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Low-molecular-weight cyclin E can bypass letrozole-induced G1 arrest in human breast cancer cells and tumors.

ABSTRACT: Low-molecular-weight cyclin E (LMW-E) in breast cancer cells induces genomic instability and resistance to inhibition by p21, p27, and fulvestrant therapy. Here, we sought to determine if LMW-E renders breast cancer cells unresponsive to aromatase inhibitors (AI), elucidate the mechanism of such resistance, and ascertain if inhibitors of LMW-E-associated kinase activity could overcome this resistance.The antiproliferative effects of the AIs were examined in aromatase-overexpressing MCF-7/Ac1 cells in the presence or absence of full-length cyclin E and LMW-E. Inhibition of LMW cyclin E kinase activity by roscovitine [a cyclin-dependent kinase (CDK) inhibitor] was examined in letrozole-unresponsive MCF-7/Ac1 cells. The role of LMW-E and CDK2 in mediating recurrence following AI treatment was also assessed in breast cancer patients.Overexpression of LMW-E in postmenopausal patients was associated with a poor prognosis. Letrozole, but not exemestane or anastrozole, mediated a pronounced G(1) arrest in MCF-7/Ac1 cells. Androstenedione-induced G(1) exit correlated with increased cyclin E-associated kinase activity and increased CDK2 levels. Letrozole treatment inhibited cyclin E-CDK2 kinase activity by preventing the androstenedione-induced increase in CDK2. LMW-E bypassed this effect and rendered the cells resistant to letrozole inhibition. Roscovitine blocked the androstenedione-induced increase in CDK2, and LMW-E overexpression could not bypass this effect. Lastly, breast cancer patients whose tumors overexpress LMW-E were not responsive to AI treatment.Roscovitine treatment can reverse intrinsic or acquired resistance to letrozole due to LMW-E expression in breast cancer cells. These data support the clinical investigation of CDK2 inhibitor therapy for postmenopausal women with estrogen receptor-positive, LMW-E-expressing breast cancer.

SUBMITTER: Akli S

PROVIDER: S-EPMC2822889 | biostudies-literature | 2010 Feb

REPOSITORIES: biostudies-literature

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Low-molecular-weight cyclin E can bypass letrozole-induced G1 arrest in human breast cancer cells and tumors.

Akli Said S Bui Tuyen T Wingate Hannah H Biernacka Anna A Moulder Stacy S Tucker Susan L SL Hunt Kelly K KK Keyomarsi Khandan K

Clinical cancer research : an official journal of the American Association for Cancer Research 20100209 4

<h4>Purpose</h4>Low-molecular-weight cyclin E (LMW-E) in breast cancer cells induces genomic instability and resistance to inhibition by p21, p27, and fulvestrant therapy. Here, we sought to determine if LMW-E renders breast cancer cells unresponsive to aromatase inhibitors (AI), elucidate the mechanism of such resistance, and ascertain if inhibitors of LMW-E-associated kinase activity could overcome this resistance.<h4>Experimental design</h4>The antiproliferative effects of the AIs were examin ...[more]

PMID: 20145171

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Project description:In response to DNA damage, eukaryotic cells initiate a complex signalling pathway, termed the DNA damage response (DDR), which coordinates cell cycle arrest with DNA repair. Studies have shown that oncogene-induced senescence, which provides a barrier to tumour development, involves activation of the DDR. Using a genome-wide RNA interference (RNAi) screen, we have identified 17 factors required for oncogenic BRAF to induce senescence in primary fibroblasts and melanocytes. One of these factors is an F-box protein, FBXO31, a candidate tumour suppressor encoded in 16q24.3, a region in which there is loss of heterozygosity in breast, ovarian, hepatocellular and prostate cancers. Here we study the cellular role of FBXO31, identify its target substrate and determine the basis for its growth inhibitory activity. We show that ectopic expression of FBXO31 acts through a proteasome-directed pathway to mediate the degradation of cyclin D1, an important regulator of progression from G1 to S phase, resulting in arrest in G1. Cyclin D1 degradation results from a direct interaction with FBXO31 and is dependent on the F-box motif of FBXO31 and phosphorylation of cyclin D1 at Thr 286, which is known to be required for cyclin D1 proteolysis. The involvement of the DDR in oncogene-induced senescence prompted us to investigate the role of FBXO31 in DNA repair. We find that DNA damage induced by gamma-irradiation results in increased FBXO31 levels, which requires phosphorylation of FBXO31 by the DDR-initiating kinase ATM. RNAi-mediated knockdown of FBXO31 prevents cells from undergoing efficient arrest in G1 after gamma-irradiation and markedly increases sensitivity to DNA damage. Finally, we show that a variety of DNA damaging agents all result in a large increase in FBXO31 levels, indicating that induction of FBXO31 is a general response to genotoxic stress. Our results reveal FBXO31 as a regulator of the G1/S transition that is specifically required for DNA damage-induced growth arrest.

Dataset Information

Low-molecular-weight cyclin E can bypass letrozole-induced G1 arrest in human breast cancer cells and tumors.

Publications

Low-molecular-weight cyclin E can bypass letrozole-induced G1 arrest in human breast cancer cells and tumors.

Similar Datasets

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