SWI/SNF染色质重塑在肿瘤中的研究进展

染色质重塑复合体SWI/SNF亚基基因在肿瘤中突变率高达20%,突变造成编码蛋白失活及整个复合体功能异常,导致肿瘤发生。目前SWI/SNF抑制肿瘤的已知机制主要包括其与Polycomb复合体间的表观拮抗及与c-Myc及PIK3CA等原癌基因信号通路协同作用等。     

Regulation of Mec1 kinase activity by the SWI/SNF chromatin remodeling complex

ATP-dependent chromatin remodeling complexes alter chromatin structure through interactions with chromatin substrates such as DNA, histones, and nucleosomes. However, whether chromatin remodeling complexes have the ability to regulate nonchromatin substrates remains unclear. Saccharomyces cerevisiae checkpoint kinase Mec1 (ATR in mammals) is an essential master regulator of genomic integrity. Here we found that the SWI/SNF chromatin remodeling complex is capable of regulating Mec1 kinase activity. In vivo, Mec1 activity is reduced by the deletion of Snf2, the core ATPase subunit of the SWI/SNF complex. SWI/SNF interacts with Mec1, and cross-linking studies revealed that the Snf2 ATPase is the main interaction partner for Mec1. In vitro, SWI/SNF can activate Mec1 kinase activity in the absence of chromatin or known activators such as Dpb11. The subunit requirement of SWI/SNF-mediated Mec1 regulation differs from that of SWI/SNF-mediated chromatin remodeling. Functionally, SWI/SNF-mediated Mec1 regulation specifically occurs in S phase of the cell cycle. Together, these findings identify a novel regulator of Mec1 kinase activity and suggest that ATP-dependent chromatin remodeling complexes can regulate nonchromatin substrates such as a checkpoint kinase.     

The SWI/SNF chromatin remodeling complexes BAF and PBAF differentially regulate epigenetic transitions in exhausted CD8+ T cells

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Frequent loss of the expression of multiple subunits of the SWI/SNF complex in large cell carcinoma and pleomorphic carcinoma of the lung

The switch/sucrose non‐fermenting (SWI/SNF) complex has recently emerged as a novel tumor suppressor in various human cancers. In the present study, we analyzed the expression of multiple SWI/SNF subunits in primary non‐small cell lung cancer (NSCLC). A total of 133 NSCLC, consisting of 25 squamous cell carcinomas (SCC), 70 adenocarcinomas (AD), 16 large cell carcinomas (LC), and 22 pleomorphic carcinomas (PL), were immunohistochemically examined for the expression of BRG1, BRM, BAF47, ARID1A, and ARID1B. The frequency at which reductions in the expression of BRG1 were observed was significantly higher in the LC‐PL group (13/38, 34.2%) than in the SCC‐AD group (7/95, 7.4%). Similarly, the frequency at which reductions in the expression of BRM were observed was significantly higher in the LC‐PL group (17/38, 44.7%) than in the SCC‐AD group (14/95, 14.7%). The loss of the expression of ARID1A, ARID1B, and BAF47 was observed only in a fraction of NSCLC cases. Furthermore, the frequency at which the concurrent loss of multiple subunits of the SWI/SNF complex was observed was significantly higher in the LC‐PL group (10/38, 26.3%) than in the SCC‐AD group (8/95, 8.4%). Collectively, these results indicate that the loss of the SWI/SNF complex was related to dedifferentiation in NSCLC.     

p53 transcriptional pathways in breast cancer: the good,the bad and the complex

A p53 network immunohistochemically‐based signature to discriminate between good and poor prognosis breast cancer would have clinical relevance, given the key role of p53 in malignancy and response to therapy. Utilizing a five‐protein signature of p53/mdm2/mdm4/bcl2/p21 discriminates good‐prognosis and poor‐prognosis patient groups, based on the functionality of the p53 network. However, the relationship of this five‐protein signature to p53 mutation, the wide range of breast cancer therapies now in use and the over‐70 age group remain uncertain. Nonetheless, confirmation of the signature in two independent series suggests that this approach should be considered in further case series and in the context of clinical trials. Copyright © 2009 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Overexpression of Rsf-1 correlates with pathological type,p53 status and survival in primary breast cancer

Aim: The incidence of breast cancer in developing countries still increasing, to identify novel molecular markers associated with carcinogenesis and prognosis of breast cancer still being implemented. The largest subunit of Remodeling and spacing factor (RSF), Rsf-1, mediates ATPase-dependent chromatin remodeling. Its oncogenic properties have been demonstrated in certain carcinomas. The aim of this study was to examine the prognostic value of Rsf-1 in patients with primary breast carcinoma. Methods: A total of 537 patients with primary breast cancer, and 54 with benign breast hyperplasia, were performed resection surgery in the same period were enrolled. Rsf-1 immunoexpression was retrospectively assessed by immunohistochemistry (IHC). As well as, it relationship with clinicopathological factors and patient survival (LRFS, DFS and OS) was investigated. Results: Compared with benign breast hyperplasia tissues, higher percentage of Rsf-1 positive expression was detected in malignant breast carcinomas. Based on IHC staining extent × intensity scores and ROC analysis, 278 of 526 cancers (52.9%) had high-expression (cut-off values 2.5) of Rsf-1, which correlated significantly to pathologic subtypes of breast cancer (DCIS vs. IDC, P < 0.001; ILC vs. IDC, P = 0.036), bigger tumor size (P = 0.030), higher TNM stage (P = 0.044), and p53-positive expression. In addition, there was a trend that high-expression of Rsf-1 associated with younger age (P = 0.053). We further prove that combined positive-expression of Rsf-1 and p53 (Rsf-1 (+)/p53 (+)) was correlated with the bigger tumor size (P = 0.018), and higher TNM stage (P = 0.024). Kaplan-Meier survival analysis showed that Rsf-1 high-expression and combined positive-expression of Rsf-1 and p53 (Rsf-1 (+)/p53 (+)) exhibited a significant correlation with poor overall survival of patients with primary breast cancer, and no association has been identified in relation to LRFS or DFS. Especially, Univariate and multivariate survival analysis demonstrated Rsf-1 expression is an independent prognostic parameter for the overall survival of patients with breast cancer. Conclusions: High-expression of Rsf-1 is associated with pathologic subtypes of breast cancer, aggressive phenotype, p53 positive and poor clinical outcome, which confers tumor aggressiveness through chromatin remodeling, and targeting Rsf-1 gene and the pathway it related may provide new therapeutic avenues for treating breast cancer.     

凋亡调节蛋白Bcl-2、p53和Caspase-3在乳腺癌组织中的表达及其相互关系

目的通过观察人乳腺癌组织中凋亡调节蛋白p53、bcl-2和caspase-3表达,探讨bcl-2、p53和caspase-3在乳腺癌发生、发展过程中的作用及其相互关系,为乳腺癌的生物治疗提供实验依据。方法收集手术切除的人乳腺癌组织和癌旁相对正常乳腺组织,用免疫组织化学方法和图像分析技术对21例乳腺癌标本进行检测。结果乳腺癌组织中bcl-2蛋白阳性表达率(52.4%,11/21)明显高于相对正常乳腺组织(19.0%,4/21);乳腺癌组织中p53蛋白阳性表达率(57.1%,12/21)也明显高于相对正常乳腺组织(0%);而乳腺癌组织中caspase-3蛋白阳性表达率(38.0%,8/21)明显低于相对正常乳腺组织(76.1%,16/21)。结论p53、bcl-2和caspase-3蛋白在乳腺癌发生、发展过程中发挥着既独立又协同的作用。     

MDM4 is a rational target for treating breast cancers with mutant p53

Mutation of the key tumour suppressor p53 defines a transition in the progression towards aggressive and metastatic breast cancer (BC) with the poorest outcome. Specifically, the p53 mutation frequency exceeds 50% in triple‐negative BC. Key regulators of mutant p53 that facilitate its oncogenic functions are potential therapeutic targets. We report here that the MDM4 protein is frequently abundant in the context of mutant p53 in basal‐like BC samples. Importantly, we show that MDM4 plays a critical role in the proliferation of these BC cells. We demonstrate that conditional knockdown (KD) of MDM4 provokes growth inhibition across a range of BC subtypes with mutant p53, including luminal, Her2⁺ and triple‐negative BCs. In vivo, MDM4 was shown to be crucial for the establishment and progression of tumours. This growth inhibition was mediated, at least in part, by the cell cycle inhibitor p27. Depletion of p27 together with MDM4 KD led to recovery of the proliferative capacity of cells that were growth‐inhibited by MDM4 KD alone. Consistently, we identified low levels of p27 expression in basal‐like tumours corresponding to high levels of MDM4 and p53. This predicts a signature for a subset of tumours that may be amenable to therapies targeted towards MDM4 and mutant p53. The therapeutic potential of MDM4 as a target in BC with mutant p53 was shown in vitro by use of a small‐molecule inhibitor. Overall, our study supports MDM4 as a novel therapeutic target for BC expressing mutant p53. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Xanthatin,a novel potent inhibitor of VEGFR2 signaling,inhibits angiogenesis and tumor growth in breast cancer cells

Anti-angiogenesis targeting vascular endothelial growth factor receptor 2 (VEGFR2) has emerged as an important tool for cancer treatment. In this study, we described a novel VEGFR2 inhibitor, xanthatin, which inhibits tumor angiogenesis and growth. The biochemical profiles of xanthatin were investigated using kinase assay, migration assay, tube formation, Matrigel plug assay, western blot, immunofluorescence and human tumor xenograft model. Xanthatin significantly inhibited growth, migration and tube formation of human umbilical vascular endothelial cell as well as inhibited vascular endothelial growth factor (VEGF)-stimulated angiogenesis. In addition, it inhibited VEGF-induced phosphorylation of VEGFR2 and its downstream signaling regulator. Moreover, xanthatin directly inhibit proliferation of breast cancer cells MDA-MB-231. Oral administration of xanthatin could markedly inhibit human tumor xenograft growth and decreased microvessel densities (MVD) in tumor sections. Taken together, these preclinical evaluations suggest that xanthatin inhibits angiogenesis and may be a promising anticancer drug candidate.     

Expression of p53 protein has no independent prognostic value in breast cancer

A series of 392 female breast carcinomas was analysed immunohistochemically for expression of p53 protein with special emphasis on the role of p53 as an independent prognostic factor. Altogether, 54·8 per cent of the carcinomas expressed p53 protein, with the mean [standard error (SE)] fraction of positive nuclei being 17·1 per cent (1·2 per cent). Expression of p53 protein was independent of tumour metastasis at diagnosis, axillary lymph node status, tumour diameter, histological type, tubule formation, proportion of intraductal growth, margin formation, necrosis, DNA ploidy, and S-phase fraction. A high fraction of p53-positive nuclei was significantly related to patient age under 70 years, high grade, severe nuclear pleomorphism, dense infiltration of tumour by lymphocytes, high mitotic index, and high apoptotic index (for all, P<0·05). Impaired survival probability in the entire cohort (P=0·05) and in the axillary lymph node-positive (ANP) tumours (P=0·015) was associated with a fraction of p53-positive nuclei less than 25 per cent, while in the axillary lymph node-negative (ANN) tumours, expression of p53 had no prognostic value. In multivariate analysis, independent prognostic predictors included axillary lymph node status, tumour diameter, and mitotic index. In the ANN tumours, tumour diameter, fraction of p53-positive nuclei, and tumour grade were independent prognostic factors, whereas in the ANP tumours, diameter and mitotic index were the two independent prognostic factors. The results suggest that abnormal expression of p53 protein is only a weak independent prognostic factor in female breast cancer.     

bcl-2、p53表达与乳腺癌预后的关系

目的：探讨ｂｃｌ２ 、ｐ５３ 表达与乳腺癌预后的关系。方法：应用免疫组化ＬＳＡＢ法检测６４ 例乳腺癌及３０ 例乳腺良性病变的表达。分析ｂｃｌ２、ｐ５３ 与乳腺癌组织学分级、腋淋巴结转移、复发和预后的关系。结果：ｂｃｌ２ 与ｐ５３ 表达之间差异有显著性,呈负相关（ Ｐ＜ ０－０５） 。ｂｃｌ２ 和ｐ５３ 表达与组织学分级有关（ Ｐ＜ ０－０５） ,ｂｃｌ２ 表达随分级增加阳性率降低,ｐ５３ 则相反。ｐ５３ 表达与腋淋巴结转移有关（ Ｐ＜ ０－０５） 。ｂｃｌ２ 表达与腋淋巴结转移无关（ Ｐ＞ ０－０５） 。ｐ５３ 表达复发组明显高于无复发组（ Ｐ＜０－０５）;ｂｃｌ２ 表达与有无复发无关（Ｐ＞０－０５）。ｐ５３ 表达阳性率≤５ 年生存组明显高于＞ ５ 年生存组,呈负相关（ Ｐ＜ ０－０５）;ｂｃｌ２ 表达与生存期无关（Ｐ＞ ０－０５） 。结论：ｂｃｌ２ 表达与预后无关,其阳性表达可反映肿瘤属分化较好或属早期阶段。ｐ５３ 可单独作为预后指标;ｐ５３ 表达与预后呈负相关。     

p53 expression in CMV-infected cells: association with the alternative expression of the p53 transactivated genes p21/WAF1 and MDM2

The p53 tumour suppressor gene is a cell cycle regulator, able to induce cell cycle arrest to allow DNA repair or apoptosis. The molecular mechanisms underlying p53 action imply transactivation of p53 dependent genes such as WAF1 (for wild type p53 associated fragment 1) and the murine double minute (MDM2) gene. In some cases, inactivation of the p53 gene results from p53 gene mutations leading to p53 protein accumulation, but in others it may results from mechanisms other than mutation, such as interaction with viral or cellular proteins. The expression of p53 protein and p53 transactivated gene proteins p21/WAF1 and MDM2, combined with in situ detection of apoptosis, was studied in specimens of CMV-infected patients as an in vivo model of p53 alteration not due to point mutation. p53 positivity was found in CMV + cells in different tissues, in cells with typical inclusion bodies, and in in situ hybridization and immunohistochemistry CMV + cells without inclusions (hidden infection). Although this p53 reactivity was accompanied by the expression of MDM2 and p21/WAF1 proteins, the patterns of MDM2 and p21/WAF1 protein expression were mutually exclusive, and were associated with the presence or absence of inclusion bodies. Nuclei bearing inclusion bodies were usually MDM2 +, p21/WAF1?, while hidden infected cells were usually MDM2?, p21/WAF1 +. Apoptosis was not detected in any tissue section from CMV-infected patients. Two alternative patterns were found in CMV-infected tissues: p53 +, p21/WAF1 +, MDM2?, or p53 +, p21/WAF1?, MDM2 + protein expression. These may represent examples of p53 dependent alternative effects in the course of CMV infection. Early stages are represented by CMV + cells without inclusion bodies, which display p53 and p21/WAF1 expression, suggesting that p53 could be acting as a growth suppressor protein. Late CMV infection is represented by cells harbouring inclusion bodies. These cells showed a p53 +, p21/WAF1?, MDM2 + profile, consistent with MDM2 mediated p53 inactivation. The absence of p21/WAF1 expression and lack of apoptosis suggest that the p53 protein expressed by MDM2 + cells could be functionally inactivated in CMV-infected cells with inclusion bodies. Previous studies have suggested that p53 inactivation by MDM2 over-expression occurs in sarcomas and lymphomas. Our observations seem to indicate that this mechanism of MDM2 mediated p53 inactivation may play a role in the late phase of CMV infection.