Physical interaction between CDK9 and B-Myb results in suppression of B-Myb gene autoregulation.
B-Myb is a transcription factor belonging to the myb family, whose activity has been associated with augmented DNA synthesis and cell cycle progression. We showed recently that B-Myb autoregulates its own expression through promoter transactivation. We report in this study that CDK9, the cyclin T associated kinase, which phosphorylates and activates RNA-Polymerase II, suppresses B-Myb autoregulation through direct interaction with the carboxyl-terminus of the B-Myb protein. Down-regulation of the transactivating ability of B-Myb is independent of the kinase activity of CDK9, because a kinase deficient mutant (dn-CDK9) also represses B-myb gene autoregulation. Overexpression of CDK9 did not result in suppression of p53-dependent transactivation or inhibition of the basal activity of the promoters tested so far, demonstrating that CDK9 is a B-Myb-specific repressor. Rather, transfection of the dominant negative dn-CDK9 construct inhibited the basal activity of the reporter genes, confirming an essential role for CDK9 in gene transcription. In addition, Cyclin T1 restores B-Myb transactivating activity when co-transfected along with CDK9, suggesting that the down-regulatory effect observed on B-Myb is specifically due to CDK9 alone. Thus, our data suggest that CDK9 is involved in the negative regulation of activated transcription mediated by certain transcription factors, such as B-Myb. This may indicate the existence of a feedback loop, mediated by the different activities of CDK9, which links basal with activated transcription.
De Falco
G
G
Department of Pathology, Anatomy & Cell Biology, Jefferson Medical College of Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Bagella
L
L
Claudio
P P
PP
De Luca
A
A
Fu
Y
Y
Calabretta
B
B
Sala
A
A
Giordano
A
A
D018797:Cell Cycle Proteins; D002460:Cell Line; D056906:Cyclin T; D042863:Cyclin-Dependent Kinase 9; D018844:Cyclin-Dependent Kinases / Q000737:chemistry / Q000502:physiology*; D016213:Cyclins / Q000502:physiology; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D015536:Down-Regulation; D005786:Gene Expression Regulation; D006801:Humans; D015534:Trans-Activators / Q000737:chemistry / Q000502:physiology*; D014158:Transcription, Genetic
C503684:CCNT1 protein, human; D018797:Cell Cycle Proteins; D056906:Cyclin T; D016213:Cyclins; D004268:DNA-Binding Proteins; C064352:MYBL2 protein, human; D015534:Trans-Activators; C467969:CDK9 protein, human; D042863:Cyclin-Dependent Kinase 9; D018844:Cyclin-Dependent Kinases