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Krüppel-Like Factor 4 Regulates B Cell Number and Activation-Induced B Cell Proliferation¹

Jettanong Klaewsongkram^*,, Yinhua Yang^*, Susanne Golech^*, Jonathan Katz, Klaus H. Kaestner and Nan-ping Weng^2,*

^* Laboratory of Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224; Department of Genetics, University of Pennsylvania Medical School, Philadelphia, PA 19104; and Division of Allergy and Clinical Immunology, Department of Medicine, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand

Krüppel-like factor 4 (Klf4) is a transcription factor and functions in regulating cell differentiation, cell growth, and cell cycle. Although Klf4 is expressed in lymphocytes, its function in lymphocytes is unknown. In this study, we report that the levels of Klf4 expression were low in pro-B cells and continuously increased in pre-B and in mature B cells. Upon activation, Klf4 was rapidly decreased in mature B cells after 2 h of activation. A modest decrease in numbers of pre-B cells in bone marrow and mature B cells in spleen was observed in Klf4-deficient mice. In the absence of Klf4, fewer B cells entered the S phase of the cell cycle and completed cell division in response to the engagement of BCR and/or CD40 in vitro. Furthermore, the delay in entering the cell cycle is associated with decreased expression of cyclin D2 in B cells that lack Klf4 expression. We then demonstrated that Klf4 directly bound to the promoter of cyclin D2 and regulated its expression. These findings demonstrate that Klf4 regulates B cell number and activation-induced B cell proliferation through directly acting on the promoter of cyclin D2.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported by the Intramural Research Program of the National Institute on Aging, National Institutes of Health.

² Address correspondence and reprint requests to Dr. Nan-ping Weng, National Institute on Aging, National Institutes of Health, 5600 Nathan Shock Drive, Box 21, Baltimore, MD 21224. E-mail address: wengn{at}mail.nih.gov

³ Abbreviations used in this paper: Klf4, Krüppel-like factor 4; PI, proliferation index; ChIP, chromatin immunoprecipitation.

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