Interleukin-6 receptor shedding is enhanced by interleukin-1beta and tumor necrosis factor alpha and is partially mediated by tumor necrosis factor alpha-converting enzyme in osteoblast-like cells.
OBJECTIVE
Interleukin-6 (IL-6) and soluble IL-6 receptor (sIL-6R) activation of gp130 represents an alternative pathway for osteoclast development in inflammatory conditions. The goal of the present study was to investigate changes in sIL-6R levels in response to the inflammatory cytokines IL-1beta and tumor necrosis factor alpha (TNFalpha) and to determine the role of TNFalpha-converting enzyme (TACE) in this process.


METHODS
Levels of sIL-6R in the culture media of MG63 and SAOS-2 osteoblast-like cell lines after exposure to various agents were determined by immunoassay. TACE protein levels were measured by Western immunoblotting. Cells were transfected with small interfering RNA (siRNA) or with an expression plasmid for IL-6R and TACE to determine the potential involvement of TACE in IL-6R shedding.


RESULTS
IL-1beta and TNFalpha increased the levels of sIL-6R in the culture media of MG63 osteoblast-like cells. This effect was not influenced by cycloheximide or 5,6-dichlorobenzimidazole riboside but was markedly inhibited by the calcium chelator EGTA and by the TACE and matrix metalloproteinase inhibitor hydroxamate (Ru36156). IL-1beta and TNFalpha had no influence on the alternatively spliced form of IL-6R RNA. Levels of sIL-6R were reduced when MG63 cells were transiently transfected with TACE siRNA. Transfection of SAOS-2 cells with expression plasmids for IL-6R and TACE produced a dose-dependent increase in sIL-6R levels.


CONCLUSIONS
IL-1beta- and TNFalpha-mediated induction of IL-6R shedding in osteoblast-like cells is at least partly dependent on TACE activation.
Franchimont
Nathalie
N
Center for Cellular and Molecular Therapy, University of Liège, Centre Hospitalier Universitaire Sart-Tilman, 4000 Liege, Belgium. nfranchimont@ulg.ac.be
Lambert
Cécile
C
Huynen
Pascale
P
Ribbens
Clio
C
Relic
Biserka
B
Chariot
Alain
A
Bours
Vincent
V
Piette
Jacques
J
Merville
Marie-Paule
MP
Malaise
Michel
M
D051722:ADAM Proteins; D000072198:ADAM17 Protein; D045744:Cell Line, Tumor; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology*; D008666:Metalloendopeptidases / Q000235:genetics / Q000378:metabolism*; D010006:Osteoblasts / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D019947:Receptors, Interleukin-6 / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology; D012995:Solubility; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D007375:Interleukin-1; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D019947:Receptors, Interleukin-6; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D051722:ADAM Proteins; D008666:Metalloendopeptidases; D000072198:ADAM17 Protein; C000606462:ADAM17 protein, human