Biology subjects

Le Thomas, A.

Publications and source records attributed to Le Thomas, A..

3 recordsLinked to original sources

bioRxiv2021

Antigen-derived peptides directly engage the unfolded-protein sensor IRE1α to curb cross-presentation by dendritic cells

Dendritic cells (DCs) promote adaptive immunity by cross-presenting antigen-based epitopes to CD8+ T cells. DCs process internalized protein antigens into peptides that enter the endoplasmic reticulum (ER) and upload onto major histocompatibility type I (MHC-I) protein complexes for cell-surface transport and cross-presentation. Perplexingly, DCs often exhibit activation of the ER-stress sensor IRE1 in the absence of classical ER stress--leaving the underlying mechanism unexplained. Here we show that antigen-derived hydrophobic peptides directly engage ER-resident IRE1 by masquerading as unfolded proteins. Furthermore, IRE1 activation depletes MHC-I heavy-chain mRNAs through regulated IRE1-dependent decay (RIDD), thereby curtailing antigen cross-presentation. In tumor-bearing mice, IRE1 disruption increased MHC-I expression on tumor-infiltrating DCs, and enhanced recruitment and activation of CD8+ T cells. Moreover, IRE1 inhibition synergized with anti-PD-L1 antibody treatment to cause tumor regression. Our findings elucidate the mechanism and consequence of antigen-driven IRE1 activation in DCs, yielding a promising combination strategy for cancer immunotherapy.

cell biology↗

bioRxiv2021

Noncanonical mRNA decay by the endoplasmic-reticulum stress sensor IRE1α promotes cancer-cell survival

Eukaryotic IRE1 mitigates endoplasmic-reticulum (ER) stress by orchestrating the unfolded-protein response (UPR). IRE1 spans the ER membrane, and signals through a cytosolic kinase-endoribonuclease module. The endoribonuclease generates the transcription factor XBP1s by intron excision between similar RNA stem-loop endomotifs, and depletes select cellular mRNAs through regulated IRE1-dependent decay (RIDD). Paradoxically, mammalian RIDD seemingly targets only mRNAs with XBP1-like endomotifs, while in flies RIDD exhibits little sequence restriction. By comparing nascent and total IRE1-controlled mRNAs in human breast cancer cells, we discovered not only canonical endomotif-containing RIDD substrates, but also many targets lacking recognizable motifs--degraded by a process we coin RIDDLE, for RIDD lacking endomotif. IRE1 displayed two basic endoribonuclease modalities: endomotif-specific cleavage, minimally requiring dimers; and endomotif-independent promiscuous processing, requiring phospho-oligomers. An oligomer-deficient mutant that did not support RIDDLE failed to rescue cancer-cell viability. These results link IRE1 oligomers, RIDDLE, and cell survival, advancing mechanistic understanding of the UPR.

cancer biology↗

bioRxiv2018

Disruption of IRE1α through its Kinase Domain Attenuates Multiple Myeloma

Multiple myeloma (MM) arises from malignant immunoglobulin-secreting plasma cells and remains an incurable, often lethal disease despite recent therapeutic advances. The unfolded-protein response sensor IRE1 supports protein secretion by deploying a kinase-endoribonuclease module to activate the transcription factor XBP1s. MM cells may coopt the IRE1-XBP1s pathway; however, the validity of IRE1 as a potential MM therapeutic target is controversial. Here we show that genetic disruption of IRE1 or XBP1s, or pharmacologic IRE1 kinase inhibition, attenuated subcutaneous or orthometastatic growth of MM tumors in mice, and augmented efficacy of two well-established frontline antimyeloma agents, bortezomib or lenalidomide. Mechanistically, IRE1 perturbation inhibited expression of key components of the ER-associated degradation machinery, as well as cytokines and chemokines known to promote MM growth. Selective IRE1 kinase inhibition reduced viability of CD138+ plasma cells while sparing CD138- cells from bone marrow of newly diagnosed MM patients or patients whose disease relapsed after 1 - 4 lines of treatment in both US- and EU-based cohorts. IRE1 inhibition preserved survival and glucose-induced insulin secretion by pancreatic microislets. Together, these results establish a strong therapeutic rationale for targeting IRE1 with kinase-based small-molecule inhibitors in MM.\n\nSignificance statementMultiple myeloma (MM) is a lethal malignancy of plasma cells. MM cells have an expanded endoplasmic reticulum (ER) that is constantly under stress due to immunoglobulin hyperproduction. The ER-resident sensor IRE1 mitigates ER stress by expanding the ERs protein-folding capacity while supporting proteasomal degradation of misfolded ER proteins. IRE1 elaborates these functions by deploying its cytoplasmic kinase-RNase module to activate the transcription factor XBP1s. The validity of IRE1 as a potential therapeutic target in MM has been questioned. Using genetic and pharmacologic disruption in vitro and in vivo, we demonstrate that the IRE1-XBP1s pathway plays a critical role in MM growth. We further show that IRE1s kinase domain is an effective and safe potential small-molecule target for MM therapy.

cancer biology↗