Cyclin-dependent kinase 9 in complex with Cyclin T1 (CDK9/Cyclin T1)

The Cyclin-dependent kinase 9 (CDK9) in complex with Cyclin T1 forms the catalytic core of the Positive Transcription Elongation Factor b (P-TEFb), a critical regulator of eukaryotic gene transcription [1.2.1, 1.4.1]. Unlike cell cycle-regulating CDKs, the CDK9/Cyclin T1 complex primarily functions in the nucleus to promote the transition of RNA polymerase II (RNAP II) from promoter-proximal pausing to productive elongation [1.2.2, 1.4.3]. It achieves this by phosphorylating Serine 2 of the RNAP II carboxyl-terminal domain (CTD) and negative elongation factors like DSIF and NELF [1.2.2, 1.4.1]. This complex is frequently dysregulated in various cancers, where it drives the expression of short-lived anti-apoptotic proteins (e.g., MCL-1) and oncogenes (e.g., MYC) that are essential for tumor cell survival [1.1.3, 1.3.4]. Additionally, the CDK9/Cyclin T1 complex is a vital host factor for HIV-1 replication, as the viral Tat protein recruits it to the viral promoter to stimulate efficient transcription [1.2.1, 1.4.1]. Therapeutic strategies include small-molecule ATP-competitive inhibitors and PROTAC degraders designed to induce apoptosis in transcriptionally addicted cancer cells, though challenges remain regarding selectivity and systemic toxicity [1.1.3, 1.3.5].

Other names

P-TEFbPositive transcription elongation factor bTAKTat-associated kinaseC-2KPITALRECCNT1

ATP-competitive inhibition of CDK9 kinase activity, which prevents the phosphorylation of the RNA polymerase II C-terminal domain (CTD) at Serine 2, thereby blocking the transition from transcription initiation to productive elongation and reducing the expression of short-lived oncogenic and anti-apoptotic proteins like MYC and MCL-1 [1.1.3, 1.3.4].