KLF9 is a novel transcriptional regulator of bortezomib- and LBH589-induced apoptosis in multiple myeloma cells

Abstract

Bortezomib, a therapeutic agent for multiple myeloma (MM) and mantle cell lymphoma, suppresses proteosomal degradation leading to substantial changes in cellular transcriptional programs and ultimately resulting in apoptosis. Transcriptional regulators required for bortezomibinduced apoptosis in MM cells are largely unknown. Using gene expression profiling, we identified 36 transcription factors that displayed altered expression in MM cells treated with bortezomib. Analysis of a publically available database identified Kruppel-like family factor 9 (KLF9) as the only transcription factor with significantly higher basal expression in MM cells from patients who responded to bortezomib compared with nonresponders. We demonstrated that KLF9 in cultured MM cells was up-regulated by bortezomib; however, it was not through the induction of endoplasmic reticulum stress. Instead, KLF9 levels correlated with bortezomib-dependent inhibition of histone deacetylases (HDAC) and were increased by the HDAC inhibitor LBH589 (panobinostat). Furthermore, bortezomib induced binding of endogenous KLF9 to the promoter of the proapoptotic gene NOXA. Importantly, KLF9 knockdown impaired NOXA up-regulation and apoptosis caused by bortezomib, LBH589, or a combination of theses drugs, whereas KLF9 overexpression induced apoptosis that was partially NOXA-dependent. Our data identify KLF9 as a novel and potentially clinically relevant transcriptional regulator of drug-induced apoptosis in MM cells. (Blood. 2012;119(6):1450-1458) IntroductionMultiple myeloma (MM) is a plasma cell disorder that accounts for approximately 10% of all hematologic malignancies. 1,2 Although the introduction of novel agents in the past decade has increased median overall survival of myeloma patients from 30 months to 45-72 months, the disease still remains incurable. [3][4][5] One of these agents, bortezomib (Velcade, PS-341), significantly increased overall survival in patients with relapsed or refractory multiple myeloma when used as a single agent in comparison to high-dose dexamethasone, one of the standard therapies for this disease. [1][2][3][4][5] Bortezomib acts via inhibition of proteasome-mediated protein degradation, ultimately causing death in cells from many types of malignancies, including MM cells. [3][4][5] Bortezomib apoptosisinducing activity has been attributed in part to the alterations in the expression of several BCL2 family proteins, 6 among which the BH3-only protein NOXA appears to play an important role. [7][8][9] NOXA triggers apoptosis by binding to the prosurvival molecule MCL1, thus preventing it from sequestering proteins BAX, BAK and BIM, which are all critical inducers of apoptosis. [9][10][11][12] It has been reported that bortezomib increases NOXA protein levels by suppressing its proteosomal degradation 8 and by transcriptional activation of its gene. 8,13 Recently, several transcription factors including C-MYC, 13,14 ATF3, 15 ATF4, 15,16 and p53 14 have been shown to functionally participate in bortezomib-induced death in cells ...

The Novel Orally Active Proteasome Inhibitor K-7174 Exerts Anti-myeloma Activity in Vitro and in Vivo by Down-regulating the Expression of Class I Histone Deacetylases

“…The caspase-8-mediated pathway is dominant over the unfolded protein response in our system. Supporting this idea, Mannava et al (31) have recently reported that KLF9, which is indirectly transactivated by bortezomib, determines the response to bortezomib independently of the induction of ER stress. They have also shown that bortezomib-induced apoptosis largely depends on the class I HDAC activity.…”

Endoplasmic-reticulum stress pathway-associated mechanisms of action of proteasome inhibitors in multiple myeloma

“…In the APEX study [23], Mannava et al have reported that the expression level of Kruppel-like factor 9 (KLF9) is involved in the response of BTZ-containing therapy for RR MM. In this study, most patients with MM who showed a high level of KLF9 expression in primary MM cells showed good response to BTZ treatment compared to patients with low KLF9 expression.…”

One siRNA pool targeting the λ constant region stops λ light-chain production and causes terminal endoplasmic reticulum stress

“…Regulation of NOXA has been related to DNA damage as well as ERAD and epigenetic changes that enhance the activity of specific transcription factors; moreover, in vitro, bortezomib-induced apoptosis has been shown to depend on NOXA. [42][43][44][45] The model we report provides the opportunity to investigate in greater detail how plasma cells may overcome, adapt, or succumb to intrinsic terminal ER stress signals.…”