Article

Multifaceted Regulation of Cell Cycle Progression by Estrogen: Regulation of Cdk Inhibitors and Cdc25A Independent of Cyclin D1-Cdk4 Function

Department of Obstetrics and Gynecology, Graduate School of Medicine, University of Tennessee Medical Center, Knoxville, Tennessee 37920, USA.
Molecular and Cellular Biology (Impact Factor: 5.04). 03/2001; 21(3):794-810. DOI: 10.1128/MCB.21.3.794-810.2001
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ABSTRACT Estrogens induce proliferation of estrogen receptor (ER)-positive MCF-7 breast cancer cells by stimulating G(1)/S transition associated with increased cyclin D1 expression, activation of cyclin-dependent kinases (Cdks), and phosphorylation of the retinoblastoma protein (pRb). We have utilized blockade of cyclin D1-Cdk4 complex formation through adenovirus-mediated expression of p16(INK4a) to demonstrate that estrogen regulates Cdk inhibitor expression and expression of the Cdk-activating phosphatase Cdc25A independent of cyclin D1-Cdk4 function and cell cycle progression. Expression of p16(INK4a) inhibited G(1)/S transition induced in MCF-7 cells by 17-beta-estradiol (E(2)) with associated inhibition of both Cdk4- and Cdk2-associated kinase activities. Inhibition of Cdk2 activity was associated with delayed removal of Cdk-inhibitory activity in early G(1) and decreased cyclin A expression. Cdk-inhibitory activity and expression of both p21(Cip1) and p27(Kip1) was decreased, however, in both control and p16(INK4a)-expressing cells 20 h after estrogen treatment. Expression of Cdc25A mRNA and protein was induced by E(2) in control and p16(INK4a)-expressing MCF-7 cells; however, functional activity of Cdc25A was inhibited in cells expressing p16(INK4a). Inhibition of Cdc25A activity in p16(INK4a)-expressing cells was associated with depressed Cdk2 activity and was reversed in vivo and in vitro by active Cdk2. Transfection of MCF-7 cells with a dominant-negative Cdk2 construct inhibited the E(2)-dependent activation of ectopic Cdc25A. Supporting a role for Cdc25A in estrogen action, antisense CDC25A oligonucleotides inhibited estrogen-induced Cdk2 activation and DNA synthesis. In addition, inactive cyclin E-Cdk2 complexes from p16(INK4a)-expressing, estrogen-treated cells were activated in vitro by treatment with recombinant Cdc25A and in vivo in cells overexpressing Cdc25A. The results demonstrate that functional association of cyclin D1-Cdk4 complexes is required for Cdk2 activation in MCF-7 cells and that Cdk2 activity is, in turn, required for the in vivo activation of Cdc25A. These studies establish Cdc25A as a growth-promoting target of estrogen action and further indicate that estrogens independently regulate multiple components of the cell cycle machinery, including expression of p21(Cip1) and p27(Kip1).

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    • "In ER-positive breast cancer treatment, ER antagonists are effective at stopping cell division, indicating that such tumors are dependent upon estrogen for proliferation and survival (Musgrove and Sutherland, 2009). It was further shown that estrogen inhibition results in cell cycle arrest in the G0/ G1 phase of the cell cycle through attenuation of CDK/cyclin complexes at multiple levels (Foster et al., 2001). In particular, cyclin D1 is a direct transcriptional target of ER signalling (Eeckhoute et al., 2006). "
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    • "ICI 182 780 or Tamoxifen) results in an arrest in the G0/G1 phase of the cell cycle (Watts et al. 1995, Carroll et al. 2000, Foster et al. 2001, Markey et al. 2007). In this context, reduced ER signaling leads to the attenuation of CDK/cyclin complexes at multiple levels (Watts et al. 1995, Carroll et al. 2000, Foster et al. 2001). Most dramatically, cyclin D1 is a known and direct transcriptional target of the ER signaling network (Watts et al. 1994, Eeckhoute et al. 2006). "
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