Erin Wolf Horrell, Ph.D. Successfully Defends Dissertation
On Thursday, June 2, 2016 Erin Wolf Horrell successfully defended her dissertation.
"Regulation of UV-Protective Pathways Downstream of the Melanocortin 1 Receptor in Melanocytes”
Abstract of Dissertation
Malignant cutaneous melanoma is the deadliest form of skin cancer, and a majority of melanoma diagnoses are a result of exposure to ultraviolet (UV) radiation. UV radiation causes DNA damage, which if not repaired correctly via nucleotide excision repair (NER) can result in mutations and melanomagenesis. The melanocortin 1 receptor (MC1R) is a Gs protein coupled receptor located on melanocyte plasma membranes and is involved in protecting the skin from UV induced damage. MC1R signaling results in the activation of two protective pathways: 1) induction of eumelanin synthesis downstream of micropthalmia-associated transcription factor (MITF) and 2) acceleration of NER downstream of ataxia telangiectaseia mutated and Rad3 related (ATR). MC1R signaling, however, also promotes melanocyte proliferation, therefore, the activation of the MC1R pathway must be regulated. The overall hypothesis of this dissertation is that the pathways downstream of MC1R can be manipulated to protect against UV induced damage.
Chapter 2 investigates the regulation of the MC1R neutral antagonist human β-defensin 3 (bD3). UV damage did not induce bD3 mRNA expression in ex vivo human skin explants. The induction of bD3 expression instead correlated with inflammatory cytokines including TNFa.
Chapter 3 investigates the interdependence and cross talk between the two protective pathways downstream of MC1R. We directly tested the effect of MITF on the acceleration of NER and the effect of ATR on the induction of eumelanin synthesis following MC1R activation. MITF was not required for the acceleration of NER as mediated by ATR, however, the induction of transcription of enzymes involved in eumelanin synthesis was dependent upon ATR kinase activity.
Finally, Chapter 4 investigates the mechanism by which MC1R promoted proliferation and whether the two UV protective pathways downstream of MC1R could be selectively activated without the risk of melanocyte proliferation. MC1R signaling resulted in activation of the mechanistic target of rapamycin complex 1 (mTORC1), a major regulator of cell growth and proliferation. Inhibition of mTORC1 signaling via rapamycin prevented MC1R induced proliferation in vitro. Rapamycin, however, did not prevent MC1R induced eumelanin synthesis or the acceleration of NER in vitro or in vivo suggesting it is possible to selectively activate the beneficial signaling pathways without the risk of melanocyte proliferation.
Doctoral Committee
Dr. John D’Orazio, Chair
Department of Pediatrics, Markey Cancer Center
Dr. Francisco Andrade, Co-Chair
Department of Physiology
Dr. John Gensel
Department of Physiology
Dr. Daret St. Clair
Department of Toxicology and Cancer Biology
Outside Examiner
Dr. Kathleen O’Connor
Department of Molecular & Cellular Biochemistry, Markey Cancer Center
Acknowledgements
I have had the privilege and good fortune to have had many wonderful mentors throughout my academic career, and without their support, I would not have succeeded.
I would first and foremost like to thank my PhD mentor and advisor, Dr. John D’Orazio, for welcoming me into his laboratory and providing me with the opportunity to finish my PhD training. He believed in my potential from the beginning, and I am very grateful for his support and mentorship. The last three years in his laboratory have been a truly enjoyable experience and have furthered my scientific training to make me the scientist I am today. I would also like to thank my lab members specifically Dr. Stuart Jarrett for helping me through the day to day aspects of lab work and making each day enjoyable.
I would next like to thank my committee members, Dr. Paco Andrade, Dr. John Gensel, Dr. Daret St Clair, and Dr. Karyn Esser for their guidance and thoughtful questions throughout my training. I would also like to thank Dr. Kathy O’Connor for taking time to be my outside examiner.
I had the wonderful opportunity to start my PhD training in the Reid laboratory. I would like to thank Dr. Michael Reid for providing me with the best foundation possible to begin my PhD training and his continued support of my goals. I would also like to thank the members of the Reid laboratory specifically Dr. Jen Moylan and Jeff Smith. Jen not only tau ght me nearly every laboratory technique I know but also has provided a constant source of support throughout the past six years. Jeff provided me with my first experience using animal models, and the day to day procedures in the Reid lab would not have been possible without him.
I would like the thank the MD/PhD program, specifically Dr. Susan Smyth and Therese Stearns for their assistance and encouragement from the first day of the program. I would also like to thank the Physiology Department. The faculty have provided a wonderful support system. I would like to specifically thank Dr. John McCarthy for always allowing me to ask questions and providing me with wonderful guidance.
Finally, I would like to thank my family and friends. My mom and dad have supported me from the beginning and provided me with every opportunity possible. I am so grateful for all the sacrifices they made throughout the years and am so proud to be their daughter. My little brother, Derek, has been my best friend since birth, and his opinion and support throughout the last 25 years has meant the world to me. My husband, Tim, has stood by my side truly from day one of this program. He has supported me every single day and never let me get discouraged. Finally, thank you to my friends, old and new, who have made Lexington home and who’s support has meant more to me than they could know.