Regulation of insulin-like growth factor (IGF) binding protein-5 in the T47D human breast carcinoma cell line by IGF-I and retinoic acid.
The T47D human breast carcinoma cell line has been shown to synthesize insulin-like growth factor-I (IGF-I) binding proteins (IGFBPs) and IGF-I receptors, and to exhibit a mitogenic response to exogenous IGF-I. We have used T47D cells to investigate the regulation of IGFBPs by IGF-I and retinoic acid (RA), agents that affect cell proliferation and have been shown to regulate IGFBP levels in other cell types. Exposure of T47D cells to IGF-I resulted in the appearance of IGFBP-2, -4, and -5 in conditioned medium but had no effect on the levels of IGFBPs in Triton X-100-extracted cells. This effect was most pronounced for IGFBP-5 and was also elicited by an IGF-I analog that retains affinity for IGFBPs but not by insulin or IGF analogs that have decreased affinity for IGFBPs. Additionally, this effect was not associated with a change in IGFBP-5 messenger RNA (mRNA) levels; however, the appearance of IGFBP-5 in the conditioned medium was inhibited by an anti-IGF-I receptor antibody (alpha IR-3). RA decreased IGFBP-5 mRNA levels and cell-associated IGFBP-5 in both the presence and absence of IGF-I and inhibited the IGF-I-stimulated secretion of IGFBP-5 into T47D cell conditioned medium. These results suggest that IGF-I increases IGFBP-5 levels in the T47D cell line both through direct interaction with IGFBP-5 as well as through a receptor-mediated process that does not require direct interaction with IGFBPs. The latter results are consistent with an effect of IGF-I on a factor that may modulate an IGFBP protease activity. The inhibitory effect of RA, on the other hand, appears to be due primarily to regulation of IGFBP-5 mRNA levels. Thus, IGFBP-5 accumulation appears to be positively regulated by IGF-I, potentially at the level of susceptibility to proteolysis, and negatively regulated at the level of gene expression by RA.
Shemer
J
J
Diabetes Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Yaron
A
A
Werner
H
H
Shao
Z M
ZM
Sheikh
M S
MS
Fontana
J A
JA
LeRoith
D
D
Roberts
C T
CT
D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D002277:Carcinoma / Q000378:metabolism* / Q000473:pathology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D003470:Culture Media / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D018975:Insulin-Like Growth Factor Binding Protein 5; D007334:Insulin-Like Growth Factor I / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*; D017451:Receptors, Somatomedin / Q000502:physiology; D013002:Somatomedins / Q000378:metabolism; D014212:Tretinoin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D003470:Culture Media; D018975:Insulin-Like Growth Factor Binding Protein 5; D017451:Receptors, Somatomedin; D013002:Somatomedins; D014212:Tretinoin; D007334:Insulin-Like Growth Factor I