sabkayak@gmail.com
Mentor: David Price, Ph.D.
Lab Phone: 335-6742

Regulation of P-TEFb

The positive transcription factor P-TEFb is required for productive transcription from most cellular promoters and for Tat-transactivation from the HIV LTR promoter. P-TEFb phosphorylates the carboxy terminal domain of the large subunit of RNA polymerase II allowing for the transition into productive elongation. P-TEFb inhibitors have unexplained lower IC50s for inhibition of transcription from the HIV LTR than from cellular promoters. Recently it was determined that there are two P-TEFb complexes. The smaller P-TEFb is comprised of cdk9 and cyclin T. The larger P-TEFb contains HEXIM1 and the small nuclear RNA, 7SK, in addition to cdk9 and cyclin T and has decreased kinase activity. Treatment of cells with P-TEFb or transcription inhibitors causes a dramatic and almost complete shift to small P-TEFb based on glycerol gradient sedimentation of P-TEFb components. A new method to examine the shift from large to small P-TEFb based on the differential salt extractability of the two complexes is being used to examine the shift from large to small P-TEFb and determine if there is a correlation with the inhibition of HIV replication.

Abstracts:

Byers SA, Biglione S, Shutt DC, Maury M, Price DH. Are large P-TEFb complexes required for transcription from the HIV LTR? Cold Spring Harbor Mechanisms of Eukaryotic Transcription 2003.

Byers SA, and Price DH. Regulation of P-TEFb by 7SK. Infectious Disease Retreat 2002, University of Iowa.

Byers SA, Biglione S, Maury W and Price DH. 7SK Regulation of P-TEFb in Tat Transactivation. Molecular Biology Retreat 2002, University of Iowa.

Byers SA, Biglione S, Maury W and Price DH. P-TEFb regulation by 7SK. Molecular Biology Retreat 2003, University of Iowa.

Byers SA, Martinez B, and Price DH. The mechanism of action of MLN944 (XR5944). Molecular Targets and Cancer Therapeutics, AACR-NCI-EORTC International Conference 2003.

Biglione S, Byers SA, Shutt DC, Price DH and Maury W. The Role of P-TEFb in HIV Replication. 11th Conference on Retroviruses and Opportunistic Infections 2004.

Byers SA, Martinez B, Sappal DS, Brown JL and Price DH. The Mechanism of Action of MLN944 is through inhibition of transcription initiation. University of Iowa Research Week 2004.

Biglione S, Byers SA, Shutt DC, Price DH and Maury W. The Role of P-TEFb in HIV Replication. University of Iowa Research Week 2004.

Publications:

Krueger BJ, Jeronimo C, Roy BB, Bouchard A, Barrandon C, Byers SA, Searcey CE, Cooper JJ, Bensaude O, Cohen EA, Coulombe B, Price DH. LARP7 is a stable component of the 7SK snRNP while P-TEFb, HEXIM1 and hnRNP A1 are reversibly associated. Nucleic Acids Res. 2008 Apr;36(7):2219-29. Epub 2008 Feb 16. PubMed PMID: 18281698; PubMed Central PMCID: PMC2367717.

Biglione S, Byers SA, Price JP, Nguyen VT, Bensaude O, Price DH, Maury W. Inhibition of HIV-1 replication by P-TEFb inhibitors DRB, seliciclib and flavopiridol correlates with release of free P-TEFb from the large, inactive form of the complex. Retrovirology. 2007 Jul 11;4:47. PubMed PMID: 17625008; PubMed Central PMCID: PMC1948018.

Sedore SC, Byers SA, Biglione S, Price JP, Maury WJ, Price DH. Manipulation of P-TEFb control machinery by HIV: recruitment of P-TEFb from the large form by Tat and binding of HEXIM1 to TAR. Nucleic Acids Res. 2007;35(13):4347-58. Epub 2007 Jun 18. PubMed PMID: 17576689; PubMed Central PMCID: PMC1935001.

Byers SA, Schafer B, Sappal DS, Brown J, Price DH. The antiproliferative agent MLN944 preferentially inhibits transcription. Mol Cancer Ther. 2005 Aug;4(8):1260-7. PubMed PMID: 16093442.

Li Q, Price JP, Byers SA, Cheng D, Peng J, Price DH. Analysis of the large inactive P-TEFb complex indicates that it contains one 7SK molecule, a dimer of HEXIM1 or HEXIM2, and two P-TEFb molecules containing Cdk9 phosphorylated at threonine 186. J Biol Chem. 2005 Aug 5;280(31):28819-26. Epub 2005 Jun 17. PubMed PMID: 15965233.

Shore SM, Byers SA, Dent P, Price DH. Characterization of Cdk9(55) and differential regulation of two Cdk9 isoforms. Gene. 2005 Apr 25;350(1):51-8. PubMed PMID: 15780980.

Byers SA, Price JP, Cooper JJ, Li Q, Price DH. HEXIM2, a HEXIM1-related protein, regulates positive transcription elongation factor b through association with 7SK. J Biol Chem. 2005 Apr 22;280(16):16360-7. Epub 2005 Feb 14. PubMed PMID: 15713662.

Shore SM, Byers SA, Maury W, Price DH. Identification of a novel isoform of Cdk9. Gene. 2003 Mar 27;307:175-82. PubMed PMID: 12706900.