| 1. |
- Buechel, David, et al.
(author)
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Parsing beta-catenins cell adhesion and Wnt signaling functions in malignant mammary tumor progression
- 2021
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In: Proceedings of the National Academy of Sciences of the United States of America. - : NATL ACAD SCIENCES. - 0027-8424 .- 1091-6490. ; 118:34
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Journal article (peer-reviewed)abstract
- During malignant progression, epithelial cancer cells dissolve their cell-cell adhesion and gain invasive features. By virtue of its dual function, beta-catenin contributes to cadherin-mediated cell-cell adhesion, and it determines the transcriptional output of Wnt signaling: via its N terminus, it recruits the signaling coactivators Bd9 and Pygo-pus, and via the C terminus, it interacts with the general transcriptional machinery. This duality confounds the simple loss-of-function analysis of Wnt signaling in cancer progression. In many cancer types including breast cancer, the functional contribution of beta-catenins transcriptional activities, as compared to its adhesion functions, to tumor progression has remained elusive. Employing the mouse mammary tumor virus (MMTV)-PyMT mouse model of metastatic breast cancer, we compared the complete elimination of beta-catenin with the specific ablation of its signaling outputs in mammary tumor cells. Notably, the complete lack of beta-catenin resulted in massive apoptosis of mammary tumor cells. In contrast, the loss of beta-catenins transcriptional activity resulted in a reduction of primary tumor growth, tumor invasion, and metastasis formation in vivo. These phenotypic changes were reflected by stalled cell cycle progression and diminished epithelial-mesenchymal transition (EMT) and cell migration of breast cancer cells in vitro. Transcriptome analysis revealed subsets of genes which were specifically regulated by beta-catenins transcriptional activities upon stimulation with Wnt3a or during TGF-beta-induced EMT. Our results uncouple the signaling from the adhesion function of beta-catenin and underline the importance of Wnt/beta-catenin-dependent transcription in malignant tumor progression of breast cancer.
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| 2. |
- Saxena, Meera, et al.
(author)
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A Pygopus 2-Histone Interaction Is Critical for Cancer Cell Dedifferentiation and Progression in Malignant Breast Cancer
- 2020
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In: Cancer Research. - : AMER ASSOC CANCER RESEARCH. - 0008-5472 .- 1538-7445. ; 80:17, s. 3631-3648
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Journal article (peer-reviewed)abstract
- Pygopus 2 (Pygo2) is a coactivator of Wnt/b-catenin signaling that can bind bi- or trimethylated lysine 4 of histone-3 (H3K4me(2/3)) and participate in chromatin reading and writing. It remains unknown whether the Pygo2-H3K4me(2/3) association has a functional relevance in breast cancer progression in vivo. To investigate the functional relevance of histone-binding activity of Pygo2 in malignant progression of breast cancer, we generated a knock-in mouse model where binding of Pygo2 to H3K4me(2/3) was rendered ineffective. Loss of Pygo2-histone interaction resulted in smaller, differentiated, and less metastatic tumors, due, in part, to decreased canonical Wnt/b-catenin signaling. RNA- and ATAC-sequencing analyses of tumor-derived cell lines revealed downregulation of TGF beta signaling and upregulation of differentiation pathways such as PDGFR signaling. Increased differentiation correlated with a luminal cell fate that could be reversed by inhibition of PDGFR activity. Mechanistically, the Pygo2-histone interaction potentiated Wnt/beta-catenin signaling, in part, by repressing the expression of Wnt signaling antagonists. Furthermore, Pygo2 and beta-catenin regulated the expression of miR-29 family members, which, in turn, repressed PDGFR expression to promote dedifferentiation of wild-type Pygo2 mammary epithelial tumor cells. Collectively, these results demonstrate that the histone binding function of Pygo2 is important for driving dedifferentiation and malignancy of breast tumors, and loss of this binding activates various differentiation pathways that attenuate primary tumor growth and metastasis formation. Interfering with the Pygo2-H3K4me(2/3) interaction may therefore serve as an attractive therapeutic target for metastatic breast cancer. Significance: Pygo2 represents a potential therapeutic target in metastatic breast cancer, as its histone-binding capability promotes beta-catenin-mediated Wnt signaling and transcriptional control in breast cancer cell dedifferentiation, EMT, and metastasis.
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| 3. |
- Vafaizadeh, Vida, et al.
(author)
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The interactions of Bcl9/Bcl9L with beta-catenin and Pygopus promote breast cancer growth, invasion, and metastasis
- 2021
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In: Oncogene. - : Springer Nature. - 0950-9232 .- 1476-5594. ; 40:43, s. 6195-6209
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Journal article (peer-reviewed)abstract
- Canonical Wnt/beta-catenin signaling is an established regulator of cellular state and its critical contributions to tumor initiation, malignant tumor progression and metastasis formation have been demonstrated in various cancer types. Here, we investigated how the binding of beta-catenin to the transcriptional coactivators B-cell CLL/lymphoma 9 (Bcl9) and Bcl9-Like (Bcl9L) affected mammary gland carcinogenesis in the MMTV-PyMT transgenic mouse model of metastatic breast cancer. Conditional knockout of both Bcl9 and Bcl9L resulted into tumor cell death. In contrast, disrupting the interaction of Bcl9/Bcl9L with beta-catenin, either by deletion of their HD2 domains or by a point mutation in the N-terminal domain of beta-catenin (D164A), diminished primary tumor growth and tumor cell proliferation and reduced tumor cell invasion and lung metastasis. In comparison, the disruption of HD1 domain-mediated binding of Bcl9/Bcl9L to Pygopus had only moderate effects. Interestingly, interfering with the beta-catenin-Bcl9/Bcl9L-Pygo chain of adapters only partially impaired the transcriptional response of mammary tumor cells to Wnt3a and TGF beta treatments. Together, the results indicate that Bcl9/Bcl9L modulate but are not critically required for canonical Wnt signaling in its contribution to breast cancer growth and malignant progression, a notion consistent with the "just-right" hypothesis of Wnt-driven tumor progression.
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