Integrin-mediated action of insulin-like growth factor binding protein-2 in tumor cells.
The neoplastic production of the insulin-like growth factor binding protein (IGFBP)-2 often correlates with tumor malignancy and aggressiveness. Since IGFBP-2 contains an RGD motif in its C-terminus, it was hypothesized that this protein may act independently of IGF on tumor cells through integrins. To investigate this, integrin binding, intracellular signaling and the impact of IGFBP-2 on cell adhesion and proliferation were examined in two tumor cell lines. In tracer displacement studies, up to 30% of the added (125)I-hIGFBP-2 specifically bound to the cells. Bound (125)I-hIGFBP-2 was reversibly displaced by IGFBP-2, IGFBP-1 and RGD-(Gly-Arg-Asp)-containing peptides, but not by IGFBP-3, -4, -5, -6 and RGE-(Gly-Arg-Glu)-containing peptides. Blocking with antibodies directed against different integrins and with fibronectin demonstrated that IGFBP-2 cell surface binding is specific for alpha5beta1-integrin. Incubation of IGFBP-2 with equimolar quantities of IGF-I and IGF-II annihilated RGD-specific binding. IGFBP-2 binding at the cell surface led to dephosphorylation of the focal adhesion-kinase (FAK) of up to 37% (P<0.01), and of the p42/44 MAP-kinases of up to 40% (P<0.01). In addition, IGFBP-2 promoted de-adhesion of the cells dose-dependently by up to 30% (P<0.05), and reduced proliferation by 24% (P<0.01). Since one of the cell lines used does not express a functional IGF-I receptor, these data demonstrate that IGFBP-2 can act in an IGF-independent manner, at least in part by an interaction with alpha5beta1-integrin.
Schütt
B S
BS
Pediatric Endocrinology Section, University Children's Hospital, 72076 Tuebingen, Germany.
Langkamp
M
M
Rauschnabel
U
U
Ranke
M B
MB
Elmlinger
M W
MW
D002448:Cell Adhesion; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006801:Humans; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000378:metabolism*; D039081:Integrin alpha5beta1 / Q000378:metabolism; D016023:Integrins / Q000378:metabolism*; D007457:Iodine Radioisotopes / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology
D018971:Insulin-Like Growth Factor Binding Protein 2; D039081:Integrin alpha5beta1; D016023:Integrins; D007457:Iodine Radioisotopes; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; D020928:Mitogen-Activated Protein Kinases