TY - JOUR
T1 - Insulin-like growth factor I induction of c-myc expression in bovine fibroblasts can be blocked by antecedent insulin receptor activation
AU - Conover, Cheryl A.
AU - Bale, Laurie K.
N1 - Funding Information:
1This work was supported by NIH Grant DK-43258 and the Mayo Foundation.
PY - 1998/1/10
Y1 - 1998/1/10
N2 - We previously reported that preexposure of cultured bovine fibroblasts to insulin at low concentrations inhibits subsequent insulin-like growth factor I (IGF-I)-stimulated DNA synthesis. This insulin-induced desensitization to IGF-I is mediated by specific insulin receptors on bovine fibroblasts and occurs distally to IGF-I receptor engagement and activation. In the present study, we use this model system to determine insulin and IGF- I receptor interplay in the regulation of proto-oncogenes involved in mitogenesis. Insulin (10 nM), IGF-I (10 nM), and 10% fetal bovine serum were each capable of stimulating rapid and transient c-fos and c-myc mRNA expression in bovine fibroblasts. Expression of e-myc was most responsive to mitogenic stimuli; IGF-I and serum had equivalent potency resulting in ~14- fold increases in c-myc mRNA expression, while insulin produced 3- to 5-fold increases. Max mRNA, which encodes the partner protein for Myc, was constitutively expressed and levels did not change with treatment or with time. When bovine fibroblasts were pretreated with 10 nM insulin for 48 h, washed, and then stimulated with 10 nM IGF-I, alterations in c-fos mRNA expression were moderate. In contrast, insulin pretreatment completely blocked IGF-I induction of c-myc expression. This block was averted if a specific inhibitor of intracellular signaling through the phosphatidylinositol 3-kinase pathway was present during the incubation period with insulin. These data indicate significant insulin/IGF-I receptor interplay in normal bovine fibroblasts and suggest that insulin receptor- initiated signaling can profoundly alter proto-oncogene expression induced by growth factors sharing components of a common intracellular signaling network.
AB - We previously reported that preexposure of cultured bovine fibroblasts to insulin at low concentrations inhibits subsequent insulin-like growth factor I (IGF-I)-stimulated DNA synthesis. This insulin-induced desensitization to IGF-I is mediated by specific insulin receptors on bovine fibroblasts and occurs distally to IGF-I receptor engagement and activation. In the present study, we use this model system to determine insulin and IGF- I receptor interplay in the regulation of proto-oncogenes involved in mitogenesis. Insulin (10 nM), IGF-I (10 nM), and 10% fetal bovine serum were each capable of stimulating rapid and transient c-fos and c-myc mRNA expression in bovine fibroblasts. Expression of e-myc was most responsive to mitogenic stimuli; IGF-I and serum had equivalent potency resulting in ~14- fold increases in c-myc mRNA expression, while insulin produced 3- to 5-fold increases. Max mRNA, which encodes the partner protein for Myc, was constitutively expressed and levels did not change with treatment or with time. When bovine fibroblasts were pretreated with 10 nM insulin for 48 h, washed, and then stimulated with 10 nM IGF-I, alterations in c-fos mRNA expression were moderate. In contrast, insulin pretreatment completely blocked IGF-I induction of c-myc expression. This block was averted if a specific inhibitor of intracellular signaling through the phosphatidylinositol 3-kinase pathway was present during the incubation period with insulin. These data indicate significant insulin/IGF-I receptor interplay in normal bovine fibroblasts and suggest that insulin receptor- initiated signaling can profoundly alter proto-oncogene expression induced by growth factors sharing components of a common intracellular signaling network.
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U2 - 10.1006/excr.1997.3815
DO - 10.1006/excr.1997.3815
M3 - Article
C2 - 9457064
AN - SCOPUS:0031843514
SN - 0014-4827
VL - 238
SP - 122
EP - 127
JO - Experimental Cell Research
JF - Experimental Cell Research
IS - 1
ER -