Insulin-like growth factor-binding protein-2 inhibits proliferation of human embryonic kidney fibroblasts and of IGF-responsive colon carcinoma cell lines.
So far, the physiological role of insulin-like growth factor binding protein-2 (IGFBP-2) has not been demonstrated directly. Therefore, we transfected 293 cells with an expression vector containing the CMV promoter and the complete cDNA of mouse IGFBP-2. Secretion of bioactive IGFBP-2 into conditioned medium was demonstrated by Western ligand and Western immunoblotting and quantified by specific RIA. For the analysis of cell proliferation three clones exhibiting either high or low/no IGFBP-2 expression were selected and compared to non-transfected parental 293 cells. IGFBP-2 secreting clones displayed reduced conversion of thiazolyl blue when compared to negative clones or non-transfected parental 293 cells (P < 0.01). The lower growth activity measured in the IGFBP-2 secreting clones was compensated in great part by the administration of exogenous IGF-I or -II. Conditioned media of IGFBP-2 secreting clones inhibited growth of IGF-responsive colon tumor cell lines (LS513, HT-29) while those of negative clones did not. In addition, conditioned medium from a clone expressing high levels of IGFBP-2 inhibited anchorage-independent growth of LS513 and HT-29 cells. In contrast, growth of an IGF-unresponsive tumor cell line (Co-115) was not affected by the conditioned media. We hypothesize that IGFBP-2 might sequester the IGFs and thus prevent them from transferring their mitogenic signals.
Höflich
A
A
Lehrstuhl für Molekulare Tierzucht und Haustiergenetik/Genzentrum, Ludwig-Maximilians-Universität, Munich, Germany. hoeflich@lmb.uni-muenchen.de
Lahm
H
H
Blum
W
W
Kolb
H
H
Wolf
E
E
D000818:Animals; D002448:Cell Adhesion; D002455:Cell Division / Q000502:physiology; D002460:Cell Line; D002999:Clone Cells; D003110:Colonic Neoplasms / Q000473:pathology*; D017077:Culture Media, Conditioned; D005347:Fibroblasts / Q000166:cytology; D006801:Humans; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000235:genetics / Q000502:physiology*; D007668:Kidney / Q000166:cytology* / Q000196:embryology; D051379:Mice; D012333:RNA, Messenger / Q000235:genetics; D013002:Somatomedins / Q000502:physiology*; D014162:Transfection; D014407:Tumor Cells, Cultured
D017077:Culture Media, Conditioned; D018971:Insulin-Like Growth Factor Binding Protein 2; D012333:RNA, Messenger; D013002:Somatomedins