JunB is a key regulator of multiple myeloma bone marrow angiogenesis

Abstract

Bone marrow (BM) angiogenesis significantly influences disease progression in multiple myeloma (MM) patients and correlates with adverse prognosis. The present study shows a statistically significant correlation of the AP-1 family member JunB with VEGF, VEGFB, and IGF1 expression levels in MM. In contrast to the angiogenic master regulator Hif-1α, JunB protein levels were independent of hypoxia. Results in tumor-cell models that allow the induction of JunB knockdown or JunB activation, respectively, corroborated the functional role of JunB in the production and secretion of these angiogenic factors (AFs). Consequently, conditioned media derived from MM cells after JunB knockdown or JunB activation either inhibited or stimulated in vitro angiogenesis. The impact of JunB on MM BM angiogenesis was finally confirmed in a dynamic 3D model of the BM microenvironment, a xenograft mouse model as well as in patient-derived BM sections. In summary, in continuation of our previous study (Fan et al., 2017), the present report reveals for the first time that JunB is not only a mediator of MM cell survival, proliferation, and drug resistance, but also a promoter of AF transcription and consequently of MM BM angiogenesis. Our results thereby underscore worldwide efforts to target AP-1 transcription factors such as JunB as a promising strategy in MM therapy.

Bone Marrow Stroma-Induced Transcriptome and Regulome Signatures of Multiple Myeloma

“…Gene ontology enrichment analysis identified responses to drugs as the top hit (Figure 6F). WikiPathway analysis revealed that the target genes were enriched in the chemokine signaling pathway and the VEGFA-VEGFR2 signaling pathway (Supplementary Figure S7A), consistent with the role of JUNB in regulating MM BM angiogenesis [67].…”

“…Consistent with earlier observations [ 68 ], BMSCs upregulated the expression of JUNB in MM cells ( Figure 6 C). The JUNB motif presented at 25% of the distal peaks showing an increase in accessibility ( Figure 6 B); a potential enhancer site located 27K bps downstream of VEGFA served as an example ( Figure 6 D), also validated by ChIP-seq data in IL6-stimulated MM.1S cells [ 67 ]. At a genome-wide scale, reference peaks overlapped with JUNB binding sites defined by ChIP-seq data [ 67 ] exhibited an overall increase in chromatin accessibility for MM cells in the transwell vs. the monoculture ( Supplementary Figure S6B ).…”

“…The JUNB motif presented at 25% of the distal peaks showing an increase in accessibility ( Figure 6 B); a potential enhancer site located 27K bps downstream of VEGFA served as an example ( Figure 6 D), also validated by ChIP-seq data in IL6-stimulated MM.1S cells [ 67 ]. At a genome-wide scale, reference peaks overlapped with JUNB binding sites defined by ChIP-seq data [ 67 ] exhibited an overall increase in chromatin accessibility for MM cells in the transwell vs. the monoculture ( Supplementary Figure S6B ). Intriguingly, GREAT-predicted target genes of JUNB-motif-containing distal peaks increased their expression in the upper transwell as relative to the monoculture ( Figure 6 E).…”

“…Compared to other AP-1 family TFs, JUNB in MM cells is specifically induced by BMSCs [ 68 ]. Predicted gene targets of distal sites containing the JUNB motifs and increasing in accessibility were enriched in the VEGFA-VEGFR2 signaling pathway and the response to drugs, consistent with its roles in angiogenesis and drug resistance in MM cells [ 67 , 68 ]. Our results supported JUNB in promoting chromatin accessibility, a role validated in other cell systems, including cardiac regeneration [ 83 ], hormone stimuli [ 84 ], and T-cell activation [ 85 ].…”

“…The proto-oncogene JUNB is an AP-1 family member known as a mediator of MM cell survival, proliferation, drug resistance, and BM angiogenesis [ 67 , 68 ]. Consistent with earlier observations [ 68 ], BMSCs upregulated the expression of JUNB in MM cells ( Figure 6 C).…”