Intracellular IL-32 regulates mitochondrial metabolism, proliferation, and differentiation of malignant plasma cells

Abstract

Summary Interleukin-32 (IL-32) is a nonclassical cytokine expressed in cancers, inflammatory diseases, and infections. Its expression is regulated by two different oxygen sensing systems; HIF1α and cysteamine dioxygenase (ADO), indicating that IL-32 may be involved in the response to hypoxia. We here demonstrate that endogenously expressed, intracellular IL-32 interacts with components of the mitochondrial respiratory chain and promotes oxidative phosphorylation. Knocking out IL-32 in three myeloma cell lines reduced cell survival and proliferation in vitro and in vivo . High-throughput transcriptomic and MS-metabolomic profiling of IL-32 KO cells revealed that cells depleted of IL-32 had perturbations in metabolic pathways, with accumulation of lipids, pyruvate precursors, and citrate. IL-32 was expressed in a subgroup of myeloma patients with inferior survival, and primary myeloma cells expressing IL-32 had a gene signature associated with immaturity, proliferation, and oxidative phosphorylation. In conclusion, we demonstrate a previously unrecognized role of IL-32 in the regulation of plasma cell metabolism.

IL-32 is induced by activation of toll-like receptors in multiple myeloma cells

“…We previously showed that IL-32 is upregulated upon relapse and that some IL-32-non-expressors start to express IL-32 in the time period between diagnosis and relapse ( 5 ). To investigate if TLR expression in a similar manner is increased in samples obtained at relapse compared with samples obtained at diagnosis we analyzed the same longitudinal RNA-sequenced samples (n=47).…”

“…RNA sequencing data from CD138 + cells were available for 795 baseline samples from patients with MM. For TLR gene expression analysis, patient samples taken at diagnosis were divided into high and low IL-32 expression based on the same percentiles (upper 10 th and lower 90 th ) as used in our previous study on IL-32 in myeloma ( 5 ). We used the upper 10th percentile (n = 54; counts per million (cpm, log2)> 1.52) and lower 90th percentile (n = 741, (cpm,log2)≤ 1.52) and significance was analyzed by one-tailed Wilcoxon signed-rank test in R. Pearson correlation analysis was performed using stat_cor function in R.…”

“…IL-32 is a pleiotropic cytokine with classical pro-inflammatory functions as well as more unconventional roles in cancer, autoimmune diseases, and infections ( 2 – 4 ). It is shown to be an important growth factor and metabolic regulator of MM cells ( 5 ). Furthermore, IL-32 is secreted by MM cells in exosomes and alters the tumor microenvironment by promoting osteoclastogenesis and bone degradation ( 6 ) as well as immune suppression ( 7 , 8 ).…”

“…Furthermore, IL-32 is secreted by MM cells in exosomes and alters the tumor microenvironment by promoting osteoclastogenesis and bone degradation ( 6 ) as well as immune suppression ( 7 , 8 ). High expression of IL-32 at diagnosis is observed in 10-15% of patients and these individuals have inferior survival compared to non-expressors ( 5 , 6 ). Moreover, IL-32 expression is upregulated upon relapse in a fraction of patients ( 5 ).…”

“…High expression of IL-32 at diagnosis is observed in 10-15% of patients and these individuals have inferior survival compared to non-expressors ( 5 , 6 ). Moreover, IL-32 expression is upregulated upon relapse in a fraction of patients ( 5 ).…”