PP2B and PP1alpha cooperatively disrupt 7SK snRNP to release P-TEFb for transcription in response to Ca2+ signaling.
The positive transcription elongation factor b (P-TEFb), consisting of Cdk9 and cyclin T, stimulates RNA polymerase II elongation and cotranscriptional pre-mRNA processing. To accommodate different growth conditions and transcriptional demands, a reservoir of P-TEFb is kept in an inactive state in the multisubunit 7SK snRNP. Under certain stress or disease conditions, P-TEFb is released to activate transcription, although the signaling pathway(s) that controls this is largely unknown. Here, through analyzing the UV- or hexamethylene bisacetamide (HMBA)-induced release of P-TEFb from 7SK snRNP, an essential role for the calcium ion (Ca2+)-calmodulin-protein phosphatase 2B (PP2B) signaling pathway is revealed. However, Ca2+ signaling alone is insufficient, and PP2B must act sequentially and cooperatively with protein phosphatase 1alpha (PP1alpha) to disrupt 7SK snRNP. Activated by UV/HMBA and facilitated by a PP2B-induced conformational change in 7SK snRNP, PP1alpha releases P-TEFb through dephosphorylating phospho-Thr186 in the Cdk9 T-loop. This event is also necessary for the subsequent recruitment of P-TEFb by the bromodomain protein Brd4 to the preinitiation complex, where Cdk9 remains unphosphorylated and inactive until after the synthesis of a short RNA. Thus, through cooperatively dephosphorylating Cdk9 in response to Ca2+ signaling, PP2B and PP1alpha alter the P-TEFb functional equilibrium through releasing P-TEFb from 7SK snRNP for transcription.
Chen
Ruichuan
R
Key Laboratory of the Ministry of Education for Cell Biology and Tumor Cell Engineering, School of Life Sciences, Xiamen University, Xiamen 361005, Fujian, China. chenrc@xmu.edu.cn
Liu
Min
M
Li
Huan
H
Xue
Yuhua
Y
Ramey
Wanichaya N
WN
He
Nanhai
N
Ai
Nanping
N
Luo
Haohong
H
Zhu
Ying
Y
Zhou
Nan
N
Zhou
Qiang
Q
D000081:Acetamides / Q000494:pharmacology; D019703:Calcineurin / Q000378:metabolism / Q000502:physiology*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D002147:Calmodulin / Q000502:physiology; D042863:Cyclin-Dependent Kinase 9 / Q000378:metabolism; D004789:Enzyme Activation / Q000502:physiology; D015497:HIV-1 / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D008954:Models, Biological; D010766:Phosphorylation; D042925:Positive Transcriptional Elongation Factor B / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects / Q000528:radiation effects; D054645:Protein Phosphatase 1 / Q000378:metabolism / Q000502:physiology*; D016601:RNA-Binding Proteins / Q000378:metabolism; D017411:Ribonucleoproteins, Small Nuclear / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014157:Transcription Factors; D014158:Transcription, Genetic; D014466:Ultraviolet Rays
D000081:Acetamides; D002147:Calmodulin; C476123:HEXIM1 protein, human; D016601:RNA-Binding Proteins; D017411:Ribonucleoproteins, Small Nuclear; D014157:Transcription Factors; D042925:Positive Transcriptional Elongation Factor B; D042863:Cyclin-Dependent Kinase 9; D019703:Calcineurin; D054645:Protein Phosphatase 1; C014026:hexamethylene bisacetamide