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Endocrinology, Vol 133, 990-995, Copyright © 1993 by Endocrine Society

ARTICLES

Rat PC12 pheochromocytoma cells synthesize insulin-like growth factor- binding protein-6

LA Bach, LY Tseng, JE Swartz and MM Rechler
Molecular and Cellular Endocrinology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.

The PC12 cell line established from a rat pheochromocytoma has been extensively studied as a model of neuronal differentiation. Insulin- like growth factor-I (IGF-I) and IGF-II are mitogenic for PC12 cells under serum-starved conditions. IGF activity is modulated by a family of six IGF-binding proteins (IGFBPs). It recently was reported that PC12 cells produced an IGFBP that had a marked preferential binding affinity for IGF-II over IGF-I. We now show that the main IGFBP produced by PC12 cells is rat IGFBP-6 and compare its properties with those of human IGFBP-6. The predominant IGFBP in medium conditioned by undifferentiated and differentiated PC12 cells migrated on sodium dodecyl sulfate-12% polyacrylamide gel electrophoresis with an apparent molecular mass of 22.5-25 kilodaltons and was recognized by polyclonal antiserum to rat IGFBP-6 by immunoblotting. Rat IGFBP-6 mRNA (1.4 kilobases) was detected by Northern hybridization of total RNA extracted from PC12 cells using a rat IGFBP-6 cDNA probe. Rat IGFBP-6, like human IGFBP-6, is O-glycosylated; incubation with neuraminidase, fucosidase, and O-glycanase reduced its apparent molecular mass to 21 kilodaltons. Competitive binding studies of rat and human IGFBP-6 with [125I]IGF-II and unlabeled IGF-II or IGF-I demonstrated that both IGFBPs bound IGF-II with similar affinities (Ka, 1.5-1.8 x 10(11) M-1) and bound IGF-I with approximately 25- to 35-fold lower affinity than IGF-II. Thus, differences in amino acid sequence, such as deletion of nine amino-terminal residues (including two conserved cysteine residues) in rat IGFBP-6 compared with human IGFBP-6, do not alter its binding characteristics. PC12 cells should provide a useful system to define the regulation of IGFBP-6 expression and the role of IGFBP-6 in modulating IGF action.


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V. Hwa, Y. Oh, and R. G. Rosenfeld
The Insulin-Like Growth Factor-Binding Protein (IGFBP) Superfamily
Endocr. Rev., December 1, 1999; 20(6): 761 - 787.
[Abstract] [Full Text]

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The N-terminal Disulfide Linkages of Human Insulin-like Growth Factor-binding Protein-6 (hIGFBP-6) and hIGFBP-1 Are Different as Determined by Mass Spectrometry
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