Silencing of SENP2 in Multiple Myeloma Induces Bortezomib Resistance by Activating NF-κB Through the Modulation of IκBα Sumoylation

Abstract

The proteasome inhibitor bortezomib is the most successfully applied chemotherapeutic drug for treating multiple myeloma. However, its clinical efficacy reduced due to resistance development. The underlying molecular mechanisms of bortezomib resistance are poorly understood. In this study, by combining in silico analysis and sgRNA library based drug resistance screening assay, we identified SENP2 (Sentrin/SUMO-specific proteases-2) as a bortezomib sensitive gene and found its expression highly downregulated in bortezomib resistant multiple myeloma patient's samples. Furthermore, down regulation of SENP2 in multiple myeloma cell line RPMI8226 alleviated bortezomib induced cell proliferation inhibition and apoptosis, whereas, overexpression of SENP2 sensitized these cells to bortezomib treatment. We further demonstrate that knockdown of SENP2 in RPMI8226 cells increased SUMO2 conjugated IκBα that resulted in the activation of NF-κB. Taken together, we report that silencing of SENP2 and consequent activation of NF-κB through the modulation of IκBα sumoylation as a novel mechanism inducing bortezomib resistance in multiple myeloma. Multiple myeloma (MM) is a malignant plasma cell tumor that account for 12% of blood malignant tumors, which is the second most commonly diagnosed hematologic malignancy 1. Despite applying multiple therapeutic drugs such as, proteasome inhibitor bortezomib 2 and immunomodulator thalidomide 3 , the median MM patient survival was only slightly improved from 3-5 years to 5-7 years 4. Moreover, MM is still featured as a recurrence and insensitive to treatment due to drug resistance development 5. The bortezomib is the first class of proteasome inhibitor approved for the treatment of MM. Bortezomib is a dipeptidyl boronic acid that reversibly binds to chymotrypsin-like catalytic subunit of 20 S proteasome and inhibits its activity 6. Proteasome plays a critical role in cellular homeostasis by degrading unwanted cellular proteins 7. The imbalance between synthesis and degradation of proteins arises due to proteasome inhibition results in the accumulation of regulatory proteins causing endoplasmic reticulum stress and activation of the unfolded protein response leading to induction of apoptosis in malignant cells via multiple mechanisms 8,9 .

Protein Kinase D 1 Predicts Poor Treatment Response and Unfavorable Survival of Bortezomib-Based Treatment, and Its Knockdown Enhances Drug Sensitivity to Bortezomib in Multiple Myeloma

“… 28 In addition, the MEK/ERK pathway cascade is associated with RAS/RAF mutations, further driving mutation-inducing MM, and the activation of NF-κB is critical in supporting MM cell growth as well as in the formation of drug resistance. 19 , 29 Therefore, we speculated that PKD1 might be upregulated and associated with clinical characteristics in patients with MM, while the related evidence is lacking. First, we found that PKD1 mRNA and protein expressions were both increased in patients with MM compared with HCs and presented good value in distinguishing patients with MM from HCs.…”

“…In addition, according to the prior evidence, PKD1 has regulatory effect on NF-κB and JNK signaling, and drug resistance to bortezomib is associated with stimulation of NF-κB signaling but inactivation of JNK signaling. 11 , 19 , 20 Moreover, PKD1 activates MEK/ERK signaling cascade, which is associated with RAS/RAF mutations, which is involved in the development of drug resistance in MM treatment. According to these aforementioned evidence, we speculated that PKD1 might be correlated with prognosis in patients with MM treated with bortezomib-based regimens and found that PKD1 was negatively associated with treatment response and survival with regard to bortezomib-based treatment in patients with MM.…”

“…Therefore, PKD1 knockdown increased drug sensitivity to bortezomib in MM cells. 19 , 20 (2) According to the abovementioned results, PKD1 was associated with genetic mutations (such as t (4; 14)), which might further contribute to the formation of drug resistance, thereby, PKD1 knockdown might increase drug sensitivity to bortezomib in MM cells. 33 …”

“…Therefore, we hypothesized that PKD1 might be implicated in the pathology and the generation of bortezomib resistance in MM. 11 , 19 , 20 However, there is still no evidence available. We performed this clinical study to explore the correlation of PKD1 with treatment response and survival in patients with MM who treated with bortezomib-based regimen and further conducted cellular experiments to investigate the effect of PKD1 knockdown on drug sensitivity to bortezomib in MM cells.…”

Ubiquitination and Ubiquitin-Like Modifications in Multiple Myeloma: Biology and Therapy

“…SENP2 has a broad substrate specificity similar to SENP1 [ 159 ]. Silencing of SENP2 in MM contributes to the development of bortezomib resistance mediated by the activation of NFκB [ 160 ]. Similarly, it has been shown in other cancers that activation of NFκB may also induce resistance to therapy [ 160 ].…”