Proteasome function is required for platelet production
Dallas S. Shi, … , Dean Y. Li, Andrew S. Weyrich
Dallas S. Shi, … , Dean Y. Li, Andrew S. Weyrich
Published July 25, 2014
Citation Information: J Clin Invest. 2014;124(9):3757-3766. https://doi.org/10.1172/JCI75247.
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Research Article Hematology

Proteasome function is required for platelet production

Abstract

The proteasome inhibiter bortezomib has been successfully used to treat patients with relapsed multiple myeloma; however, many of these patients become thrombocytopenic, and it is not clear how the proteasome influences platelet production. Here we determined that pharmacologic inhibition of proteasome activity blocks proplatelet formation in human and mouse megakaryocytes. We also found that megakaryocytes isolated from mice deficient for PSMC1, an essential subunit of the 26S proteasome, fail to produce proplatelets. Consistent with decreased proplatelet formation, mice lacking PSMC1 in platelets (Psmc1fl/fl Pf4-Cre mice) exhibited severe thrombocytopenia and died shortly after birth. The failure to produce proplatelets in proteasome-inhibited megakaryocytes was due to upregulation and hyperactivation of the small GTPase, RhoA, rather than NF-κB, as has been previously suggested. Inhibition of RhoA or its downstream target, Rho-associated protein kinase (ROCK), restored megakaryocyte proplatelet formation in the setting of proteasome inhibition in vitro. Similarly, fasudil, a ROCK inhibitor used clinically to treat cerebral vasospasm, restored platelet counts in adult mice that were made thrombocytopenic by tamoxifen-induced suppression of proteasome activity in megakaryocytes and platelets (Psmc1fl/fl Pdgf-Cre-ER mice). These results indicate that proteasome function is critical for thrombopoiesis, and suggest inhibition of RhoA signaling as a potential strategy to treat thrombocytopenia in bortezomib-treated multiple myeloma patients.

Authors

Dallas S. Shi, Matthew C.P. Smith, Robert A. Campbell, Patrick W. Zimmerman, Zechariah B. Franks, Bjorn F. Kraemer, Kellie R. Machlus, Jing Ling, Patrick Kamba, Hansjörg Schwertz, Jesse W. Rowley, Rodney R. Miles, Zhi-Jian Liu, Martha Sola-Visner, Joseph E. Italiano Jr., Hilary Christensen, Walter H.A. Kahr, Dean Y. Li, Andrew S. Weyrich

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Figure 7

Genetic deletion of Psmc1 in megakaryocytes is associated with increased RhoA protein and activity.

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Genetic deletion of Psmc1 in megakaryocytes is associated with increased...
(A) Representative Western blot of total RhoA and RhoA-GTP in megakaryocytes derived from Psmc1fl/wt and Psmc1fl/fl Pf4-Cre mice at P1. Also shown is densitometry quantification relative to Psmc1fl/wt control; for RhoA-GTP, megakaryocytes were isolated from 10 P1 mice, lysed, and then the lysates were pooled together for each pulldown experiment (see Methods). Data are mean ± SEM of 3 (total RhoA) and 2 (RhoA-GTP) experiments. *P < 0.05 vs. Psmc1fl/wt. (B) Bone marrow–derived megakaryocytes from Psmc1fl/wt and Psmc1fl/fl Pf4-Cre mice were treated with vehicle or fasudil, and the number of proplatelet-producing megakaryocytes was quantified and expressed relative to Psmc1fl/wt controls. Data are mean ± SEM of 3 independent experiments. *P < 0.05 vs. vehicle-treated Psmc1fl/wt.