Noncanonical SQSTM1/p62-Nrf2 pathway activation mediates proteasome inhibitor resistance in multiple myeloma cells via redox, metabolic and translational reprogramming

Abstract

Multiple Myeloma (MM) is a B-cell malignancy characterized by the accumulation of clonal plasma cells in the bone marrow, with drug resistance being a major cause of therapeutic failure. We established a carfilzomib-resistant derivative of the LP-1 MM cell line (LP-1/Cfz) and found that the transcription factor NF-E2 p45-related factor 2 (Nrf2; gene symbol NFE2L2) contributes to carfilzomib resistance. The mechanism of Nrf2 activation involved enhanced translation of Nrf2 as well as its positive regulator, the autophagy receptor sequestosome 1 (SQSTM1)/p62. The eukaryotic translation initiation factor gene EIF4E3 was among the Nrf2 target genes upregulated in LP-1/Cfz cells, suggesting existence of a positive feedback loop. In line with this, we found that siRNA knockdown of eIF4E3 decreased Nrf2 protein levels. On the other hand, elevated SQSTM1/p62 levels were due at least in part to activation of the PERK-eIF2α pathway. LP-1/Cfz cells had decreased levels of reactive oxygen species as well as elevated levels of fatty acid oxidation and prosurvival autophagy. Genetic and pharmacologic inhibition of the Nrf2-EIF4E3 axis or the PERK-eIF2α pathway, disruption of redox homeostasis or inhibition of fatty acid oxidation or autophagy conferred sensitivity to carfilzomib. Our findings were supported by clinical data where increased EIF4E3 expression was predictive of Nrf2 target gene upregulation in a subgroup of patients with chemoresistant minimal residual disease and relapsed/refractory MM. Thus, our data offer a preclinical rationale for including inhibitors of the SQSTM1/p62-Nrf2 pathway to the treatment regimens for certain advanced stage MM patients.

Combinatorial ixazomib and belinostat therapy induces NFE2L2‐dependent apoptosis in Hodgkin and T‐cell lymphoma

“…Several recent studies have highlighted involvement of NFE2L2 in the resistance to multiple proteasome inhibitors, including carfilzomib and bortezomib, in multiple myeloma (Li et al , ; Riz et al , ). In bortezomib‐treated mantle cell lymphoma, activation of endoplasmic reticulum and NFE2L2‐dependent oxidative stress response pathways were observed and higher NFE2L2 gene expression was reported in bortezomib‐resistant cells (Weniger et al , ).…”

A metabolic switch in proteasome inhibitor-resistant multiple myeloma ensures higher mitochondrial metabolism, protein folding and sphingomyelin synthesis

“…The data highlight increased antioxidant capacity, higher redox homeostasis and NAD + levels as the key metabolic changes in PI-resistance and are consistent with findings from earlier models including our own proteomic data. [5][6][7][8][9][10][11][12][13] We functionally validated the increased capacity of PIresistant cells to buffer the formation of reactive oxygen species (ROS), demonstrating 2-to 4-fold lower ROS levels in these cells than in PI-sensitive cells, confirming a significantly higher antioxidant capacity (Figure 2A). Consistent with this, PI-resistant cells are more resistant than PI-sensitive cells to H2O2-induced cytotoxicity (Online Supplementary Figure S4, Online Supplementary Table S2).…”

p62/SQSTM1 – steering the cell through health and disease

“…Accordingly, in HCC, the SQSTM1-Keap1-Nrf2 axis promotes metabolic reprogramming that includes enhanced production of uridine diphosphate (UDP)-glucuronate and glutathione, both of which promote cancer development as well as its resistance to anticancer drugs (Saito et al, 2016;Umemura et al, 2016). This prominent role of the SQSTM1-Keap1-Nrf2 axis in tumorigenesis has been extended to other cancer forms, including ovarian (Xia et al, 2014), pancreatic (Todoric et al, 2017), breast (Ryoo et al, 2018;Xu et al, 2017), lung (Huang et al, 2016) and arsenic-induced skin cancers (Shah et al, 2017), as well as multiple myeloma (Riz et al, 2016) and esophageal squamous cell carcinoma (Shi et al, 2018). In the case of pancreatic ductal adenocarcinoma (PDAC), SQSTM1mediated activation of Nrf2 also results in the induction of the ubiquitin ligase MDM2, which further aggravates cancer progression by promoting degradation of p53 and inducing the Notch signaling pathway (Todoric et al, 2017).…”