A pivotal role for Mcl-1 in Bortezomib-induced apoptosis

Oncogene. 2008 Jan 31;27(6):721-31. doi: 10.1038/sj.onc.1210679. Epub 2007 Jul 23.


Bortezomib is a proteasome inhibitor for the treatment of relapsed/refractory multiple myeloma (MM). Mechanisms of resistance to Bortezomib are undefined. Myeloid cell leukemia-1 (Mcl-1) is an antiapoptotic protein, which protects tumor cells against spontaneous and chemotherapy-induced apoptosis. In MM, specific downregulation of Mcl-1 induces apoptosis. Here, we examined the role of Mcl-1 in Bortezomib- and doxorubicin-induced apoptosis. We demonstrate that Bortezomib, but not doxorubicin, triggers caspase-dependent generation of a 28 kDa Mcl-1-fragment, in several MM cell lines, including MM.1S cells. Conversely, transient transfection of MM.1S cells with a previously reported 28 kDa Mcl-1(128-350) fragment, but not with the Mcl-1(1-127) fragment, induces apoptosis. Therefore, both downregulation of full-length antiapoptotic Mcl-1, as well as Bortezomib-induced generation of Mcl-1(128-350) cleaved protein, contribute to MM cell apoptosis. To verify further these findings, we next compared effects triggered by Bortezomib, doxorubicin and melphalan in Mcl-1(wt/wt) and Mcl-1(Delta/null) murine embryonic fibroblasts (MEFs). Our results show that Bortezomib, but not doxorubicin or melphalan, triggers Mcl-1 cleavage in Mcl-1(wt/wt), but not Mcl-1(Delta/null) MEFs and induces sub-G(1) phase cells; caspase-3 and -9, and PARP cleavage as well as morphological signs of apoptosis. Taken together, these results support an important role of Mcl-1 and a Mcl-1 fragment in Bortezomib-induced cell death in general, and in MM in particular. To prevent relapse of MM in patients treated with Bortezomib, we therefore recommend the combination of Bortezomib with agents that induce MM cell death independent of Mcl-1.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antineoplastic Agents / pharmacology*
  • Apoptosis*
  • Boronic Acids / pharmacology*
  • Bortezomib
  • Caspase Inhibitors
  • Caspases / metabolism
  • Cell Line, Tumor
  • Doxorubicin / pharmacology
  • Humans
  • Melphalan / pharmacology
  • Mice
  • Multiple Myeloma / enzymology*
  • Myeloid Cell Leukemia Sequence 1 Protein
  • Neoplasm Proteins / antagonists & inhibitors
  • Neoplasm Proteins / genetics
  • Neoplasm Proteins / metabolism*
  • Poly(ADP-ribose) Polymerases / metabolism
  • Protease Inhibitors / pharmacology*
  • Proto-Oncogene Proteins c-bcl-2 / antagonists & inhibitors
  • Proto-Oncogene Proteins c-bcl-2 / genetics
  • Proto-Oncogene Proteins c-bcl-2 / metabolism*
  • Pyrazines / pharmacology*
  • RNA, Small Interfering / pharmacology
  • Up-Regulation


  • Antineoplastic Agents
  • Boronic Acids
  • Caspase Inhibitors
  • Mcl1 protein, mouse
  • Myeloid Cell Leukemia Sequence 1 Protein
  • Neoplasm Proteins
  • PMAIP1 protein, human
  • Protease Inhibitors
  • Proto-Oncogene Proteins c-bcl-2
  • Pyrazines
  • RNA, Small Interfering
  • Bortezomib
  • Doxorubicin
  • Poly(ADP-ribose) Polymerases
  • Caspases
  • Melphalan