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Molecular and Cellular Biology, April 2000, p. 2581-2591, Vol. 20, No. 7
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Cooperation of p27Kip1 and p18INK4c in Progestin-Mediated Cell Cycle Arrest in T-47D Breast Cancer Cells

Alexander Swarbrick, Christine S. L. Lee, Robert L. Sutherland, and Elizabeth A. Musgrove*

Cancer Research Program, Garvan Institute of Medical Research, St. Vincent's Hospital, Sydney, New South Wales 2010, Australia

Received 14 July 1999/Returned for modification 13 September 1999/Accepted 10 January 2000

The steroid hormone progesterone regulates proliferation and differentiation in the mammary gland and uterus by cell cycle phase-specific actions. The long-term effect of progestins on T-47D breast cancer cells is inhibition of cellular proliferation. This is accompanied by decreased G1 cyclin-dependent kinase (CDK) activities, redistribution of the CDK inhibitor p27Kip1 among these CDK complexes, and alterations in the elution profile of cyclin E-Cdk2 upon gel filtration chromatography, such that high-molecular-weight complexes predominate. This study aimed to determine the relative contribution of CDK inhibitors to these events. Following progestin treatment, the majority of cyclin E- and D-CDK complexes were bound to p27Kip1 and few were bound to p21Cip1. In vitro, recombinant His6-p27 could quantitatively reproduce the effects on cyclin E-Cdk2 kinase activity and the shift in molecular weight observed following progestin treatment. In contrast, cyclin D-Cdk4 was not inhibited by His6-p27 in vitro or p27Kip1 in vivo. However, an increase in the expression of the Cdk4/6 inhibitor p18INK4c and its extensive association with Cdk4 and Cdk6 were apparent following progestin treatment. Recombinant p18INK4c led to the reassortment of cyclin-CDK-CDK inhibitor complexes in vitro, with consequent decrease in cyclin E-Cdk2 activity. These results suggest a concerted model of progestin action whereby p27Kip1 and p18INK4c cooperate to inhibit cyclin E-Cdk2 and Cdk4. Since similar models have been developed for growth inhibition by transforming growth factor beta  and during adipogenesis, interaction between the Cip/Kip and INK4 families of inhibitors may be a common theme in physiological growth arrest and differentiation.

* Corresponding author. Mailing address: Cancer Research Program, Garvan Institute of Medical Research, 384 Victoria St., Darlinghurst, NSW 2010 Australia. Phone: 61-2-9295-8328. Fax: 61-2-9295-8321. E-mail: e.musgrove{at}garvan.unsw.edu.au.

Molecular and Cellular Biology, April 2000, p. 2581-2591, Vol. 20, No. 7
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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