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Notch-2 and the Notch signaling pathway are regulated by Wnt signaling in colorectal cancer
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Experimental Hematology . Linköping University, Faculty of Health Sciences.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Both Notch and Wnt pathways are key regulators of intestinal homeostasis and alterations in these pathways can lead to development of colorectal cancer, where the Apc/β-catenin-genes in the Wnt signaling pathway are frequently mutated, and active Notch signaling contributes to tumorigenesis by keeping the epithelial cells in a proliferative state. These pathways are simultaneously active in proliferative adenoma cells and a crosstalk between them has been indicated.

Using bioinformatics, we identified and screened proximal Notch pathway gene promoters for putative TCF/LEF1 sites, targets for β-catenin. Wild type (wt)-Apc negatively regulates β-catenin and by using semi-quantitative PCR, induction of wt-Apc or β-catenin silencing in HT29 cells, we observed that several genes in the Notch pathway, including Notch-2, were downregulated. Electrophoretic mobility-shift assay (EMSA) confirmed binding of Lef-1 to Notch-2 as well as other Notch pathway gene promoters and luciferase assays showed an increased activity for the LEF1/TCF-site at position -110 in the Notch-2 promoter upon cotransfection of HT29 or HCT116 cells with mutated β-catenin. Taken together, these results indicate that activation of the Wnt pathway with increased levels of β-catenin can function as a transcriptional regulator of the Notch pathway in colon cancer cell lines.

Keyword [en]
Notch signaling, Notch-2, APC, β-catenin, crosstalk, colorectal cancer
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-51728OAI: oai:DiVA.org:liu-51728DiVA: diva2:277159
Available from: 2009-11-16 Created: 2009-11-16 Last updated: 2009-11-19Bibliographically approved
In thesis
1. Notch signalling in carcinogenesis: With special emphasis on T-cell lymphoma and colorectal cancer
Open this publication in new window or tab >>Notch signalling in carcinogenesis: With special emphasis on T-cell lymphoma and colorectal cancer
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The Notch signalling pathway is an evolutionary conserved pathway, named after the Notch receptors, Notch1-4 in mammals, which upon cell-cell contact and ligand binding releases the intracellular domain (NICD). NICD translocates into the nucleus where it binds the transcriptional repressor RBP-Jk, which together with co-activators belonging to the Mastermind-like family of proteins form a transcriptional activation complex. This complex activates genes controlling cell fate decision, embryonic development, proliferation, differentiation, adult homeostasis and stem cell maintenance. On the other hand, disrupted Notch signalling may result in pathological conditions like cancer, although the mechanisms behind the disruption are often complex and in many cases largely unknown.

Notch1 drives the lymphocyte differentiation towards a T-cell fate and activating mutations in the gene have been suggested to be involved in T-cell lymphoma. In paper I, genetic alterations in Notch1 and the Notch1 regulating gene CDC4 were investigated in tumours from murine T-cell lymphoma induced with phenolphthalein, 1,3-butadiene or 2’,3’-dideoxycytidine. We identified activating Notch1 mutations in 39% of the lymphomas, suggesting that Notch1 is an important target gene for mutations in chemically induced lymphomas.

While it is known that constitutively activated Notch signalling has a clear oncogenic function in several solid malignancies as well, the molecular mechanisms are less known in this context. Unpublished data of our lab, together with other recent studies, suggest that mutations of Notch and Notch-related genes per se are uncommon in solid malignancies including colorectal cancer, while a growing body of evidence indicates that aberrant Wnt/b-catenin signalling may result in pro-tumoural Notch activation in these contexts. In paper II, we therefore investigated potential transcriptional interactions between the Notch and Wnt signalling pathways in colorectal cancer cell lines. The proximal Notch and Wnt pathway gene promoters were bioinformatically identified and screened for putative TCF/LEF1 and RBP-Jk sites. In canonical Wnt signalling, Apc negatively regulates b-catenin leading to repression of TCF/LEF1 target genes. Upon repression of the Wnt pathway we observed that several genes in the Notch pathway, including Notch2, were transcriptionally downregulated. We also confirmed binding of Lef1 to Notch2 as well as other Notch pathway gene promoters and luciferase assays showed an increased activity for at least one LEF1/TCF-site in the Notch2 promoter upon co-transfection of HT29 or HCT116 cells with mutated b-catenin. HT29 cell lines were also treated with the g-secretase inhibitor DAPT, leading to inactivation of the Notch pathway by preventing release of NICD. However, results showed no effects on Apc, b-catenin or their target cyclin D1. Taken together, these results indicate that the Wnt pathway may function as a regulator of the Notch pathway through the TCF/LEF1 target gene program in colon cancer cell lines.

In summary, Notch pathway deregulation is of importance in both murine T-cell lymphoma and human colorectal cancer, although the mechanisms differ. The current results give new insights in Notch pathway alterations as well as the signalling networks in which the Notch pathway interacts, and thus increase the understanding of Notch’s involvement in malignant diseases.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2009. 52 p.
Series
Linköping Studies in Health Sciences. Thesis, ISSN 1100-6013 ; 106
Keyword
Notch signalling, T-cell lymphoma, colorectal cancer, Wnt signalling, transcription
National Category
Cell and Molecular Biology
Identifiers
urn:nbn:se:liu:diva-51692 (URN)978-91-7393-510-4 (ISBN)
Presentation
2009-11-12, Conrad, Universitetssjukhuset, Campus US, Linköpings Universitet, Linköping, 09:00 (English)
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Studies on molecular genetic alterations in colorectal cancer
Available from: 2009-11-19 Created: 2009-11-13 Last updated: 2009-11-19Bibliographically approved

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Ungerbäck, JonasElander, NilsSigvardsson, MikaelSöderkvist, Peter

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