Cyclin-dependent kinase 9–Cyclin T1 complex (CDK9–CCNT1) (CDK9–CCNT1)

The Cyclin-dependent kinase 9 (CDK9)–Cyclin T1 complex, also known as the Positive Transcription Elongation Factor b (P-TEFb), is a critical regulator of eukaryotic gene expression [1][3]. Unlike other CDKs that primarily control cell cycle progression, CDK9 functions as a transcriptional kinase by phosphorylating the C-terminal domain (CTD) of RNA polymerase II at Serine 2 [2]. This phosphorylation event triggers the transition from promoter-proximal pausing to productive elongation, allowing for the synthesis of full-length mRNA transcripts [3]. In many cancers, particularly hematological malignancies and MYC-driven tumors, CDK9 is hyperactivated, leading to the overexpression of short-lived anti-apoptotic proteins like MCL-1 and oncogenes like MYC [2][5]. Consequently, the CDK9 ATP-binding site has become a prominent therapeutic target for small-molecule inhibitors designed to induce apoptosis in malignant cells by blocking transcriptional elongation [4][5]. Beyond oncology, CDK9 is essential for HIV-1 replication, as the viral Tat protein recruits P-TEFb to the viral promoter to drive transcription of the viral genome [1]. However, therapeutic targeting of CDK9 faces challenges regarding selectivity and potential systemic toxicity due to its fundamental role in basal transcription across various tissues [5].

Other names

Positive Transcription Elongation Factor bP-TEFbPITALREC-terminal domain kinase

Competitive inhibition of the ATP-binding site of CDK9, preventing the phosphorylation of the RNA polymerase II C-terminal domain (CTD) and inhibiting transcriptional elongation.