The mitogen-activated protein kinase pathway tonically inhibits both basal and IGF-I-stimulated IGF-binding protein-5 production in mammary epithelial cells.
The IGF system plays a key role in mammary gland growth and development. Our lab previously reported that IGF-I primarily regulates IGF-binding protein (BP)-3 in bovine mammary epithelial cells (MEC) and IGFBP-5 in mammary fibroblasts (MF). Presently, we examined the signaling pathways used by IGF-I to elicit this distinct, cell-type specific regulation. The phosphatidylinositol-3 kinase pathway was required for IGF-I to increase IGFBP-3 and -5 in MF and IGFBP-3 in MEC. Surprisingly, inhibiting the mitogen-activated protein kinase (MAPK) pathway in MEC increased IGFBP-5 mRNA levels 2- to 4-fold under basal conditions and 8- to 12-fold in cells treated with IGF-I within 4 h. Similar patterns of IGFBP-3 and -5 regulation were observed in murine MEC. Cells treated with IGF-I in the presence of MAPK inhibitors secreted more IGFBP-5 protein into conditioned media relative to cells treated with IGF-I alone; however, IGFBP-5 protein was not detected in conditioned media of cells treated with only a MAPK inhibitor. The IGFBP-5 mRNA response to MAPK inhibitors was specific for MEC, as blocking MAPK activity decreased the ability of IGF-I to induce IGFBP-5 in MF. In addition, no other IGFBP was increased in either cell type when MAPK activity was inhibited. These increases in IGFBP-5 expression in response to inhibition of the MAPK pathway corresponded with the induction of apoptosis. In conclusion, we report the novel observation that the MAPK/extracellular signal regulated kinase (ERK) pathway specifically represses IGFBP-5 expression in MEC. The corresponding changes in apoptosis and IGFBP-5 expression support a role for this specific IGFBP in mammary gland involution.
Fleming
Jodie M
JM
Rutgers, The State University of New Jersey, 59 Dudley Road, New Brunswick, NJ 08901-8520, USA.
Brandimarto
Jeffrey A
JA
Cohick
Wendie S
WS
D000818:Animals; D017209:Apoptosis; D002417:Cattle; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D004847:Epithelial Cells / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D005260:Female; D005419:Flavonoids / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D015151:Immunoblotting; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000235:genetics / Q000378:metabolism; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000235:genetics / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000502:physiology*; D008321:Mammary Glands, Animal / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D012333:RNA, Messenger / Q000032:analysis; D017526:Receptor, IGF Type 1 / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D002867:Chromones; D005419:Flavonoids; D018972:Insulin-Like Growth Factor Binding Protein 3; D018975:Insulin-Like Growth Factor Binding Protein 5; D007334:Insulin-Like Growth Factor I; D020928:Mitogen-Activated Protein Kinases; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D012333:RNA, Messenger; D017526:Receptor, IGF Type 1; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one