Differential gene expression upon shRNA-mediated silencing of APC in HT-29 colorectal cancer cells
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ABSTRACT: Wnt signaling plays a pivotal role in colorectal cancer. Intrinsic activation of Wnt by mutational events, such as mutations in the tumor suppressor gene APC, represents the most frequent initiating event in this disease background. Long truncated versions of APC retain partial functionality, which leads to a sub-maximal, “just right” activation state of Wnt signaling supposed to be beneficial for disease initiation. In order to study the transcriptomic alterations of an over-stimulated Wnt signaling pathway, conditional shRNA-mediated silencing of APC was performed in chromosomal instable HT-29 CRC cells which express a 1555 amino acid variant of APC protein able to bind and partially inactivate β-catenin. To achieve this, cells were stably transduced with lentiviral particles encoding for a doxycyline-inducible shRNA directed against APC, or, as a control, a non-silencing shRNA (pTRIPZ inducible shRNA vectors, RHS4740-EG324, Horizon Dharmacon, CO, USA). 72 hours after APC silencing, total RNA was isolated and quality controlled for subsequent RNA-Seq Analysis (DKFZ Heidelberg, Genomic and Proteomic Core Facility) on a HiSeq 2000 instrument (Illumina). Overall, we observed bona-fide Wnt target genes, such as NKD1, AXIN2, PTK7, ASCL2, and SMOC2, and additional putative direct or indirect targets of Wnt signaling up-regulated upon shRNA-mediated APC silencing.
Project description:APC is a key regulator of canonical Wnt signalling since it participates to beta-catenin targeting to proteasomal degradation when the pathway is inactive. Moreover, independently of Wnt signaling, APC regulates several cellular functions such as mycrotubule dynamics, chromosome segregation, cell adhesion. Although APC has been widely studied for its implication in initation and progression of several cancers, its role in satellite cells (skeletal muscle stem cells) has never been investigated. Here we used microarrays and to clarify APC functions and we identified several pathways and cellular processes to be affected following APC silencing.
Project description:Mutations in APC or β-catenin that cause aberrant activation of Wnt signaling are responsible for the initiation of colorectal tumor development. LGR5 is specifically expressed in stem cells of the intestine, stomach and hair follicle, and plays essential roles in maintaining tissue homeostasis. LGR5-positive stem cells have been shown to be responsible for the intestinal adenoma initiated by some mutations in APC . Furthermore, it has recently been reported that Lgr5, which is associated with the Frizzled/Lrp Wnt receptor complex, interacts with R-spondins and thereby activates Wnt signaling. However, the function of LGR5 in colorectal tumorigenesis has been unclear. Here we show that LGR5 is required for the tumorigenicity of colorectal cancer cells. We also show that the transcription factor GATA6 directly enhances the expression of LGR5. DLD1 cells were infected with a lentivirus expressing an shRNA targeting GATA6 or LGR5.
Project description:Although the role of the Wnt pathway in colon carcinogenesis has been described previously, it has been recently demonstrated that Wnt signaling originates from highly dynamic nano-assemblies at the plasma membrane. However, little is known regarding the role of oncogenic APC in reshaping Wnt nanodomains. This is noteworthy, because oncogenic APC does not act autonomously and requires activation of Wnt effectors upstream of APC to drive aberrant Wnt signaling. Here, we demonstrate the role of oncogenic APC in increasing plasma membrane free cholesterol and rigidity, thereby modulating Wnt signaling hubs. This results in an overactivation of Wnt signaling in the colon. Finally, using the Drosophila sterol auxotroph model, we demonstrate the unique ability of exogenous free cholesterol to disrupt plasma membrane homeostasis and drive Wnt signaling in a wildtype APC background. Collectively, these findings provide a mechanistic link between oncogenic APC, loss of plasma membrane homeostasis and CRC development.
Project description:Wnt signaling is a highly conserved metazoan pathway that plays a crucial role in cell-fate determination and morphogenesis during development. Wnt ligands can induce disparate cellular responses. The exact mechanism behind these different outcomes is not fully understood but may be due to interactions with different receptors on the cell membrane. PTK7/Otk is a transmembrane receptor that is implicated in various developmental and physiological processes including cell polarity, cell migration, and invasion. Here we examine two roles of Otk1 and Otk2 in patterning and neurogenesis. We find that Otk1 is a positive regulator of signaling and Otk2 functions as its inhibitor. We propose that PTK7/Otk functions in signaling and in particular cell migration and polarity contributing to the diversity of cellular responses seen in Wnt-mediated processes.
Project description:The Adenomatous Polyposis Coli (APC) tumor suppressor is mutated in the vast majority of human colorectal cancers (CRC) and leads to deregulated Wnt signaling. To determine whether Apc disruption is required for tumor maintenance, we developed a mouse model of CRC whereby Apc can be conditionally suppressed using a doxycycline-regulated shRNA. Apc suppression produces adenomas in both the small intestine and colon that, in the presence of Kras and p53 mutations, can progress to invasive carcinoma. In established tumors, Apc restoration drives rapid and widespread tumor-cell differentiation and sustained regression without relapse. Tumor regression is accompanied by the re-establishment of normal crypt-villus homeostasis, such that once aberrantly proliferating cells reacquire self-renewal and multi-lineage differentiation capability. Our study reveals that CRC cells can revert to functioning normal cells given appropriate signals, and provide compelling in vivo validation of the Wnt pathway as a therapeutic target for treatment of CRC Analysis of RNA isolated from colon polyps that presented in shAPC or shAPC/Kras mice as compared to shRenilla (neutral) mouse colon mucosa
Project description:PTK7 was identified from a meta-analysis of 1905 non-small-cell lung cancer (NSCLC) samples across 12 datasets to be one of seven genes commonly up-regulated in lung adenocarcinoma (ADC). Using ADC cell lines NCI-H1299 and NCI-H2009, disruption of PTK7 resulted in decreased cell viability and induction of apoptosis. A xenotransplantation model of the cell lines with PTK7 knock-down also resulted in decreased tumor burden. We assayed gene expression in these cell lines after PTK7 knock-down by shRNA to uncover deregulated pathways and genes.
Project description:The Adenomatous Polyposis Coli (APC) tumor suppressor is mutated in the vast majority of human colorectal cancers (CRC) and leads to deregulated Wnt signaling. To determine whether Apc disruption is required for tumor maintenance, we developed a mouse model of CRC whereby Apc can be conditionally suppressed using a doxycycline-regulated shRNA. Apc suppression produces adenomas in both the small intestine and colon that, in the presence of Kras and p53 mutations, can progress to invasive carcinoma. In established tumors, Apc restoration drives rapid and widespread tumor-cell differentiation and sustained regression without relapse. Tumor regression is accompanied by the re-establishment of normal crypt-villus homeostasis, such that once aberrantly proliferating cells reacquire self-renewal and multi-lineage differentiation capability. Our study reveals that CRC cells can revert to functioning normal cells given appropriate signals, and provide compelling in vivo validation of the Wnt pathway as a therapeutic target for treatment of CRC
Project description:Ovarian cancer (OC) presents a significant challenge in clinical settings due to its difficulty in early diagnosis and its resistance to treatment. FOXP4 is a member of the FOXP subfamily and is involved in various biological processes including embryonic development, cell cycle regulation, and tumorigenesis. Despite its potential role in cancer, the exact function and significance of FOXP4 in OC remain uncertain. Here we showed that FOXP4 was expressed at high levels in OC, and its high expression was associated with poor prognosis. Furthermore, RNA sequencing and functional analysis of cells lacking FOXP4 suggest that FOXP4 contributes to the activation of the Wnt signaling pathway, leading to the amplification of the malignant phenotype in OV. Mechanistically, FOXP4 directly induces the expression of protein tyrosine kinase 7 (PTK7), a Wnt-binding receptor tyrosine pseudokinase, leading to abnormal activation of the Wnt signaling pathway. Disrupting the FOXP4-Wnt feedback loop by inactivating the Wnt signaling pathway or reducing FOXP4 expression resulted in the reduction of the malignant phenotype of OC cells, while restoring PTK7 expression reversed this effect. In conclusion, our findings highlight the importance of FOXP4 in the activation of the Wnt signaling pathway in OC and provide evidence for the potential therapeutic value of targeting this pathway in the treatment of the disease.
Project description:The highly conserved Wnt signaling pathway drives intestinal homeostasis across species. Apc is a negative regulator of Wnt signaling. Loss of function mutations in Apc are found in 80-90% of human colorectal cancers. Importantly, Apc loss is widely known as the key driving event in the disease. We used microarray analysis of adult Drosophila midguts to study the molecular mechanisms regulated upon loss of Apc in the intestine.
Project description:PTK7 was identified from a meta-analysis of 1905 non-small-cell lung cancer (NSCLC) samples across 12 datasets to be one of seven genes commonly up-regulated in lung adenocarcinoma (ADC). Using ADC cell lines NCI-H1299 and NCI-H2009, disruption of PTK7 resulted in decreased cell viability and induction of apoptosis. A xenotransplantation model of the cell lines with PTK7 knock-down also resulted in decreased tumor burden. We assayed gene expression in these cell lines after PTK7 knock-down by shRNA to uncover deregulated pathways and genes. 8 samples were analyzed. In each cell line, we knocked down PTK7 with 2 independent hairpins, and 2 control hairpins targeting luciferase and GFP. Thus, NCI-H1299 has 2 samples of PTK7 knock-down, and 2 samples of control knock down. NCI-H2009 has similar samples.