title: IGF binding protein-3 mediates stress-induced apoptosis in non-transformed mammary epithelial cells.
abstract: Mammary epithelial cell (MEC) number is an important determinant of milk production in lactating dairy cows. IGF-I increases IGF binding protein-3 (IGFBP-3) production in these cells, which plays a role in its ability to enhance proliferation. In the present study, we show that the apoptotic factor anisomycin (ANS) also increases IGFBP-3 mRNA and protein in a dose- and concentration-dependent manner that mirrors activation of caspase-3 and -7, with significant increases in both IGFBP-3 protein and caspase activation observed by 3 h. Knock-down of IGFBP-3 with small interfering (si) RNA attenuated the ability of ANS to induce apoptosis, while knock-down of IGFBP-2, the other major IGFBP made by bovine MEC, had no effect. Reducing IGFBP-3 also decreased the ability of ANS to induce mitochondrial cytochrome c release, indicating its involvement in the intrinsic apoptotic pathway. In contrast, transfection with IGFBP-3 in the absence of ANS failed to induce apoptosis. Since both the mitogen IGF-I and the apoptotic inducer ANS increase IGFBP-3 production in MEC, we proposed that cellular localization might determine IGFBP-3 action. While both IGF-I and ANS stimulated the release of IGFBP-3 into conditioned media, only ANS induced nuclear localization of IGFBP-3. A pan-caspase inhibitor had no effect on ANS-induced nuclear localization of IGFBP-3, indicating that nuclear entry of IGFBP-3 precedes caspase activation. Treatment with IGF-I had no effect on ANS-induced nuclear localization, but did block ANS-induced apoptosis. In summary, our data indicate that IGFBP-3 plays a role in stress-induced apoptosis that may require nuclear localization in non-transformed MEC.
authors.affiliation: Graduate Program in Endocrinology and Animal Biosciences, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901-8520, USA.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Leibowitz
authors.forename: Allyson
authors.initials: A
authors.lastname: Agostini-Dreyer
authors.forename: Amanda E
authors.initials: AE
authors.lastname: Jetzt
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Krumm
authors.forename: Wendie S
authors.initials: WS
authors.lastname: Cohick
mesh_terms: D000818:Animals; D000841:Anisomycin / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism; D053179:Caspase 7 / Q000235:genetics / Q000378:metabolism; D002417:Cattle; D002460:Cell Line; D002467:Cell Nucleus / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D045304:Cytochromes c / Q000235:genetics / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000235:genetics / Q000378:metabolism; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000235:genetics / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000187:drug effects / Q000378:metabolism*; D008928:Mitochondria / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D014162:Transfection / Q000379:methods
chemical_list: D018971:Insulin-Like Growth Factor Binding Protein 2; D018972:Insulin-Like Growth Factor Binding Protein 3; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D000841:Anisomycin; D045304:Cytochromes c; D053148:Caspase 3; D053179:Caspase 7