CST6 suppresses osteolytic bone disease in multiple myeloma by blocking osteoclast differentiation
Dongzheng Gai, … , John D. Shaughnessy Jr., Fenghuang Zhan
Dongzheng Gai, … , John D. Shaughnessy Jr., Fenghuang Zhan
Published July 26, 2022
Citation Information: J Clin Invest. 2022;132(18):e159527. https://doi.org/10.1172/JCI159527.
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Research Article Bone biology Hematology

CST6 suppresses osteolytic bone disease in multiple myeloma by blocking osteoclast differentiation

Abstract

Osteolytic bone disease is a hallmark of multiple myeloma (MM). A significant fraction (~20%) of MM patients do not develop osteolytic lesions (OLs). The molecular basis for the absence of bone disease in MM is not understood. We combined PET-CT and gene expression profiling (GEP) of purified BM CD138+ MM cells from 512 newly diagnosed MM patients to reveal that elevated expression of cystatin M/E (CST6) was significantly associated with the absence of OL in MM. An enzyme-linked immunosorbent assay revealed a strong correlation between CST6 levels in BM serum/plasma and CST6 mRNA expression. Both recombinant CST6 protein and BM serum from patients with high CST6 significantly inhibited the activity of the osteoclast-specific protease cathepsin K and blocked osteoclast differentiation and function. Recombinant CST6 inhibited bone destruction in ex vivo and in vivo myeloma models. Single-cell RNA-Seq showed that CST6 attenuates polarization of monocytes to osteoclast precursors. Furthermore, CST6 protein blocks osteoclast differentiation by suppressing cathepsin-mediated cleavage of NF-κB/p100 and TRAF3 following RANKL stimulation. Secretion by MM cells of CST6, an inhibitor of osteoclast differentiation and function, suppresses osteolytic bone disease in MM and probably other diseases associated with osteoclast-mediated bone loss.

Authors

Dongzheng Gai, Jin-Ran Chen, James P. Stewart, Intawat Nookaew, Hasem Habelhah, Cody Ashby, Fumou Sun, Yan Cheng, Can Li, Hongwei Xu, Bailu Peng, Tarun K. Garg, Carolina Schinke, Sharmilan Thanendrarajan, Maurizio Zangari, Fangping Chen, Bart Barlogie, Frits van Rhee, Guido Tricot, John D. Shaughnessy Jr., Fenghuang Zhan

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Figure 1

High expression of CST6 is linked to the absence of bone lesions in MM.

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High expression of CST6 is linked to the absence of bone lesions in MM. ...
(A) Workflow of the study. BMMC, BM mononuclear cells. (B) Heatmap showing that 54 genes were significantly differentially expressed in MM cells from patients with no (n = 178) or 1 or more focal lesions (n = 334) on PET-CT (P < 0.0001). Shown are 17 genes with elevated levels of expression in MM cells from patients with no lesions on PET-CT and ranked from top to bottom by significance; and 37 genes with significantly upregulated expression in tumor cells with 1 or more lesions on PET-CT and ranked from bottom to top by significance. Gene symbols are listed on the right. (C) Affymetrix MAS5.0 normalized mRNA expression signal is indicated on the y axis. Expression level of CST6 in each sample is indicated by the height of the bar. Samples are ordered from the lowest to highest level of expression of CST6 from left to right on the x axis. P value was obtained using 2-tailed, unpaired Student’s t test. (D) Dot plot shows the correlation between CST6 mRNA in purified MM tumor cells and BM serum CST6 levels. The level of expression of CST6 mRNA was quantified by microarray analysis, and CST6 protein was measured by ELISA in 75 NDMM patients. Each spot indicates the relative relation of CST6 mRNA and protein expression levels for a patient. There was a significant correlation between the level of CST6 mRNA in MM cells and the level of CST6 protein in MM BM serum/plasma (r = 0.60, P < 0.0001). P value was obtained by Pearson’s correlation and a linear regression analysis.