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Regulation of iASPP expression by chemotherapeutic drugs

Breyssens, H.; (2009) Regulation of iASPP expression by chemotherapeutic drugs. Doctoral thesis, UCL (University College London).

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Abstract

The tumour suppressor p53, is a key regulator in deciding between cell survival or cell death by its ability to induce cell cycle arrest and apoptosis. It is one of the most frequently mutated genes in human cancers and influences the efficacy of many cancer therapies. The newly identified ASPP family of proteins is a specific regulator of p53-, p63- and p73-mediated apoptosis. The family consists of three members, two pro-apoptotic proteins ASPP1 and ASPP2, which selectively stimulate p53's apoptotic function and one anti-apoptotic member, iASPP, which inhibits p53-mediated cell death. This thesis has focused on identifying changes in iASPP protein expression in response to chemotherapeutic drugs. Our data describes a substantial decrease in mobility of iASPP by Western blot analysis, following treatment of cells with arsenic trioxide and microtubule drugs such as nocodazole, taxol and colchicine. Importantly, the iASPP expression pattern correlated with the cellular physiology. More precisely, a small decrease in iASPP mobility was associated with cells arrested in mitosis, while a more substantial mobility shift was related to cell death. These observations were confirmed in a variety of cell lines derived from solid tumours and haematological malignancies. We found that this mobility shift was caused by post-translational modifications of iASPP at the N-terminus in a defined region spanning amino acids 91 until 125. Mass spectrometric analysis provided evidence for phosphorylation on specific serines. Moreover, analysis of antibody epitopes and iASPP point mutants, provided evidence for the involvement of other residues within this epitope, suggesting multiple modifications. Furthermore, the signalling pathways leading to this iASPP modification following treatment with arsenic trioxide and nocodazole involve oxidative stress, mitogen-activated protein kinases, nuclear factor-B, glycogen synthase kinase-3, prolyl hydroxylases and cyclin-dependent kinases. All these data leads to a better understanding of the regulation of iASPP expression and function in cancer cells under normal and stress conditions. Additionally, increased knowledge of the mechanisms of action of these drugs could lead to new applications or improved strategies for treating malignancies.

Type:Thesis (Doctoral)
Title:Regulation of iASPP expression by chemotherapeutic drugs
Language:English
Additional information:Authorisation for digitisation not received
UCL classification:UCL > School of Life and Medical Sciences > Faculty of Medical Sciences > Wolfson Institute and Cancer Institute Administration > Cancer Institute > Research Department of Pathology

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