Myeloma cells release soluble interleukin-6Ralpha in relation to disease progression by two distinct mechanisms: alternative splicing and proteolytic cleavage.
Multiple myeloma (MM) is a plasma-cell malignancy characterized by the accumulation of malignant plasma cells within the bone marrow. Interleukin (IL)-6 is an essential survival and growth factor for myeloma cells that exerts its activity through a cell surface receptor composed of an 80-kDa ligand binding molecule (IL-6Ralpha) and a 130-kDa signal-transducing molecule. Of major interest, the soluble form of the IL-6Ralpha (sIL-6Ralpha) is an agonistic molecule able to potentiate IL-6 activity and a strong prognostic factor in MM. In the present study, we demonstrate that purified myeloma cells from all of the patients with MM and human myeloma cell lines release sIL-6Ralpha. The level of sIL-6Ralpha release correlates with disease activity and is clearly up-regulated during tumoral expansion in vivo and immortalization in vitro. Of note, this sIL-6Ralpha release is strongly reduced (50%) by a hydroxamate-based metalloproteinase inhibitor underlying the importance of shedding in the production of sIL-6Ralpha by myeloma cells. Using specific IL-6Ralpha primers flanking the transmembrane domain, we demonstrate by PCR the presence of two IL-6R mRNAs corresponding to the membrane IL-6Ralpha and to the sIL-6Ralpha generated through alternative splicing in myeloma cells. In conclusion, we show that: (a) native myeloma cells and human myeloma cell lines release sIL-6Ralpha by two distinct mechanisms: alternative splicing and proteolytic cleavage of the membrane IL-6Ralpha; and (b) the release of the sIL-6Ralpha, which is an agonist of IL-6, correlates with disease progression, explaining in part its strong prognostic value in vivo.
Thabard
W
W
Institut National de la Santé et de la Recherche Médicale Unité 463, Nantes, France.
Barillé
S
S
Collette
M
M
Harousseau
J L
JL
Rapp
M J
MJ
Bataille
R
R
Amiot
M
M
D017398:Alternative Splicing; D010450:Endopeptidases / Q000502:physiology*; D006801:Humans; D009101:Multiple Myeloma / Q000378:metabolism* / Q000473:pathology; D012333:RNA, Messenger / Q000032:analysis; D019947:Receptors, Interleukin-6 / Q000235:genetics* / Q000378:metabolism
D012333:RNA, Messenger; D019947:Receptors, Interleukin-6; D010450:Endopeptidases