Molecular Cancer - Latest articles

Human ESCs predisposition to karyotypic instability: Is a matter of cell culture adaptation or differential vulnerability among hESC lines due to inherent properties?

2008-10-03

Karyotypic changes by human ESCs represent a pitfall for potential future applications. Here, molecular cytogenetics revealed genetic stability of two hESC lines maintained in feeders up to 185 passages using either mechanical or enzymatic methods. Upon transfer to a feeder-free culture system, the younger hESC line (71 passages) gained a chromosome 12 by passage 17 and a marker by passage 21, characterized as a gain of chromosome 20 by SKY. The mosaicism for trysomy 12 gradually increased up to 89% by passage 30, suggesting that this karyotypic abnormality provides a selective advantage. However, a much older hESC line (185 passages) did not undergo any chromosomal change after 30 passages in a feeder-free culture (215 passages in total). This data supports the idea that regardless of the cell culture conditions/length, some hESCs are inherently more vulnerable than others to karyotypic instability.

Similarity of aberrant DNA methylation in Barrett's esophagus and esophageal adenocarcinoma

2008-10-02

Background: Barrett's esophagus (BE) is the metaplastic replacement of squamous with columnar epithelium in the esophagus, as a result of reflux. It is the major risk factor for the development of esophageal adenocarcinoma (EAC). Methylation of CpG dinucleotides of normally unmethylated genes is associated with silencing of their expression, and is common in EAC. This study was designed to determine at what stage, in the progression from BE to EAC, methylation of key genes occurs. Results: We examined 9 genes (APC, CDKN2A, ID4, MGMT, RBP1, RUNX3, SFRP1, TIMP3, and TMEFF2), frequently methylated in multiple cancer types, in a panel of squamous (19 biopsies from patients without BE or EAC, 16 from patients with BE, 22 from patients with EAC), BE (40 metaplastic, 7 high grade dysplastic) and 40 EAC tissues. The methylation frequency, the percentage of samples that had any extent of methylation, for each of the 9 genes in the EAC (88%, 56%, 73%, 56%, 66%, 66%, 93%, 70% and 80% respectively) was significantly higher than any of the squamous groups. The methylation frequency for each of the 9 genes in the metaplastic BE (95%, 28%, 78%, 48%, 58%, 48%, 93%, 88% and 75% respectively) was significantly higher than in the squamous samples except for CDKN2A and RBP1. The methylation frequency did not differ between BE and EAC samples, except for CDKN2A which was significantly higher in EAC. The methylation extent was an estimate of both the number of methylated alleles and the density of methylation on these alleles. This was significantly greater in EAC than in metaplastic BE for only 4 of the 9 genes: CDKN2A, RBP1, RUNX3 and TMEFF2. There was no significant differences for any gene in methylation extent between dysplastic BE and EAC. Conclusions: We found significant methylation in metaplastic BE, which for 8 of the 9 genes studied did not differ in frequency from that found in EAC. This is also the first report of gene silencing by methylation of ID4 in BE or EAC. This study suggests that BE is a highly abnormal tissue, more similar to cancer tissue than to normal epithelium.

A quantitative PCR method to detect blood microRNAs associated with tumorigenesis in transgenic mice

2008-09-30

MicroRNA (miRNA) dysregulation frequently occurs in cancer. Analysis of whole blood miRNA in tumor models has not been widely reported, but could potentially lead to novel assays for early detection and monitoring of cancer. To determine whether miRNAs associated with malignancy could be detected in the peripheral blood, we used real-time reverse transcriptase-PCR to determine miRNA profiles in whole blood obtained from transgenic mice with c-MYC-induced lymphoma, hepatocellular carcinoma and osteosarcoma. The PCR-based assays used in our studies require only 10 nanograms of total RNA, allowing serial mini-profiles (20 - 30 miRNAs) to be carried out on individual animals over time. Blood miRNAs were measured from mice at different stages of MYC-induced lymphomagenesis and regression. Unsupervised hierarchical clustering of the data identified specific miRNA expression profiles that correlated with tumor type and stage. The miRNAs found to be altered in the blood of mice with tumors frequently reverted to normal levels upon tumor regression. Our results suggest that specific changes in blood miRNA can be detected during tumorigenesis and tumor regression.

Rac1 GTPase and the Rac1 exchange factor Tiam1 associate with Wnt-responsive promoters to enhance beta-catenin/TCF-dependent transcription in colorectal cancer cells

2008-09-30

Background: Beta-catenin is a key mediator of the canonical Wnt pathway as it associates with members of the T-cell factor (TCF) family at Wnt-responsive promoters to drive the transcription of Wnt target genes. Recently, we showed that Rac1 GTPase synergizes with beta-catenin to increase the activity of a TCF-responsive reporter. This synergy was dependent on the nuclear presence of Rac1, since inhibition of its nuclear localization effectively abolished the stimulatory effect of Rac1 on TCF-responsive reporter activity. We hypothesised that Rac1 plays a direct role in enhancing the transcription of endogenous Wnt target genes by modulating the beta-catenin/TCF transcription factor complex. Results: We employed chromatin immunoprecipitation studies to demonstrate that Rac1 associates with the beta-catenin/TCF complex at Wnt-responsive promoters of target genes. This association served to facilitate transcription, since overexpression of active Rac1 augmented Wnt target gene activation, whereas depletion of endogenous Rac1 by RNA interference abrogated this effect. In addition, the Rac1-specific exchange factor, Tiam1, potentiated the stimulatory effects of Rac1 on the canonical Wnt pathway. Tiam1 promoted the formation of a complex containing Rac1 and beta-catenin. Furthermore, endogenous Tiam1 associated with endogenous beta-catenin, and this interaction was enhanced in response to Wnt3a stimulation. Intriguingly, Tiam1 was recruited to Wnt-responsive promoters upon Wnt3a stimulation, whereas Rac1 was tethered to TCF binding elements in a Wnt-independent manner. Conclusions: Taken together, our results suggest that Rac1 and the Rac1-specific activator Tiam1 are components of transcriptionally active beta-catenin/TCF complexes at Wnt-responsive promoters, and the presence of Rac1 and Tiam1 within these complexes serves to enhance target gene transcription. Our results demonstrate a novel functional mechanism underlying the cross-talk between Rac1 and the canonical Wnt signalling pathway.

Metabolite profiling of human colon carcinoma - deregulation of TCA cycle and amino acid turnover

2008-09-18

Background: Apart from genetic alterations, development and progression of colorectal cancer has been linked to influences from nutritional intake, hyperalimentation, and cellular metabolic changes that may be the basis for new diagnostic and therapeutic approaches. However, in contrast to genomics and proteomics, comprehensive metabolomic investigations of alterations in malignant tumors have rarely been conducted. Results: In this study we investigated a set of paired samples of normal colon tissue and colorectal cancer tissue with gas-chromatography time-of-flight mass-spectrometry, which resulted in robust detection of a total of 206 metabolites. Metabolic phenotypes of colon cancer and normal tissues were different at a Bonferroni corrected significance level of p=0.00170 and p=0.00005 for the first two components of an unsupervised PCA analysis. Subsequent supervised analysis found 82 metabolites to be significantly different at p<0.01. Metabolites were connected to abnormalities in metabolic pathways by a new approach that calculates the distance of each pair of metabolites in the KEGG database interaction lattice. Intermediates of the TCA cycle and lipids were found down-regulated in cancer, whereas urea cycle metabolites, purines, pyrimidines and amino acids were generally found at higher levels compared to normal colon mucosa. Conclusion: This study demonstrates that metabolic profiling facilitates biochemical phenotyping of normal and neoplastic colon tissue at high significance levels and points to GC-TOF-based metabolomics as a new method for molecular pathology investigations.

Eplin-alpha expression in human breast cancer, the impact on cellular migration and clinical outcome

2008-09-16

IntroductionTo investigate the expression of EPLIN-α, epithelial protein lost in neoplasm, in human breast cancer tissues/cells and investigate the cellular impact of EPLIN-α on breast cancer cells.Experimental designEPLIN-α was determined in tumour (n = 120) and normal mammary tissues (n = 32), and cancer cell lines (n = 16). Cell invasion, in vitro and in vivo growth of cells transfected with EPLIN-α were evaluated using in vitro invasion assay, in vitro and in vivo tumour model. Cellular migration was analysed using Electric Cell Impedance Sensing assays. Results: Low level of EPLIN-α was seen in tumour tissues. Grade-2/3 tumours had significantly lower levels of EPLIN-α compared with grade-1 (p = 0.047 and p = 0.046 vs grade-1, respectively). Patients with poor prognosis had a significantly lower levels of EPLIN-α compared with those with good prognosis (p = 0.0081). Patients who developed recurrence and died of breast cancer had significantly lower levels of EPLIN-α compared with those who remained disease free (p = 0.0003 and p = 0.0008, respectively) (median follow-up 10 years). Patients with high levels of EPLIN-α transcript had a longer survival than those with low levels. Over-expression of EPLIN-α in breast cancer cells by way of transfection rendered cells less invasive, less motile and growing at a slower pace in vitro and in vivo. An ERK inhibitor was shown to be able to abolish the effect of EPLIN expression. Conclusion: It is concluded that expression of EPLIN-α in breast cancer is down-regulated in breast cancer cells and tissues, a change linked to the prognosis. EPLIN-α acts as a potential tumour suppressor by inhibition of growth and migration of cancer cells.

Differential effects of class I isoform histone deacetylase depletion and enzymatic inhibition by belinostat or valproic acid in HeLa cells

2008-09-12

Background: Histone acetylation is an epigenetic modification involved in the regulation of gene expression, balanced by histone acetyl transferases and histone deacetylase (HDAC) enzymes. HDAC inhibitors (HDACi) induce growth arrest and cell death in transformed cells, and are currently in many clinical cancer trials. The transcriptional response to HDACi is complex, as is the response to HDAC isoform knockdown (KD). Here, we describe for the first time in a human cancer cell line, a transcriptional comparison of treatment by two structurally unrelated HDACi; belinostat and valproic acid with the KD of HDAC1, 2 and 3 isoforms. Results: HDAC KD showed anti-proliferative effects, although to a lesser extent than HDACi treatment. Moreover, we found a 2-fold increased resistance of HDAC1 knockdown cells to belinostat, suggesting this isoenzyme as a selective target. While both HDACi treatment and individual class I HDAC KD produce significant transcriptional effects, three-times higher for HDACi, the gene-expression profiles of class I HDAC KD compared with that obtained by HDACi treatment exhibited less than 4% of altered genes in common between the two modes of inhibition. Further, cell-specific effects of HDAC KD are evident by comparison with a recent study in a different cell line. Conclusion: The increased resistance to belinostat in response to HDAC1 depletion indicates the possibility of using this isoform as a predictive biomarker of response to HDACi treatment. Further, the transcriptional response to chemical inhibition of HDACs is very different from that of KD of individual class I HDAC isoforms. These data suggest that the anti-tumor effect of HDACi is indeed linked to class I inhibition, but may be more complex than simply targeting individual HDAC enzymes.

Radiation-induced caveolin-1 associated EGFR internalization is linked with nuclear EGFR transport and activation of DNA-PK

Klaus Dittmann, Claus Mayer, Rainer Kehlbach and H Peter Rodemann — 2008-09-12

Background: To elucidate the role of src kinase in caveolin-1 driven internalization and nuclear transport of EGFR linked to regulation of DNA-repair in irradiated cells. Results: Ionizing radiation resulted in src kinase stabilization, activation and subsequent src mediated caveolin-1 Y14- and EGFR Y845-phosphorylations. Both phosphorylations were radiation specific and could not be observed after treatment with EGF. Inhibition of EGFR by the antibody Erbitux resulted in a strong accumulation of caveolin/EGFR complexes within the cytoplasm, which could not be further increased by irradiation. Radiation-induced caveolin-1- and EGFR-phosphorylations were associated with nuclear EGFR transport and activation of DNA-PK, as detected by phosphorylation at T2609. Blockage of src activity by the specific inhibitor PP2, decreased nuclear transport of EGFR and inhibited caveolin-1- and DNA-PK-phosphorylation. Knockdown of src by specific siRNA blocked EGFR phosphorylation at Y845, phosphorylation of caveolin-1 at Y14 and abolished EGFR transport into the nucleus and phosphorylation of DNA-PK. Consequently, both knockdown of src by specific siRNA and also inhibition of src activity by PP2 resulted in an enhanced residual DNA-damage as quantified 24 h after irradiation and increased radiosensitivity. Conclusion: Src kinase activation following irradiation triggered caveolin-1 dependent EGFR internalization into caveolae. Subsequently EGFR shuttled into the nucleus. As a consequence, inhibition of internalization and nuclear transport of EGFR blocked radiation-induced phosphorylation of DNA-PK and hampered repair of radiation-induced double strand breaks.

Impact of BRAF, MLH1 on the incidence of microsatellite instability high colorectal cancer in populations based study

2008-08-21

We have identified an alternative pathway of tumorigenesis in sporadic colon cancer, involving microsatellite instability due to mismatched repair methylation, which may be driven by mutations in the BRAF gene (V600E). Colorectal cancer (CRC) is the most common cancer in the world, and African Americans show a higher incidence than other populations in the United States. We analyzed sporadic CRCs in Omani (of African origin, N = 61), Iranian (of Caucasian origin, N = 53) and African American (N = 95) patients for microsatellite instability, expression status of mismatched repair genes (hMLH1, hMSH2) and presence of the BRAF (V600E) mutation. In the Omani group, all tumors with BRAF mutations were located in the left side of the colon, and for African Americans, 88% 7 of tumors with BRAF mutations were found in the right side of the colon. In African Americans, 31% of tumors displayed microsatellite instability at two or more markers (MSI-H), while this rate was 26% and 13% for tumors in the Iranian and Omani groups, respectively. A majority of these MSI-H tumors were located in the proximal colon (right side) in African American and Iranian subjects, whereas most were located in the distal colon (left side) in Omani subjects. Defects in hMLH1 gene expression were found in 77% of MSI-H tumors in both African Americans and Iranians and in 38% of tumors in Omanis. BRAF mutations were observed in all subjects: 10% of tumors in African Americans (8/82), 2% of tumors in Iranians (1/53), and 19% of tumors in Omanis (11/59). Our findings suggest that CRC occurs at a younger age in Omani and Iranian patients, and these groups showed a lower occurrence of MSI-H than did African American patients. Our multivariate model suggests an important and significant role of hMLH1 expression and BRAF mutation in MSI-H CRC in these populations. The high occurrence of MSI-H tumors in African Americans may have significant implications for treatment, since patients with MSI-H lesions display a different response to chemotherapeutic agents such as 5-fluorouracil.

Exit of pediatric pre-B acute lymphoblastic leukaemia cells from the bone marrow to the peripheral blood is not associated with cell maturation or alterations in gene expression

2008-08-11

Background: Childhood pre-B acute lymphoblastic leukemia (ALL) is a bone marrow (BM) derived disease, which often disseminates out of the BM cavity, where malignant cells to a variable degree can be found circulating in the peripheral blood (PB). Normal pre-B cells are absolutely dependent on BM stroma for survival and differentiation. It is not known whether transformed pre-B ALL cells retain any of this dependence, which possibly could impact on drug sensitivity or MRD measurements. Results: Pre-B ALL cells, highly purified by a novel method using surface expression of CD19 and immunoglobulin light chains, from BM and PB show a very high degree of similarity in gene expression patterns, with differential expression of vascular endothelial growth factor (VEGF) as a notable exception. In addition, the cell sorting procedure revealed that in 2 out of five investigated patients, a significant fraction of the malignant cells had matured beyond the pre-B cell stage. Conclusion: The transition of ALL cells from the BM into the circulation does not demand, or result in, major changes of gene expression pattern. This might indicate an independence of BM stroma on the part of transformed pre-B cells, which contrasts with that of their normal counterparts.