Thesis Examination: MSc Student Apurva Bhardwaj

Wed. Dec. 4 02:00 PM - Wed. Dec. 4 04:00 PM
Contact: Dylan Armitage
Location: Room 1RC028

Apurva Bhardwaj - MSc Student in Bioscience, Technology, and Public Policy

Mechanistic study of Insulin-like Growth Factor Binding Protein-3 (IGFBP-3) in regulating cellular functions

Insulin-like growth (IGF) factor binding protein-3 (IGFBP-3), one of the six members of the IGFBP family, is the most abundant IGFBPs present in serum. Considered to be amongst the key proteins in the IGF pathway, it also serves as a transport vehicle for the IGFs and thereby regulates its bioavailability to its receptors. Secretory in nature, IGFBP-3 has been demonstrated to be present in blood serum, inside the cytosol as well as in the nucleus. IGFBP-3 can function in an IGF-dependent as well as in IGF-independent manner. The IGF-dependent role of IGFBP-3 include its endocrine role in the delivery of IGFs from the site of synthesis to the target cells that possess IGF receptors (IGFRs) and the activation of its associated downstream signaling. IGF-independent role of IGFBP-3 include its interactions with the extracellular matrix (ECM), its association and translocation through the plasma membrane into the cytoplasm and into the nucleus. A significant amount of literature outlines the interactive nature of IGFBP-3 wherein the protein has been reported to bind to several nuclear receptors and proteins. Proteins that translocate into the nucleus could potentially function as transcription factors or contribute towards the regulation of gene transcription. Therefore, we were keen to investigate the potential nuclear binding partners of IGFBP-3 and also understand its purpose of translocation into the nucleus.

Through our work, documented in this thesis, we have studied the IGF-independent processes. We demonstrate that rapamycin, an inhibitor of mTOR causes translocation of IGFBP-3 into the nucleus. Nuclear IGFBP-3 binds with proteins in the nucleus to regulate transcription. To the best of our knowledge, there are no reports on the protein-protein interaction between IGFBP-3 and histone 3. We report for the first time that IGFBP-3 interacts with histone 3. The interaction between IGFBP-3 and histone 3 was established using biochemical techniques co-immunoprecipitation and ligand-dot blot. Our studies indicate that the binding with IGFBP-3 showed a proportional increase with histone 3 concentrations between 75 mM and 4.0625 mM. The interaction of IGFBP-3 with histone 3 is suggestive of its role in chromatin modeling.