The RANK/RANK ligand system is involved in interleukin-6 and interleukin-11 up-regulation by human myeloma cells in the bone marrow microenvironment.
OBJECTIVE
The receptor activator of NF-kB ligand (RANKL) has a critical role in osteoclast activation. Recently it has been demonstrated that human multiple myeloma (MM) cells do not express RANKL but up-regulate RANKL in bone marrow stromal cells (BMSC). To further investigate the role of RANKL in the pathophysiology of MM we evaluated the expression of its receptor RANK in MM cells and in the BM environment and the potential role of RANKL in the interaction of myeloma cells with the microenvironment.


METHODS
RANK mRNA and protein expression were evaluated by reverse transcription polymerase chain reaction and Western blot analysis in human myeloma cell lines (HMCL), fresh purified MM cells, BMSC and endothelial cells. Moreover the effect and the role of RANKL on cytokine secretion were evaluated in BMSC, in endothelial cells and in co-culture conditions with myeloma cells.


RESULTS
We found that RANK is expressed in BMSC and endothelial cells but not in myeloma cells. Consistently, RANKL did not have a direct effect on myeloma cell survival, but RANKL treatment induced a significant increase of interleukin (IL)-6 and IL-11 secretion by both BMSC and endothelial cells. Moreover, in a co-culture system we found that myeloma cells up-regulated both IL-6 and IL-11 secretion by BMSC and endothelial cells through cell-to-cell contact. The presence of the RANK-Fc that blocks the RANK/RANKL interaction significantly inhibited HMCL-induced secretion of IL-6 and IL-11.


CONCLUSIONS
Our data provide new notions on the role of the RANKL system in the pathophysiology of MM.
Giuliani
Nicola
N
BMT Unit, University of Parma, Italy. n_giuliani@yahoo.com
Colla
Simona
S
Morandi
Francesca
F
Rizzoli
Vittorio
V
D001853:Bone Marrow / Q000378:metabolism / Q000473:pathology; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D002450:Cell Communication; D018920:Coculture Techniques; D042783:Endothelial Cells / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007141:Immunoglobulin Fc Fragments / Q000494:pharmacology; D017370:Interleukin-11 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D015850:Interleukin-6 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D009101:Multiple Myeloma / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D010010:Osteoclasts / Q000378:metabolism; D053245:RANK Ligand; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D012334:RNA, Neoplasm / Q000096:biosynthesis / Q000235:genetics; D053246:Receptor Activator of Nuclear Factor-kappa B; D017154:Stromal Cells / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000378:metabolism; D015854:Up-Regulation
D002352:Carrier Proteins; D007141:Immunoglobulin Fc Fragments; D017370:Interleukin-11; D015850:Interleukin-6; D008562:Membrane Glycoproteins; D053245:RANK Ligand; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D053246:Receptor Activator of Nuclear Factor-kappa B; C505686:TNFRSF11A protein, human; C505688:TNFSF11 protein, human