The aspartyl protease DDI2 drives adaptation to proteasome inhibition in multiple myeloma

Abstract

Proteasome inhibitors, such as bortezomib, are first-line therapy against multiple myeloma (MM). Unfortunately, patients frequently become refractory to this treatment. The transcription factor NRF1 has been proposed to initiate an adaptation program that regulates proteasome levels. In the context of proteasome inhibition, the cytosolic protease DDI2 cleaves NRF1 to release an active fragment that translocates to the nucleus to promote the transcription of new proteasome subunits. However, the contribution of the DDI2-NRF1 pathway to bortezomib resistance is poorly understood. Here we show that upon prolonged bortezomib treatment, MM cells become resistant to proteasome inhibition by increasing the expression of DDI2 and consequently activation of NRF1. Furthermore, we found that many MM cells became more sensitive to proteasome impairment in the context of DDI2 deficiency. Mechanistically, we demonstrate that both the protease and the HDD domains of DDI2 are required to activate NRF1. Finally, we show that partial inhibition of the DDI2-protease domain with the antiviral drug nelfinavir increased bortezomib susceptibility in treated MM cells. Altogether, these findings define the DDI2-NRF1 pathway as an essential program contributing to proteasome inhibition responses and identifying DDI2 domains that could be targets of interest in bortezomib-treated MM patients.

Early recovery of proteasome activity in cells pulse-treated with proteasome inhibitors is independent of DDI2

“…Several studies found that the knockout of DDI2 sensitizes cells to proteasome inhibitors [11,12,21,22,31]. This was further interpreted as supportive of a role for DDI2-dependent recovery in the de-sensitization of cells to PI-induced apoptosis.…”

“…This activity recovery may explain discrepancies between robust activity against cell lines derived from various cancers, continuously treated with Btz (www.carcerrxgene.org) [6], and a lack of clinical efficacy except in MM and MCL. In addition, recovery of activity has recently been implicated in PI resistance in MM [12].…”

The protease DDI2 regulates NRF1 activation in response to cadmium toxicity

“…Gene knockout (KO) cell lines were generated by viral transfection of LentiCRISPR-v2 vector (Addgene reference: 52,961) containing the target single guide RNA (sgRNA) sequence as described in ( Op et al., 2022 ). The sgRNA sequence of the Luciferase gene was used as control and denominated as Cr-luci cell line.…”

The transcription factor NRF1 (NFE2L1) activates aggrephagy by inducingp62 and GABARAPL1 after proteasome inhibition to maintain proteostasis

“…Supporting these findings, neuron-specific Nrf1 deletion led to mice exhibiting neurodegeneration disease accompanied by the accumulation of ubiquitinated proteins (hereafter referred to as Ub-proteins) due to the reduced proteasome activity 12,13 . Importantly, the proteasome bounce-back response exhibits significant medical relevance because therapeutic proteasome inhibition by bortezomib promptly triggers the upregulation of proteasome genes in cancer cells, such as multiple myeloma cells, leading to cancer cell resistance to anticancer drugs [14][15][16][17][18][19] . Nevertheless, whether NRF1 enhances other protein degradation systems, such as autophagy, when proteasome activity is fully suppressed is unclear.…”