Decreased expression of the candidate tumor suppressor gene ING1 is associated with poor prognosis in advanced neuroblastomas

ING1 has been identified as a novel candidate tumor suppressor gene using a genetic suppressor element (GSE) strategy. Ectopic expression of ING1 in mammalian cultured cells causes cell cycle arrest and apoptosis through a p53-dependent and/or p53-independent pathway. However, there has been no report on the prognostic significance of the ING1 expression level in human cancers, though the expression of the wild-type ING1 gene is significantly decreased in breast, lymphoid and gastric cancers as compared with their corresponding normal tissues. In order to explore the possible involvement of ING1 in tumorigenesis of neuroblastoma, we examined the expression levels of ING1 mRNA in 32 primary neuroblastomas by using a quantitative real-time PCR. ING1 mRNA was expressed independently of the disease stages. however, low levels of ING1 mRNA were significantly associated with a poor prognosis (log-rank test, p=0.017). Multivariate analysis showed that the expression level of ING1 was closely related to survival (p=0.020), even after controlling with age (p=0.008) or stage (p=0.025), while it was only marginally significant after controlling with TrkA expression (p=0.063). Mutation analysis revealed that there was no mutation or deletion of the ING1 gene except 1 silent mutation at codon 188 in primary neuroblastomas examined. Taken together, our results suggest for the first time that a decreased level of ING1 expression is a novel indicator of poor prognosis in advanced stages of neuroblastoma, and that ING1 may play a crucial role in genesis and progression of neuroblastoma.     

Expression and sequence analysis of candidates for the 1p36.31 tumor suppressor gene deleted in neuroblastomas

Neuroblastomas are characterized by 1p deletions, suggesting that a tumor suppressor gene (TSG) resides in this region. We have mapped the smallest region of deletion (SRD) to a 2 Mb region of 1p36.31 using microsatellite and single nucleotide polymorphisms. We have identified 23 genes in this region, and we have analysed these genes for mutations and RNA expression patterns to identify candidate TSGs. We sequenced the coding exons of these genes in 30 neuroblastoma cell lines. Although rare mutations were found in 10 of the 23 genes, none showed a pattern of genetic change consistent with homozygous inactivation. We examined the expression of these 23 genes in 20 neuroblastoma cell lines, and most showed readily detectable expression, and no correlation with 1p deletion. However, 7 genes showed uniformly low expression in the lines, and 2 genes (CHD5, RNF207) had virtually absent expression, consistent with the expected pattern for a TSG. Our mutation and expression analysis in neuroblastoma cell lines, combined with expression analysis in normal tissues, putative function and prior implication in neuroblastoma pathogenesis, suggests that the most promising TSG deleted from the 1p36 SRD is CHD5, but TNFRSF25, CAMTA1 and AJAP1 are also viable candidates.     

Expression of OVCA1, a candidate tumor suppressor, is reduced in tumors and inhibits growth of ovarian cancer cells.

Loss of all or part of one copy of chromosome 17p is very common in ovarian and breast tumors. OVCA1 is a candidate tumor suppressor gene mapping to a highly conserved region on chromosome 17p13.3 that shows frequent loss of heterozygosity in breast and ovarian carcinomas. Western blot analysis of extracts prepared from breast and ovarian carcinomas revealed reduced expression of OVCA1 compared with extracts from normal epithelial cells from these tissues. Subcellular localization studies indicate that OVCA1 is localized to punctate bodies scattered throughout the cell but is primarily clustered around the nucleus. Attempts to create cell lines that stably expressed OVCA1 from the cytomegalovirus promoter were generally unsuccessful in a variety of different cell lines. This reduction of colony formation was quantified in the ovarian cancer cell line A2780, where it was demonstrated that cells transfected with plasmids expressing OVCA1 had a 50-60% reduction in colony number as compared with appropriate controls, and only a few of these clones expressed OVCA1, albeit at low levels. The clones that expressed exogenous OVCA1 were found to have dramatically reduced rates of proliferation. Reduced growth rates correlated with an increased proportion of the cells in the G1 fraction of the cell cycle compared with the parental cell line and decreased levels of cyclin D1. The low levels of cyclin D1 appeared to be caused by an accelerated rate of cyclin D1 degradation. Overexpression of cyclin D1 was able to override OVCA1's suppression of clonal outgrowth. These results suggest that slight alterations in the level of OVCA1, such as would occur after reduction of chromosome 17p13.13 to hemizygosity, may result in cell cycle deregulation and promote tumorigenesis.     

Expression of TSLC1, a candidate tumor suppressor gene mapped to chromosome 11q23, is downregulated in unfavorable neuroblastoma without promoter hypermethylation

Although it has been well documented that loss of human chromosome 11q is frequently observed in primary neuroblastomas, the smallest region of overlap (SRO) has not yet been precisely identified. Previously, we performed array-comparative genomic hybridization (array-CGH) analysis for 236 primary neuroblastomas to search for genomic aberrations with high-resolution. In our study, we have identified the SRO of deletion (10-Mb or less) at 11q23. Within this region, there exists a TSLC1/IGSF4/CADM1 gene (Tumor suppressor in lung cancer 1/Immunoglobulin superfamily 4/Cell adhesion molecule 1), which has been identified as a putative tumor suppressor gene for lung and some other cancers. Consistent with previous observations, we have found that 35% of primary neuroblastomas harbor loss of heterozygosity (LOH) on TSLC1 locus. In contrast to other cancers, we could not detect the hypermethylation in its promoter region in primary neuroblastomas as well as neuroblastoma-derived cell lines. The clinicopathological analysis demonstrated that TSLC1 expression levels significantly correlate with stage, Shimada's pathological classification, MYCN amplification status, TrkA expression levels and DNA index in primary neuroblastomas. The immunohistochemical analysis showed that TSLC1 is remarkably reduced in unfavorable neuroblastomas. Furthermore, decreased expression levels of TSLC1 were significantly associated with a poor prognosis in 108 patients with neuroblastoma. Additionally, TSLC1 reduced cell proliferation in human neuroblastoma SH-SY5Y cells. Collectively, our present findings suggest that TSLC1 acts as a candidate tumor suppressor gene for neuroblastoma.     

Hint1 is a haplo-insufficient tumor suppressor in mice

The HINT1 protein, a member of the histidine triad (HIT) family, is highly conserved in diverse species and ubiquitously expressed in mammalian tissues. However, its precise function in mammalian cells is not known. As a result of its structural similarity to the tumor-suppressor protein FHIT, we used homozygous-deleted Hint1 mice to study its role in tumorigenesis. We discovered that after 2 to 3 years of age the spontaneous tumor incidence in Hint1 -/- mice was significantly greater than that in wild-type Hint1 +/+ mice (P < 0.05). Using a well-established mouse model of 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis we found a marked and significant (P < 0.05) increase in the incidence of mammary and ovarian tumors in both, Hint1 -/- and +/- mice versus +/+ mice. The Hint1 -/- and +/- mice had similar tumor incidence and similar tumor histologies. Therefore, deletion of Hint1 in mice enhances both spontaneous tumor development and susceptibility to tumor induction by DMBA. In addition, since the Hint1 +/- tumors retained expression of the unmutated wild-type allele, Hint1 is haplo-insufficient with respect to tumor suppression in this model system.     

TSLC1 is a tumor suppressor gene associated with metastasis in nasopharyngeal carcinoma

In up to 87% of nasopharyngeal carcinoma (NPC) clinical tumor specimens, there was either down-regulation or loss of TSLC1 gene expression. Using a tissue microarray and immunohistochemical staining, the frequency of down-regulated or loss of expression of TSLC1 in metastatic lymph node NPC was 83% and the frequency of loss of expression of TSLC1 was 35%, which was significantly higher than that in primary NPC (12%). To examine the possible growth-suppressive activity of TSLC1 in NPC, three NPC cell lines, HONE1, HNE1, and CNE2, were transfected with the wild-type TSLC1 gene cloned into the pCR3.1 expression vector; a reduction of colony formation ability was observed for all three cell lines. A tetracycline-inducible expression vector, pETE-Bsd, was also used to obtain stable transfectants of TSLC1. There was a dramatic difference between colony formation ability in the presence or absence of doxycycline when the gene is shut off or expressed, respectively, with the tetracycline-inducible system. Tumorigenicity assay results show that the activation of TSLC1 suppresses tumor formation in nude mice and functional inactivation of this gene is observed in all the tumors derived from tumorigenic transfectants. Further studies indicate that expression of TSLC1 inhibits HONE1 cell growth in vitro by arresting cells in G(0)-G(1) phase in normal culture conditions, whereas in the absence of serum, TSLC1 induced apoptosis. These findings suggest that TSLC1 is a tumor suppressor gene in NPC, which is significantly associated with lymph node metastases.     

High-level expression of angiogenic factors is associated with advanced tumor stage in human neuroblastomas.

Angiogenesis is essential for tumor growth and metastasis and depends on the production of angiogenic factors by tumor cells. Neuroblastoma (NB) is a common pediatric tumor of neural crest origin, which is biologically and clinically heterogeneous. Increased tumor vascular index correlates with poor outcome of NB. To determine which angiogenic factors contribute to NB angiogenesis and thereby support tumor progression, we examined the expression of eight angiogenic factors [vascular endothelial growth factor (VEGF), VEGF-B, VEGF-C, basic fibroblast growth factor, angiopoietin (Ang)-1, Ang-2, transforming growth factor alpha, and platelet-derived growth factor (PDGF)] by semiquantitative RT-PCR in 37 NB primary tumors and in 22 NB cell lines. We also analyzed the relationship between angiogenic factor expression and clinicopathological factors as well as patient survival. All eight angiogenic factors examined were expressed at various levels in NB cell lines and tumors, suggesting their involvement in NB angiogenesis. The expression levels of most angiogenic factors were correlated with each other, suggesting their synergy in regulating the angiogenic process. Significantly higher expression levels of VEGF, VEGF-B, VEGF-C, basic fibroblast growth factor, Ang-2, transforming growth factor alpha, and PDGF-A (P < 0.0001-0.026) were found in advanced-stage tumors (stages 3 and 4) compared with low-stage tumors (stages 1, 2, and 4S). Expression of PDGF-A was significantly associated with patient survival (P = 0.04). The redundancy in angiogenic factor expression suggests that inhibition of VEGF bioactivity alone might not be a sufficient approach for antiangiogenic therapy of human NB.     

抑癌基因PRDM1在肺癌组织中的表达

目的探讨抑癌基因PRDM1在肺癌组织中的表达情况及其意义。方法45例肺癌患者中,鳞状细胞癌20例、腺癌15例、小细胞肺癌10例。用免疫组织化学方法,研究肺癌石蜡包埋组织中PRDM1蛋白的表达情况;激光微切割技术捕捉冰冻肺癌组织中的肿瘤细胞,抽提RNA、采用逆转录聚合酶链式反应(RT-PCR)技术研究PRDM1基因表达;Western blot技术研究冰冻肺癌组织中PRDM1蛋白表达。结果(1)免疫组织化学结果表明鳞状细胞癌、腺癌、小细胞肺癌患者的PRDM1蛋白阳性率分别为90.0%(18/20)、13.3%(2/15)和0(0/10),统计学分析显示,PRDM1蛋白主要在鳞状细胞癌患者中表达(P<0.01)。(2)激光微切割技术联合RT-PCR证实,PRDM1基因特异表达于鳞状细胞癌患者中,腺癌和小细胞肺癌中未发现其基因表达。进一步研究发现,鳞状细胞肺癌患者中,PRDM1基因的DNA结合区表达缺陷。Western blot在鳞状细胞肺癌组织中检测出约70 000的异常PRDM1蛋白。结论PRDM1在鳞状细胞肺癌中优势表达,可作为肺癌诊断的新的肿瘤标志;鳞状细胞肺癌中PRDM1在转录和蛋白水平上均存在异常,失去了抑癌基因的正常功能,可能成为新的研究治疗靶点。     

Losses of the tumor suppressor BIN1 in breast carcinoma are frequent and reflect deficits in programmed cell death capacity

Oncogenic activation of MYC occurs often in breast carcinoma and is associated with poor prognosis. Loss or inactivation of mechanisms that restrain MYC may therefore be involved in tumor progression. In this study, we show that the MYC-interacting adaptor protein BIN1 is frequently missing in malignant breast cells and that this loss is functionally significant. BIN1 was expressed in normal and benign cells and tissues but was undetectable in 6/6 estrogen receptor-positive or estrogen receptor-negative carcinoma cell lines examined. Similarly, complete or partial losses of BIN1 were documented in 30/50 (60%) cases of malignant breast tissue analyzed by immuno-histochemistry or RT-PCR. Abnormalities in the organization of the BIN1 gene were apparent in only a minority of these cases, suggesting that most losses were due to epigenetic causes. Nevertheless, they were functionally significant because ectopic BIN1 induced programmed cell death in malignant cells lacking endogenous BIN1 but had no effect on the viability of benign cells. We propose that loss of BIN1 may contribute to breast cancer progression by eliminating a mechanism that restrains the ability of activated MYC to drive cell division inappropriately.     

The tumor suppressor gene LKB1 is associated with prognosis in human breast carcinoma.

PURPOSE: LKB1 (also called STK11) is a recently identified tumor suppressor gene in which its mutation can lead to Peutz-Jeghers syndrome, characterized by gastrointestinal polyps and cancers of different organ systems. Weak expression of this gene does occur at a certain frequency in sporadic breast cancer. This indicates that LKB1 gene may relate to the tumorigenesis of breast cancer. EXPERIMENTAL DESIGN: To investigate the function of the LKB1 gene in sporadic breast cancer, we reintroduced LKB1 into breast cancer cell lines which lack the LKB1 gene. Also, we examined the LKB1 protein expression in human breast cancer samples. RESULTS: We found that reintroducing LKB1 into breast cancer cell lines suppresses cell growth by G(1) cell cycle block. The LKB1-mediated G(1) cell cycle arrest is caused by up-regulation of the expression of p21(WAF1/CIP1) in breast cancer MDA-MB-435 cells. We also demonstrated that low LKB1 protein expression correlates with higher histological grade (P = 0.013), larger tumor size (P = 0.001), progesterone receptor status (P = 0.048), and presence of lymph node metastasis (P = 0.003). Furthermore, LKB1 low expression was associated with a higher relapse rate (P = 0.002) and a worse OS (P = 0.008). CONCLUSIONS: LKB1 plays a role in tumor suppressor function in human breast cancer. LKB1 expression may be a useful prognostic marker in human breast cancer.