Positive transcription elongation factor b (P-TEFb) is a therapeutic target in human multiple myeloma
Metrics: PDF 1062 views | HTML 1711 views | ?
Yu Zhang1,*, Liang Zhou1,*, Yun Leng1,2, Yun Dai3, Robert Z. Orlowski4 and Steven Grant1,5,6,7
1Division of Hematology/Oncology, Department of Medicine, Virginia Commonwealth University and The Massey Cancer Center, Richmond, VA, USA
2Department of Hematology, Beijing Chaoyang Hospital of Capital Medical University, Beijing, China
3Cancer Center, The First Hospital of Jilin University, Changchun, China
4Department of Myeloma and Lymphoma, MD Anderson Cancer Center, Houston, TX, USA
5Virginia Institute of Molecular Medicine, Virginia Commonwealth University, Richmond, VA, USA
6Department of Biochemistry, Virginia Commonwealth University, Richmond, VA, USA
7Department of Pharmacology Virginia Commonwealth University, Richmond, VA, USA
*These authors contributed equally to this work
Steven Grant, email: email@example.com
Keywords: P-TEFb, bortezomib resistance, myeloma, MCL-1, CDK inhibitors
Abbreviations: Alvocidib (Flavopiridol, FP); Dinaciclib (SCH727965, SCH); Bortezomib (btz); Carfilzomib (cfz); Hematoxylin and eosin (H&E)
Received: May 18, 2017 Accepted: July 03, 2017 Published: August 01, 2017
The role of the positive RNA Pol II regulator, P-TEFb (positive transcription elongation factor b), in maintenance of the anti-apoptotic protein Mcl-1 and bortezomib (btz) resistance was investigated in human multiple myeloma (MM) cells. Mcl-1 was up-regulated in all MM lines tested, including bortezomib-resistant lines, human MM xenograft mouse models, and primary CD138+ MM cells. Mcl-1 over-expression significantly reduced bortezomib lethality, indicating a functional role for Mcl-1 in bortezomib resistance. MM cell lines, primary MM specimens, and murine xenografts exhibited constitutive P-TEFb activation, manifested by high CTD (carboxy-terminal domain) S2 phosphorylation, associated with a) P-TEFb subunit up-regulation i.e., CDK9 (42 and 55 kDa isoforms) and cyclin T1; and b) marked CDK9 (42 kDa) T186 phosphorylation. In marked contrast, normal hematopoietic cells failed to exhibit up-regulation of p-CTD, CDK9, cyclin T1, or Mcl-1. CDK9 or cyclin T1 shRNA knock-down dramatically inhibited CTD S2 phosphorylation and down-regulated Mcl-1. Moreover, CRISPR-Cas CDK9 knock-out triggered apoptosis in MM cells and dramatically diminished cell growth. Pan-CDK e.g., dinaciclib or alvocidib and selective CDK9 inhibitors (CDK9i) recapitulated the effects of genetic P-TEFb disruption. CDK9 shRNA or CDK9 inhibitors significantly potentiated the susceptibility of MM cells, including bortezomib-resistant cells, to proteasome inhibitors. Analogously, CDK9 or cyclin T1 knock-down or CDK9 inhibitors markedly increased BH3-mimetic lethality in bortezomib-resistant cells. Finally, pan-CDK inhibition reduced human drug-naïve or bortezomib-resistant CD138+ cells and restored bone marrow architecture in vivo. Collectively, these findings implicate constitutive P-TEFb activation in high Mcl-1 maintenance in MM, and validate targeting the P-TEFb complex to circumvent bortezomib-resistance.
All site content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 License.