Sequence, expression and function of an mRNA encoding a soluble form of the human interleukin-6 receptor (sIL-6R).
Soluble receptors have been shown to be potent immunomodulators of their respective ligands. Since IL-6 is a central growth factor for myeloma cells, an sIL-6R may modulate IL-6 activity. We have previously reported a novel IL-6R mRNA from myeloma cells that exhibits a 94-nt deletion of the entire transmembrane domain from codons 356 (G-TG) to 387 (AG-G). The transmembrane domain deletion results in a shift in the translational reading frame with the insertion of 10 new amino acids followed by a stop codon. Sequence analysis shows the ligand-binding domain of the sIL-6R to be identical to that of the membrane-bound IL-6R up to the transmembrane domain deletion. The sIL-6R cDNA was expressed in QT-6 fibroblasts and PA-1 ovarian cells using the expression vector pCDM8. Supernates were immunoprecipitated with anti-IL-6R antibody and cells transfected with the sIL-6R cDNA produced a single band with a molecular weight of 50-55 kDa. This molecular weight corresponds to the size of the sIL-6R protein observed in normal human urine. Supernates were collected from mock or sIL-6R transfected PA-1 cells after 48 hours and assayed for their ability to stimulate or suppress the growth of an IL-6 dependent cell line, ANBL-6. Soluble IL-6R alone had no effect on the growth of the ANBL-6 cells. However, the growth of ANBL-6 cells by sIL-6R was potentiated in the presence of IL-6 and could be blocked by anti-IL-6 antibody. The above results suggest that, in the presence of IL-6, sIL-6R associates with gp130 leading to signal transduction and cell growth.
Lust
J A
JA
Department of Laboratory Medicine, Mayo Clinic, Rochester, MN.
Jelinek
D F
DF
Donovan
K A
KA
Frederick
L A
LA
Huntley
B K
BK
Braaten
J K
JK
Maihle
N J
NJ
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D003370:Coturnix; D004273:DNA, Neoplasm / Q000235:genetics; D005260:Female; D005354:Fibrosarcoma / Q000473:pathology; D005786:Gene Expression Regulation; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism; D007952:Leukemia, Plasma Cell / Q000473:pathology; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009101:Multiple Myeloma / Q000473:pathology*; D009363:Neoplasm Proteins / Q000235:genetics; D010051:Ovarian Neoplasms / Q000473:pathology; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics*; D012334:RNA, Neoplasm / Q000235:genetics; D018123:Receptors, Interleukin / Q000737:chemistry / Q000235:genetics*; D019947:Receptors, Interleukin-6; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017384:Sequence Deletion; D012995:Solubility; D018243:Teratocarcinoma / Q000473:pathology; D014162:Transfection; D014407:Tumor Cells, Cultured
D004273:DNA, Neoplasm; D015850:Interleukin-6; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D018123:Receptors, Interleukin; D019947:Receptors, Interleukin-6; D011993:Recombinant Fusion Proteins