Cloning of the cDNA for the human beta 1-adrenergic receptor.

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1987-11

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Abstract

Screening of a human placenta lambda gt11 library has led to the isolation of the cDNA for the human beta 1-adrenergic receptor (beta 1AR). Used as the probe was the human genomic clone termed G-21. This clone, which contains an intronless gene for a putative receptor, was previously isolated by virtue of its cross hybridization with the human beta 2-adrenergic receptor (beta 2AR). The 2.4-kilobase cDNA for the human beta 1AR encodes a protein of 477 amino acid residues that is 69% homologous with the avian beta AR but only 54% homologous with the human beta 2AR. This suggests that the avian gene encoding beta AR and the human gene encoding beta 1AR evolved from a common ancestral gene. RNA blot analysis indicates a message of 2.5 kilobases in rat tissues, with a pattern of tissue distribution consistent with beta 1AR binding. This pattern is quite distinct from the pattern obtained when the beta 2AR cDNA is used as a probe. Expression of receptor protein in Xenopus laevis oocytes conveys adenylate cyclase responsiveness to catecholamines with a typical beta 1AR specificity. This contrasts with the typical beta 2 subtype specificity observed when the human beta 2AR cDNA is expressed in this system. Mammalian beta 1AR and beta 2AR are thus products of distinct genes, both of which are apparently related to the putative G-21 receptor.

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Collins

Sheila Collins

Adjunct Associate Professor in Psychiatry and Behavioral Sciences

Research Focus
One only has to open the newspaper or turn on the radio to hear about the epidemic of obesity in America. Not only does obesity exact a heavy toll on the population's health, but the medical costs associated with obesity, especially those related to treatment for type 2 diabetes and cardiovascular disease, are astronomical.

Our laboratory is interested in the biochemical mechanisms that regulate body weight. Until the mid-1990s, adipose tissue had been largely considered to be an inert storage depot for excess metabolic fuel. In the ensuing years, there has been a deeper appreciation that a fairly large number of cytokines and growth factors are secreted from adipose tissue and may play significant roles in insulin resistance and cell differentiation and growth.

Accumulation of excess calories as triglycerides in adipose tissue is largely driven by insulin, and subsequent access to this stored fuel is gated by the catecholamine to stimulate lipolysis. Activation of the adrenaline receptors, specifically the members of the beta-adrenergic receptor (beta-AR) family, are a major stimulus for the hydrolysis and release of stored lipids. There are three known beta-AR subtypes, one of which is expressed predominantly in the adipocyte: the beta3-AR. Our lab has been deciphering how the beta-ARs on fat cells are regulated and how their structural features dictate their signal transduction properties, including a process called nonshivering thermogenesis, in brown fat. Brown fat cells are specialized cells rich in mitochondria and defined by their ability to express the mitochondrial uncoupling protein UCP1, which allows the dissipation of the proton gradient in the inner mitochondrial membrane to yield heat at the expense of ATP production. Although known to exist in newborns humans, it was largely considered to be absent from adult humans. It is now understood that this assumption is incorrect and once again opens the opportunity to consider brown adipocytes as a potential means for improving energy expenditure and the ‘burning’ of calories as heat instead of storing them as fat.

We also study the cardiac natriuretic peptides ANP and BNP, which also can stimulate lipolysis by a parallel set of receptors, also increase the amount and activity of brown adipocytes, and we are investigating the regulation of this system, including in human subjects.  

These discoveries, as well as the realization that a host of biochemical and environmental factors contribute to the obesity epidemic, mark a new era in understanding how organ systems communicate their energy demands and reserves to regulate body weight.

Biography
Dr. Collins received her B.S., degree in Zoology from the University of Massachusetts at Amherst, after which she was a research technician at the Mass.General Hospital (Boston) and at the California Institute of Technology in Pasadena CA. She received her doctorate in biochemistry and drug metabolism from the Massachusetts Institute of Technology with Dr. Michael Marletta, and conducted postdoctoral research in the lab of Dr. Robert Lefkowitz at Duke University. Dr. Collins continued her research career at Duke University Medical Center by joining the faculty, being awarded tenure.  She was then a Professor of Integrative Metabolism at the Sanford BurnhamPrebys Medical Discovery Institute in Orlando, FL (home base La Jolla CA). She is currently Professor of Cardiovascular Medicine at Vanderbilt University Medical Center.  Dr. Collins has served on numerous review committees and advisory panels for the National Institutes of Health, the American Diabetes Association, and has been an organizer of many national and international scientific meetings.

Lefkowitz

Robert J. Lefkowitz

The Chancellor's Distinguished Professor of Medicine

Dr. Lefkowitz’s memoir, A Funny Thing Happened on the Way to Stockholm, recounts his early career as a cardiologist and his transition to biochemistry, which led to his Nobel Prize win.

Robert J. Lefkowitz, M.D. is Chancellor’s Distinguished Professor of Medicine and Professor of Biochemistry and Chemistry at the Duke University Medical Center. He has been an Investigator of the Howard Hughes Medical Institute since 1976. Dr. Lefkowitz began his research career in the late 1960’s and early 1970’s when there was not a clear consensus that specific receptors for drugs and hormones even existed. His group spent 15 difficult years developing techniques for labeling the receptors with radioactive drugs and then purifying the four different receptors that were known and thought to exist for adrenaline, so called adrenergic receptors. In 1986 Dr. Lefkowitz transformed the understanding of what had by then become known as G protein coupled receptors because of the way the receptor signal for the inside of a cell through G proteins, when he and his colleagues cloned the gene for the beta2-adrenergic receptor. They immediately recognized the similarity to a molecule called rhodopsin which is essentially a light receptor in the retina. This unexpected finding established the beta receptor and rhodopsin as the first member of a new family of proteins. Because each has a peptide structure, which weaves across the cell membrane seven times, these receptors are referred to as seven transmembrane receptors. This super family is now known to be the largest, most diverse and most therapeutically accessible of all the different kinds of cellular receptors. There are almost a thousand members of this receptor family and they regulate virtually all known physiological processes in humans. They include the receptors not only to numerous hormones and neurotransmitters but for the receptors which mediate the senses of sweet and bitter taste and smell amongst many others. Dr. Lefkowitz also discovered the mechanism by which receptor signaling is turned off, a process known as desensitization. Dr. Lefkowitz work was performed at the most fundamental and basic end of the research spectrum and has had remarkable consequences for clinical medicine. Today, more than half of all prescription drug sales are of drugs that target either directly or indirectly the receptors discovered by Dr. Lefkowitz and his trainees. These include amongst many others beta blockers, angiotensin receptor blockers or ARBs and antihistamines. Over the past decade he has discovered novel mechanisms by which the receptors function which may lead to the development of an entirely new class of drugs called “biased agonists”. Several such compounds are already in advanced stages of clinical testing. Dr. Lefkowitz has received numerous honors and awards, including the National Medal of Science, the Shaw Prize, the Albany Prize, and the 2012 Nobel Prize in Chemistry. He was elected to the USA National Academy of Sciences in 1988, the Institute of Medicine in 1994, and the American Academy of Arts and Sciences in 1988.


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