FoxP1 Represses MEF2A in Striated Muscle

Abstract

Myocyte Enhancer Factor 2 (MEF2) is a transcription factor complex encoded by genes mef2a-d.MEF2 proteins belong to the MADS-box DNA binding protein superfamily involved in many developmental pathways including myogenesis and the survival of cardiomyocytes. MEF2 proteins interact with myogenic regulatory factors and modulate the expression of muscle-specific genes. Thus, unbiased characterization of the MEF2A interactome would expand our understanding of MEF2 functions. A GFP-nanotrap purification followed by LC-MS/MS proteomic analysis was employed to identify MEF2A interacting proteins. Following gene ontology analysis, we focused on an interaction between MEF2A and its novel interacting protein, FOXP1, in striated muscle. FOXP1 was found in the MEF2A-immunocomplex in muscle cells, and ectopic expression of FOXP1 delays myogenic differentiation. FOXP1 inhibited MEF2A activation on myogenic reporter genes driven by the regulatory regions of creatine kinase muscle and myogenin genes. Additionally, siRNA-mediated deletion of FOXP1 in myoblasts and cardiomyocytes enhances MEF2A transactivation properties. Lastly, various biochemical experiments indicate that FOXP1 antagonizes p38 MAPK activation of MEF2A through Threonine-312 phosphorylation. Collectively, we documented a novel repressive interaction of FOXP1 and MEF2A in proliferating striated muscle cells. iii Acknowledgements I would like to begin by expressing my gratitude to Dr. McDermott for recognizing my potential beyond my math grades and providing me an opportunity to pursue my research ambitions. Your expertise and guidance have laid a strong foundation for my journey in this everevolving field. Dr. Tetsuaki Miyake, I cannot thank you enough for your dedication to helping me design experiments and succeed as a graduate student. Thank you for making me feel smarter than I am is. Catherine, I am very grateful for your patience with my high maintenance tendencies, I will miss our weekly lunches dearly. Xiao Dong (XD), I cannot thank you enough for generously spending your weekends with me at the lab to teach me new techniques. To my fellow lab mates, past and present, thank you for your support and always making me laugh. Thank you, Jonathan Kelebeev, my concert buddy, for training me. Thank you, Gurnoor Brar and Dr. Amira Moustafa, for your help with animal care. Thank you, Anastasia MacKeracher, for always making me laugh, good luck at regionals! Thank you, FATIMA Farhat, for keeping me sane these past 2 years. I would also like to thank my previous research mentors who helped me start my research journey, Dr.