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Cyclin D1 is required for transformation by activated Neu and is induced through an E2F-dependent signaling pathway
1Department of Developmental Biology, The Albert Einstein Cancer Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Abstract:
The neu (c-erbB-2) proto-oncogene encodes a tyrosine kinase receptor that is overexpressed in 20 to 30% of human breast tumors. Herein, cyclin D1 protein levels were increased in mammary tumors induced by overexpression of wild-type Neu or activating mutants of Neu in transgenic mice and in MCF7 cells overexpressing transforming Neu. Analyses of 12 Neu mutants in MCF7 cells indicated important roles for specific C-terminal autophosphorylation sites and the extracellular domain in cyclin D1 promoter activation. Induction of cyclin D1 by NeuT involved Ras, Rac, Rho, extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38, but not phosphatidylinositol 3-kinase. NeuT induction of the cyclin D1 promoter required the E2F and Sp1 DNA binding sites and was inhibited by dominant negative E2F-1 or DP-1. Neu-induced transformation was inhibited by a cyclin D1 antisense or dominant negative E2F-1 construct in Rat-1 cells. Growth of NeuT-transformed mammary adenocarcinoma cells in nude mice was blocked by the cyclin D1 antisense construct. These results demonstrate that E2F-1 mediates a Neu-signaling cascade to cyclin D1 and identify cyclin D1 as a critical downstream target of neu-induced transformation.
Insights
The neu proto-oncogene (c-erbB-2) drives breast tumor growth by increasing cyclin D1. Targeting cyclin D1 or E2F-1 inhibits neu-induced cancer cell proliferation and tumor development.
Area of Science:
- Oncology
- Molecular Biology
- Cell Signaling
Background:
- The neu (c-erbB-2) proto-oncogene encodes a tyrosine kinase receptor.
- Neu overexpression occurs in 20-30% of human breast tumors, indicating its oncogenic potential.
Purpose of the Study:
- To investigate the role of the neu proto-oncogene in regulating cyclin D1 expression.
- To elucidate the signaling pathways and molecular mechanisms by which neu influences cyclin D1 and promotes tumor growth.
Main Methods:
- Overexpression of wild-type Neu and its mutants in transgenic mice and MCF7 cells.
- Analysis of cyclin D1 promoter activation using various Neu mutants.
- Investigating signaling pathways including Ras, Rac, Rho, ERK, JNK, p38, and PI3K.
- Utilizing dominant-negative constructs and antisense oligonucleotides to inhibit neu-induced transformation and tumor growth.
Main Results:
- Neu overexpression significantly increased cyclin D1 protein levels in mammary tumors and cancer cells.
- Specific C-terminal autophosphorylation sites and the extracellular domain of Neu are crucial for cyclin D1 promoter activation.
- Neu-induced cyclin D1 expression involves Ras, Rac, Rho, ERK, JNK, and p38 pathways, but not PI3K.
- Activation of the cyclin D1 promoter by Neu requires E2F and Sp1 DNA binding sites.
Conclusions:
- E2F-1 acts as a mediator in the neu-signaling cascade leading to cyclin D1 induction.
- Cyclin D1 is identified as a critical downstream target of neu in promoting cellular transformation and tumor progression.
- Inhibition of cyclin D1 or E2F-1 effectively blocks neu-induced cancer cell proliferation and tumor growth in vivo.