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, 1 (27), 2656-2666
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Hypoxia Promotes IL-32 Expression in Myeloma Cells, and High Expression Is Associated With Poor Survival and Bone Loss

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Hypoxia Promotes IL-32 Expression in Myeloma Cells, and High Expression Is Associated With Poor Survival and Bone Loss

Muhammad Zahoor et al. Blood Adv.

Abstract

Multiple myeloma (MM) is a hematologic cancer characterized by expansion of malignant plasma cells in the bone marrow. Most patients develop an osteolytic bone disease, largely caused by increased osteoclastogenesis. The myeloma bone marrow is hypoxic, and hypoxia may contribute to MM disease progression, including bone loss. Here we identified interleukin-32 (IL-32) as a novel inflammatory cytokine expressed by a subset of primary MM cells and MM cell lines. We found that high IL-32 gene expression in plasma cells correlated with inferior survival in MM and that IL-32 gene expression was higher in patients with bone disease compared with those without. IL-32 was secreted from MM cells in extracellular vesicles (EVs), and those EVs, as well as recombinant human IL-32, promoted osteoclast differentiation both in vitro and in vivo. The osteoclast-promoting activity of the EVs was IL-32 dependent. Hypoxia increased plasma-cell IL-32 messenger RNA and protein levels in a hypoxia-inducible factor 1α-dependent manner, and high expression of IL-32 was associated with a hypoxic signature in patient samples, suggesting that hypoxia may promote expression of IL-32 in MM cells. Taken together, our results indicate that targeting IL-32 might be beneficial in the treatment of MM bone disease in a subset of patients.

Conflict of interest statement

Conflict-of-interest disclosure: The authors declare no competing financial interests.

Figures

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Figure 1.
Figure 1.
IL-32 is expressed by MM cells, and high expression is correlated with inferior survival. (A) Heat map of top 25 most highly expressed genes as determined by Nanostring analyses in BM-derived CD138+ MM cells obtained from patients (n = 8). (B) IL32 mRNA expression was quantified by quantitative PCR in BM-derived CD138+ MM cells (n = 40) and MM cell lines (n = 9). Immunoblotting of total cell lysates from MM cell lines (n = 9) (C) and CD138+ primary MM cells (n = 6) (D). (E) IL-32 was quantified by ELISA in BM plasma obtained from healthy persons (n = 5; median, 360 pg/mL), patients with monoclonal gammopathy of unknown significance (MGUS; n = 16; median, 565.6 pg/mL), and patients with MM (n = 41; median, 906.5 pg/mL). The differences between the groups are not statistically significant. (F) Survival curves generated from the CoMMpass data (IA8 release) by comparing the IL32 upper 15th percentile (IL-32 expressors; n = 82; median survival, 464 days) with the lower 85th percentile (IL-32 nonexpressors; n = 466; median survival, 914 days). Log-rank P < .0001. Bars indicate median values in panels A and C.
Figure 2.
Figure 2.
IL-32 is secreted from myeloma cells on EVs. (A) JJN3 cells were stained for IL-32 (red), GM130 (Golgi marker; green), CD63 (EV marker; green), and CD81 (EV marker; green). Scale bar, 15 μm. (B) Total cell lysates and lysates of EVs isolated from cell culture supernatants were immunoblotted as indicated. (C) EVs were isolated from media from JJN3 cells cultured for 48 hours. IL-32 in the EV fraction treated with or without NP-40 detergent was quantified by ELISA. (D) EVs were isolated from BM plasma obtained from patients with myeloma (n = 18), and amount of IL-32 in the EV fraction was determined by ELISA.
Figure 3.
Figure 3.
Hypoxia increases IL-32 expression in an HIF1α-dependent manner. (A) BM-derived CD138+ MM cells were cultured for 24 hours in normoxia (20% oxygen) or hypoxia (2% oxygen) as indicated, and IL-32, HIF1α, and β-actin were detected by immunoblotting in total cellular lysates. (B) MM cell lines were cultured for 48 hours under normoxia or hypoxia before collection of cells and cell culture supernatant for EV isolation. Total cell lysates and isolated EVs were immunoblotted as indicated. (C) IL-32 mRNA expression was determined by quantitative PCR in JJN3 cells cultured in hypoxia for the indicated time before reoxygenation as indicated. (D) JJN3 cells were transfected with scrambled control siRNA (siCtr) or HIF1α siRNA (siHIF1α), and expression of IL-32 and HIF1α was examined by immunoblotting after 24 hours. (E) Density of IL-32 and HIF1α bands was quantified by Image Studio Software and normalized to levels of β-actin. Data presented are mean + standard error of the mean from 4 independent experiments. (F) RNA sequencing data were downloaded from the CoMMPass IA8 release and analyzed using GSEA software v2.2.3 to identify functionally related groups of genes with statistically significant enrichment. The figure shows the enrichment plot for the hypoxia-related gene set for patients with IL32 levels in the upper 15th percentile. (G) The same RNA sequencing data in panel F were also analyzed to determine the correlation between relative IL32 mRNA expression vs relative hypoxic gene signature expression in MM as defined previously. Relative IL32 gene expression significantly correlated with the hypoxic signature (Spearman ρ = 0.4; P < .0001). ***P < .001.
Figure 4.
Figure 4.
IL-32 in EVs induces osteoclast differentiation in vitro and in vivo. (A-B) Preosteoclasts were treated with rhIL-32 (25 ng/mL), RANKL (50 ng/mL), or JJN3-derived EVs (5 μL) for 3 days before the cells were TRAP stained. (Original magnification ×200 in panel A.) Number of osteoclasts was determined by counting TRAP+ cells with >2 nuclei. Bars indicate relative number of osteoclasts (mean ± standard error of the mean [SEM]) from 5 independent experiments using peripheral blood mononuclear cells (PBMCs) from 5 different donors. (C-D) EVs (30 μL) from JJN3 cells cultured in normoxia (N) or hypoxia (H), rhIL-32 (3 μg in 30 μL of PBS), and PBS control (30 μL) were injected on top of the calvaria of NOD-SCID mice (n = 8 per group) every day for 5 days. After 3 more days, the mice were euthanized and the calvaria harvested. (Original magnification ×200 in panel C.) Amount TRAP+ bone surface (BS) was quantified using NIS-Elements BR software. (E) JJN3 cells in which IL-32 was silenced using CRISPR/Cas9 (KO) or control cells (WT) were cultured in normoxia or hypoxia for 48 hours. Cells and EVs obtained from the culture media were harvested and lysed before immunoblotting as indicated. (F) Preosteoclasts were treated with rhIL-32 (25 ng/mL), RANKL (50 ng/mL), or EVs (5 μL) obtained from JJN3 KO and JJN3 WT cells as indicated for 3 days. Number of osteoclasts was determined by counting TRAP+ cells with >2 nuclei. Bars indicate relative number of osteoclasts (mean + SEM) from 6 independent experiments using PBMCs from 6 different donors. (G-H) 100 000 JJN3 WT or JJN3 KO cells were injected intratibially in RAG2/GC KO mice. After 20 days, tibiae were harvested and examined by µCT. Representative images from the 2 groups are shown in panel G. Bars in panel H represents number of osteolytic lesions (mean + SEM). Significance was determined by Student t test. (I) NFκB p65 nuclear localization was examined in preosteoclast serum starved for 3 hours and then treated with EVs isolated from IL-32–expressing JJN3 cells (WT) or from IL-32 KO cells for 1 hour. p65 in red; Dapi nuclear stain in blue. (Original magnification ×400.) (J) Number of cells with NFκB p65 in the nucleus was counted to estimate percentage of nuclear localization. Data were obtained from 4 independent experiments using 4 different PBMC donors. For all experiments, unless otherwise stated, significance was determined by 1-way analysis of variance followed by Fisher’s least significant difference post hoc test. *P < .05, **P < .01, ***P < .001, ****P < .0001. TBS, total bone surface.
Figure 5.
Figure 5.
High IL-32 expression is associated with osteolytic bone disease. (A) IL32 gene expression in MM cells from patients without bone disease (BD; median, 0.42; n = 36) compared with patients with BD (median, 0.53; n = 137). Data obtained from GSE755. BD was defined as having ≥1 osteolytic lesion as assessed by magnetic resonance imaging. Mann-Whitney U test P < .001. (B) Summary of main findings presented in the article. In response to hypoxia, MM cells secrete IL-32 in EVs, which promote osteoclast differentiation.

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