Overexpression of ovine insulin-like growth factor-I stimulates autonomous autocrine or paracrine growth in bovine mammary-derived epithelial cells.
To test the hypothesis that insulin-like growth factor-I (IGF-I) affects the growth of bovine mammary epithelial cells through an autocrine and/or paracrine pathway, a cell line (MD-IGF-I) was originated from MAC-T cells by cotransfection with a construct containing the cDNA for an ovine exon 2-encoded prepro-IGF-I under control of the mouse mammary tumor virus-long terminal repeat promoter. Clone MD-IGF-I contained multiple copies of the plasmid integrated into the genome, expressed the highest level of IGF-I mRNA, and secreted radioimmunoactive IGF-I into the medium. The mitogenic activity of MD-IGF-I cells was stimulated 80% by dexamethasone (DEX). The total DNA in MD-IGF-I cells was 2.5-fold higher than that in parental MAC-T cells in the presence of DEX. Conditioned medium from MD-IGF-I cells, induced with DEX, stimulated [3H]thymidine incorporation into DNA of MAC-T cells and uninduced MD-IGF-I cells. These data provide evidence that IGF-I was secreted into medium by MD-IGF-I cells. It is suggested that IGF-I can stimulate the growth of mammary epithelial cells by an autocrine and/or paracrine mode of action. The MD-IGF-I cell line may be a suitable system to study translational and posttranslational modifications of IGF-I peptides.
Romagnolo
D
D
Department of Dairy and Animal Science, Virginia Polytechnic Institute and State University, Blacksburg 24061-0315.
Akers
R M
RM
Wong
E A
EA
Boyle
P L
PL
McFadden
T B
TB
Turner
J D
JD
D000818:Animals; D002417:Cattle; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology; D004848:Epithelium / Q000187:drug effects; D005260:Female; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000494:pharmacology*; D008321:Mammary Glands, Animal / Q000166:cytology / Q000187:drug effects*; D008954:Models, Biological; D011498:Protein Precursors / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000494:pharmacology*; D012756:Sheep / Q000235:genetics; D013268:Stimulation, Chemical; D014162:Transfection
D011498:Protein Precursors; D011993:Recombinant Fusion Proteins; D007334:Insulin-Like Growth Factor I; D003907:Dexamethasone