Interferon regulatory factor 4 mediates nonenzymatic IRE1 dependency in multiple myeloma cells

Area of Science:

• Oncology
• Molecular Biology
• Cell Biology

Background:

• Multiple myeloma (MM) is a cancer of plasma cells.
• MM often depends on endoplasmic reticulum (ER) stress pathways, particularly inositol-requiring enzyme 1 (IRE1), for survival.
• The non-enzymatic role of IRE1 in MM is not well understood.

Purpose of the Study:

• To elucidate the non-enzymatic mechanisms by which IRE1 promotes MM cell proliferation.
• To identify key molecular players involved in IRE1's non-canonical functions in MM.

Main Methods:

• Investigated the role of interferon regulatory factor 4 (IRF4) in IRE1-dependent MM growth.
• Utilized IRE1 silencing, IRF4 knockdown, and phospho-deficient/mimetic IRF4 mutants.
• Analyzed IRF4 phosphorylation, chromatin binding, transcriptional activity, and engagement with cell-cycle genes (E2F1, CDC25A) and CDK2.

Main Results:

• IRE1 silencing led to increased inhibitory phosphorylation of IRF4 (at S114/S270), impairing its function.
• IRF4 knockdown mimicked IRE1 silencing's anti-proliferative effects, while IRF4 repletion reversed them.
• Phospho-deficient IRF4 mutants rescued proliferation under IRE1 silencing, unlike phospho-mimetic mutants.
• IRF4 was shown to regulate E2F1 and CDC25A, promoting CDK2 activation and cell-cycle progression.

Conclusions:

• Interferon regulatory factor 4 (IRF4) is a crucial mediator of IRE1's non-enzymatic control over cell-cycle progression in multiple myeloma.
• IRE1 influences IRF4 activity through phosphorylation, impacting its role in driving MM cell proliferation.
• These findings provide new mechanistic insights into IRE1 and IRF4 functions in MM pathogenesis.