IKKβ inhibitor in combination with bortezomib induces cytotoxicity in breast cancer cells.
Bortezomib is a proteasome inhibitor with remarkable clinical antitumor activity in multiple myeloma (MM) and is under evaluation in clinical trials in various types of cancer including breast cancer. Although the initial rationale for its use in cancer treatment was the inhibition of NF-κB activity by blocking proteasomal degradation of IκBα, direct evidence indicating inhibition of constitutive NF-κB activity by bortezomib in tumor cells in patients has not yet been reported. Moreover, recent studies have shown that bortezomib activates constitutive NF-κB activity via stimulating the canonical pathway in MM cells. In this study, we first examined protein expression of IκBα after bortezomib treatment. We observed that bortezomib upregulated the phosphorylation and downregulated IκBα protein expression in a dose- and time-dependent manner in MCF7 and T47D cells, associated with phosphorylation of IKKβ. Since IκBα is an inhibitor of nuclear translocation of NF-κB, we further examined alteration of NF-κB activity by bortezomib. Importantly, bortezomib significantly upregulates NF-κB activity in both MCF7 and T47D in a dose-dependent fashion, demonstrated by electrophoretic mobility shift analysis (EMSA). Furthermore, immunocytochemical analysis confirmed enhanced nuclear translocation of p65 NF-κB (RelA) by bortezomib treatment. Supershift assay showed supershifted bands by anti-p65 and -p50 antibodies. Taken together, these results indicate that bortezomib activates the canonical NF-κB pathway in both cell lines. Finally, we demonstrated that IKKβ inhibitor enhanced cytotoxicity, associated with inhibition of NF-κB activity induced by bortezomib in MCF7 and T47D breast cancer cells.
Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, USA.
Hiromasa
H
Hideshima
Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, USA.
Yasuhiro
Y
Yoshida
Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, USA.
Hiroshi
H
Ikeda
Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, USA.
Maya
M
Hide
Department of Thoracic, Endocrine and Pediatric Surgery, Faculty of Medicine, Fukuoka University, Jonan-ku, Fukuoka, Japan.
Akinori
A
Iwasaki
Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, USA.
Kenneth C
KC
Anderson
Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, USA.
Teru
T
Hideshima
D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000970:Antineoplastic Agents / Q000494:pharmacology; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D001943:Breast Neoplasms / Q000188:drug therapy*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D005260:Female; D006801:Humans; D051550:I-kappa B Kinase / Q000037:antagonists & inhibitors*; D020672:I-kappa B Proteins / Q000096:biosynthesis; D007093:Imidazoles / Q000494:pharmacology; D061986:MCF-7 Cells; D000072000:NF-KappaB Inhibitor alpha; D010766:Phosphorylation / Q000187:drug effects; D011719:Pyrazines / Q000494:pharmacology*; D011810:Quinoxalines / Q000494:pharmacology; D051996:Transcription Factor RelA / Q000378:metabolism*
C471109:4(2'-aminoethyl)amino-1,8-dimethylimidazo(1,2-a)quinoxaline; D000970:Antineoplastic Agents; D001897:Boronic Acids; D020672:I-kappa B Proteins; D007093:Imidazoles; C000606204:NFKBIA protein, human; D011719:Pyrazines; D011810:Quinoxalines; C498143:RELA protein, human; D051996:Transcription Factor RelA; D000072000:NF-KappaB Inhibitor alpha; D000069286:Bortezomib; D051550:I-kappa B Kinase; C496560:IKBKB protein, human