IGF-I-induced IGFBP-3 potentiates the mitogenic actions of IGF-I in mammary epithelial MD-IGF-I cells.
Limited information is available concerning the molecular and cellular mechanisms that regulate expression of insulin-like growth factor-I (IGF-I) binding proteins (IGFBPs) in bovine mammary epithelial cells. Here, we report on the autocrine mechanisms of action of IGF-I and hormonal regulation of expression of IGFBPs in bovine mammary epithelial MD-IGF-I cells which express recombinant IGF-I under the control of the glucocorticoid-inducible mouse mammary tumor virus-long terminal repeat (MMTV-LTR). Levels of IGFBP-3 mRNA and secretion of IGFBP-3 by MD-IGF-I cells were stimulated by IGF-I, insulin (INS), and IGF-I analogs but not prolactin (PRL). Conversely, parental MAC-T cells expressed little IGF-I and secreted primarily IGFBP-2 (29-32 kDa) in response to stimulation with INS, dexamethasone (DEX), or IGF-I analogs. Secretion of recombinant IGF-I caused a 26.5-fold increase in secretion of IGFBP-3, as measured by densitometric analysis of ligand blots, which was associated with a 1.7-fold increase in total DNA. Conditioned media (CM) from MD-IGF-I cells induced with DEX stimulated a 2.8-fold increase in [3H]thymidine incorporation into DNA of parental MAC-T cells, compared with uninduced cells. Moreover, inclusion of exogenous IGF-I with CM from MD-IGF-I cells triggered an additional 3.0-fold increase in label incorporation, but only a 1.6-fold increase in the presence of IGFBP-2-containing media conditions by MAC-T cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Ramagnolo
D
D
Department of Dairy and Animal Science, Virginia Polytechnic Institute and State University, Blacksburg 24061-0315.
Akers
R M
RM
Byatt
J C
JC
Wong
E A
EA
Turner
J D
JD
D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D002352:Carrier Proteins / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics / Q000494:pharmacology; D002417:Cattle; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D017077:Culture Media, Conditioned / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis / Q000187:drug effects; D003907:Dexamethasone / Q000494:pharmacology; D005260:Female; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000187:drug effects / Q000494:pharmacology; D008321:Mammary Glands, Animal / Q000166:cytology* / Q000187:drug effects; D012333:RNA, Messenger / Q000096:biosynthesis / Q000187:drug effects
D002352:Carrier Proteins; D017077:Culture Media, Conditioned; D018969:Insulin-Like Growth Factor Binding Proteins; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D003907:Dexamethasone; D004247:DNA