Cytotoxic effects of bortezomib in myelodysplastic syndrome/acute myeloid leukemia depend on autophagy-mediated lysosomal degradation of TRAF6 and repression of PSMA1.

Abstract

Bortezomib (Velcade) is used widely for the treatment of various human cancers; however, its mechanisms of action are not fully understood, particularly in myeloid malignancies. Bortezomib is a selective and reversible inhibitor of the proteasome. Paradoxically, we find that bortezomib induces proteasome-independent degradation of the TRAF6 protein, but not mRNA, in myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) cell lines and primary cells. The reduction in TRAF6 protein coincides with bortezomib-induced autophagy, and subsequently with apoptosis in MDS/AML cells. RNAi-mediated knockdown of TRAF6 sensitized bortezomib-sensitive and -resistant cell lines, underscoring the importance of TRAF6 in bortezomib-induced cytotoxicity. Bortezomib-resistant cells expressing an shRNA targeting TRAF6 were resensitized to the cytotoxic effects of bortezomib due to down-regulation of the proteasomal subunit α-1 (PSMA1). To determine the molecular consequences of loss of TRAF6 in MDS/AML cells, in the present study, we applied gene-expression profiling and identified an apoptosis gene signature. Knockdown of TRAF6 in MDS/AML cell lines or patient samples resulted in rapid apoptosis and impaired malignant hematopoietic stem/progenitor function. In summary, we describe herein novel mechanisms by which TRAF6 is regulated through bortezomib/autophagy-mediated degradation and by which it alters MDS/AML sensitivity to bortezomib by controlling PSMA1 expression.

• Authors: Jing Fang, Garrett Rhyasen, Lyndsey Bolanos, Christopher Rasch, Melinda Varney, Mark Wunderlich, Susumu Goyama, Gerrit Jansen, Jacqueline Cloos, Carmela Rigolino, Agostino Cortelezzi, James C Mulloy, Esther N Oliva, Maria Cuzzola, Daniel T Starczynowski
• Journal: Blood (Blood) Vol. 120 Issue 4 Pg. 858-67 (Jul 26 2012) ISSN: 1528-0020 [Electronic] United States
• PMID: 22685174 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Antineoplastic Agents
• Biomarkers, Tumor
• Boronic Acids
• Proteasome Inhibitors
• Pyrazines
• TNF Receptor-Associated Factor 6
• Bortezomib
• Proteasome Endopeptidase Complex

Topics

• Antineoplastic Agents (pharmacology)
• Autophagy (drug effects)
• Biomarkers, Tumor (genetics, metabolism)
• Blotting, Western
• Boronic Acids (pharmacology)
• Bortezomib
• Cell Proliferation (drug effects)
• Clinical Trials, Phase II as Topic
• Gene Expression Profiling
• Humans
• Leukemia, Myeloid, Acute (genetics, metabolism, pathology)
• Lysosomes (metabolism)
• Multicenter Studies as Topic
• Myelodysplastic Syndromes (genetics, metabolism, pathology)
• Oligonucleotide Array Sequence Analysis
• Proteasome Endopeptidase Complex (genetics, metabolism)
• Proteasome Inhibitors
• Pyrazines (pharmacology)
• TNF Receptor-Associated Factor 6 (genetics, metabolism)