PREFACE G protein-coupled receptors (GPCRs) (also known as seventransmembrane domain receptors or 7TMRs) constitute the largest family of cell surface receptors involved in signal regulation under diverse physiological and pathological conditions and are drug targets for many diseases. Extensive studies carried out over the past 2–3 decades have clearly demonstrated that the spatiotemporal regulation of GPCR intracellular trafficking, including the cell surface export, internalization, recycling, and degradation, is a crucial mechanism that controls receptor transport to the right place which in turn dictates the integrated responses of the cell to hormones and drugs at the right time. Adding to the complexity, each of these trafficking processes is mediated by multiple pathways and is highly regulated by many factors, such as structural determinants, specific motifs, interacting proteins, posttranslational modifications, and transport machineries, altogether coordinating receptor transport using very specialized routes. GPCR trafficking is rapidly evolving and has great potential to translate into new therapeutics. The main purpose of this book is to review our current understanding of intracellular trafficking of some well-characterized GPCRs. In addition, this book will also highlight the roles of trafficking in regulating the functionality of the receptors and pinpoint current challenges and future directions in studying GPCR trafficking. The contributors are experts in this area with many years of experience. It is my hope that this book will be useful to graduate students, postdoctoral fellows, and researchers who are interested in general GPCR biology or intracellular trafficking of GPCRs. I am grateful to each of the contributors for their valuable time and tremendous efforts to make this book possible. It is my great pleasure to work with them to put together a book on this very important topic in GPCR biology. I thank Dr. P. Michael Conn, the Chief Editor of the Progress in Molecular Biology and Translational Science series, for inviting me to edit this volume and always being supportive. I also would like to take this opportunity to thank my former mentor, Dr. Stephen M. Lanier, for leading me into the GPCR field. GUANGYU WU

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