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Molecular and Cellular Biology, July 2007, p. 5079-5089, Vol. 27, No. 14
0270-7306/07/$08.00+0     doi:10.1128/MCB.00029-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Hematopoiesis and Thymic Apoptosis Are Not Affected by the Loss of Cdk2

Cyril Berthet,^1, Maria Cecilia Rodriguez-Galan,² Deborah L. Hodge,² John Gooya,^3, Véronique Pascal,² Howard A. Young,² Jonathan Keller,³ Remy Bosselut,⁴ and Philipp Kaldis^1*

Mouse Cancer Genetics Program,¹ Laboratory of Experimental Immunology, Center for Cancer Research, National Cancer Institute—Frederick, Bldg. 560/22-56, 1050 Boyles Street, Frederick, Maryland 21702-1201,² Basic Research Program, Science Applications International Corporation, National Cancer Institute—Frederick, Bldg. 560, Frederick, Maryland 21702-1201,³ Laboratory of Immune Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892⁴

Received 5 January 2007/ Returned for modification 1 February 2007/ Accepted 29 April 2007

Cell cycle regulation is essential for proper homeostasis of hematopoietic cells. Cdk2 is a major regulator of S phase entry, is activated by mitogenic cytokines, and has been suggested to be involved in antigen-induced apoptosis of T lymphocytes. The role of Cdk2 in hematopoietic cells and apoptosis in vivo has not yet been addressed. To determine whether Cdk2 plays a role in these cells, we performed multiple analyses of bone marrow cells, thymocytes, and splenocytes from Cdk2 knockout mice. We found that Cdk2 is not required in vivo to induce apoptosis in lymphocytes, a result that differs from previous pharmacological in vitro studies. Furthermore, thymocyte maturation was not affected by the lack of Cdk2. We then analyzed the hematopoietic stem cell compartment and found similar proportions of stem cells and progenitors in Cdk2^–/– and wild-type animals. Knockouts of Cdk2 inhibitors (p21, p27) affect stem cell renewal, but a competitive graft experiment indicated that renewal and multilineage differentiation are normal in the absence of Cdk2. Finally, we stimulated T lymphocytes or macrophages to induce proliferation and observed normal reactivation of Cdk2^–/– quiescent cells. Our results indicate that Cdk2 is not required for proliferation and differentiation of hematopoietic cells in vivo, although in vitro analyses consider Cdk2 to be a major player in proliferation and apoptosis in these cells and a potential target for therapy.

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* Corresponding author. Mailing address: Mouse Cancer Genetics Program, Center for Cancer Research, National Cancer Institute—Frederick, Bldg. 560/22-56, 1050 Boyles Street, Frederick, MD 21702-1201. Phone: (301) 846-1988. Fax: (301) 846-7017. E-mail: kaldis{at}ncifcrf.gov

Published ahead of print on 7 May 2007.

Present address: Oncodesign, Dijon 21076, France.

Present address: MedImmune Inc., Gaithersburg, MD 20878.

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Molecular and Cellular Biology, July 2007, p. 5079-5089, Vol. 27, No. 14
0270-7306/07/$08.00+0     doi:10.1128/MCB.00029-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

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