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Molecular and Cellular Biology, March 2003, p. 1688-1702, Vol. 23, No. 5
0270-7306/03/$08.00+0     DOI: 10.1128/MCB.23.5.1688-1702.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

The Growth Factor Granulin Interacts with Cyclin T1 and Modulates P-TEFb-Dependent Transcription

Mainul Hoque,¹ Tara M. Young,^1,2 Chee-Gun Lee,^1,2 Ginette Serrero,³ Michael B. Mathews,^1,2* and Tsafi Pe'ery^1,2,4

Departments of Biochemistry and Molecular Biology,¹ Medicine, New Jersey Medical School,⁴ Graduate School of Biomedical Sciences, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 07013-1709,² Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland 21201-1180³

Received 25 September 2002/ Returned for modification 7 November 2002/ Accepted 10 November 2002

Cyclin T1, together with the kinase CDK9, is a component of the transcription elongation factor P-TEFb which binds the human immunodeficiency virus type 1 (HIV-1) transactivator Tat. P-TEFb facilitates transcription by phosphorylating the carboxy-terminal domain (CTD) of RNA polymerase II. Cyclin T1 is an exceptionally large cyclin and is therefore a candidate for interactions with regulatory proteins. We identified granulin as a cyclin T1-interacting protein that represses expression from the HIV-1 promoter in transfected cells. The granulins, mitogenic growth factors containing repeats of a cysteine-rich motif, were reported previously to interact with Tat. We show that granulin formed stable complexes in vivo and in vitro with cyclin T1 and Tat. Granulin bound to the histidine-rich domain of cyclin T1, which was recently found to bind to the CTD, but not to cyclin T2. Binding of granulin to P-TEFb inhibited the phosphorylation of a CTD peptide. Granulin expression inhibited Tat transactivation, and tethering experiments showed that this effect was due, at least in part, to a direct action on cyclin T1 in the absence of Tat. In addition, granulin was a substrate for CDK9 but not for the other transcription-related kinases CDK7 and CDK8. Thus, granulin is a cellular protein that interacts with cyclin T1 to inhibit transcription.

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* Corresponding author. Mailing address: Department of Biochemistry and Molecular Biology, New Jersey Medical School, and Graduate School of Biomedical Sciences, University of Medicine and Dentistry of New Jersey, 185 South Orange Ave., Newark, NJ 07013-1709. Phone: (973) 972-4411. Fax: (973) 972-5594. E-mail: mathews{at}umdnj.edu.

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Molecular and Cellular Biology, March 2003, p. 1688-1702, Vol. 23, No. 5
0022-538X/03/$08.00+0     DOI: 10.1128/MCB.23.5.1688-1702.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

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