Triggering of toll-like receptor-4 in human multiple myeloma cells promotes proliferation and alters cell responses to immune and chemotherapy drug attack.

Multiple myeloma (MM) is an incurable B-cell malignancy characterized by accumulation of malignant plasma cells in the bone marrow and by recurrent or persistent infections. Toll-like receptors (TLRs) are essential in the host defense against infections. The aim of this study was to investigate TLR initiated responses in MM cells including proliferation, anti-apoptosis and immune escape. Myeloma cell lines gene transcription, cell cycle and protein expression were detected by RT-PCR, real-time PCR, western blot, ELISA and flow cytometry analysis. 3H-thymidine was used for measuring cell proliferation, and Annexin V-PI flow cytometry for the detection of cell apoptosis. We show that human myeloma cell lines expressed TLRs，and LPS induced the proliferation and partially protected MM.1S and ARP-1 cells from adriamycin-induced apoptosis. LPS appears to induce proliferation via MyD88 and MAPKs signaling. In addition, LPS treatment upregulated myeloma cell secretion of cytokine IL-18 and expression of immunoregulatory factors B7-H1, B7-H2 and CD40 mRNA and helped myeloma cells to escape immune surveillance. Our results show that TLRs are functional on myeloma tumor cells, and the ligands to these TLRs have a functional role in affecting myeloma cell proliferation, survival, and response to chemotherapy and immune attacks.