Endocrinology, Vol 132, 1677-1681, Copyright © 1993 by Endocrine Society

ARTICLES

Synthesis and regulation of insulin-like growth factor binding protein- 5 in FRTL-5 cells

PF Backeljauw, Z Dai, DR Clemmons and AJ D'Ercole
Department of Pediatrics, University of North Carolina, Chapel Hill 27599-7220.

FRTL-5 cells, a diploid nontransformed line of rat thyroid follicular cells, exhibit a marked mitogenic response to insulin-like growth factors (IGFs) when they are exposed to TSH. Because IGF binding proteins (IGFBPs) are important modulators of IGF actions, we investigated the capacity of FRTL-5 cells to synthesize IGFBPs. We found that FRTL-5 cell conditioned media contained a single band of approximately 31 kilodaltons on ligand blot analysis. This band represents IGFBP-5 because: 1) it can be immunostained with a specific antibody raised against human IGFBP-5; 2) by Northern analysis, total RNA from FRTL-5 cells contains a major 6-kilobase transcript when hybridized with a cDNA for rat IGFBP-5; and 3) no transcripts were observed when Northern blots of FRTL-5 cells were hybridized with complementary DNAs for rat IGFBP-1, -2, -3, -4 or -6. Conditioned media IGFBP-5 increased in response to IGF-I, IGF-II, and insulin in a dose- dependent fashion, compared with unstimulated FRTL-5 cells. At maximally effective concentrations IGF-I was 3.5- and 6-fold more potent than IGF-II and insulin, respectively. The addition of a monoclonal antibody (Sm 1.2) to IGF-I completely inhibited IGF-I stimulation of the IGFBP-5 6-kilobase transcript and the appearance of IGFBP-5 in FRTL-5 conditioned media. Stimulation of IGFBP-5 synthesis by the IGFs and insulin appeared to be regulated at the messenger RNA (mRNA) level, because each stimulated similar increases in both IGFBP-5 mRNA and media protein at maximally effective concentrations. TSH, on the other hand, inhibited basal levels of IGFBP-5 mRNA and attenuated the increase in IGFBP-5 mRNA stimulated by IGF-I. FRTL-5 cells provide a relatively uncomplicated model to study the regulation and action of IGFBP-5 and the mechanisms by which IGFs interact with this binding protein.

This article has been cited by other articles:

				C. W. Gregory, D. Kim, P. Ye, A. J. D’Ercole, T. G. Pretlow, J. L. Mohler, and F. S. French Androgen Receptor Up-Regulates Insulin-Like Growth Factor Binding Protein-5 (IGFBP-5) Expression in a Human Prostate Cancer Xenograft Endocrinology, May 1, 1999; 140(5): 2372 - 2381. [Abstract] [Full Text]

				P. Ye and J. D'Ercole Insulin-Like Growth Factor I (IGF-I) Regulates IGF Binding Protein-5 Gene Expression in the Brain Endocrinology, January 1, 1998; 139(1): 65 - 71. [Abstract] [Full Text] [PDF]

				C. Duan, S. B. Hawes, T. Prevette, and D. R. Clemmons Insulin-like Growth Factor-I (IGF-I) Regulates IGF-binding Protein-5 Synthesis through Transcriptional Activation of the Gene in Aortic Smooth Muscle Cells J. Biol. Chem., February 23, 1996; 271(8): 4280 - 4288. [Abstract] [Full Text] [PDF]

				C. Duan and D. R. Clemmons Transcription Factor AP-2 Regulates Human Insulin-like Growth Factor Binding Protein-5 Gene Expression J. Biol. Chem., October 20, 1995; 270(42): 24844 - 24851. [Abstract] [Full Text] [PDF]

				E. Canalis and B. Gabbitas Skeletal Growth Factors Regulate the Synthesis of Insulin-like Growth Factor Binding Protein-5 in Bone Cell Cultures J. Biol. Chem., May 5, 1995; 270(18): 10771 - 10776. [Abstract] [Full Text] [PDF]

				J. G. Reeve, A. Guadaņo, J. Xiong, J. Morgan, and N. M. Bleehen Diminished Expression of Insulin-like Growth Factor (IGF) Binding Protein-5 and Activation of IGF-I-mediated Autocrine Growth in Simian Virus 40-transformed Human Fibroblasts J. Biol. Chem., January 6, 1995; 270(1): 135 - 142. [Abstract] [Full Text] [PDF]