Cyclin-dependent kinase 9-cyclin T1 complex (P-TEFb) (P-TEFb)

The Cyclin-dependent kinase 9-cyclin T1 complex, also known as the core of the Positive Transcription Elongation Factor b (P-TEFb), is a vital regulator of the eukaryotic transcription cycle [1, 4]. Structurally, the complex consists of the CDK9 catalytic subunit and a regulatory cyclin T1 subunit, which together form a pliable interface that can be modulated by various cellular factors like HEXIM1 and 7SK snRNA [1, 5]. It functions as a serine/threonine kinase that phosphorylates the C-terminal domain (CTD) of RNA polymerase II, as well as the negative elongation factors DSIF and NELF, to facilitate the transition from promoter-proximal pausing to productive transcription elongation [5, 7]. Because many oncogenes and anti-apoptotic factors, such as MYC and MCL-1, have short-lived mRNAs and proteins, they are highly dependent on continuous CDK9-mediated transcription, a phenomenon termed "transcriptional addiction" [8, 14]. Consequently, the CDK9-cyclin T1 complex has become a major therapeutic target in various hematological malignancies and solid tumors [1, 15]. Additionally, the complex is a critical host factor for HIV-1 replication, where it is recruited by the viral Tat protein to the long terminal repeat (LTR) to drive viral gene expression [5, 13]. While early pan-CDK inhibitors faced clinical challenges due to narrow therapeutic windows, newer highly selective CDK9 inhibitors and PROTAC degraders are currently being evaluated to minimize off-target toxicities like neutropenia and gastrointestinal distress [6, 12].

Other names

CDK9-cyclin T1Positive transcription elongation factor bCDK9/CCNT1PITALRE/Cyclin T1Tat-associated kinase complex

ATP-competitive inhibition of the CDK9 kinase subunit within the P-TEFb complex, preventing the phosphorylation of the RNA polymerase II C-terminal domain at Ser2 and the negative elongation factors DSIF and NELF, which collectively inhibits the transition to productive transcription elongation and suppresses the expression of short-lived oncogenic and anti-apoptotic proteins.