Non-homologous end joining (NHEJ) is a major repair pathway for DNA double-strand breaks (DSBs) generated by ionizing radiation (IR) and anti-cancer drugs. Therefore, inhibiting the activity of ...proteins involved in this pathway is a promising way of sensitizing cancer cells to both radiotherapy and chemotherapy. In this study, we developed an assay for evaluating NHEJ activity against DSBs in chromosomal DNA in human cells to identify the chromatin modification/remodeling proteins involved in NHEJ. We showed that ablating the activity of the homologous histone acetyltransferases, CBP and p300, using inhibitors or small interfering RNAs-suppressed NHEJ. Ablation of CBP or p300 impaired IR-induced DSB repair and sensitized lung cancer cells to IR and the anti-cancer drug, etoposide, which induces DSBs that are repaired by NHEJ. The CBP/p300 proteins were recruited to sites of DSBs and their ablation suppressed acetylation of lysine 18 within histone H3, and lysines 5, 8, 12, and 16 within histone H4, at the DSB sites. This then suppressed the recruitment of KU70 and KU80, both key proteins for NHEJ, to the DSB sites. Ablation of CBP/p300 also impaired the recruitment of BRM, a catalytic subunit of the SWI/SNF complex involved in chromatin remodeling at DSB sites. These results indicate that CBP and p300 function as histone H3 and H4 acetyltransferases at DSB sites in NHEJ and facilitate chromatin relaxation. Therefore, inhibition CBP and p300 activity may sensitize cancer cells to radiotherapy and chemotherapy.
Ovarian cancer is the most common cause of death from gynecological cancer. Understanding the biology of this disease, particularly how tumor-associated lymphocytes and fibroblasts contribute to the ...progression and metastasis of the tumor, has been impeded by the lack of a suitable tumor xenograft model. We report a simple and reproducible system in which the tumor and tumor stroma are successfully engrafted into NOD-scid IL2Rγ(null) (NSG) mice. This is achieved by injecting tumor cell aggregates derived from fresh ovarian tumor biopsy tissues (including tumor cells, and tumor-associated lymphocytes and fibroblasts) i.p. into NSG mice. Tumor progression in these mice closely parallels many of the events that are observed in ovarian cancer patients. Tumors establish in the omentum, ovaries, liver, spleen, uterus, and pancreas. Tumor growth is initially very slow and progressive within the peritoneal cavity with an ultimate development of tumor ascites, spontaneous metastasis to the lung, increasing serum and ascites levels of CA125, and the retention of tumor-associated human fibroblasts and lymphocytes that remain functional and responsive to cytokines for prolonged periods. With this model one will be able to determine how fibroblasts and lymphocytes within the tumor microenvironment may contribute to tumor growth and metastasis, and will make it possible to evaluate the efficacy of therapies that are designed to target these cells in the tumor stroma.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The introduction of new therapies against particular genetic mutations in non-small-cell lung cancer is a promising avenue for improving patient survival, but the target population is small. There is ...a need to discover new potential actionable genetic lesions, to which end, non-conventional cancer pathways, such as RNA editing, are worth exploring. Herein we show that the adenosine-to-inosine editing enzyme ADAR1 undergoes gene amplification in non-small cancer cell lines and primary tumors in association with higher levels of the corresponding mRNA and protein. From a growth and invasion standpoint, the depletion of ADAR1 expression in amplified cells reduces their tumorigenic potential in cell culture and mouse models, whereas its overexpression has the opposite effects. From a functional perspective, ADAR1 overexpression enhances the editing frequencies of target transcripts such as NEIL1 and miR-381. In the clinical setting, patients with early-stage lung cancer, but harboring ADAR1 gene amplification, have poor outcomes. Overall, our results indicate a role for ADAR1 as a lung cancer oncogene undergoing gene amplification-associated activation that affects downstream RNA editing patterns and patient prognosis.
Germline LKB1 mutations cause Peutz-Jeghers syndrome, a hereditary disorder that predisposes to gastrointestinal hamartomatous polyposis and several types of malignant tumors. Somatic LKB1 ...alterations are rare in sporadic cancers, however, a few reports showed the presence of somatic alterations in a considerable fraction of lung cancers. To determine the prevalence and the specificity of LKB1 alterations in lung cancers, we examined a large number of lung cancer cell lines and lung adenocarcinoma (AdC) specimens for the alterations. LKB1 genetic alterations were frequently detected in the cell lines (21/70, 30%), especially in non-small cell lung cancers (NSCLCs) (20/51, 39%), and were significantly more frequent in cell lines with KRAS mutations. Point mutations were detected only in AdCs and large cell carcinomas, whereas homozygous deletions were detected in all histological types of lung cancer. Among lung AdC specimens, LKB1 mutations were found in seven (8%) of 91 male smokers but in none of 64 females and/or nonsmokers, and were significantly more frequent in poorly differentiated tumors. The difference in the frequency of LKB1 alterations between cell lines and tumor specimens was likely to be owing to masking of deletions by the contamination of noncancerous cells in the tumor specimens. These results indicate that somatic LKB1 genetic alterations preferentially occur in a subset of poorly differentiated lung AdCs that appear to correlate with smoking males.
LKB1/STK11 is a tumor suppressor gene responsible for Peutz-Jeghers syndrome, an inherited cancer disorder associated with genome instability. The LKB1 protein functions in the regulation of cell ...proliferation, polarization and differentiation. Here, we suggest a role of LKB1 in non-homologous end joining (NHEJ), a major DNA double-strand break (DSB) repair pathway. LKB1 localized to DNA ends upon the generation of micro-irradiation and I-SceI endonuclease-induced DSBs. LKB1 inactivation either by RNA interference or by kinase-dead mutation compromised NHEJ-mediated DNA repair by suppressing the accumulation of BRM, a catalytic subunit of the SWI/SNF complex, at DSB sites, which promotes the recruitment of an essential NHEJ factor, KU70. AMPK2, a major substrate of LKB1 and a histone H2B kinase, was recruited to DSBs in an LKB1-dependent manner. AMPK2 depletion and a mutation of H2B that disrupted the AMPK2 phoshorylation site impaired KU70 and BRM recruitment to DSB sites. LKB1 depletion induced the formation of chromosome breaks and radials. These results suggest that LKB1-AMPK signaling controls NHEJ and contributes to genome stability.
8-Hydroxyguanine (oh8G) is a major base lesion produced by reactive oxygen species. oh8G in DNA causes G:C to T:A transversions and, thus, could be responsible for mutations that lead to ...carcinogenesis. A human DNA glycosylase/AP lyase encoded by the OGG1 gene has an activity to remove directly oh8G from DNA, and suppresses the mutagenic effect of oh8G. OGG1 protein has a helix-hairpin-helix-GPD motif as a domain for both DNA binding and catalysis, a nuclear localization signal, and a mitochondria targeting signal. Among multiple OGG1 isoforms, OGG1-type la is expressed predominantly in human cells and repairs chromosomal DNA in the nucleus. Inactivation of the OGG1 gene in yeast and mice leads to elevated spontaneous mutation frequency in the cells. The human OGG1 gene maps to chromosome 3p26.2, and allelic deletions of this region occur frequently in a variety of human cancers. Moreover, the OGG1 gene is somatically mutated in some cancer cells and is highly polymorphic among human populations. Repair activities of some mutated and polymorphic OGG1 proteins are lower than those of wild-type OGG1-type la-Ser326 protein and, thus, could be involved in human carcinogenesis.
Loss of heterozygosity (LOH) is a major genetic event causing inactivation of tumor suppressor genes in human carcinogenesis. To elucidate chromosomal mechanisms causing LOH, 201 LOHs in 10 cases of ...human lung cancer, which were detected by a genome-wide single nucleotide polymorphism array analysis, were investigated for responsible chromosome alterations by integrating information on breakpoints for DNA copy number changes obtained by array-comparative genome hybridization and on numerical and structural chromosomal alterations obtained by spectral karyotyping. The majority (80%) of LOHs were partial chromosome LOHs caused by structural chromosomal alterations, while the remaining (20%) were whole chromosome LOHs caused by whole chromosome deletions. Unbalanced translocation was defined as the most frequent alteration, and it accounted for 30% of all LOHs. Three other structural alterations-interstitial deletion (19%), mitotic recombination (9%) and gene conversion (6%)-also contributed to the occurrence of LOH, while terminal deletion contributed to only a small subset (1%). Since unbalanced translocation is a common chromosomal alteration in lung cancer cells, the results in the present study strongly indicate that a considerable fraction of LOHs detected in lung cancer cells are caused by unbalanced translocation.
ABSTRACT
Native Hawaiians/Pacific Islanders experience a high prevalence of overweight/obesity. The Diabetes Prevention Program Lifestyle Intervention (DPP-LI) was translated into a 3-month ...community-based intervention to benefit these populations. The weight loss and other clinical and behavioral outcomes of the translated DPP-LI and the socio-demographic, behavioral, and biological factors associated with the weight loss were examined. A total of 239 Native Hawaiian/Pacific Islander adults completed the translated DPP-LI through four community-based organizations (CBOs). Changes from pre- to post-intervention assessments in weight, blood pressure, physical functioning, exercise frequency, and fat in diet were measured. Significant improvements on all variables were found, with differences observed across the four CBOs. CBOs with predominately Native Hawaiian and ethnically homogenous intervention groups had greater weight loss. General linear modeling indicated that larger baseline weight and CBO predicted weight loss. The translated DPP-LI can be effective for Native Hawaiians/Pacific Islanders, especially when socio-cultural, socio-economic, and CBO-related contextual factors are taken into account.
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