Insulinlike growth factor-binding protein modulates the growth response to insulinlike growth factor 1 by human gastric cancer cells.
BACKGROUND
This study determined whether the resistance to the mitogenic effect of insulinlike growth factor 1 (IGF-1) in AGS (we found that IGF-1 had almost no effect on the growth of AGS) cells is caused by the absence of IGF-1 receptor on the cells or by the interference of endogenous IGFs and IGF-binding protein (IGFBP).


METHODS
IGF-1 receptors were examined by radioligand binding assay. The protein in conditioned medium and the molecular weight of IGF-1 receptors on AGS cells were determined by affinity cross-linking with 125I-IGF-1 followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Messenger RNAs for IGF-1, IGF-2, and IGFBP-4 were detected by Northern analysis.


RESULTS
AGS cells possessed a single class of high-affinity binding sites for IGF-1 (dissociation constant [Kd], 0.51), with a binding capacity approximately 4 x 10(4) sites per cell. The size of the alpha subunit of IGF-1 receptors on cell membranes was approximately 130 kilodaltons. des (1-3) IGF-1, a truncated IGF-1 with very low affinity to IGFBPs, stimulated AGS cell growth in dose-dependent fashion. The medium conditioned by AGS cells contained IGFBPs of 27-32 and 37-42 kilodaltons. AGS cells expressed messenger (mRNA) RNAs for IGF-2 and IGFBP-4 but not for IGF-1, whereas another gastric carcinoma cell line (SIIA), whose growth is stimulated by IGF-1, expressed mRNA IGF-2 but did not express mRNA for IGF-1 or IGFBP-4:


CONCLUSIONS
The relative absence of growth response of AGS cells to IGF-1 is due to the endogenously produced IGFBPs sequestering IGF-1 and preventing receptor interaction.
Guo
Y S
YS
Department of Surgery, University of Texas Medical Branch, Galveston.
Beauchamp
R D
RD
Jin
G F
GF
Townsend
C M
CM
Thompson
J C
JC
D000230:Adenocarcinoma / Q000378:metabolism / Q000473:pathology*; D002352:Carrier Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D002455:Cell Division; D017077:Culture Media, Conditioned; D006801:Humans; D018974:Insulin-Like Growth Factor Binding Protein 4; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D007335:Insulin-Like Growth Factor II / Q000235:genetics; D010446:Peptide Fragments / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D017526:Receptor, IGF Type 1 / Q000032:analysis; D013274:Stomach Neoplasms / Q000378:metabolism / Q000473:pathology*; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D017077:Culture Media, Conditioned; D018974:Insulin-Like Growth Factor Binding Protein 4; D018969:Insulin-Like Growth Factor Binding Proteins; D010446:Peptide Fragments; D012333:RNA, Messenger; C058957:insulin-like growth factor 1, des-(1-3)-; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D017526:Receptor, IGF Type 1