PP2B and PP1α cooperatively disrupt 7SK snRNP to release P-TEFb for transcription in response to Ca2+ signaling (original) (raw)

  1. Ruichuan Chen1,3,5,
  2. Min Liu1,3,
  3. Huan Li1,3,
  4. Yuhua Xue1,
  5. Wanichaya N. Ramey2,
  6. Nanhai He2,
  7. Nanping Ai1,
  8. Haohong Luo1,
  9. Ying Zhu1,
  10. Nan Zhou1, and
  11. Qiang Zhou2,4
  12. 1 Key Laboratory of the Ministry of Education for Cell Biology and Tumor Cell Engineering, School of Life Sciences, Xiamen University, Xiamen 361005, Fujian, China;
  13. 2 Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California 94720, USA
  14. ↵3 These authors contributed equally to this work.

Abstract

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 1α (PP1α) to disrupt 7SK snRNP. Activated by UV/HMBA and facilitated by a PP2B-induced conformational change in 7SK snRNP, PP1α 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 PP1α alter the P-TEFb functional equilibrium through releasing P-TEFb from 7SK snRNP for transcription.

Footnotes