E-cadherin as a tumor (invasion) suppressor gene

Diffuse-type gastric carcinomas show diminished cell-cell adhesion. A recent paper⁽¹⁾ reports that 50% of these carcinomas contain mutations in the E-cadherin gene, resulting in the destruction of the calcium-binding sites of E-cadherin, and providing strong in vivo evidence that alterations in E-cadherin play a major role in the development of this particular type of cancer and the short survival of the patients.     

Uncovering a tumor suppressor for triple-negative breast cancers

"Triple-negative" breast cancers are aggressive malignancies that respond poorly to treatments. Now Sun et al. (2011) find that the activity of the protein tyrosine phosphatase PTPN12 is lost in a large percentage of this breast cancer subtype, offering molecular drivers and possible therapeutic targets for this heterogeneous and intractable cancer.     

Functional classification analysis of somatically mutated genes in human breast and colorectal cancers

A recent study published by Sjoblom and colleagues [T. Sjoblom, S. Jones, L.D. Wood, D.W. Parsons, J. Lin, T.D. Barber, D. Mandelker, R.J. Leary, J. Ptak, N. Silliman, S. Szabo, P. Buckhaults, C. Farrell, P. Meeh, S.D. Markowitz, J. Willis, D. Dawson, J.K. Willson, A.F. Gazdar, J. Hartigan, L. Wu, C. Liu, G. Parmigiani, B.H. Park, K.E. Bachman, N. Papadopoulos, B. Vogelstein, K.W. Kinzler, V.E. Velculescu, The consensus coding sequences of human breast and colorectal cancers. Science 314 (2006) 268-274.] performed comprehensive sequencing of 13,023 human genes and identified mutations in genes specific to breast and colorectal tumors, providing insight into organ-specific tumor biology. Here we present a systematic analysis of the functional classifications of Sjoblom's “CAN” genes, a subset of these validated mutant genes, that identifies novel organ-specific biological themes and molecular pathways associated with disease-specific etiology. This analysis links four somatically mutated genes associated with diverse oncological types to colorectal and breast cancers through established TGF-β1-regulated interactions, revealing mechanistic differences in these cancers and providing potential diagnostic and therapeutic targets.     

Vascular invasion in human breast cancer is correlated to T-->786C polymorphism of NOS3 gene.

BACKGROUND: Nitric oxide (NO) is a free radical known to be a major regulator of vascular tonus, to inhibit cell proliferation, induce apoptosis, and be a mediator of macrophage cytostatic and cytotoxic effects. Recently, NO synthesis has been reported to be elevated in different cancers and is expected to promote metastasis by maintaining a vasodilator tone in blood vessels in and around the tumour. Two different common genetic polymorphisms were found on endothelial NO synthase (NOS3) gene: Glu298Asp on exon 7 and T-->786C in the promoter region. PURPOSE: To evaluate the impact of the NOS3 polymorphisms on vascular invasion and metastasis in breast cancer patients. DESIGN: Two NOS3 gene polymorphisms (Glu298Asp and T-->786C) were genotyped in 71 patients operated for breast cancer and followed for 6-30 months (median 21). A control population of 91 age and sex matched tumour-free subjects was also genotyped for the same polymorphisms. RESULTS: The distribution of both polymorphisms was not different between cases and controls. In patients without vascular invasion, T allele frequency was significantly lower than in patients with vascular invasion (p=0.033). At the end of the follow-up, T allele frequency was found to be less frequent in the metastasis free group than normal population (0.51 vs 0.64; p=0.047). CONCLUSION: Our results suggest that T allele reduction at the NOS3 promoter region may reduce vascular invasion in breast cancer and consequently reduce metastatic spread and be a favorable prognostic factor. These results need further validation in larger studies.     

Alterations in tumour suppressor gene p53 in human gliomas from Indian patients

Alterations in the tumour suppressorp53 gene are among the most common defects seen in a variety of human cancers. In order to study the significance of thep53 gene in the genesis and development of human glioma from Indian patients, we checked 44 untreated primary gliomas for mutations in exons 5–9 of thep53 gene by PCR-SSCP and DNA sequencing. Sequencing analysis revealed six missense mutations. The incidence of p53 mutations was 13⋅6% (6 of 44). All the six mutations were found to be located in the central core domain of p53, which carries the sequence-specific DNA-binding domain. These results suggest a rather low incidence but a definite involvement of p53 mutations in the gliomas of Indian patients.     

Synergistic chromatin repression of the tumor suppressor gene RARB in human prostate cancers

DNA methylation and polycomb proteins are well-known mediators of epigenetic silencing in mammalian cells. Usually described as mutually exclusive, this statement is today controversial and recent in vitro studies suggest the co-existence of both repressor systems. We addressed this issue in the study of Retinoic Acid Receptor β (RARβ), a tumor suppressor gene frequently silenced in prostate cancer. We found that the RARβ promoter is hypermethylated in all studied prostate tumors and methylation levels are positively correlated with H3K27me3 enrichments. Thus, by using bisulfite conversion and pyrosequencing of immunoprecipitated H3K27me3 chromatin, we demonstrated that DNA methylation and polycomb repression co-exist in vivo at this locus. We found this repressive association in 6/6 patient tumor samples of different Gleason score, suggesting a strong interplay of DNA methylation and EZH2 to silence RARβ during prostate tumorigenesis.     

Synergistic chromatin repression of the tumor suppressor gene RARB in human prostate cancers

DNA methylation and polycomb proteins are well-known mediators of epigenetic silencing in mammalian cells. Usually described as mutually exclusive, this statement is today controversial and recent in vitro studies suggest the co-existence of both repressor systems. We addressed this issue in the study of Retinoic Acid Receptor β (RARβ), a tumor suppressor gene frequently silenced in prostate cancer. We found that the RARβ promoter is hypermethylated in all studied prostate tumors and methylation levels are positively correlated with H3K27me3 enrichments. Thus, by using bisulfite conversion and pyrosequencing of immunoprecipitated H3K27me3 chromatin, we demonstrated that DNA methylation and polycomb repression co-exist in vivo at this locus. We found this repressive association in 6/6 patient tumor samples of different Gleason score, suggesting a strong interplay of DNA methylation and EZH2 to silence RARβ during prostate tumorigenesis.     

Induction of E-cadherin endocytosis by loss of protein phosphatase 2A expression in human breast cancers

The cell-cell adhesion molecule E-cadherin is stabilized by linking intracellularly with the actin cytoskeleton through PP2A-mediated recruitment of IQGAP1 to Rac1-bound E-cadherin-catenins complex in nonmalignant HME cells. However, little is known about the dysfunction of E-cadherin by loss or reduced expression of PP2A in human breast cancer cells. We report here that both human breast cancer MDA-MB-231 and MCF-7 cells were deficient in expression of the PP2A-A protein and lost the IQGAP1 recruitment to Rac1-bound catenins. In MDA-MB-231 cells, E-cadherin was also deficient. Immunohistochemical analysis of the normal-carcinoma matched human breast tissue arrays revealed that PP2A-A was expressed in 96% of normal tissue specimens but not in 57% of carcinoma specimens. Expression of E-cadherin in MCF-7 cells was 1.5-fold higher than that in HME cells, however, 80% of E-cadherin was endocytosed and incompletely anchored to F-actin. Therefore, we propose that the dysfunction of E-cadherin due to its endocytosis may occur in some proportion of human breast carcinomas in which the PP2A-A protein is lost or significantly reduced.     

mMaspin: the mouse homolog of a human tumor suppressor gene inhibits mammary tumor invasion and motility.

BACKGROUND: The human maspin gene encodes a protein in the serine proteinase inhibitor (serpin) family with tumor-suppressing functions in cell culture and in nude mice. In order to examine the role of maspin in an intact mammal, we cloned and sequenced the cDNA of mouse maspin. The recombinant protein was produced and its activity in cell culture was assessed. MATERIALS AND METHODS: Mouse maspin (mMaspin) was cloned by screening a mouse mammary gland cDNA library with the human maspin cDNA probe. Northern blot analysis was used to examine the expression patterns in mouse tissues, mammary epithelial cells, and carcinomas. Recombinant mMaspin protein was produced in E. coli. Invasion and motility assays were used to assess the biological function of mMaspin. RESULTS: mMaspin is 89% homologous with human maspin at the amino acid level. Like its human homolog, mMaspin is expressed in normal mouse mammary epithelial cells and down-regulated in mouse breast tumor cell lines. The expression is altered at different developmental stages in mammary gland. Addition of the recombinant mMaspin protein to mouse tumor cells was shown to inhibit invasion in a dose-dependent manner. As with the human protein, recombinant mMaspin protein also inhibited mouse mammary tumor motility. Deletion in the putative mMaspin reactive site loop (RSL) region resulted in the loss of its inhibitory functions. CONCLUSIONS: mMaspin is the mouse homolog of a human tumor suppressor gene. The expression of mMaspin is down-regulated in tumor cells and is altered at different developmental stages of mammary gland. mMaspin has inhibitory properties similar to those of human maspin in cell culture, suggesting that the homologous proteins play similar physiological roles in vivo.     

Down-regulation of ECRG4, a candidate tumor suppressor gene, in human breast cancer

Introduction

ECRG4/C2ORF40 is a potential tumor suppressor gene (TSG) recently identified in esophageal carcinoma. Its expression, gene copy number and prognostic value have never been explored in breast cancer.

Methods

Using DNA microarray and array-based comparative genomic hybridization (aCGH), we examined ECRG4 mRNA expression and copy number alterations in 353 invasive breast cancer samples and normal breast (NB) samples. A meta-analysis was done on a large public retrospective gene expression dataset (n = 1,387) in search of correlations between ECRG4 expression and histo-clinical features including survival.

Results

ECRG4 was underexpressed in 94.3% of cancers when compared to NB. aCGH data revealed ECRG4 loss in 18% of tumors, suggesting that DNA loss is not the main mechanism of underexpression. Meta-analysis showed that ECRG4 expression was significantly higher in tumors displaying earlier stage, smaller size, negative axillary lymph node status, lower grade, and normal-like subtype. Higher expression was also associated with disease-free survival (DFS; HR = 0.84 [0.76–0.92], p = 0.0002) and overall survival (OS; HR = 0.72 [0.63–0.83], p = 5.0E-06). In multivariate analysis including the other histo-clinical prognostic features, ECRG4 expression remained the only prognostic factor for DFS and OS.

Conclusions

Our data suggest that ECRG4 is a candidate TSG in breast cancer, the expression of which may help improve the prognostication. If functional analyses confirm this TSG role, restoring ECRG4 expression in the tumor may represent a promising therapeutic approach.     

The human tumour suppressor LATS1 is activated by human MOB1 at the membrane

Downregulation of the LATS1 tumour suppressor protein kinase contributes to tumour formation in mammals and flies. Strikingly, the tumour suppressor activity depends on the interaction with Dmob (Drosphila Mps1-One binder) in Drosophila melanogaster. Recently, human LATS1 was reported to interact with human MOB1 (hMOB1), but the activation of LATS1 was not addressed. Here, we identified a highly conserved hMOB1-binding motif within LATS1's primary structure. While co-expression of LATS1 with hMOB1 did not elevate LATS1 kinase activity in mammalian cells, membrane-targeting of hMOB1 resulted in a significant increase of LATS1 activity. This stimulation was dependent on intact activation segment and hydrophobic motif phosphorylation sites, and was further found to occur a few minutes after membrane association. Therefore, we suggest a potential in vivo mechanism of LATS1 activation through rapid recruitment to the plasma membrane by hMOB1 followed by multi-site phosphorylation, thereby providing insight into the molecular regulation of the LATS tumour suppressor.