Structural Biology and Signal Transduction Research Overview - Molecular Pathology

Research Overview - Structural Biology and Signal Transduction

Complex networks of molecules enable cells to receive signals from their environment and to modify their behavior in response to these signals. Many signals are received at the cell surface by adhesion molecules and other receptors, such as receptor tyrosine kinases and G-protein-linked receptors. Cascades of intracellular molecules then transmit the signals by influencing each other through direct binding and through modifications such as phosphorylation and proteolytic cleavage. Signals can travel from the cell surface to the nucleus (where they ultimately affect protein synthesis) or to the cytoskeleton (where they change cell shape and motility). Understanding the structure of signaling proteins and how they function together allows the design of drugs that can be used to manipulate cellular signaling networks for therapeutic purposes.

SIGNALING BY PHOSPHORYLATION: Phosphorylation of certain amino acids--such as tyrosine, serine, and threonine--is one of the main ways in which the function of proteins is regulated during signal transduction. Phosphate groups are added by kinases and removed by phosphatases. Dr. Pasquale, whose work spans both neurosciences and cancer, studies how the Eph family of receptor tyrosine kinases and their ephrin ligands impact tumor growth and angiogenesis as well as the remodeling of neuronal connections in the adult brain. Dr. Donoghue studies how mutations in the FGF family of receptor tyrosine kinases cause skeletal dwarfism syndromes as well as certain types of human cancer. Dr. Yaksh investigates the involvement of a family of serine/threonine kinases (MAP kinases) in pain caused by tissue and nerve injury or by cancer. These studies interface with the investigation of strategies for the pharmacological management of pain. Dr. Mustelin studies the role of both tyrosine kinases and tyrosine phosphatases in the physiology of T lymphocytes. His laboratory has catalogued all the tyrosine phosphatases expressed in T lymphocytes and is characterizing their involvement in the signaling steps leading to T lymphocyte activation. Dr. Dixon studies several families of protein phosphatases that play critical roles in axon guidance, cell division, cancer, and the pathogenesis of plague-causing bacteria. Dr. Feng uses conditional mouse knock out models and biochemical approaches to characterize the role of the Shp-2 tyrosine phosphatase and of several adaptor proteins that transduce signals from cell adhesion receptors and receptor tyrosine kinases to the nucleus. Dr. Walter focuses on protein phosphatase 2A, one of the most predominant serine/threonine phosphatases involved in cell cycle regulation and signal transduction. Of special interest is to determine how this phosphatase may act as a tumor suppressor.

SIGNALING BY PROTEOLYSIS: Cancer cells secrete proteases that digest the surrounding tissue allowing the cells to invade, thereby allowing the tumor to expand and cause metastasis. Inside the cell, cascades of enzymes that regulate each other by proteolysis are essential for cell death by apoptosis--a process that is often faulty in cancer cells. Dr. Strongin studies matrix metalloproteases that are present at the invasive front of migrating cells as well as tumor cells and investigates novel approaches to control the activity of these extracellular proteases. Dr. Gonias is interested in identifying and characterizing novel pathways that extracellular proteases and their cell surface receptors use to regulate cell physiology and how defects in these pathways contribute to cancer, cardiovascular disease, and Alzheimer's disease. Dr. Salvesen is an expert in a family of intracellular proteases known as caspases, which are the key regulators of the intracellular pathways leading to apoptosis. He uses information from molecular structures to design experiments aimed at gaining new insights into the physiological regulation of proteolysis.

CELL SURVIVAL AND GROWTH SIGNALS: A proper balance of cell growth and cell death shapes tissues during development and maintains them healthy in the adult. Increased ability to survive under unfavorable conditions and defects in programmed cell death (apoptosis) can promote cancer growth and resistance to chemotherapeutic drugs. Dr. Abraham investigates a variety of signaling pathways related to cell-cycle control and cancer development. His laboratory has cloned several members of a novel family of protein kinases (PI 3-kinase related kinases), which regulate cell growth and are sensitive to DNA damage. This work is leading to the identification of novel targets for anticancer drug discovery. Dr. Donoghue studies proteins that regulate the cell cycle and, therefore, the ability of cells to divide. Current studies focus on cyclin B1 and its binding partners. Dr. Johnson studies the signal transduction pathways activated in cells deprived of oxygen and their biological effects, for example in the stimulation of tumor angiogenesis. Of particular interest are the transcription factors that regulate gene expression patterns in response to hypoxia. Dr. Gottlieb is exploring programmed cell death pathways in ischemic heart disease, which may contribute to heart failure. She uses isolated rodent heart preparations and a novel peptide delivery system to elucidate cardiac responses to hypoxia and identify signaling pathways that could be perturbed to protect against cardiac cell death. Efforts to identify and characterize cardioprotective compounds are ongoing. Dr. Reed has made major contributions to our understanding of the diverse signal transduction pathways that link stimuli in the cell's environment to cell death responses. In particular, he elucidated the role of the protein Bcl-2 in the establishment of cancer chemoresistance. Efforts in Dr. Reed's laboratory aim to develop anti-cancer drugs that enhance cell death by interfering with the expression and function of relevant genes. Dr. Huang is interested in modulating signal transduction cascades that regulate programmed cell death in human disease by generating novel chemical regulators of protein biological function. A major focus has been to inhibit the function of the anti-apoptotic protein Bcl-2 in cancer by using membrane-permeable peptides and organic compounds that mimic the peptides, which were identified by computer screening techniques. Dr. Dawson uses chemical approaches to optimize the therapeutic index of compounds that trigger cancer cell death and investigates the mechanism of action of these compounds by synthesizing analogs and antagonists. A second area of interest is the design and synthesis of retinoic acid analogs that can selectively regulate the transcriptional activity of one retinoic acid receptor and not others. Such compounds can be used to selectively perturb cell morphogenesis, differentiation, or proliferation by retinoic acid in normal and cancer tissue.

SIGNALING THROUGH G PROTEINS: G protein-coupled receptors are the largest family of cell surface receptors as well as major drug targets. Dr. Insel studies signal transduction by G protein-coupled receptors in primary cultures of rodent cardiomyocytes and vascular smooth muscle cells . The Insel laboratory has discovered that signaling pathways may be determined by grouping of signaling proteins within lipid rafts in cardiomyocytes. Recently, the Insel lab has begun to investigate the crosstalk between cardiac fibroblasts and cardiac myocytes. These studies have relevance for diseases such as cardiac hypertrophy. Dr. Farquhar studies signaling by G protein-coupled receptors and receptor tyrosine kinases as well as how trafficking of these receptors to different membrane compartments in the cell affects the nature of their signals. Another long-standing interest of the Farquhar laboratory are the signaling and protein trafficking events that regulate protein filtration and absorption in the normal and diseased kidney.

CELL ADHESION SIGNALS: Dr. Ginsberg has made major contributions in characterizing a large family of cell surface adhesion receptors called integrins and their role in normal and cancer cells. Integrins bind to extracellular matrix proteins and transmit information in both directions across the plasma membrane. The Ginsberg laboratory has discovered several cytoplasmic signaling pathways that regulate the ability of integrins to bind their extracellular ligands (inside-out signaling) as well as the cytoplasmic pathways that are triggered by integrins upon cell adhesion and that regulate cell behavior (outside-in signaling). These pathways are important in cancer, inflammation, and angiogenesis. Dr. Liddington uses X-ray crystallography to study both the structure of integrins in complex with extracellular ligands and the structure of proteins that bind to the intracellular region of integrins and transmit cell adhesion signals. Dr. Shattil is interested in integrin cell adhesion receptors in platelets and how they are involved in platelet aggregation at sites of vascular injury. In particular, the laboratory studies genes regulating the binding ability of platelet integrins and the signal transduction events linking integrins to cell adhesion-dependent responses and the platelet cytoskeleton. Mutant mice are also being developed to study the mechanism of platelet involvement in hemostasis and thrombosis. Dr. Chen is a human geneticist who has created many state-of-the-art mouse models to facilitate tissue-specific knockout of target genes. Research in the Chen laboratory focuses on intracellular signaling proteins that are associated with the cytoskeleton and required for adhesion between muscle cells. Of particular interest are the regulation and signaling interactions of these proteins and their role in human diseases such as dilated cardiomyopathy.

SIGNALING TO THE NUCLEUS: Many signaling cascades originating at the cell surface reach the nucleus and affect gene expression. Dr. Karin is a leader in the field of signal transduction and gene regulation by transcription factors that have the potential of becoming oncogenic by mutation. Signal transduction cascades in normal and tumor cells are generally controlled by protein kinases and phosphatases. Dr. Karin's laboratory has characterized some of the key oncogenic protein kinases, such as Jun, Fos, and NF-kB, which function as transcription factors. Dr. Ren studies transcriptional regulatory networks controlled by developmental and oncogenic signaling pathways. In particular, he uses high throughput approaches to delineate transcriptional regulatory elements in the human genome. Another focus is the identification of altered patterns of transcriptional targets in malignant transformation. Dr. Rose investigates co-factors that positively and negatively regulate signal transduction by nuclear receptors and other classes of transcription factors. Interests of the laboratory include regulatory schemes used by cancer cells to bypass the effects of nuclear receptor antagonists used as therapeutics as well as gene expression responses in the inflamed endothelium. Microinjection allows analysis of signaling pathways at the single cell level.

PROTEIN STRUCTURE: Elucidating the structure of individual proteins and protein complexes is essential for a molecular understanding of the mechanisms of signal transduction. Dr. Liddington has characterized the atomic structure of a number of key proteins that transmit cell adhesion signals. A particular interest of the laboratory is to explain the structural basis for the binding of cell surface adhesion receptors called integrins to their extracellular ligands and how this leads to integrin conformational changes involved in signal transduction across the plasma membrane. The laboratory also studies the structure of proteins that bind to the intracellular domain of integrins and how their molecular interactions mediate intracellular signals. Dr. Hanein uses cryo-electron microscopy for the structural characterization of the large complexes of proteins that assemble at sites of cell adhesion and regulate cell growth and motility. A strategy used to build atomic models of these large macromolecular complexes is to combine the high-resolution X-ray crystallographic information available for individual proteins with the electron microscopy data from the complexes. Dr. Ely uses X-ray crystallography, nuclear magnetic resonance, circular dichroism, and molecular modeling to characterize protein-protein interactions that play a role in cell adhesion and cell death signal transduction pathways. Her aim is to define protein interaction surfaces and use them as targets for therapeutic intervention. Dr. Dixon focuses on defining the structure of phosphatases by X-ray crystallography. Dr. Wilson uses X-ray crystallography to understand the structural details of a wide variety of protein-ligand complexes. He investigates the structure of molecular assemblies found in the immune system and of cancer targets in complex with inhibitors. This allows the rational design and improvement of artificial ligands that modulate signal transduction in disease. The laboratory also studies the structure of HIV envelope proteins in complex with antibodies to help efforts towards an HIV vaccine and the structure of catalytic antibodies in complex with their antigens to understand the mechanism of enzymatic reactions mediated by antibodies.

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