Interactions of high affinity insulin-like growth factor-binding proteins with the type V transforming growth factor-P receptor in mink lung epithelial cells

High affinity insulin-like growth factor-binding proteins (IGFBP-1 to -6) a re a family of structurally homologous proteins that induce cellular respon ses by insulin-libe growth factor (IGF)-dependent and -independent mechanis ms. The IGFBP-3 receptor, which mediates the IGF-independent growth inhibit ory response, has recently been identified as the type V transforming growt h factor-beta receptor (T beta R-V) (Leal, S.M, Liu, Q,L,, Huang, S.S., and Huang, J, S, (1997) J, Biob Chem, 272, 20572-20576), To characterize the i nteractions of high affinity IGFBPs with T beta R-V, mink lung epithelial c ells (Mv1Lu cells) were incubated with I-125-labeled recombinant human IGFB Ps (I-125-IGFBP-1 to -6) in the presence of the cross-linking agent disucci nimidyl suberate and analyzed by 5% SDS-polyacrylamide gel electrophoresis and autoradiography. I-125-IGFBP-3, -4, and -5 but not I-125-IGFBP-1, -2, a nd -6 bound to T beta R-V as demonstrated by the detection of the similar t o 400-kDa I-125-IGFBP T beta R-V cross-linked complex in the cell lysates a nd immunoprecipitates. The analyses of 125I-labeled Ligand binding competit ion and DNA synthesis inhibition revealed that IGFBP-3 was a more potent Li gand for TPR-V than IGFBP-4 or -5, Most of the high affinity I-125-IGFBPs f ormed dimers at the cell surface. The cell-surface dimer of I-125-IGFBP-3 p referentially bound to and was cross-linked to TPR-V in the presence of dis uccinimidyl suberate, IGFBP-3 did not stimulate the cellular phosphorylatio n of Smad2 and Smad3, key transducers of the transforming growth factor-bet a type I/type II receptor (T beta R-IT beta R-II) heterocomplex-mediated si gnaling. These results suggest that IGFBP-3, -4, and -5 are specific ligand s for T beta R-V, which mediates the growth inhibitory response through a s ignaling pathway(s) distinct from that mediated by the T beta R-I and T bet a R-II heterocomplex.