Identification of KLF13 Interacting Partners in the Heart
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Identification of KLF13 Interacting Partners in the Heart A Thesis Submitted to the Faculty of Graduate and Postdoctoral Studies University of Ottawa In Partial Fulfillment of the Requirements for the Degree of Master of Science Department of Biochemistry, Microbiology and Immunology Faculty of Medicine By Rami Darwich © Rami Darwich, Ottawa, Canada, 2011 i Abstract. Identifying the molecular and genetic pathways important for heart development and deciphering the causes of CHD are still a challenging puzzle. A newly identified piece of this puzzle is KLF13, a member of the Krüppel-like family of zinc-finger proteins, was found to be important for atrial septation and ventricular trabeculation of Xenopus embryos. The protein is expressed predominantly in the heart, binds evolutionarily- conserved regulatory elements on cardiac promoters, and activates cardiac transcription. In this study we examined KLF13 mechanism of action by investigating its transcriptional activity on the ANF promoter using a deletion/mutagenesis approach. We reported the identification of a new synergistic partnership between KLF13 and the individual cardiac transcription factors TBX5, NKX2.5, PEX1, and CATF1. Also, we localized KLF13’s transcriptional activation domain, the nuclear localization region/zinc- fingers, and the DNA binding zinc-fingers. This study will provide insight into the contribution of KLF13 to the development of CHDs. ii Acknowledgment: Another two years have passed and I have gained a wealth of knowledge about cardiac development that has paradoxically emphasized that I know nothing. I am forcefully adopting the engineering motto “Question everything. Learn something. Answer nothing.” However, I am certain that one day I will be reading the above lines with a smirk on my face, scrutinizing my foolishness. I would like to express my most sincere gratitude to my supervisor Dr. Mona Nemer for mentoring me and providing a creative and open environment to work in. Her vast knowledge of cardiovascular research, positivity, innovative attitude towards scientific work, and guidance and encouragement throughout this project was of great importance. Thank you for paving my first stretch of road towards being an independent researcher. I would also like to express my appreciation to Dr. Alexandre Blais and Dr. Alexandre Stewart for their constructive criticism and insights during the course of this thesis. I owe my gratitude to all present and former members of the “Nemer Lab”: Hiba Komati and Brigitte Laforest for your thesis corrections and helpful discussions concerning my work; Abir Yamak and Wael Maharsy for friendship, cooperation and protocol guidance during the last couple of years; and Janie Beauregard for expert technical assistance, comic relief, and insight into life (without you I would have been studying chaos theory). My deepest thanks go to my mother, family, and my better half Jessica, whose endless love, understanding, and confidence in me have been essential for the completion of this thesis. Ottawa, April 2011 Rami Darwich iii Table of Contents Abstract. ...................................................................................................................................................................... ii Acknowledgment: ...................................................................................................................................................... iii List of Figures .............................................................................................................................................................vi List of Tables ............................................................................................................................................................ viii List of Abbreviations ..................................................................................................................................................ix 1. Introduction ............................................................................................................................................................. 1 1.1 Morphology of heart development. ................................................................................................................. 1 1.2. Cardiac transcription: Different levels of control ......................................................................................... 3 1.3. Natriuretic peptides: A tool to decipher cardiac transcription. ................................................................... 5 1.4. Congenital Heart Diseases: ............................................................................................................................. 6 1.5. Essential cardiac regulators ............................................................................................................................ 9 1.5.1 GATA4 ....................................................................................................................................................... 10 1.5.2 NKX2.5 ...................................................................................................................................................... 12 1.5.3 TBX5 ......................................................................................................................................................... 14 1.5.4 PEX1 ......................................................................................................................................................... 18 1.5.5 CATF1 ....................................................................................................................................................... 21 1.6 The Kruppel-like transcription factor KLF13 ................................................................................................. 24 1.6.1 Introducing the family ............................................................................................................................... 24 1.6.2 KLF13: A portrait of the family’s structural features ............................................................................... 32 1.6.3. KLF13: Mechanisms of regulation........................................................................................................... 35 2. Material and Methods ........................................................................................................................................... 39 2.1 Plasmid Constructions .................................................................................................................................... 39 2.2 Cell cultures and transfections: ..................................................................................................................... 41 2.3 Preparation of nuclear extracts for downstream assays: ............................................................................ 41 2.4 Western Blotting ............................................................................................................................................. 42 2.5 Electromobility Gel Shift AnalysisWestern Blotting ................................................................................... 43 2.6 Fluorescence microscopy. ............................................................................................................................... 45 2.7 Pull-down: a protein–protein binding assay ................................................................................................ 45 3. Results ..................................................................................................................................................................... 47 3.1 Mapping of KLF13 response elements on the ANF promoter. ................................................................... 47 3.2 Combinatorial interactions of KLF13 on the ANF promoter. .................................................................... 56 3.2.1 KLF13 and CATF1 synergistically activate the ANF promoter. .............................................................. 56 3.2.2 KLF13 and PEX synergistically activate the ANF promoter. ................................................................... 57 3.2.3 KLF13 and NKX2.5 synergistically activate the ANF promoter. ............................................................. 58 3.2.4 KLF13 and TBX5 synergistically activate the ANF promoter. ................................................................. 63 3.2.5 Physical interaction of KLF13 with TBX5, NKX2.5, and PEX1. ............................................................. 68 3.3 Structure-Function Analysis of KLF13 ......................................................................................................... 71 3.4 Determination of KLF13’s synergy domains ................................................................................................ 82 iv 4. Discussion: .............................................................................................................................................................. 94 4.1. CACCC boxes, KLFs and cardiac transcription. ........................................................................................ 94 4.2. KLF13 and NKX2.5. ...................................................................................................................................... 96 4.3. KLF13 and TBX5. .........................................................................................................................................