Loss of heterozygosity on hromosome 1 in sporadic colorectal carcinoma

Recurring EPHB1 mutations in human cancers alter receptor signalling and compartmentalisation of colorectal cancer cells

BACKGROUND

Ephrin (EPH) receptors have been implicated in tumorigenesis and metastasis, but the functional understanding of mutations observed in human cancers is limited. We previously demonstrated reduced cell compartmentalisation for somatic EPHB1 mutations found in metastatic colorectal cancer cases. We therefore integrated pan-cancer and pan-EPH mutational data to prioritise recurrent EPHB1 mutations for functional studies to understand their contribution to cancer development and metastasis.

METHODS

Here, 79,151 somatic mutations in 9,898 samples of 33 different tumour types were analysed with a bioinformatic pipeline to find 3D-mutated cluster pairs and hotspot mutations in EPH receptors. From these, 15 recurring EPHB1 mutations were stably expressed in colorectal cancer followed by confocal microscopy based in vitro compartmentalisation assays and phospho-proteome analysis.

RESULTS

The 3D-protein structure-based bioinformatics analysis resulted in 63% EPHB1 mutants with compartmentalisation phenotypes vs 43% for hotspot mutations. Whereas the ligand-binding domain mutations C61Y, R90C, and R170W, the fibronectin domain mutation R351L, and the kinase domain mutation D762N displayed reduced to strongly compromised cell compartmentalisation, the kinase domain mutations R743W and G821R enhanced this phenotype. While mutants with reduced compartmentalisation also had reduced ligand induced receptor phosphorylation, the enhanced compartmentalisation was not linked to receptor phosphorylation level. Phosphoproteome mapping pinpointed the PI3K pathway and PIK3C2B phosphorylation in cells harbouring mutants with reduced compartmentalisation.

CONCLUSIONS

This is the first integrative study of pan-cancer EPH receptor mutations followed by in vitro validation, a robust way to identify cancer-causing mutations, uncovering EPHB1 mutation phenotypes and demonstrating the utility of protein structure-based mutation analysis in characterization of novel cancer genes. Video Abstract.

CAMK2N1 has a cancer-suppressive function in colorectal carcinoma via effects on the Wnt/β-catenin pathway

The deregulation of calcium/calmodulin-dependent protein kinase II inhibitor 1 (CAMK2N1) is linked to the carcinogenesis reported in several malignancies. To date, studies describing the role of CAMK2N1 in colorectal carcinoma are scarce. The current project was carried out to study the relationship between CAMK2N1 and colorectal carcinoma progression. CAMK2N1 levels were lowered in colorectal carcinoma tissue, which also correlated to poor overall survival in patients. Colorectal carcinoma cell lines with overexpressed CAMK2N1 showed a reduction in transformative phenotypes, including proliferation suppression, the blocking of cell cycle progression, metastasis inhibition and chemoresistance reduction, whereas CAMK2N1-silenced cells showed the opposite effect. Mechanistic studies revealed a novel regulatory role of CAMK2N1 on Wnt/β-catenin transduction. Up-regulation of CAMK2N1 lowered the level of disheveled 2, phosphorylated GSK-3β, β-catenin, c-myc and cyclin D1. Re-expression of β-catenin decreased the CAMK2N1-mediated tumor-inhibiting effects. Moreover, blocking of Wnt/β-catenin diminished CAMK2N1-silencing-elicited cancer-enhancing effect. Critically, the tumorigenicity of CAMK2N1-overexpressed cells was markedly weakened in nude mice. To conclude, the study demonstrated a cancer-suppressive function of CAMK2N1 in colorectal carcinoma and illustrated that CAMK2N1 exerts the tumor-inhibiting effects via suppression of the Wnt/β-catenin pathway.

Systematic characterization of germline variants from the DiscovEHR study endometrial carcinoma population

Background

Endometrial cancer (EMCA) is the fifth most common cancer among women in the world. Identification of potentially pathogenic germline variants from individuals with EMCA will help characterize genetic features that underlie the disease and potentially predispose individuals to its pathogenesis.

Methods

The Geisinger Health System’s (GHS) DiscovEHR cohort includes exome sequencing on over 50,000 consenting patients, 297 of whom have evidence of an EMCA diagnosis in their electronic health record. Here, rare variants were annotated as potentially pathogenic.

Results

Eight genes were identified as having increased burden in the EMCA cohort relative to the non-cancer control cohort. None of the eight genes had an increased burden in the other hormone related cancer cohort from GHS, suggesting they can help characterize the underlying genetic variation that gives rise to EMCA. Comparing GHS to the cancer genome atlas (TCGA) EMCA germline data illustrated 34 genes with potentially pathogenic variation and eight unique potentially pathogenic variants that were present in both studies. Thus, similar germline variation among genes can be observed in unique EMCA cohorts and could help prioritize genes to investigate for future work.

Conclusion

In summary, this systematic characterization of potentially pathogenic germline variants describes the genetic underpinnings of EMCA through the use of data from a single hospital system.

Electronic supplementary material

The online version of this article (10.1186/s12920-019-0504-9) contains supplementary material, which is available to authorized users.

Somatic mosaicisms of chromosome 1 at two different stages of ontogenetic development detected by Rh blood group discrepancies

Spontaneous Rh blood group changes are a striking sign, reported to occur mainly in patients with hematologic disorders. Upon routine blood grouping, 2 unrelated individuals showed unexplained mixed red cell phenotype regarding the highly immunogenic c antigen (RH4), clinically relevant for blood transfusion and fetomaternal incompatibility. About half of their red cells were c-positive, whereas the other half were c-negative. These apparently hematologically healthy females had no history of transfusion or transplantation, and they tested negative for chimerism. Genotyping of flanking chromosome 1 microsatellites in blood, finger nails, hair, leukocyte subpopulations, and erythroid progenitor cells showed partial loss of heterozygosity encompassing the RHD/RHCE loci, spanning a 1p region of 26.7 or 42.4 Mb, respectively. Remarkably, in one case this was detected in all investigated tissues, whereas in the other, exclusively myeloid cells showed loss of heterozygosity. Both carried the RhD-positive haplotypes CDe and the RhD-negative haplotype cde. RHD/RHCE genotypes of single erythroid colonies and dual-color fluorescent in situ hybridization analyses indicated loss of the cde haplotype and duplication of the CDe haplotype in the altered cell line. Accordingly, red cell C antigen (RH2) levels of both propositae were higher than those of heterozygous controls. Taken together, the Rhc phenotype splitting appeared to be caused by deletion of a part of 1p followed by duplication of homologous stretches of the sister chromosome. In one case, this phenomenon was confined to myeloid stem cells, while in the other, a pluripotent stem cell line was affected, demonstrating somatic mosaicism at different stages of ontogenesis.

Downregulation of nuclear and cytoplasmic Chibby is associated with advanced cervical cancer

Chibby has been identified as a putative tumor suppressor and antagonist to β-catenin, thereby controlling the Wnt signaling pathway. Chibby is typically downregulated in numerous types of cancer and may be associated with tumorigenesis. The present study aimed at clarifying the following: i) Whether Chibby antagonizes β-catenin in cervical cancer; ii) whether Chibby and β-catenin mRNA expression is associated with cancer progression; and iii) whether Chibby and β-catenin expression may be used as a biomarker. A total of 87 paraffin-embedded cervical sections with distinct cervical intraepithelial neoplasia (CIN) stages (chronic cervicitis, CIN 1, CIN 2, CIN 3 and invasive squamous cell carcinoma) were collected between June 2004 and October 2012 The mRNA expression level of Chibby and β-catenin was determined using the polymerase chain reaction. Protein expression and cellular localization of Chibby and β-catenin were determined using immunohistochemistry. Chibby and β-catenin were analyzed for possible association with the progression of cervical cancer. Chibby mRNA expression and the Chibby/β-catenin ratio were identified to be downregulated in invasive tumors. Positive cytoplasmic and nuclear staining for Chibby was associated with CIN staging and decreased as the CIN stage increased. In addition, the cytoplasmic and membrane intensity of β-catenin was associated with invasive tumors, in which a significantly increased level of protein expression was detected. Chibby may be a tumor suppressor in cervical cancer, since the dysregulation of Chibby expression is associated with tumorigenesis in cervical cancer. Chibby and β-catenin expression together may potentially to a biomarker for disease progression in cervical cancer.

Decreased expression and aberrant methylation of RASSF5A correlates with malignant progression of gastric cardia adenocarcinoma

Due to alternative splicing and differential promoter usage, RASSF5 exists in at least three isoforms, RASSF5A, RASSF5B, and RASSF5C. Expression and epigenetic inactivation of different transcripts of RASSF5 in gastric cardia adenocarcinoma (GCA) progression have not been evaluated. Quantitative real-time RT-PCR and immunohistochemistry (IHC) methods were used respectively to detect the role of RASSF5A, RASSF5B, and RASSF5C in 132 GCA cases and BS-MSP method was used to clarify the critical CpG sites of RASSF5A. Expression of RASSF5A and RASSF5C transcripts were easily detectable in all normal gastric cardia epithelial tissues; however, expression of RASSF5B was rare detected in normal gastric cardia epithelial tissues and tumor tissues. Both RASSF5A and RASSF5C expression were frequently downregulated in GCA tumor tissues and RASSF5A was more commonly down-regulated compared to RASSF5C. Abnormal reduction of RASSF5A was more commonly observed in advanced stage and poor differentiated tumors. The methylation frequency of CpG island 1 region of RASSF5A in GCA tumor tissues was significantly higher than that in corresponding normal tissues and was inversely correlated with RASSF5A expression. Aberrant promoter methylation of RASSF5C was not found in GCA. RASSF5A methylation and protein expression were independently associated with GCA patients' survival. These results indicate that down-regulation of RASSF5A and RASSF5C expression is a tumor-specific phenomenon and RASSF5A may be a more common target for inactivation in GCA. Inactivation of RASSF5A through CpG island 1 methylation may play an important role in GCA carcinogenesis and may serve as a prognostic biomarker for GCA.

The tumor suppressor Chd5 is induced during neuronal differentiation in the developing mouse brain

Epigenetic regulation of gene expression orchestrates dynamic cellular processes that become perturbed in human disease. An understanding of how subversion of chromatin-mediated events leads to pathologies such as cancer and neurodevelopmental syndromes may offer better treatment options for these pathological conditions. Chromodomain Helicase DNA-binding protein 5 (CHD5) is a dosage-sensitive tumor suppressor that is inactivated in human cancers, including neural-associated malignancies such as neuroblastoma and glioma. Here we report a detailed analysis of the temporal and cell type-specific expression pattern of Chd5 in the mammalian brain. By analyzing endogenous Chd5 protein expression during mouse embryogenesis, in the neonate, and in the adult, we found that Chd5 is expressed broadly in multiple brain regions, that Chd5 sub-cellular localization undergoes a switch from the cytoplasm to the nucleus during mid-gestation, and that Chd5 expression is retained at high levels in differentiated neurons of the adult. These findings may have important implications for defining the role of CHD5-mediated chromatin dynamics in the brain and for elucidating how perturbation of these epigenetic processes leads to neuronal malignancies, neurodegenerative diseases, and neurodevelopmental syndromes.

Molecular and cellular pathways associated with chromosome 1p deletions during colon carcinogenesis

Chromosomal instability is a major pathway of sporadic colon carcinogenesis. Chromosome arm 1p appears to be one of the "hot spots" in the non-neoplastic mucosa that, when deleted, is associated with the initiation of carcinogenesis. Chromosome arm 1p contains genes associated with DNA repair, spindle checkpoint function, apoptosis, multiple microRNAs, the Wnt signaling pathway, tumor suppression, antioxidant activities, and defense against environmental toxins. Loss of 1p is dangerous since it would likely contribute to genomic instability leading to tumorigenesis. The 1p deletion-associated colon carcinogenesis pathways are reviewed at the molecular and cellular levels. Sporadic colon cancer is strongly linked to a high-fat/low-vegetable/low-micronutrient, Western-style diet. We also consider how selected dietary-related compounds (eg, excess hydrophobic bile acids, and low levels of folic acid, niacin, plant-derived antioxidants, and other modulatory compounds) might affect processes leading to chromosomal deletions, and to the molecular and cellular pathways specifically altered by chromosome 1p loss.

DPEP1, expressed in the early stages of colon carcinogenesis, affects cancer cell invasiveness

BACKGROUND

We investigated changes in the gene expression profile in colon cancer in order to identify gene markers that may be useful in the management of this disease.

METHODS

The Cancer Genome Anatomy Project was used to detect differences in gene expression between normal and cancer tissue. The overexpression of dipeptidase-1 (DPEP1) in cancer tissue was confirmed in a sample of 76 patients by real-time PCR. To identify the function of DPEP1, RNA interference (RNAi) was used to inactivate this gene in the colon cancer cell line. Immunohistochemical analysis was performed to characterize the pattern of DPEP1 expression in colon cancer.

RESULTS

DPEP1 expression in cancer was significantly higher than that in normal tissue. However, DPEP1 expression decreased with pathological differentiation, lymph-node and distant metastasis. Patients with tumors with decreased DPEP1 expression showed a poorer prognosis, and this was also true of patients with tumors who are treated with curative intent. RNAi-mediated DPEP1 reduction in the colon cancer cell line did not result in cell proliferation or apoptosis, but was associated with an increased invasive ability. DPEP1 protein was observed on the apical side of the cancer cells, and is expressed in the early stages of carcinogenesis, even in adenomas of both sporadic colorectal cancer and familial adenomatous polyposis patients.

CONCLUSIONS

DPEP1 expression in normal colonic mucosa is very low, but it is highly expressed in colorectal adenoma and cancer specimens and is negatively correlated with parameters of pathological aggressiveness and poor prognosis. DPEP1 is expressed in the early stages of colon carcinogenesis and affects cancer cell invasiveness.

Epigenetic inactivation of the NORE1 gene correlates with malignant progression of colorectal tumors

Background

NORE1 (RASSF5) is a newly described member of the RASSF family with Ras effector function. NORE1 expression is frequently inactivated by aberrant promoter hypermethylation in many human cancers, suggesting that NORE1 might be a putative tumor suppressor. However, expression and mutation status of NORE1 and its implication in colorectal tumorigenesis has not been evaluated.

Methods

Expression, mutation, and methylation status of NORE1A and NORE1B in 10 cancer cell lines and 80 primary tumors were characterized by quantitative PCR, SSCP, and bisulfite DNA sequencing analyses. Effect of NORE1A and NORE1B expression on tumor cell growth was evaluated using cell number counting, flow cytometry, and colony formation assays.

Results

Expression of NORE1A and NORE1B transcript was easily detectable in all normal colonic epithelial tissues, but substantially decreased in 7 (70%) and 4 (40%) of 10 cancer cell lines and 31 (38.8%) and 25 (31.3%) of 80 primary carcinoma tissues, respectively. Moreover, 46 (57.6%) and 38 (47.5%) of 80 matched tissue sets exhibited tumor-specific reduction of NORE1A and NORE1B, respectively. Abnormal reduction of NORE1 was more commonly observed in advanced stage and high grade tumors compared to early and low grade tumors. While somatic mutations of the gene were not identified, its expression was re-activated in all low expressor cells after treatment with the demethylating agent 5-aza-dC. Bisulfite DNA sequencing analysis of 31 CpG sites within the promoter region demonstrated that abnormal reduction of NORE1A is tightly associated with promoter CpG sites hypermethylation. Moreover, transient expression and siRNA-mediated knockdown assays revealed that both NORE1A and NORE1B decrease cellular growth and colony forming ability of tumor cells and enhance tumor cell response to apoptotic stress.

Conclusion

Our data indicate that epigenetic inactivation of NORE1 due to aberrant promoter hypermethylation is a frequent event in colorectal tumorigenesis and might be implicated in the malignant progression of colorectal tumors.

Throwing the cancer switch: reciprocal roles of polycomb and trithorax proteins

The discovery that cancer can be governed above and beyond the level of our DNA presents a new era for designing therapies that reverse the epigenetic state of a tumour cell. Understanding how altered chromatin dynamics leads to malignancy is essential for controlling tumour cells while sparing normal cells. Polycomb and trithorax group proteins are evolutionarily conserved and maintain chromatin in the 'off' or 'on' states, thereby preventing or promoting gene expression, respectively. Recent work highlights the dynamic interplay between these opposing classes of proteins, providing new avenues for understanding how these epigenetic regulators function in tumorigenesis.

Deletion mapping of chromosome region 12q13-24 in colorectal cancer

Colorectal cancer is one of the most common cancers in the world. Colorectal cancer develops after a long and multistep process of carcinogenesis. Inactivation of tumor suppressor genes is among the most important steps in development of colorectal cancer. Analysis of loss of heterozygosity (LOH) is an effective method to determine the localization of tumor suppressor genes. In this study, we used five microsatellite markers to analyze the region 12q13-24 among 47 patients with colorectal cancer. The frequency of LOH and the clinicopathological data were compared using logistic regression and a chi-square test. In 34 of 47 tumor tissues (72%), LOH was detected at least in one marker. The highest LOH frequency was 34%, on the D12S129 locus; the lowest frequency was 23%, on the D12S78 locus. Loss of heterozygosity was detected as 32% on D12S83, 30% on D12S346, and 26% on D12S1660. No statistically significant correlation was found between the frequency of LOH and clinicopathological features (P > 0.05). Chromosome region 12q13-24 contains several known genes that may be candidate tumor suppressor genes, including RASAL1, ITGA7, STAB2, GLIPR1, and SLC5A8. Although the exact roles of these genes in colorectal cancer formation remain to be clarified, the present data point to a tumor suppressor role.

Loss of heterozygosity at 1p, 7q, 17p, and 22q in meningiomas

OBJECTIVE

Allelic losses or loss of heterozygosity (LOH) at many chromosomal loci have been found in the cells of meningiomas. The objective of this study was to evaluate LOH at several loci of different chromosomes (1p32, 17p13, 7q21, 7q31, and 22q13) in different grades of meningiomas.

METHODS

Forty surgical specimens were obtained and classified as benign, atypical, and anaplastic meningiomas. After DNA extraction, ten polymorphic microsatellite markers were used to detect LOH. Medical and surgical records, as well as pathologic findings, were reviewed retrospectively.

RESULTS

LOH at 1p32 was detected in 24%, 60%, and 60% in benign, atypical, and anaplastic meningiomas, respectively. Whereas LOH at 7q21 was found in only one atypical meningioma. LOH at 7q31 was found in one benign meningioma and one atypical meningioma. LOH at 17p13 was detected in 4%, 40%, and 80% in benign, atypical, and anaplastic meningiomas, respectively. LOH at 22q13 was seen in 48%, 60%, and 60% in benign, atypical, and anaplastic meningiomas, respectively. LOH results at 1p32 and 17p13 showed statistically significant differences between benign and non-benign meningiomas.

CONCLUSION

LOH at 1p32 and 17p13 showed a strong correlation with tumor progression. On the other hand, LOH at 7q21 and 7q31 may not contribute to the development of the meningiomas.

The quest for the 1p36 tumor suppressor

Genomic analyses of late-stage human cancers have uncovered deletions encompassing 1p36, thereby providing an extensive body of literature supporting the idea that a potent tumor suppressor resides in this interval. Although several genes have been proposed as 1p36 candidate tumor suppressors, convincing evidence that their encoded products protect from cancer has been scanty. A recent functional study identified chromodomain helicase DNA-binding protein 5 (CHD5) as a novel tumor suppressor mapping to 1p36. Here, we discuss evidence supporting the tumor-suppressive role of CHD5. Together, these findings suggest that strategies designed to enhance CHD5 activity could provide novel approaches for treating a broad range of human malignancies.

Refined mapping of loss of heterozygosity on 1q31.1-32.1 in sporadic colorectal carcinoma

AIM: To explore precise deleted regions and screen the candidate tumor suppressor genes related to sporadic colorectal carcinoma.

METHODS: Six markers on 1q31.1-32.1 were chosen. These polymorphic microsatellite markers in 83 colorectal cancer patients tumor and normal DNA were analyzed via PCR. PCR products were electrophoresed on an ABI 377 DNA sequencer. Genescan 3.1 and Genotype 2.1 software were used for Loss of heterozygosity (LOH) scanning and analysis. Comparison between LOH frequency and clinicopathological factors was performed by χ² test.

RESULTS: 1q31.1-32.1 exhibited higher LOH frequency in colorectal carcinoma. The average LOH frequency of 1q31.1-32.1 was 23.0%, with the highest frequency of 36.7% (18/49) at D1S2622, and the lowest of 16.4% (11/67) at D1S412, respectively. A minimal region of frequent deletion was located within a 2 cM genomic segment at D1S413-D1S2622 (1q31.3-32.1). There was no significant association between LOH of each marker on 1q31.1-32.1 and the clinicopathological data (patient sex, age, tumor size, growth pattern or Dukes stage), which indicated that on 1q31.1-32.1, LOH was a common phenomenon in all kinds of sporadic colorectal carcinoma.

CONCLUSION: Through our refined deletion mapping, the critical and precise deleted region was located within 2 cM chromosomal segment encompassing 2 loci (D1S413, D1S2622). No significant association was found between LOH and clinicopathologic features in 1q31.1-32.1.

Accumulation of beta-catenin protein, mutations in exon-3 of the beta-catenin gene and a loss of heterozygosity of 5q22 in solid pseudopapillary tumor of the pancreas

BACKGROUND

Solid pseudopapillary tumors (SPT) of the pancreas are neoplasms with a low malignant potential. The molecular events contributing to the pathogenesis of SPTs are still unknown.

OBJECTIVES

This study was intended to help better understand the early steps of human SPT development.

METHODS

We microdissected 20 SPTs and normal pancreatic tissue. In addition, we examined the DNA from each SPT for mutations in exon-3 of beta-catenin and loss of heterozygosity (LOH) on 9 chromosome arms using 10 microsatellite markers. Immunohistochemical staining for beta-catenin was performed.

RESULTS

Activating mutations between codons 32 and 37 of beta-catenin exon-3 were present in 16 cases (80%). Allelic loss on chromosome 5q22.1 was present in 10 cases (55.5%), while no allelic loss was found on chromosomes 1p, 6q, 9p, 9q, 11p, 11q, 17p, or 22q. Nuclear accumulation of beta-catenin was found in 20 cases (100%).

CONCLUSION

Mutations in exon-3 of the beta-catenin gene, nuclear accumulation of beta-catenin, and LOH on chromosome 5q22.1 in SPT tissue suggest that these mutations are involved in SPT tumorigenesis.

The impact of genomic alterations on the transcriptome: a prostate cancer cell line case study

Genetic instability may lead to the loss/gain of transcriptional control. Here we investigated the effect of genomic instability, that is loss/gain of chromosomal regions on the global transcriptome of prostate cancer cell line DU145. The genomic loss/gain map obtained through BAC array-based CGH was superimposed on the dynamic transcriptome of DU145 cells treated with serum for 0 h (serum starved), 2 h and 12 h. The genomic analysis suggested that in DU145 cells: (1) chromosomal gains are prominent than losses and (2) copy number changes are associated with chromosome-specific and dynamic gene expression regulatory mechanisms. A significant proportion of the genes in the stable regions of the chromosome were up-regulated whereas a higher proportion of genes were down-regulated at 2 and 12 h in the deleted regions of the chromosomes following serum treatment. No change in expression was observed for the genes in the gained regions over a period of time. This analysis led us to propose that loss of heterozygosity leads to an overall transcriptional down-regulation that may further lead to a decrease in the expression of putative tumor suppressors. The genomic profile of DU145 is similar to pathological specimens of prostate cancer, hence the genomic/transcriptomic signature of DU145 can be used to understand the pathology of prostate cancer. It is expected that this analysis will allow a better understanding of transcriptional regulatory mechanisms in the context of genomic loss and gain and may lead to the discovery of novel oncogenes and tumor suppressors and the underlying regulatory pathways.

Reduced expression of β-catenin inhibitor Chibby in colon carcinoma cell lines

AIM: To analyse the Chibby expression and its function in colon carcinoma cell lines and colorectal carcinoma (CRC).

METHODS: Chibby expression levels were investigated by quantitative RT-PCR in a panel of seven different colon carcinoma cell lines. By sequencing, we analysed mutational status of Chibby. To test whether Chibby exhibited effects on β-catenin signalling in colon carcinoma cells, we transfected SW480 cells with Chibby expression plasmid and, subsequently, analysed activity of β-catenin and tested for alterations in cellular phenotype. In addition, we examined Chibby mRNA levels in samples of colorectal carcinomas and adjacent normal tissues by using quantitative RT-PCR and hybridised gene chips with samples from CRC and normal tissues.

RESULTS: Chibby mRNA expression was strongly down-regulated in colon carcinoma cell lines in comparison to normal colon epithelial cells and no mutation in any of the examined colon carcinoma cell lines was found. Further, we could show that Chibby inhibited β-catenin activity in TOPflash assays when over-expressed in SW480 cells. Proliferation and invasion assays with Chibby transfected SW480 cells did not reveal profound differences compared to control cells. In contrast to these in vitro data, quantitative RT-PCR analyses of Chibby mRNA levels in CRC tumor samples did not show significant differences to specimens in adjacent non-cancerous tissue. Consistent with these findings, gene chips analysing tissue samples of tumors and corresponding normal tissue did not show altered Chibby expression

CONCLUSION: Altered Chibby expression might be observed in vitro in different colon carcinoma cell lines. However, this finding could not be confirmed in vitro in CRC tumors, indicating that Chibby is not likely to promote CRC tumor development or progression. As Chibby is an important inhibitor of ß-catenin signalling, our data implicate that the usability of colon carcinoma cell lines for in vitro studies analysing the Wnt/β-catenin pathway in colorectal carcinoma needs extensive verification.

Induction of renal tumorigenesis with elevated levels of somatic loss of heterozygosity in Tsc1+/- mice on a Blm-deficient background

A Bloom's deficient mouse model (Blm(m3/m3)) has been shown to induce colorectal tumorigenesis when crossed with Apc+/Min mice. Here, we investigated whether the Blm(m3/m3) genotype could induce tumorigenesis in extracolonic tissues in tuberous sclerosis 1-deficient (Tsc1+/-) mice that are predisposed to renal cystadenomas and carcinomas. Genotyping of offspring from Tsc1+/- Blm+/m3 intercrosses showed that a approximately 24% excess of Tsc1+/- over Tsc1+/+ mice died before weaning (P = 0.016), although Blm deficiency had no cumulative effect on Tsc1+/- survival. Tsc1+/- Blm(m3/m3) mice had significantly more macroscopic and microscopic renal lesions at 3 to 6 months compared with Tsc1+/- Blm+/m3 mice (P =0.0003 and 0.0203, respectively), and their tumors showed significantly increased levels of somatic loss of heterozygosity (LOH) of the wild-type Tsc1 (Tsc1wt) allele compared with those from Tsc1+/- Blm+/+ mice (P < 0.0001). Tsc1+/- Blm+/m3 mice did not show significantly more renal lesions compared with Tsc1+/- Blm+/+ animals; however, their lesions still showed significantly increased levels of somatic LOH of the Tsc1wt allele (P = 0.03). Ninety-five percent (19 of 20) of lesions from Tsc1+/- Blm+/m3 mice retained the wild-type Blm (Blm(wt)) allele, indicating that the increased somatic LOH at Tsc1 was mediated by Blm haploinsufficiency. Renal lesions from a Blm-deficient background stained positively with anti-phospho-S6 ribosomal protein (Ser240/244), suggesting that these lesions develop through the normal pathway of Tsc-associated tumorigenesis. This work shows the use of the Blm(m3/m3) mice for inducing renal tumorigenesis, and the high levels (approximately 87%) of LOH in the resultant tumors will help facilitate mapping of loci involved in tumor progression.