TY - JOUR
T1 - Factors regulating insulin-like growth factor-binding protein-3 binding, processing, and potentiation of insulin-like growth factor action
AU - Conover, Cheryl A.
AU - Clarkson, Jay T.
AU - Bale, Laurie K.
PY - 1996
Y1 - 1996
N2 - In this study, we investigated the effects of various biochemical and pharmacological agents on insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3) cell binding and action in cultured bovine fibroblasts. When cells were preincubated for 48 h with 50 nM recombinant human (rhIGFBP-3, IGF-I- stimulated [3H]aminoisobutyric acid ([125H]AIB) uptake was enhanced 2- to 3-fold. The addition of cytoskeletal disrupting agents during the preincubation with rhIGFBP-3 did not affect IGFBP-3 potentiation of IGF-I action, nor did a variety of serine, aspartate, and metalloproteinase inhibitors. On the other hand, ammonium chloride and chloroquine, weak bases that neutralize the pH of acidic cell compartments, blocked IGFBP-3 potentiation of IGF-I-stimulated [3H]AIB uptake. Chloroquine and ammonium chloride had no effect alone and did Bafilomycin A, a specific inhibitor of ATP-dependent hydrogen ion pumps, also inhibited IGFBP-3 potentiation of IGF- I-stimulated [3H]AIB uptake. Competitive [125I]IGF-I binding and affinity cross-linking experiments suggested structure/function changes in cell-bound IGFBP-3 that were altered in the presence of chloroquine and bafilomycin. Heparin markedly decreased initial IGFBP-3 cell adherence, but could not promote dissociation of IGFBP-3 from cells after the 48-h preincubation. Moreover, heparin did not inhibit IGFBP-3 potentiation of IGF-I action. In summary, these data indicate that IGFBP-3 under goes specific pH-dependent structural and/or environmental modifications that mediate the enhancing effect of IGFBP-3 on IGF-I action in bovine fibroblasts. They also suggest that IGFBP-3 binding to heparinlike molecules on the cell surface is not directly involved in this process.
AB - In this study, we investigated the effects of various biochemical and pharmacological agents on insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3) cell binding and action in cultured bovine fibroblasts. When cells were preincubated for 48 h with 50 nM recombinant human (rhIGFBP-3, IGF-I- stimulated [3H]aminoisobutyric acid ([125H]AIB) uptake was enhanced 2- to 3-fold. The addition of cytoskeletal disrupting agents during the preincubation with rhIGFBP-3 did not affect IGFBP-3 potentiation of IGF-I action, nor did a variety of serine, aspartate, and metalloproteinase inhibitors. On the other hand, ammonium chloride and chloroquine, weak bases that neutralize the pH of acidic cell compartments, blocked IGFBP-3 potentiation of IGF-I-stimulated [3H]AIB uptake. Chloroquine and ammonium chloride had no effect alone and did Bafilomycin A, a specific inhibitor of ATP-dependent hydrogen ion pumps, also inhibited IGFBP-3 potentiation of IGF- I-stimulated [3H]AIB uptake. Competitive [125I]IGF-I binding and affinity cross-linking experiments suggested structure/function changes in cell-bound IGFBP-3 that were altered in the presence of chloroquine and bafilomycin. Heparin markedly decreased initial IGFBP-3 cell adherence, but could not promote dissociation of IGFBP-3 from cells after the 48-h preincubation. Moreover, heparin did not inhibit IGFBP-3 potentiation of IGF-I action. In summary, these data indicate that IGFBP-3 under goes specific pH-dependent structural and/or environmental modifications that mediate the enhancing effect of IGFBP-3 on IGF-I action in bovine fibroblasts. They also suggest that IGFBP-3 binding to heparinlike molecules on the cell surface is not directly involved in this process.
UR - http://www.scopus.com/inward/record.url?scp=0029889690&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0029889690&partnerID=8YFLogxK
U2 - 10.1210/endo.137.6.8641177
DO - 10.1210/endo.137.6.8641177
M3 - Article
C2 - 8641177
AN - SCOPUS:0029889690
SN - 0013-7227
VL - 137
SP - 2286
EP - 2292
JO - Endocrinology
JF - Endocrinology
IS - 6
ER -