Insulin-like growth factor-binding protein-5 (IGFBP-5) inhibits TNF-α-induced NF-κB activity by binding to TNFR1.
IGFBP-5 is known to be involved in various cell phenomena such as proliferation, differentiation, and apoptosis. However, the exact mechanisms by which IGFBP-5 exerts its functions are unclear. In this study, we demonstrate for the first time that IGFBP-5 is a TNFR1-interacting protein. We found that ectopic expression of IGFBP-5 induced TNFR1 gene expression, and that IGFBP-5 interacted with TNFR1 in both an in vivo and an in vitro system. Secreted IGFBP-5 interacted with GST-TNFR1 and this interaction was blocked by TNF-α, demonstrating that IGFBP-5 might be a TNFR1 ligand. Furthermore, conditioned media containing secreted IGFBP-5 inhibited PMA-induced NF-κB activity and IL-6 expression in U-937 cells. Coimmunoprecipitation assays of TNFR1 and IGFBP-5 wild-type and truncation mutants revealed that IGFBP-5 interacts with TNFR1 through its N- and L-domains. However, only the interaction between the L-domain of IGFBP-5 and TNFR1 was blocked by TNF-α in a dose-dependent manner, suggesting that the L-domain of IGFBP-5 can function as a TNFR1 ligand. Competition between the L-domain of IGFBP-5 and TNF-α resulted in inhibition of TNF-α-induced NF-κΒ activity. Taken together, our results suggest that the L-domain of IGFBP-5 is a novel TNFR1 ligand that functions as a competitive TNF-α inhibitor.
Molecular Therapy Research Center, Sungkyunkwan University, Seoul 135-710, Republic of Korea.
Jae Ryoung
JR
Hwang
Jae Ho
JH
Huh
Yoonna
Y
Lee
Sang Il
SI
Lee
Seung Bae
SB
Rho
Je-Ho
JH
Lee
D045744:Cell Line, Tumor; D017077:Culture Media, Conditioned / Q000737:chemistry / Q000494:pharmacology; D006801:Humans; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D047888:Receptors, Tumor Necrosis Factor, Type I / Q000235:genetics / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000378:metabolism*
D017077:Culture Media, Conditioned; D018975:Insulin-Like Growth Factor Binding Protein 5; D016328:NF-kappa B; D012333:RNA, Messenger; D047888:Receptors, Tumor Necrosis Factor, Type I; D014409:Tumor Necrosis Factor-alpha