Assignment of the human alpha-catenin gene (CTNNA1) to chromosome 5q21-q22

Modulation of the tumor suppressor protein alpha-catenin by ischemic microenvironment

Dysregulation or mislocalization of cell adhesion molecules and their regulators, such as E-cadherin, beta-catenin, and alpha-catenin, usually correlates with loss of polarity, dedifferentiation, invasive tumor growth, and metastasis. A subpopulation of alpha-catenin-negative cells within the DLD-1 colorectal carcinoma cell line causes it to display a heterogeneous morphological makeup, thus providing an excellent model system in which to investigate the role of alpha-catenin in tumorigenesis. We re-established expression of alpha-catenin protein in an alpha-catenin-deficient subpopulation of the DLD-1 cell line and used it to demonstrate that loss of alpha-catenin resulted in increased in vitro tumorigenic characteristics (increased soft agarose colony formation, clonogenic survival after suspension, and survival in suspension). When the cells were used to form tumor xenografts, those lacking alpha-catenin showed faster growth rates because of increased cellular cycling but not increased tumor microvascular recruitment. alpha-Catenin-expressing cells were preferentially located in well perfused areas of xenografts when tumors were formed from mixed alpha-catenin-positive and -negative cells. We therefore evaluated the role of the ischemic tumor microenvironment on alpha-catenin expression and demonstrated that cells lose expression of alpha-catenin after prolonged exposure in vitro to hypoglycemic conditions. Our findings illustrate that the tumor microenvironment is a potent modulator of tumor suppressor expression, which has implications for localized nutrient deficiency and ischemia-induced cancer progression.

Biological relevance of E-cadherin-catenin complex proteins in primary epithelial ovarian tumours

This study analysed the biological relevance of E-cadherin, alpha-catenin, beta-catenin and gamma-catenin immunoexpression pattern (reduced vs. preserved phenotype) in epithelial ovarian tumours. Immunohistochemistry was used to evaluate the expression of these proteins in 154 epithelial ovarian tumours, consisting of 17 benign, 33 borderline and 104 malignant tumours. In borderline tumours, the immunoexpression pattern of E-cadherin (p = 0.014) and alpha-catenin (p = 0.030) associated with histological type. In malignant tumours, the immunoexpression pattern of E-cadherin was related with histological type (p = 0.001). The immunoexpression pattern of beta-catenin associated with histological type and tumour differentiation (p = 0.005, p = 0.025, respectively). The preserved phenotype of E-cadherin was most frequently observed in mucinous tumours, whereas reduced E-cadherin was most frequently observed in serous tumours. The preserved phenotype of beta-catenin associated with endometrioid carcinomas, while reduced beta-catenin associated with poorly differentiated serous and clear cell carcinomas. Although the reduced phenotype was the most frequent immunoexpression observed for all proteins of the E-cadherin-catenin complex in epithelial ovarian tumours, only beta-catenin showed a significant difference between benign, borderline and malignant tumours (p = 0.045), since borderline and malignant tumours most frequently showed the reduced phenotype. The immunohistochemical profile of beta-catenin was shown to be of biological relevance: reduced beta-catenin was correlated with loss of tumour differentiation and serous carcinomas that are known to depict aggressive biological behaviour in epithelial ovarian tumours.

Loss of beta-catenin is associated with poor survival in ovarian carcinomas

The catenins (alpha-, beta- and gamma-) are cytoplasmic proteins that bind to the conserved tail of the epithelial cadherin molecule. The function of epithelial cadherin at the adherens junctions is dependent on the catenins for efficient cell-to-cell adhesion. Loss of catenin expression has been reported in several human cancers and associated with poor tumor differentiation, advanced tumor stage, and poor patient survival. In this study, we investigated the clinical relevance of alpha-, beta-, and gamma-catenin immunoexpression in 104 cases of primary ovarian carcinoma with respect to clinicopathological features and as predictors of disease recurrence and prognosis. The clinicopathological parameters studied were International Federation of Gynaecology and Obstetrics (FIGO) stage, histological type, tumor differentiation, peritoneal metastases, residual postoperative tumor, integrity of the tumor's serosal surface, peritoneal cytology, and lymphatic/vascular invasion. Negative immunoreactivity of alpha-catenin, beta-catenin, and gamma-catenin was observed in 22 (21%), 15 (14%) and 23 (22%) cases, respectively. Immunoreactivity of alpha-catenin and gamma-catenin did not correlate with any of the clinicopathological parameters tested. The immunoexpression pattern of beta-catenin correlated with histological type (p = 0.026) and with a poorer overall survival in univariate analyses (p = 0.022). In the group of serous carcinomas, beta-catenin-immunoexpression associated significantly with overall survival. Patients with beta-catenin-negative serous carcinomas had a poorer overall survival than patients with beta-catenin-positive serous carcinomas (p = 0.013). In the multivariate analysis, negative expression of beta-catenin (p = 0.003) and the presence of residual tumor (p = 0.019) were the two most important independent prognostic factors predicting poorer overall survival. In conclusion, negative immunoreactivity of beta-catenin in serous carcinomas and the presence of residual tumor seem to be useful markers in selecting patients likely to have an unfavorable course.

Dual roles of E-cadherin in prostate cancer invasion

The role(s) of E-cadherin in tumor progression, invasion, and metastasis remains somewhat enigmatic. In order to investigate various aspects of E-cadherin biological activity, particularly in prostate cancer progression, our laboratory cloned unique subpopulations of the heterogeneous DU145 human prostatic carcinoma cell line and characterized their distinct biological functions. The data revealed that the highly invasive, fibroblastic-like subpopulation of DU145 cells (designated DU145-F) expressed less than 0.1-fold of E-cadherin protein when compared to the parental DU145 or the poorly invasive DU145 cells (designated DU145-E). Experimental disruption of E-cadherin function stimulated migration and invasion of DU145-E and other E-cadherin-positive prostate cancer cell lines, but did not affect the fibroblastic-like DU145-F subpopulation. Within the medium of parental DU145 cells, the presence of an 80 kDa E-cadherin fragment was detected. Subsequent functional analyses revealed the stimulatory effect of this fragment on the migratory and invasive capability of E-cadherin-positive cells. These results suggest that E-cadherin plays an important role in regulating the invasive potential of prostate cancer cells through an unique paracrine mechanism.

Association of Lbc Rho guanine nucleotide exchange factor with alpha-catenin-related protein, alpha-catulin/CTNNAL1, supports serum response factor activation

The Rho GTPase signaling pathway is required for actin cytoskeletal organization and serum response factor-dependent gene transcription. Lbc is a Rho-specific guanine nucleotide exchange factor that contains a modulatory C-terminal region. To elucidate Lbc regulatory mechanism(s), a yeast two-hybrid screen for proteins that interact with the Lbc C-terminal region was carried out, resulting in multiple isolation of cDNAs encoding the same 734-amino acid Lbc interacting protein. The Lbc interacting protein has homology with the alpha-catenin cell adhesion component and is identical to the alpha-catenin-like alpha-catulin protein of unknown function. The human alpha-catulin gene (CTNNAL1) maps to 9q31-32. Here we identify the predicted endogenous alpha-catulin product, document alpha-catulin and Lbc co-expression in multiple human cell lines, and show alpha-catulin and Lbc subcellular co-fractionation and intracellular localization. The required regions for Lbc and alpha-catulin interaction were mapped, and complex formation between Lbc and alpha-catulin in mammalian cells was detected. Functionally, alpha-catulin co-expression leads to increased Lbc-induced serum response factor activation in vivo as measured by a transcriptional reporter assay. Furthermore, alpha-catulin co-expression enhances Lbc-induced GTP-Rho formation in vivo. These results support the concept that the recently identified alpha-catulin protein may modulate Rho pathway signaling in vivo by providing a scaffold for the Lbc Rho guanine nucleotide exchange factor.

Different pattern of loss of heterozygosity among endocervical-type adenocarcinoma, endometrioid-type adenocarcinoma and adenoma malignum of the uterine cervix

It is unclear which chromosome arms frequently show loss of heterozygosity (LOH) in adenocarcinoma of the uterine cervix. To identify such chromosomal arms, LOH on 52 different chromosome loci was examined using laser capture microdissection and PCR-LOH analysis in 25 common-type adenocarcinomas, comprising 13 cases of endocervical type, 12 cases of endometrioid type and 7 cases of adenoma malignum without the component of conventional endocervical-type adenocarcinoma (designated as "pure" form). In adenocarcinomas of endocervical type and endometrioid type, LOH was commonly detected on chromosome arms 17p (62% and 50%, respectively), 1p (33% and 67%) and 22q (40% and 33%). In addition, endocervical-type adenocarcinoma frequently (> or = 30%) showed LOH on 18p (71%), 19q (50%), 19p (38%) and 16q (38%), whereas endometrioid-type adenocarcinoma frequently showed LOH on 10q (43%) and 5q (40%). LOH was only sporadically detected on 9q, 18q, or 21q in 3 of 7 cases of "pure" adenoma malignum. In a case of coexistence of "pure" adenoma malignum and adenocarcinoma in situ (AIS), LOH on 1q, 5p, 11p, 17p, 18p and 18q was detected only in AIS. LOH was accumulated on a number of chromosome arms in the adenocarcinoma at the early developmental stage before stromal invasion. Chromosomal arms that are prone to show LOH appeared to differ between the 2 types of cervical adenocarcinoma. We could suggest that "pure" adenoma malignum is of clonal and neoplastic nature in view of the detection of LOH.

The E-cadherin cell-cell adhesion pathway in urologic malignancies

Alterations in the E-cadherin-mediated cell-cell adhesion pathway are commonly observed in urologic malignancies. This issue has been addressed most thoroughly in prostate cancer. Whereas both cadherin and catenin dysfunction have been seen in human prostate cancers, only down-regulation of E-cadherin has been shown for bladder cancer and renal-cell carcinoma. Although studies in bladder cancer and renal-cell carcinoma are less mature than studies in prostate cancer, they support the hypothesis that immunostaining for E-cadherin may be of significance for both diagnostic and prognostic purposes. Finally, the E-cadherin-mediated cell-cell adhesion pathway may represent a novel chemotherapeutic target for bladder cancer, prostate cancer, and renal-cell carcinoma. Obviously, more work lies ahead to translate these important observations from the bench to the bedside.

The E-cadherin-catenin complex in tumour metastasis: structure, function and regulation

E-cadherin and the associated catenin complex have been recognised as performing a key role in cell adhesion. Loss of cell adhesion is seen as a key step in the cascade leading to tumour metastasis. The ability of both extra- and intracellular factors to regulate E-cadherin-mediated cell adhesion in physiological processes has provided insight into both the interactions of the E-cadherin-catenin complex, and possible mechanisms utilised by tumours in the process of metastasis. The interaction of the E-cadherin-catenin complex with various regulating factors, their effect on cell signalling pathways, and the relationship with the metastatic potential of tumours are reviewed.

Regulation of E-cadherin: does hypoxia initiate the metastatic cascade?

The ability of tumours to metastasis is regarded as one of the hallmarks of malignancy. The process through which tumours evolve to achieve this has been termed the metastatic cascade. This cascade has been the subject of much investigation over many years. One of the vital events identified by these investigations is the reduction of adhesion between tumour cells facilitating invasion of the surrounding tissues and vascular channels, ultimately leading to the development of a distant metastasis. E-cadherin and its associated catenin complex have been identified as key molecules in cell adhesion. This review looks at the structure and interaction of the E-cadherin-catenin complex and the factors that appear to regulate E-cadherin expression and thus cell adhesion. From the data gathered, it has become possible to propose the hypothesis that the development of tumour hypoxia is the initiating factor that sets the tumour on the road to metastasis.

Duplication of two distinct regions on chromosome 5q in non-papillary renal-cell carcinomas

RFLP studies have indicated a duplication of DNA sequences at the chromosome 5q22 region and showed a breakpoint cluster between the apc and mcc genes in nonpapillary renal-cell carcinoma (RCC). We have now made a high-density fluorescent microsatellite assay to investigate the allelic status and determine the smallest duplication at this region in 62 sporadic non-papillary RCCs. Duplication at each informative locus was found in 27 cases. Partial duplications in 3 tumors delineated 2 distinct regions. One was found at loci D5S659, D5S1720 and w2005 at chromosome band 5q22; this region partially overlaps with the smallest duplicated region found by previous RFLP analysis. Another small duplication was marked by loci D5S816 and D5S476 at chromosome band 5q31.1 and included the alpha-catenin gene (ctnna1).

Regional mapping panels for chromosomes 3, 4, 5, 11, 15, 17, 18, and X

The NIGMS Human Genetic Mutant Cell Repository collects and distributes well-characterized human/rodent somatic cell hybrid regional mapping panels for human chromosomes 3, 4, 5, 11, 15, 17, 18, and X. Each regional mapping panel consists of 4 to 11 hybrids that divide the chromosome into 5 to 11 intervals. These panels have been extensively characterized by the submitters and the NIGMS Repository.

A radiation hybrid map of human chromosome 5 with integration of cytogenetic, genetic, and transcript maps

One of the major goals of the human genome project is to establish a physical map of each human chromosome with a density of sequence-tagged site (STS) markers exceeding one every 100 kb. We report here the generation of a human chromosome 5-specific radiation hybrid (RH) map that includes 556 markers. Of these markers, 132 loci are ordered with a maximum likelihood ratio of >1000:1 compared with the next most likely order. An additional 113 loci were ordered relative to these backbone markers with a maximum likelihood ratio of >10:1 but <1000:1. Together, these 245 loci form an ordered framework map for the chromosome. Using this framework, >300 more markers were localized based on two-point analysis with the ordered set. On average, there are 50 markers in common with the RH map presented here and other chromosome 5 maps included in the current whole genome cytogenetic, genetic, and physical maps. The accuracy of all the maps is evident in that there are no more than two discrepancies between any one of them and these data. All of the maps encompassing chromosome 5 complement each other providing excellent STS coverage with >2200 loci combined. The chromosome 5-specific RH map contains 20% of these independent loci. In addition, our RH map contains STSs derived from clones suitable for fluorescent in situ hybridization, allowing alignment to the cytogenetic map. Together, these maps will assist in the assembly of sequence-ready contigs and will aid in the identification of disease loci on chromosome 5 by positional cloning and positional candidate approaches.

Molecular analysis of the APC gene in 105 Dutch kindreds with familial adenomatous polyposis: 67 germline mutations identified by DGGE, PTT, and southern analysis

Germline mutations of the adenomatous polyposis coli (APC) gene are responsible for familial adenomatous polyposis (FAP), an autosomal dominant predisposition to colorectal cancer. We screened the entire coding region of the APC gene for mutations in an unselected series of 105 Dutch FAP kindreds. For the analysis of exons 1-14, we employed the GC-clamped denaturing gradient gel electrophoresis (DGGE), while the large exon 15 was examined using the protein truncation test. Using this approach, we identified 65 pathogenic mutations in the above 105 apparently unrelated FAP families. The mutations were predominantly either frameshifts (39/65) or single base substitutions (18/65), resulting in premature stop codons. Mutations that would predict abnormal RNA splicing were identified in seven cases. In one of the families, a nonconservative amino acid change was found to segregate with the disease. In spite of the large number of APC mutations reported to date, we identified 27 novel germline mutations in our patients, which reiterates the great heterogeneity of the mutation spectrum in FAP. In addition to the point mutations identified in our patients, structural rearrangements of APC were found in two pedigrees, by Southern blot analysis. The present study indicates that the combined use of DGGE, protein truncation test, and Southern blot analysis offers an efficient strategy for the presymptomatic diagnosis of FAP by direct mutation detection. We found that the combined use of the currently available molecular approaches still fails to identify the underlying genetic defect in a significant subset of the FAP families. The possible causes for this limitation are discussed.

E-cadherin and its associated protein catenins, cancer invasion and metastasis

E-cadherin is a cell-cell adhesion molecule which is anchored to the cytoskeleton via catenins. There is increasing evidence which suggests that E-cadherin also acts as a suppressor of tumour invasion and metastasis. Both in vitro and in vivo studies have revealed that expression of E-cadherin correlates inversely with the motile and invasive behaviour of a tumour cell; it also correlates inversely with metastasis in patients with cancer. The function of E-cadherin is highly dependent on the functional activity of catenins. This review summarizes progress, from both basic and clinical research, in our understanding of the roles of E-cadherin and catenins, and discusses the clinical relevance of the discoveries.

Human chromosome-specific cDNA libraries: new tools for gene identification and genome annotation

To date, only a small percentage of human genes have been cloned and mapped. To facilitate more rapid gene mapping and disease gene isolation, chromosome 5-specific cDNA libraries have been constructed from five sources. DNA sequencing and regional mapping of 205 unique cDNAs indicates that 25 are from known chromosome 5 genes and 138 are from new chromosome 5 genes (a frequency of 79.5%). Sequence complexity estimates indicate that each library contains -20% of the approximately 5000 genes that are believed to reside on chromosome 5. This study more than doubles the number of genes mapped to chromosome 5 and describes an important new tool for disease gene isolation.

Development of a panel of monochromosomal somatic cell hybrids for rapid gene mapping

We have assembled a panel of monochromosomal somatic cell hybrids for use in gene mapping. DNA from each individual hybrid was used as a probe on normal human metaphases to identify the human chromosome and any fragments by reverse painting. To test the efficiency of the panel PCR amplification of DNA from the monochromosomal somatic cell hybrid panel was used in combination with human specific oligonucleotide primers to assign alpha-catenin (CTNNA1) and p21/WAF1 to chromosomes 5 and 6 respectively. These genes were localized further using hybrids containing specific translocations to 5q11-qter and 6p21 respectively. We also developed primers to enable us to assign 17 ESTs sequenced by the HGMP Resource Centre. The hybrid panel was developed with support of the UK HGMP and the DNA is available to all registered users.

Isolation and characterization of a human pseudogene (CTNNAP1) for alpha E-catenin (CTNNA1): assignment of the pseudogene to 5q22 and the alpha E-catenin gene to 5q31

A pseudogene (CTNNAP1) for the human alpha E-catenin gene was isolated from a human genomic phage library. The pseudogene sequence shows 90% similarity to the alpha E-catenin mRNA at the nucleotide level. Thirty-eight stop codons in all three reading frames and multiple other mutations were found, indicating that the pseudogene does not encode a functional protein. No introns were found in the region corresponding to the open reading frame of the alpha E-catenin cDNA, and two direct repeats flank this same region. Hence, the pseudogene can be classified as a processed pseudogene. Polymerase chain reaction with pseudogene-specific primers on genomic DNA and cDNA from human cell lines and healthy blood donors demonstrated the general occurrence of the pseudogene and the lack of its transcription. By fluorescence in situ hybridization the pseudogene was mapped to human chromosome 5q22 and the alpha E-catenin gene to the formerly disputed locus 5q31. This is the first report of a pseudogene for a member of the cadherin-catenin cell-cell adhesion complex.

Molecular cloning of the microfibrillar protein MFAP3 and assignment of the gene to human chromosome 5q32-q33.2

Microfibrils having a diameter of 10-12 nm, found either in association with elastin or independently, are an important component of the extracellular matrix of many tissues, but characterization of these microfibrils is incomplete. To further our understanding of the gene structure of proteins composing the microfibrils and to identify their chromosomal location, we have cloned and characterized another microfibril protein, designated microfibril-associated protein-3 (MFAP3). The human gene encoding MFAP3 has a very simple structure, containing only two translated exons encoding a protein of 362 amino acids. Monospecific antibodies prepared against the recombinantly expressed protein reacted with the microfibrils found in ocular zonules. MFAP3 does not appear to share homology with any other known protein. The gene was found to be located on chromosome 5q32-q33.2, near the locus 5q21-q31 reported for the fibrillin gene, FBN2, which has been linked to congenital contractural arachnodactyly. MFAP3 is a candidate gene for heritable diseases affecting microfibrils.