The CXCL12gamma chemokine immobilized by heparan sulfate on stromal niche cells controls adhesion and mediates drug resistance in multiple myeloma.

ABSTRACT:

Background

The survival and proliferation of multiple myeloma (MM) cells in the bone marrow (BM) critically depend on interaction with stromal cells expressing the chemokine CXCL12. CXCL12 regulates the homing to the BM niche by mediating the transendothelial migration and adhesion/retention of the MM cells. The gamma isoform of CXCL12 (CXCL12?) has been reported to be highly expressed in mouse BM and to show enhanced biological activity compared to the 'common' CXCL12? isoform, mediated by its unique extended C-terminal domain, which binds heparan sulfate proteoglycans (HSPGs) with an extraordinary high affinity. Here, we investigated the expression of CXCL12? in human BM and studied its functional role in the interaction of MM cells with BM stromal cells (BMSCs).

Methods

We assessed CXCL12? mRNA and protein expression by human BMSCs using qPCR, flow cytometry, and immunohistochemistry. CRISPR-Cas9 was employed to delete CXCL12? and the heparan sulfate (HS) co-polymerase EXT1 in BMSCs. To study the functional roles of BMSC-derived CXCL12? and HSPGs in the interaction of MM cells with BMSCs cells, MM cell lines and primary MM cells were co-cultured with BMSCs.

Results

We observed that CXCL12? is expressed in situ by reticular stromal cells in both normal and MM BM, as well as by primary BMSC isolates and BMSC lines. Importantly, upon secretion, CXCL12?, unlike the CXCL12? isoform, was retained on the surface of BMSCs. This membrane retention of CXCL12? is HSPG mediated, since it was completely annulated by CRISPR-Cas9-mediated deletion of the HS co-polymerase EXT1. CXCL12? expressed by BMSCs and membrane-retained by HSPGs supported robust adhesion of MM cells to the BMSCs. Specific genetic deletion of either CXCL12? or EXT1 significantly attenuated the ability of BMSCs to support MM cell adhesion and, in addition, impaired their capacity to protect MM cells from bortezomib-induced cell death.

Conclusions

We show that CXCL12? is expressed by human BMSCs and upon secretion is retained on their cell surface by HSPGs. The membrane-bound CXCL12? controls adhesion of MM cells to the stromal niche and mediates drug resistance. These findings designate CXCL12? and associated HSPGs as partners in mediating MM-niche interaction and as potential therapeutic targets in MM.

SUBMITTER: Ren Z 

PROVIDER: S-EPMC7802348 | biostudies-literature | 2021 Jan

REPOSITORIES: biostudies-literature