Uniform TitleMolecular regulation of insulin-like growth factor binding protein-3 and its role in ribotoxic stress-induced apoptosis
NameLeibowitz, Brian J. (author), Cohick, Wendie (chair), Bagnell, Carol (internal member), Uzumcu, Mehmet (internal member), Brewer, Gary (outside member), Rutgers University, Graduate School - New Brunswick,
Insulin-like growth factor-binding proteins,
DescriptionInsulin-like growth factor binding protein-3 (IGFBP-3) is one of six high affinity binding proteins for IGF-I. However, new and exciting IGF-independent functions have begun to emerge for IGFBP-3 in the regulation of cell growth. Specifically, the biological role of IGFBP-3 in apoptosis has been found to be extremely complex, with a number of possible functions suggested, but few well-characterized mechanisms determined. The overall goal of this work was to elucidate the role of IGFBP-3 within the context of ribotoxic stress-induced apoptosis, with specific aims to determine how ribotoxic stressors regulate IGFBP-3 expression and how IGFBP-3 influences the apoptotic pathway. Studies involving both chemical inhibitors and siRNA determined that the ribotoxic stressors anisomycin (ANS) and ricin A chain (RTA) both induced IGFBP-3 expression through the p38 signaling pathway, and that both stressors enhanced IGFBP-3 mRNA stability through a 3'untranslated region-mediated, p38 dependent mechanism. Additional studies demonstrated that RTA also activated the IGFBP-3 promoter in a p38-dependent manner. Subsequent work allowed for the conclusion that IGFBP-3 is specifically required for ANS and RTA-induced apoptosis. Knockdown of IGFBP-3 with siRNA prevented ANS-induced cytochrome c release, caspase activation and PARP cleavage. Knockdown of JNK-2 also inhibited caspase activation and PARP cleavage, suggesting that it and IGFBP-3 were involved in the same apoptotic mechanism. These findings led to the discovery that the orphan nuclear receptor Nur77 translocated to the cytosol following ANS treatment, where it is known to induce apoptosis. Additionally, knockdown of either IGFBP-3 or JNK-2, pre-treatment with the nuclear export inhibitor leptomycin B (LMB) or treatment with IGF-I could both prevent this translocation and prevent ANS-induced apoptosis. In conclusion, this work describes the novel regulation of IGFBP-3 by the p38 pathway, and helps to shed light on the complex role that IGFBP-3 plays in apoptosis. These findings suggest that IGFBP-3 may be an integral part of the inherent apoptotic machinery in normal cells and may play a crucial role in the response of normal cells to toxic stressors.
NoteIncludes bibliographical references (p. 138-165).
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.