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Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229-3900
Address all correspondence and requests for reprints to: Dr. Martin L. Adamo, Department of Biochemistry, MSC7760, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, Texas 78229-3900. E-mail: adamo{at}biochem.uthscsa.edu
The effect of cellular density on insulin-like growth factor I (IGF-I) gene expression was characterized in several tumor-derived cell lines. IGF-I messenger RNA (mRNA) transcripts increased more than 200-fold when C6 glioma cells grew to postconfluence. IGF-I receptor and ß-actin mRNAs were induced by 6- and 2-fold, respectively, as a function of confluence. IGF-I mRNA transcripts in GH3 and SK-N-MC cells increased about 4- to 5-fold in confluent cultures compared with sparse cultures. In OVCAR-3 cells, the IGF-I mRNA level remained constant as the cell density increased. Transient transfection experiments were performed with IGF-I exon 1 promoter/luciferase fusion constructs in C6 cells. The luciferase activity of a construct containing exon 1 sequence between +75 and +282 (the most 5' transcription initiation site was designated +1) was stimulated by 2.5-fold in dense cultures compared with that in sparse cultures of C6 cells. Luciferase activities of other constructs containing at least 282 bp of exon 1 sequence were also stimulated about 2- to 4-fold by cell density. However, 3' deletion to +192 led to loss of the cell density stimulatory effect. In contrast, luciferase activities of IGF-I promoter constructs were not altered by cell density in SK-N-MC cells. When the conditioned medium of low density C6 cultures was exchanged with that of high density cultures, the IGF-I mRNA level remained the same. In summary, cell density has a cell type- and gene type-specific effect on IGF-I gene expression. A cell density response element(s) may be located between +192 and +282 of the exon 1 promoter region in C6 cells.
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  S. Gao, M. McGarry, T. Ferrier, B. Pallante, B. Gasparrini, J. Fletcher, L. Harkness, P. De Sousa, J. McWhir, and I. Wilmut Effect of Cell Confluence on Production of Cloned Mice Using an Inbred Embryonic Stem Cell Line Biol Reprod, February 1, 2003; 68(2): 595 - 603. [Abstract] [Full Text] [PDF]
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 M. S. Chacko and M. L. Adamo Double-Stranded RNA Decreases IGF-I Gene Expression in a Protein Kinase R-Dependent, but Type I Interferon-Independent, Mechanism in C6 Rat Glioma Cells Endocrinology, February 1, 2002; 143(2): 525 - 534. [Abstract] [Full Text] [PDF]
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L. Wang, X. Ma, L.-C. C. Yeh, and M. L. Adamo Differential Regulation of IGF-Binding Protein Gene Expression by cAMP in Rat C6 Glioma Cells Endocrinology, September 1, 2001; 142(9): 3917 - 3925. [Abstract] [Full Text] [PDF]
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L. Wang and M. L. Adamo Cyclic Adenosine 3',5'-Monophosphate Inhibits Insulin-Like Growth Factor I Gene Expression in Rat Glioma Cell Lines: Evidence for Regulation of Transcription and Messenger Ribonucleic Acid Stability Endocrinology, July 1, 2001; 142(7): 3041 - 3050. [Abstract] [Full Text] [PDF]
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M. S. Chacko and M. L. Adamo Double-Stranded Ribonucleic Acid Decreases C6 Rat Glioma Cell Numbers: Effects on Insulin-Like Growth Factor I Gene Expression and Action Endocrinology, October 1, 2000; 141(10): 3546 - 3555. [Abstract] [Full Text] [PDF]
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