|T H E N I H C A T A L Y S T||J A N U A R Y F E B R U A R Y 2004|
|P E O P L E|
Bruce Cumming earned his D.Phil. and M.D. degrees at Oxford University in the U.K. in 1985 and 1988. He did his postdoctoral training at Oxford and came to NEI in 2000. He is now a senior investigator in NEIs Laboratory of Sensorimotor Research.
Action potentials generated by neurons in the cerebral cortex eventually give rise to conscious sensations. To understand the relationship between neural firing and conscious judgments, I study both of them simultaneously in awake, behaving monkeys. I study a relatively simple perceptual systemstereopsis, the ability to perceive depth by combining images from the two eyes. Stereopsis is sufficiently well understood that the goal of explaining perceptions in terms of the activity of cortical neurons is feasible with this experimental system.
One focus of the lab has been on explaining the exact neuronal mechanisms that generate signals related to binocular disparity (differences between the images falling on the two retinae) in single neurons. Over the last 10 years, detailed quantitative models have successfully described how neurons respond to a wide range of binocular stimuli. This is especially true of neurons at the earliest cortical stage, known as V1.
An ongoing experimental effort by my lab and by others to test this model has generated a growing body of evidence at odds with the original model. Recently, Jenny Read, working in my group, successfully reconciled all of this evidence with a modified version of the model of the mechanism of disparity selectivity, making it one of the best-understood functions of cortical neurons.
Although the psychophysical properties of stereopsis have been extensively studied in humans and monkeys, many of these properties are not straightforwardly reflected in the activity of single neurons, at least in V1. One of my important contributions was to use our knowledge of the underlying neuronal mechanisms to devise a variety of stimuli that reliably altered the activity of disparity-selective neurons without producing the corresponding depth sensation.
By dissociating the activity of early cortical neurons from visual perception, we gain important insights into subsequent neural processing that is required from other parts of the brain. At the same time, we can identify what properties of perceptual experience are constrained by this early processing.
In parallel experiments, I demonstrated that neurons in subsequent brain areas"extrastriate" cortexare more closely linked to the perception of stereoscopic depth than V1 neurons. Small groups of cortical neurons can be artificially activated by passing current out of recording electrodes. I found that stimulating a brain area known as MT in this way systematically biases animals depth reports, in the direction expected from the tuning properties of neurons recorded at those sites.
I also demonstrated a close connection between the activity of single neurons and perception by exploiting ambiguous stimuli: An identical visual stimulus is seen as close on some trials but distant on other trials. By recording the activity of single MT neurons while animals report the perceived configuration, I showed that the neuronal activity was correlated with the animals reported sensation. We measured this correlation between neuronal and behavioral responses to the same physical stimulus; thus, the activity of single neurons in this area carries information not only about the disparity of external stimuli, but also about the depth sensations experienced by the animal.
These experiments offer insights into how hierarchical processing by a series of cortical areas leads from machine-like processing of input images to conscious perception of the visual world. My lab will aim to advance this understanding through three approaches:
1. Challenging current mathematical models of the mechanism of disparity selectivity in V1 with new stimuli. Measuring neuronal responses to these stimuli will improve our understanding of the underlying mechanisms.
2. Exploiting these models to construct explicit models of how neurons in extrastriate cortex generate new signals from the outputs of V1. Combining these two approaches will identify what aspects of perception are supported by processing in extrastriate cortex, and how.
3. New stimuli may then allow us to activate extrastriate neurons without producing corresponding depth sensations. Demonstrations of a tight link between neuronal activity and perceptual states mentioned above may be possible in the same neurons. The ultimate goal will be to control separately neuronal activity, perceptual state, and the correlation between these two. This process will identify features of activity in populations of neurons that are required to support perception.
Myriam Gorospe received her Licenciatura in biology from the Universidad Complutense de Madrid in Spain in 1990. She earned her Ph.D. in cell and developmental biology from the State University of New York in Albany in 1993. In 1994, she joined the NIA intramural program as a postdoctoral fellow in the Laboratory of Biological Chemistry, later renamed the Laboratory of Cellular and Molecular Biology (LCMB), where she worked under the mentorship of Nikki Holbrook. She currently heads the RNA Regulation Section, LCMB.
I have had a long-standing interest in understanding basic mechanisms of gene regulation. My graduate studies in the laboratory of Corrado Baglioni focused on the investigation of post-transcriptional mechanisms regulating cytokine expression. Subsequent postdoctoral work centered on the transcriptional and post-transcriptional regulation of genes associated with cancer and cell cycle control.
As a tenure-track scientist, I investigated basic mechanisms of post-transcriptional gene regulation in mammalian cells. These studies focused primarily on genes whose production is linked to stressful and proliferative stimulationtwo important responses that are critically impaired with aging.
While the bulk of my labs work has centered on the analysis of mRNA turnover affecting specific genes, we have also investigated the regulation of protein degradation by the von HippelLindau tumor-suppressor protein. More recently our research efforts have expanded to include mRNA transport and translation, events that are functionally coupled with mRNA stability.
Over the years, our work has provided insight into basic mechanisms of mRNA stabilization and mRNA decay by uncovering RNA elements and RNA-binding proteins involved in regulating mRNA stability and signaling events influencing these processes.
Specifically, we have demonstrated the critical role of RNA-binding protein HuR in the stabilization and enhanced translation of mRNAs encoding proteins that control cell growth and proliferation (such as p21, cyclin A, cyclin B1, and p53). Our studies have shown that through its influence on target mRNAs, HuR plays a pivotal role in important processes such as the cellular stress response, the cell division cycle, carcinogenesis, and the maintenance of a young phenotype in models of cellular senescence.
Our research has also contributed significantly to the demonstration that, on a global level, changes in mRNA stability are critically involved in regulating gene expression patterns during complex cellular processes such as the cellular response to genotoxicity, heat-shock, and oxidative stress.
Through the development of a nuclear run-on protocol adapted to cDNA arrays, we have studied the relative contribution of transcriptional events to the implementation of changes in gene expression patterns.
Using the cellular stress response as study system, we discovered large sets of mRNAs whose altered steady-state levels did not result from transcriptional control, but were instead due to changes in mRNA stability. These studies demonstrated the central role of mRNA turnover in gene regulatory events.
Looking ahead, my lab is uniquely poised to address fundamental aspects of post-transcriptional gene regulation and cell biology. We are currently pursuing this goal by investigating, on a global scale, links between mRNA stability and translation in response to genotoxic damage and endoplasmic reticulum stress.
Other studies are underway in our laboratory to identify sets of mRNAs that are jointly regulated by specific RNA-binding proteins, such as HuR, AUF1, TIAR, TIA-1, and TTP, as we seek a more complete understanding of post-transcriptional gene regulation.
Larry Kwak received his M.D. in 1982 through an accelerated 6-year B.S.-M.D. honors program and his Ph.D. in tumor cell biology in 1984 from Northwestern University Medical School.in Chicago. He completed clinical training in internal medicine and medical oncology at Stanford University in Stanford, Calif.. Originally recruited to the Biological Response Modifiers Program at the NCI-Frederick campus in 1992, Kwak joined the Experimental Transplantation and Immunology Branch in 1996, where he is now a senior investigator.
My interest in tumor immunology, in general, and the idea that the host immune system might be harnessed to neutralize cancer cells, in particular, began as an M.D.Ph.D. student. My laboratory is now focused on the hypothesis that B-cell tumor-derived Ig idiotype can serve as a tumor-specific antigen for therapeutic vaccine development.
My work studying this specific tumor antigen began as a fellow in the laboratory of Ronald Levy, where I led the first human study of idiotype vaccination. This work suggested that antibody responses were possible. Our central hypothesis now is that sustained, potent, T-cellmediated responses, especially CD8+ T-cell responses, will be required for achieving clinical efficacy.
At the forefront of my labs current efforts is a multicenter, randomized, controlled Phase III clinical trial, designed to provide a definitive answer to the question of whether a prototype Id-KLH protein plus GM-CSF vaccine, developed in my NCI laboratory, can achieve clinical benefit in patients with follicular lymphoma.
This trial is now the subject of a Cooperative Research and Development Agreement with an industry partner. To date, more than 150 of an eventual 450 patients have been enrolled.
Central elements of my lab research program are its translational orientation and the bidirectional flow of unique materials between the clinic and the lab to study biology. As an example of this, pre- and post-vaccine T cells, tumor cells, and purified idiotype protein from vaccinated patients have been prospectively stored and will serve as source reagents for characterizing and determining the precise specificity of human idiotype- and lymphoma-specific T-cell clones in the patients.
We are now actively investigating:
The dominant and subdominant peptide epitopes derived from Ig VH and VL sequences
Evidence for epitope spreading (in this case, cross-presentation of non-idiotype lymphoma antigens) in vivo
The cellular and molecular mechanisms by which T cells kill autologous lymphoma targets
Further characterization of human T-cell responses from vaccinated patients has the potential not only to identify the precise peptide determinants recognized, but may also increase our understanding of the role of such T cells in anti-lymphoma immunity.
Another major focus of my research lab is elucidating the mechanism of action of second-generation DNA vaccines, encoding chemokine-antigen fusions, which we pioneered as a novel strategy for targeting tumor and HIV vaccine delivery. Our current results are consistent with the proposition that plasmid DNA is first taken up by cells that are not necessarily professional antigen-processing cells (APC)for example, epidermal cells.
In this pathway, the cell that takes up the DNA expresses the protein and secretes this chemokine-antigen fusion protein into the extracellular milieu, where it is then selectively taken up by professional APCs, which have the relevant chemokine receptor. Uptake of the fusion protein is therefore chemokine receptormediated.
Once the chemokine-antigen fusion protein has been internalized, antigenic determinants are then processed and subsequently presented on the surface of the APC, complexed to major histocompatibility complex molecules for presentation to T cells. In addition to targeted antigen delivery, it is also highly possible that such chemokine-antigen fusion vaccines trigger chemokine receptormediated maturation of dendritic cells, as we reported recently in Science.
We hope to develop novel second-generation idiotype vaccines and apply them clinically to other B-cell malignancies in the future. In addition to using this approach in follicular and mantle cell lymphomas, we are considering future collaborative trials in chronic lymphocytic leukemia. In collaboration with Mike Bishop, a colleague in my branch, we are already testing a novel strategy of stem cell transplant donor immunization for multiple myeloma.
Rui-Ping Xiao was trained as a cardiologist and physiologist at Tong-Ji Medical University in Wuhan, China, and the University of Maryland Medical School, Baltimore, where she earned her M.D. in 1987 and Ph.D. in 1995, respectively. She joined the Laboratory of Cardiovascular Science, NIA, in 1990 as a postdoctoral fellow. In 1996, she became the head of the Receptor Signaling Unit at LCS, where she is a senior investigator.
The scope of my research covers three intertwined programs:
b-Adrenergic receptor subtype signaling in the cardiovascular system
Modulation of cardiac excitation-contraction coupling by Ca/calmodulindependent protein kinase II (CaMKII) in normal and failing hearts
Identification and characterization of cardiovascular disease-related genes
My main scientific focus has been G-proteincoupled receptor (GPCR) signaling in the cardiovascular system. Using interdisciplinary approaches, including physiological and pharmacological techniques in conjunction with genetic manipulations (such as gene-targeted animal models and adenoviral gene transfer systems), I revealed the dual coupling of b2-adrenergic receptor (b2AR) to two functionally opposite G-protein families, Gs and Gi proteins.
This counterintuitive finding was the first demonstration that a given GPCR can couple to more than one class of G-proteins in a physiological contextsuch as in intact cardiac myocytes.
My research has demonstrated that the additional Gi coupling creates a microscopic compartmentalization of the concurrent Gs-cAMP signaling and, more importantly, dictates the opposing outcomes of bAR subtype stimulation with respect to cardiac cell survival and apoptotic cell death.
I envisioned and promoted the perception that b1AR and b2AR subtypes play distinctly differenteven opposingroles in the context of heart failure. Specifically, while b1AR is widely recognized as a "foe," b2AR might be a "friend in need" due to its concurrent anti-apoptotic effect and contractile support.
This new perception of bAR signal transduction has been increasingly appreciated in the cardiovascular research community and provides a novel rationale for new therapeutic strategies, particularly a combination of b1AR blockade with b2AR activation for improving the function of the failing heart.
The Human Genome Project has demonstrated that the GPCR family is the largest gene family in the human genome. This superfamily has also long been considered the most important target in the pharmaceutical industry. Remarkably, 70 percent of today's therapeutic agents used for the treatment of cardiovascular diseases are targeted at GPCR signaling pathways.
Thus, one of my major future goals is the identification and target validation of orphan GPCRs. These studies will not only provide novel insights into basic mechanisms of novel GPCR actions, but also reveal new rationales for ligand screens as well as clinical applications.
My research has not been limited to G-proteincoupled receptor signaling. I was also the first to characterize the role of CaMKII in regulating cardiac L-type Ca2+ currents and in the control of cardiac pacemaker activity.
Our recent in vivo and in vitro studies have shown that activation of p38 MAPK produces a potent inhibitory effect on cardiac contractility. Im also aiming my research at understanding the mechanisms underlying cardiac aging and heart failure.
Identification and characterization of cardiovascular diseaserelated genes is another new initiative of my lab. Using RNA differential display analysis of vascular smooth muscle cells from spontaneously hypertensive rats and Wistar Kyoto rats, we have identified seven novel genes:
Murine and human hyperplasia suppressor gene, HSG, (GenBank U41803-rat, AF3841-mouse, and AF03653-human)
Hyper-hemocysdine-induced gene HCY2 (AF036537)
Apoptosis-related genes: TFAR19 (AF014955); TFAR15 (AF022385); hhLIM, also known as Myogenic Factor LIM3 (AF12126).
Among our ongoing research aims is to characterize the function of the identified gene in vivo and in vitro. We also plan to develop gene-targeted mouse models to characterize the physiological and pathological functions of these genes.
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