Background/objective: Bone marrow stromal cells (BMSCs) can support multiple myeloma (MM) disease progression and resistance to chemotherapy. The proliferation of MM cells may be suppressed by modifying the hematopoietic microenvironment (HME). We have previously isolated human umbilical cord blood-derived stromal cells (hUCBDSCs) and observed that hUCBDSCs suppressed proliferation and induced apoptosis in KM3 cells. To examine the mechanism by which hUCBDSCs drive the inhibition of MM, KM3 cells were co-cultured with hUCBDSCs.
Methods: Interleukin (IL)-6 and soluble IL-6 receptor (sIL-6R) expression levels were measured by enzyme-linked immunosorbent assay. The expression levels of membrane IL-6 receptor (mIL-6R), intercellular cell adhesion molecule-1 (ICAM-1), B-cell lymphoma/leukemia-2 (Bcl-2), and Bcl-XL as well as the location of nuclear factor κB (NF-κB) were assessed by laser confocal microscopy. The expression profiles of mIL-6R and ICAM-1 were also more precisely examined by flow cytometry, and Bcl-2, Bcl-XL and inhibitor kappa B expression levels were analyzed by western blot. The mRNA expression levels of IL-6R, ICAM-1, Bcl-2, and Bcl-XL were assessed by real-time polymerase chain reaction. NF-κB DNA-binding activity was examined by electrophoretic mobility shift assay.
Results: The protein expression levels of both sIL-6R and mIL-6R were reduced in culture conditions when KM3 cells were co-cultured with hUCBDSCs; moreover, the mRNA expression levels of IL-6R were also reduced. Nuclear translocation of the NF-κB p65 subunit was inhibited in KM3 cells by co-culture with hUCBDSCs. Moreover, hUCBDSCs inhibited NF-κB DNA-binding activity, thereby resulting in the downregulation of NF-κB-regulated proteins.
Conclusion: hUCBDSCs can suppress proliferation and induce apoptosis in KM3 cells by both downregulating IL-6R expression and inhibiting NF-κB activity.
Keywords: Hematopoietic microenvironment; Human umbilical cord blood-derived cells; Interleukin-6; Multiple myeloma; Nuclear factor-kappa B.