The Regulation of Htert by Alternative Splicing
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THE REGULATION OF HTERT BY ALTERNATIVE SPLICING APPROVED BY SUPERVISORY COMMITTEE First Name Last Name, credentials Jerry Shay, Ph.D. Woodring Wright, M.D., Ph.D. Hongtao Yu, Ph.D. Melanie Cobb, Ph.D. Beatriz Fontoura, Ph.D. DEDICATION I would like to thank the members of my Graduate Committee and mentors, Jerry Shay and Woodring Wright, all of the members of the Shay/Wright lab, my collaborators, the UTSW MSTP, my friends, my family, my significant other and my two cats, Kerrigan and Tofu. THE REGULATION OF HTERT BY ALTERLATIVE SPLICING by LAURA YU YUAN DISSERTATION Presented to the Faculty of the Graduate School of Biomedical Sciences The University of Texas Southwestern Medical Center at Dallas In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY The University of Texas Southwestern Medical Center at Dallas Dallas, Texas May, 2019 Copyright by Laura Yu Yuan, 2019 All Rights Reserved THE REGULATION OF HTERT BY ALTERNATIVE SPLICING Publication No. Laura Yu Yuan, M.D., Ph.D. The University of Texas Southwestern Medical Center at Dallas, 2019 Supervising Professors: Jerry Shay, Ph.D., and Woodring Wright, M.D., Ph.D. Telomeres are non-coding DNA hexameric repeats (TTAGGG in mammals) located at the ends of linear chromosomes that, along with their associated proteins, protect against the loss of genomic material during cell division and prevent the recognition of chromosome ends as double-strand breaks. Human telomeres shorten with continued cell proliferation but are maintained by human telomerase reverse transcriptase (hTERT), an enzyme that synthesizes telomeric repeats using an RNA template. The regulation of telomerase has been studied at many levels—from epigenetic and transcriptional regulation to the alternative splicing of hTERT pre-mRNA into catalytically ixv inactive splice variants. Our hypothesis is that if the regulation of telomerase reverse transcriptase splicing is necessary for telomere length homeostasis, altering telomerase splicing to decrease the production of full-length hTERT and will result in decreased telomerase activity and subsequently telomere shortening. We focused our efforts on identifying splicing factors are involved in hTERT splicing and characterized the role of two splicing factors, NOVA1 and PTBP1, in regulation of hTERT splicing in non-small cell lung cancer cells. We show that these splicing factors are important for full-length hTERT, telomerase activity and telomere length maintenance in vitro. Xenograft studies suggest that NOVA1 is also important for tumor growth in vivo. We found that these splicing factors are able to directly interact with hTERT in a region our group previously identified to be important for hTERT splicing. Altogether, our work suggests that splicing factors are important for hTERT regulation and telomerase activity in cancer. Since telomerase activity is undetectable in most somatic tissues but is increased in the vast majority of human cancers, dependence on telomerase represents a key vulnerability in cancer tissues which could be therapeutically targetable. viiivi TABLE OF CONTENTS ABSTRACT ........................................................................................................................... v CHAPTER ONE: INTRODUCTION .................................................................................... 1 INTRODUCTION TO TELOMERES AND TELOMERASE ....................................... 1 TELOMERASE REVERSE TRANSCRIPTASE ........................................................... 4 TERT REGULATION ..................................................................................................... 6 CHAPTER TWO: REVIEW OF LITERATURE ................................................................ 13 INTRODUCTION TO SPLICING ................................................................................ 13 MUTATED SPLICING FACTORS AS ONCOGENES ................................................ 15 DYSREGULATED SPLICING FACTORS AS ONCOGENES .................................. 19 SPLICING FACTORS AS TUMOR SUPPRESSORS ................................................. 22 OTHER REGULATORY FACTORS ............................................................................ 24 CHAPTER THREE: METHODS AND MATERIALS ...................................................... 27 CHAPTER FOUR: NOVA1 RESULTS .............................................................................. 39 BACKGROUND ............................................................................................................ 39 RESULTS ....................................................................................................................... 40 DISCUSSION ................................................................................................................. 70 CHAPTER FIVE: PTBP1 RESULTS ................................................................................. 72 BACKGROUND ............................................................................................................ 72 RESULTS ....................................................................................................................... 73 DISCUSSION ................................................................................................................. 81 CHAPTER SIX: CONCLUSIONS AND RECOMMENDATIONS ................................... 83 viiix CHAPTER SEVEN: BIBLIOGRAPHY .............................................................................. 98 viii PRIOR PUBLICATIONS Gao, Z., Ure, K., Ding, P., Nashaat, M., Yuan, L., Ma, J., Hammer, R. E., & Hsieh, J. (2011). The master negative regulator REST/NRSF controls adult neurogenesis by restraining the neurogenic program in quiescent stem cells. J Neurosci.,31 (26), 9772-86. ix LIST OF FIGURES FIGURE ONE ......................................................................................................................... 2 FIGURE TWO ....................................................................................................................... 3 FIGURE THREE ................................................................................................................... 5 FIGURE FOUR ................................................................................................................... 15 FIGURE FIVE ..................................................................................................................... 16 FIGURE SIX ........................................................................................................................ 17 FIGURE SEVEN ................................................................................................................. 41 FIGURE EIGHT .................................................................................................................. 50 FIGURE NINE ..................................................................................................................... 53 FIGURE TEN ...................................................................................................................... 58 FIGURE ELEVEN ............................................................................................................... 61 FIGURE TWELVE .............................................................................................................. 66 FIGURE THIRTEEN ........................................................................................................... 69 FIGURE FOURTEEN ......................................................................................................... 73 FIGURE FIFTEEN .............................................................................................................. 74 FIGURE SIXTEEN ............................................................................................................. 75 FIGURE SEVENTEEN ....................................................................................................... 76 FIGURE EIGHTEEN .......................................................................................................... 76 FIGURE NINETEEN .......................................................................................................... 78 FIGURE TWENTY ............................................................................................................. 78 FIGURE TWENTY-ONE .................................................................................................... 79 ixx FIGURE TWENTY-TWO ................................................................................................... 80 FIGURE TWENTY-THREE ............................................................................................... 81 FIGURE TWENTY-FOUR ................................................................................................. 89 viiixi LIST OF TABLES TABLE ONE ....................................................................................................................... 90 TABLE TWO ....................................................................................................................... 91 xiiix LIST OF APPENDICES APPENDIX ONE ................................................................................................................. 90 xiiiviii LIST OF DEFINITIONS ATM – ataxia-telangiectasia mutated Bcl-x – B-cell lymphoma x CDC40 - cell division cycle 40 CLIP – cross-linking immunoprecipitation CLIP-ddPCR – crosslinking immunoprecipitation followed by RT-ddPCR CLK – CDC