Inhibition of NGLY1 Inactivates the Transcription Factor Nrf1 and Potentiates Proteasome Inhibitor Cytotoxicity

Abstract

Proteasome inhibitors are used to treat blood cancers such as multiple myeloma (MM) and mantle cell lymphoma. The efficacy of these drugs is frequently undermined by acquired resistance. One mechanism of proteasome inhibitor resistance may involve the transcription factor Nuclear Factor, Erythroid 2 Like 1 (NFE2L1, also referred to as Nrf1), which responds to proteasome insufficiency or pharmacological inhibition by upregulating proteasome subunit gene expression. This “bounce-back” response is achieved through a unique mechanism. Nrf1 is constitutively translocated into the ER lumen, N-glycosylated, and then targeted for proteasomal degradation via the ER-associated degradation (ERAD) pathway. Proteasome inhibition leads to accumulation of cytosolic Nrf1, which is then processed to form the active transcription factor. Here we show that the cytosolic enzyme N-glycanase 1 (NGLY1, the human PNGase) is essential for Nrf1 activation in response to proteasome inhibition. Chemical or genetic disruption of NGLY1 activity results in the accumulation of misprocessed Nrf1 that is largely excluded from the nucleus. Under these conditions, Nrf1 is inactive in regulating proteasome subunit gene expression in response to proteasome inhibition. Through a small molecule screen, we identified a cell-active NGLY1 inhibitor that disrupts the processing and function of Nrf1. The compound potentiates the cytotoxicity of carfilzomib, a clinically used proteasome inhibitor, against MM and T cell-derived acute lymphoblastic leukemia (T-ALL) cell lines. Thus, NGLY1 inhibition prevents Nrf1 activation and represents a new therapeutic approach for cancers that depend on proteasome homeostasis.

Variants in NGLY1 lead to intellectual disability, myoclonus epilepsy, sensorimotor axonal polyneuropathy and mitochondrial dysfunction

“…The researchers suggest that the mitochondrial network fragmentation is due to absence of NGLY1 which alters the glycosylation of Nrf1, hampering its function and resulting in a fragmented mitochondrial network. 28 However, we did not note fragmentation of the mitochondrial network when assessing the mitochondrial morphology in patient fibroblasts as observed previously. 8 To date, 13 patients have been investigated with a pathogenic variant in NGLY1 and with clinical signs and symptoms suggestive of a mitochondrial disorder, including intellectual disability, involuntary movements, and muscular hypotonia.…”

“…This article suggests that the mitochondrial network, visualized with an anti‐body directed against Hsp60, is fragmented in patient fibroblasts and Ngly1 −/− mouse embryonic fibroblasts. The researchers suggest that the mitochondrial network fragmentation is due to absence of NGLY1 which alters the glycosylation of Nrf1, hampering its function and resulting in a fragmented mitochondrial network . However, we did not note fragmentation of the mitochondrial network when assessing the mitochondrial morphology in patient fibroblasts as observed previously …”

“…This might indicate that NGLY1 is involved in the degradation of mitochondrial outer membrane proteins. Furthermore, it was shown that mitochondrial function is influenced in NGLY1 patients via glycosylated Nrf1 . This article suggests that the mitochondrial network, visualized with an anti‐body directed against Hsp60, is fragmented in patient fibroblasts and Ngly1 −/− mouse embryonic fibroblasts.…”

“…Furthermore, it was shown that mitochondrial function is influenced in NGLY1 patients via glycosylated Nrf1. 28 This article suggests that the mitochondrial network, visualized with an anti-body directed against Hsp60, is fragmented in patient fibroblasts and Ngly1 −/− mouse embryonic fibroblasts. The researchers suggest that the mitochondrial network fragmentation is due to absence of NGLY1 which alters the glycosylation of Nrf1, hampering its function and resulting in a fragmented mitochondrial network.…”

Functional glycomics: Application to medical science and hepatology

“…This common lack of NFE2L1 activation (and possibly other molecules that are activated through similar reactions) might represent the molecular mechanism underlying the similar clinical features between some CDGs and NGLY1 deficiency. Figures based on references . [Color figure can be viewed at wileyonlinelibrary.com]…”