Endogenous IGFBP-3 is required for both growth factor-stimulated cell proliferation and cytokine-induced apoptosis in mammary epithelial cells.
TNF-alpha and IGF-I exert opposing effects on mammary epithelial cell (MEC) growth and survival. However, both increase IGF binding protein-3 (IGFBP-3) expression, a multifunctional protein that plays both IGF-dependent as well as independent roles in these processes. We have reported that IGF-I utilizes the PI3-K and MAPK pathways to induce IGFBP-3 expression in bovine MEC. Here we show that TNF-alpha requires the SAPK pathway p38, but not JNK, to induce IGFBP-3 expression. Contrary to reports in cancer cell lines, TNF-alpha retained its ability to decrease DNA synthesis in cells transfected with IGFBP-3 siRNA. It also retained its ability to inhibit IGF-I-stimulated DNA synthesis in these cells. In contrast, the ability of IGF-I to increase DNA synthesis was attenuated with IGFBP-3 knockdown. IGFBP-3 knockdown also decreased basal DNA synthesis, indicating that a certain level of IGFBP-3 may be required for cell proliferation. While TNF-alpha alone failed to induce apoptosis, it increased cell death when added with the JNK agonist anisomycin (ANS). TNF-alpha and ANS were unable to induce apoptosis when either IGFBP-3 or JNK-2 was knocked-down, suggesting that both JNK and IGFBP-3 may interact with a downstream molecule central to apoptosis. There are reports that IGFBP-3 promotes either cell proliferation or apoptosis in different cell systems. However, this is the first report that endogenous IGFBP-3 is required for the action of both stimulatory and inhibitory factors within the same cell line. Therefore, the actions of IGFBP-3 are not pre-determined, but instead governed by cellular context such as JNK activation.
Leibowitz
Brian J
BJ
Department of Animal Sciences, Rutgers, The State University of New Jersey, New Brunswick, New Jersey, USA.
Cohick
Wendie S
WS
D000818:Animals; D000841:Anisomycin / Q000494:pharmacology; D000873:Anthracenes / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D002417:Cattle; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D004261:DNA Replication; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000187:drug effects / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D005260:Female; D007093:Imidazoles / Q000494:pharmacology; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000235:genetics / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000187:drug effects / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D015854:Up-Regulation; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
D000873:Anthracenes; D007093:Imidazoles; D018972:Insulin-Like Growth Factor Binding Protein 3; D047428:Protein Kinase Inhibitors; D011725:Pyridines; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D014409:Tumor Necrosis Factor-alpha; C432165:pyrazolanthrone; D007334:Insulin-Like Growth Factor I; D000841:Anisomycin; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580