Toxins 2011, 3(1), 105-119; doi:10.3390/toxins3010105
Article

The Discodermia calyx Toxin Calyculin A Enhances Cyclin D1 Phosphorylation and Degradation, and Arrests Cell Cycle Progression in Human Breast Cancer Cells

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Received: 8 October 2010; in revised form: 8 January 2011 / Accepted: 21 January 2011 / Published: 24 January 2011
(This article belongs to the Special Issue Toxins as Therapeutics)
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract: Cyclin D1 is a key regulator of the cell cycle that is over expressed in more than half of breast cancer patients. The levels of cyclin D1 are controlled primarily through post-translational mechanisms and phosphorylation of cyclin D1 at T286 induces its proteasomal degradation. To date, no studies have explored the involvement of phosphatases in this process. Here we treated human breast cancer cells with the structurally distinct toxins calyculin A, okadaic acid, and cantharidin, which are known to inhibit Ser/Thr phosphatases of the PPP family. At low nanomolar concentrations calyculin A induced T286 phosphorylation and degradation of cyclin D1 via the proteosome in MDA-MB-468 and MDA-MB-231 cells. Cyclin D1 degradation also was dose-dependently induced by okadaic acid and catharidin, implicating a negative regulatory role for type-2A phosphatases. These effects occurred without increasing phosphorylation of p70S6K, cyclin D3, or myosin light chain that were used as endogenous reporters of cellular PP2A and PP1 activity. A reverse phase phosphoprotein array analysis revealed increased phosphorylation of only 6 out of 33 Ser/Thr phosphosites, indicating selective inhibition of phosphatases by calyculin A. Calyculin A treatment induced cell cycle arrest in MDA-MB-468 and MCF-7 breast cancer cells. These findings suggest that a specific pool of type-2A phosphatase is inhibited by calyculin A leading to the degradation of cyclin D1 in human breast cancer cells. The results highlight the utility of toxins as pharmacological probes and points to the T286 cyclin D1 phosphatase inhibited by calyculin A as a possible target for chemotherapy to treat triple negative breast cancer.
Keywords: toxins; phosphatases; cyclin D1; calyculin A; okadaic acid; cantharidin
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MDPI and ACS Style

Edelson, J.R.; Brautigan, D.L. The Discodermia calyx Toxin Calyculin A Enhances Cyclin D1 Phosphorylation and Degradation, and Arrests Cell Cycle Progression in Human Breast Cancer Cells. Toxins 2011, 3, 105-119.

AMA Style

Edelson JR, Brautigan DL. The Discodermia calyx Toxin Calyculin A Enhances Cyclin D1 Phosphorylation and Degradation, and Arrests Cell Cycle Progression in Human Breast Cancer Cells. Toxins. 2011; 3(1):105-119.

Chicago/Turabian Style

Edelson, Jessica R.; Brautigan, David L. 2011. "The Discodermia calyx Toxin Calyculin A Enhances Cyclin D1 Phosphorylation and Degradation, and Arrests Cell Cycle Progression in Human Breast Cancer Cells." Toxins 3, no. 1: 105-119.

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