekeeper genes. The DNA repair genes are the best candidates for caretaker genes as exemplified by the human hereditary xeroderma pigmentosum (XP) syndrome. Cultured XP cells are hypermutable after UVB irradiation. This increased mutation frequency is also found in gatekeeper genes, which govern signalling pathways implicated in the control of cellular proliferation, differentiation and survival of human epidermal keratinocytes. We describe and discuss the role of mutated gatekeeper genes in five specific signalling pathways which have been implicated in skin carcinogenesis. The pathways we focus on in this review are: (i) P16(INK4A)-CDK4/6-RB; (ii) P14(ARF)-HDM2-P53; (iii) Sonic hedgehog (SHH)/GLI; (iv) WNT/beta-catenin; and (v) Bone Morphogenetic Protein (BMP)/SMAD. 70-80% of XP skin cancers exhibit one or several mutations in the P53, PTCH-1, SMO or CDKN2A genes, the type and frequency of mutated genes being different between squamous cell (SCCs) and basal cell carcinomas (BCCs). In XP cancers, the typically UVB-induced CC to TT tandem transitions represent approximately 60% of total mutations compared to 10-15% in skin tumours from DNA repair-proficient patients. Acquired activation of the pathways described herein can alter proliferation and differentiation of keratinocytes, allowing a damaged cell to replicate and give rise to mutated daughter cells, then eventually to the development of the carcinogenic process following clonal selection.

Profiling of differentially expressed genes induced by high linear energy transfer radiation in breast epithelial cells.

Methods to define patterns of gene expression have applications in a wide range of biological systems. Several molecular biological techniques are used to study expression patterns during the neoplastic progression of breast epithelial cells. In the present study, differential expression of human oncogenes/tumor suppressor genes in human breast epithelial cell lines irradiated with low doses of high linear energy transfer radiation and treated with estrogen was assessed with cDNA expression arrays. Transformed and tumorigenic cell lines were compared with the control cell line to identify differentially expressed genes during tumorigenic progression. Autoradiographic analysis showed that of the 190 genes analyzed, 49 genes showed a high level of altered expression, and 12 genes had minor differences in expression levels. Among these 49 genes, 17 genes were altered at all stages of transformation, 21 were altered only at the early stage, and the remaining 11 were at the late stage of transformation to the tumorigenic stage of progression. Among the 11 late stage-associated genes, seven genes were altered exclusively in the tumorigenic cell lines and in Tumor-T. Of the 17 all-stage genes, six were randomly selected, and we confirmed their altered expression by gene-specific semiquantitative reverse transcription polymerase chain reaction, followed by Northern blot analysis. The results showed that the mRNA expression patterns of all these genes were consistent with the expression pattern seen on the array. Among these six genes, five genes, including c-myc, puf, MNDA, c-yes, and Fra-1 showed upregulation, and the other gene, RBA/p48, showed downregulation in the transformed and tumorigenic cell lines compared with the control MCF-10F cell line. Investigation of these genes should help establish the molecular mechanisms of progression that are altered by radiation and estrogen treatment. A number of candidates reported here should be useful as biomarkers involved in breast carcinogenesis.

Down-regulation of telomerase activity in malignant lymphomas by radiation and chemotherapeutic agents.

The effects of radiation and cytotoxic agents on telomerase activity in lymphoma cells were analyzed by a polymerase chain reaction-based telomeric repeat amplification protocol coupled with an enzyme-linked immunosorbent assay, reverse transcriptase-polymerase chain reaction for the expression of the catalytic subunit of telomerase (hTERT), and by Western blot analysis in three lymphoma cell lines (Jurkat, Raji, CEM-6). Telomeric repeat amplification protocol-enzyme-linked immunosorbent assay demonstrated high basal levels of telomerase activity in all cell lines compared to normal and activated peripheral blood lymphocytes. A significant decrease in telomerase activity was observed in all cell lines after exposure to vincristine for 24 hours. The decrease in telomerase activity paralleled the decrease in cell viability in Jurkat and CEM-6 cells but not in Raji cells. Radiation exposure inhibited the telomerase activity of Jurkat and CEM-6 cells whereas Raji cells were unaffected. Cell cycle analysis demonstrated a significant G(2)/M arrest by cisplatin, VP-16, and vincristine. In contrast to the decline in telomerase activity, the level of hTERT RNA and protein increased. Furthermore, the induction of hTERT was preceded by increased expression of the cyclin-dependent kinase inhibitor, p27/Kip1 protein, and p53. These results indicate that telomerase activity is down-regulated by anti-neoplastic agents in lymphoma cells, however expression of hTERT may not be correlated with telomerase activity. We also show that p27/Kip1 may be involved in the G(2)/M growth arrest induced by anti-neoplastic agents.

UV-specific p53 and PTCH mutations in sporadic basal cell carcinoma of sun-exposed skin.

UVB irradiation is known to produce DNA damage at mutation hotspots in the p53 tumor suppressor gene, leading to the development of skin cancers. Mutations in the PTCH tumor suppressor gene, which is known to be responsible for the development of nevoid basal cell carcinoma syndrome, have also been identified in sporadic basal cell carcinomas (BCCs). We describe the case of an 80-year-old welder in whom 3 novel p53 mutations, as well as UV-specific PTCH mutations, were detected in two BCC samples from sun-exposed skin. The simultaneous presence of UV-specific p53 and PTCH mutations in the same BCC sample has not previously been reported.

Expression of the novel tumour suppressor p33(ING1)is independent of p53.

A recently cloned tumour suppressor candidate, p33ING1, has been shown in vitro to collaborate with p53 to execute growth arrest and apoptosis. However, it is unclear as to how the expression of ING1 is regulated in normal and stress conditions. Using a p53-knockout mouse model, we investigated if the expression of ING1 was dependent on p53. We found that there was no difference in ING1 mRNA and protein levels between p53+/+ and p53-/- murine organs. In addition, when normal human epithelial keratinocytes (NHEK) and a keratinocyte cell line, HaCaT, which lacks wild-type p53 function, were exposed to UVB irradiation, the expression levels of ING1 were elevated in both NHEK and HaCaT cells. It is interesting, however, that UVB irradiation did not induce ING1 expression in dermal fibroblasts isolated from p53+/+ and p53-/- mice. Based on our findings, we therefore conclude that the expression of ING1 is independent of p53 status. UV induction of ING1 in keratinocytes suggests that ING1 may play a role in cellular stress response and skin carcinogenesis.

Radiation-induced meningioma: a distinct molecular genetic pattern?

Radiation-induced meningiomas arise after low-dose irradiation treatment of certain medical conditions and are recognized as clinically separate from sporadic meningioma. These tumors are often aggressive or malignant, they are likely to be multiple, and they have a high recurrence rate following treatment compared with sporadic meningiomas. To understand the molecular mechanism by which radiation-induced meningioma (RIM) arise, we compared genetic changes in 7 RIM and 8 sporadic meningioma (SM) samples. The presence of mutations in the 17 exons of the neurofibromatosis type 2 (NF2) gene, which has been shown to be inactivated in sporadic meningiomas, was analyzed in RIM and SM using single-strand conformation polymorphism (SSCP) and DNA sequencing. In contrast to SM, which showed NF2 mutations in 50% of specimens, no mutations were found in RIM. In addition, Western blot analysis of schwannomin/merlin protein, the NF2 gene product, demonstrated protein levels comparable to normal brain in 4/4 RIM tumor samples analyzed. Loss of heterozygosity (LOH) of genomic regions, which were reported for SM, was also analyzed in all cases of RIM using 22 polymorphic DNA markers. Allele losses were found on chromosomes 1p (4/7), 9p (2/7), 19q (2/7), 22q (2/7), and 18q (1/7). From these observations we conclude that unlike sporadic meningiomas, NF2 gene inactivation and chromosome 22q deletions are far less frequent in RIM, and their role in meningioma development following low dose irradiation is less significant. Other chromosomal lesions, especially loss of 1p, possibly induced by irradiation, may be more important in the development of these tumors.

Biological basis of radiation sensitivity. Part 2: Cellular and molecular determinants of radiosensitivity.

Recent studies have elucidated some of the molecular and cellular mechanisms that determine the sensitivity or resistance to ionizing radiation. These findings ultimately may be useful in devising new strategies to improve the therapeutic ratio in cancer treatment. Despite the rapid advances in knowledge of cellular functions that affect radiosensitivity, we still cannot account for most of the clinically observed heterogeneity of normal tissue and tumor responses to radiotherapy, nor can we accurately predict which individual tumors will be controlled locally and which patients will develop more severe normal tissue damage after radiotherapy. However, several candidate genes for which deletion or loss of function mutations may be associated with altered cellular radiosensitivity (e.g., ATM, p53, BRCA1, BRCA2, DNA-PK) have been identified. Some of the differences in normal tissue sensitivity to radiation may stem from mutations with milder effects, heterozygosity, or polymorphisms of these genes. Finally, molecular mechanisms linking genetic instability, radiosensitivity, and predisposition to cancer are being unraveled.

BTG gene expression in the p53-dependent and -independent cellular response to DNA damage.

Exposure of mammalian cells to genotoxic agents evokes a complex cellular response. An ordered series of molecular events is necessary to sense DNA damage, transduce the signal, and ultimately delay the cell cycle or trigger apoptosis. Recently, we have shown that BTG2/TIS21 gene expression was induced in response to DNA damage through a p53-dependent pathway. This gene belongs to a newly identified family of structurally related genes whose other known human members are BTG1, BTG3, and Tob. To define the respective involvement of these four related genes in the cellular response to DNA damage, we studied their expression in human cell lines after a variety of genotoxic treatments. Our results demonstrated that were BTG1, BTG2/TIS21, and Tob genes the DNA damage--inducible genes. However, BTG2/TIS21 appeared to be the only p53-transcriptional target gene. We speculate that BTG proteins may play a coordinate role in a general transduction pathway that is induced in response to DNA damage. It has been previously described that recombinant BTG1 and BTG2/TIS21 can physically interact with PRMT1, an arginine methyl transferase, suggesting that BTG1 and BTG2/TIS21 induction may lead to posttranslational modifications of cellular proteins. In support of this hypothesis, we showed that the endogenous induction of BTG1 and BTG2 after genotoxic treatment was correlated with a modulation of protein methylation.