ARID1A , encoding a subunit of the SWI/SNF chromatin-remodelling complex, is the most frequently mutated epigenetic regulator across all human cancers. ARID1A and TP53 mutations are typically mutually exclusive. Therapeutic approaches that correlate with this genetic characteristic remain to be explored. Here, we show that HDAC6 activity is essential in ARID1A-mutated ovarian cancers. Inhibition of HDAC6 activity using a clinically applicable small molecule inhibitor significantly improved the survival of mice bearing ARID1A-mutated tumours. This correlated with the suppression of growth and dissemination of ARID1A-mutated, but not wildtype, tumours. The dependence on HDAC6 activity in ARID1A-mutated cells correlated with a direct transcriptional repression of HDAC6 by ARID1A. HDAC6 inhibition selectively promoted apoptosis of ARID1A-mutated cells. HDAC6 directly deacetylates Lys-120 of p53, a pro-apoptotic post-translational modification. Thus, ARID1A mutation inactivates p53’s apoptosis-promoting function by upregulating HDAC6. Together, these results indicate that pharmacological inhibition of HDAC6 is a therapeutic strategy for ARID1A-mutated cancers.

Precise regulation of DNA damage response is crucial for cellular survival after DNA damage, and its abrogation often results in genomic instability in cancer. Phosphorylated histone H2AX (γH2AX) forms nuclear foci at sites of DNA damage and facilitates DNA damage response and repair. MicroRNAs are short, non-protein-encoding RNA molecules, which post-transcriptionally regulate gene expression by repressing translation of and/or degrading mRNA. How microRNAs modulate DNA damage response is largely unknown. In this study, we developed a cell-based screening assay utilizing ionizing radiation-induced γH2AX foci formation in a human osteosarcoma cell line, U2OS, as the readout. By screening a library of human microRNA mimics, we identified several microRNAs that inhibited γH2AX foci formation. Among them, miR-138 directly targeted the histone H2AX 3′-UTR, reduced histone H2AX expression and induced chromosomal instability after DNA damage. Overexpression of miR-138 inhibited homologous recombination and enhanced cellular sensitivity to multiple DNA damaging agents (cisplatin, camptothecin, and ionizing radiation). Reintroduction of histone H2AX in miR-138 overexpressing cells attenuated miR-138-mediated sensitization to cisplatin and camptothecin. Our study suggests that miR-138 is an important regulator of genomic stability and a potential therapeutic agent to improve the efficacy of radiotherapy and chemotherapy with DNA damaging agents.

Small cell carcinoma of the ovary, hypercalcaemic type (SCCOHT) is a lethal and sometimes familial ovarian tumour of young women and children. We and others recently discovered that over 90% of SCCOHTs harbour inactivating mutations in the chromatin remodelling gene SMARCA4 with concomitant loss of its encoded protein SMARCA4 (BRG1), one of two mutually exclusive ATPases of the SWI/SNF chromatin remodelling complex. To determine the specificity of SMARCA4 loss for SCCOHT, we examined the expression of SMARCA4 by immunohistochemistry in more than 3000 primary gynaecological tumours. Among ovarian tumours, it was only absent in clear cell carcinoma (15 of 360, 4%). In the uterus, it was absent in endometrial stromal sarcomas (4 of 52, 8%) and high‐grade endometrioid carcinomas (2 of 338, 1%). Recent studies have shown that SMARCA2 (BRM), the other mutually exclusive ATPase of the SWI/SNF complex, is necessary for survival of tumour cells lacking SMARCA4. Therefore, we examined SMARCA2 expression and discovered that all SMARCA4‐negative SCCOHTs also lacked SMARCA2 protein by IHC, including the SCCOHT cell lines BIN67 and SCCOHT1. Among ovarian tumours, the SMARCA4/SMARCA2 dual loss phenotype appears completely specific for SCCOHT. SMARCA2 loss was not due to mutation but rather from an absence of mRNA expression, which was restored by treatment with the histone deacetylase inhibitor trichostatin A. Re‐expression of SMARCA4 or SMARCA2 inhibited the growth of BIN67 and SCCOHT1 cell lines. Our results indicate that SMARCA4 loss, either alone or with SMARCA2, is highly sensitive and specific for SCCOHT and that restoration of either SWI/SNF ATPase can inhibit the growth of SCCOHT cell lines. © 2015 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Melatonin as an adjuvant therapy for cancer led to substantial improvements in tumor remission, 1-year survival, and alleviation of radiochemotherapy-related side effects.

Cell survival after DNA damage relies on DNA repair, the abrogation of which causes genomic instability. The DNA repair protein RAD51 and the trans-lesion synthesis DNA polymerase REV1 are required for resistance to DNA interstrand crosslinking agents such as cisplatin. In this study, we show that overexpression of miR-96 in human cancer cells reduces the levels of RAD51 and REV1 and impacts the cellular response to agents that cause DNA damage. miR-96 directly targeted the coding region of RAD51 and the 3′-untranslated region of REV1. Overexpression of miR-96 decreased the efficiency of homologous recombination and enhanced sensitivity to the poly(ADP-ribose) polymerase (PARP) inhibitor AZD2281 in vitro and to cisplatin both in vitro and in vivo. Taken together, our findings indicate that miR-96 regulates DNA repair and chemosensitivity by repressing RAD51 and REV1. As a candidate therapeutic, miR-96 may improve chemotherapeutic efficacy by increasing the sensitivity of cancer cells to DNA damage.

Lantibiotics are a type of ribosomally synthesized and post‐translationally modified peptides (termed lanthipeptides) with often potent antimicrobial activity. Herein, we report the discovery of a new lantibiotic, lexapeptide, using the library expression analysis system (LEXAS) approach. Lexapeptide has rare structural modifications, including N‐terminal (N,N)‐dimethyl phenylalanine, C‐terminal (2‐aminovinyl)‐3‐methyl‐cysteine, and d‐Ala. The characteristic lanthionine moiety in lexapeptide is formed by three proteins (LxmK, LxmX, and LxmY), which are distinct from enzymes known to be involved in lanthipeptide biosynthesis. Furthermore, a novel F420H2‐dependent reductase (LxmJ) from the lexapeptide biosynthetic gene cluster (BGC) is identified to catalyze the reduction of dehydroalanine to install d‐Ala. Our findings suggest that lexapeptide is the founding member of a new class of lanthipeptides that we designate as class V. We also identified further class V lanthipeptide BGCs in actinomycetes and cyanobacteria genomes, implying that other class V lantibiotics await discovery.

Cutaneous malignant melanoma is a life-threatening skin cancer, and the incidence of melanoma has doubled in the last decade (1, 2). Melanoma metastasizes rapidly to other organs, and there is no effective treatment for metastatic melanoma. Even the most established adjuvant immunotherapy using interferon ␣ has encountered the resistance caused by the overexpression and activation of signal transducers and activators of transcription 5 (3-5). Patients with metastatic melanoma have a poor prognosis, with a 5-year survival of a mere 10% of patients (1, 6). Epidemiological studies strongly implicate ultraviolet (UV) exposure in early life as the main environmental factor for the development of malignant melanoma (6, 7). UV-induced mutation and/or aberrant expression of certain genes, including cdk6, p16INK4a , N-ras, and BRAF, have been known to mediate the pathogenesis of melanoma (8 -10).The novel ING tumor-suppressor family proteins (ING1-5) have been discovered during the past decade and are recognized as regulators of transcription, cell cycle checkpoints, DNA repair, and apoptosis (11). They are also reported to promote cellular senescence, inhibit angiogenesis, and function as nuclear phosphoinositide receptors (11-13). All these proteins share a highly conserved C-terminal plant homeodomain motif that mediates signal transduction, possibly by regulating chromatin remodeling, histone acetyltransferase/deacetylase activities, and phosphoinositide signaling (11, 12). The ING1 proteins were frequently down-regulated but less frequently mutated in human malignancies, including neuroblastomas, colon carcinoma, head and neck squamous cell carcinomas, breast, gastric, esophageal, lymphoid, lung, and brain tumors, whereas they were increased in melanoma, papillary thyroid carcinoma, and ductal breast carcinoma, concomitant with loss of nuclear localization (11, 14 -17). The ING4 protein was also frequently deleted and reduced in human breast cancer, head and neck squamous cell carcinomas, and gliomas (18 -20). Although most studies have focused on ING1, especially its splicing isoform ING1b, the multiple amino acid sequence alignment of human ING proteins revealed a few conserved domains other than plant homeodomain motifs, including nuclear localization signals and potential chromatin regulatory domains (21). These conserved domains suggest that the ING family proteins may share common biological functions. However, the exact functions of these domains remain to be elucidated.The ING3 gene, mapped to 7q31.3, consists of 12 exons and encodes a 46.8-kDa protein that modulates p53-mediated transcription, cell cycle control, and apoptosis (22). Gunduz et al. (23) showed that the expression of ING3 gene is reduced in human head and neck squamous cell carcinomas because of loss of heterozygosity. As a subunit of the NuA4 2 histone acetyltransferase multisubunit complex, ING3 protein is associated with p53 function and can reconstitute robust nucleosomal histone acetyltransferase activity in vitro by forming a recombinan...

Purpose:The novel tumor-suppressor ING3 has been shown to modulate transcription, cell cycle control, and apoptosis. Our previous study showed that ING3 promotes UV-induced apoptosis via the Fas/caspase-8^dependent pathway in melanoma cells. To investigate the putative role of ING3 in the development of melanoma, we examined the expression of ING3 in melanocytic lesions at different stages and analyzed the correlation between ING3 expression and clinicopathologic variables and patient survival. Experimental Design: Using tissue microarray and immunohistochemistry, we evaluated nuclear and cytoplasmic ING3 staining in 58 dysplastic nevi, 114 primary melanomas, and 50 metastatic melanomas. Results: Nuclear ING3 expression was remarkably reduced in malignant melanomas compared with dysplastic nevi (P < 0.001), which was significantly correlated with the increased ING3 level in cytoplasm (P < 0.05). Furthermore, the reduced nuclear ING3 expression was significantly correlated with a poorer disease-specific 5-year survival of patients with primary melanoma, especially for the high-risk melanomas (thickness z2.0 mm) with the survival rate reducing from 93% for patients with strong nuclear ING3 staining in their tumor biopsies to 44% for those with negative-to-moderate nuclear ING3 staining (P = 0.004). Strikingly, our multivariate Cox regression analysis revealed that reduced nuclear ING3 expression is an independent prognostic factor to predict patient outcome in primary melanomas (P = 0.038). Conclusions: Our data indicate that ING3 may be an important marker for human melanoma progression and prognosis as well as a potential therapeutic target.