1993 — 1997 |
Simon, Michael A |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Molecular Genetics of Tyrosine Kinase and Ras Function
Protein Tyrosine Kinases (PTKs) are important cellular regulators whose activation can control cellular metabolism (e.g., the insulin receptor), differentiation (the CSF-1 receptor), and growth (PDGF and EGF receptors). The goal of the proposed research is to understand how PTKs have these effects on cells. We are addressing this issue by studying the action of a particular receptor PTK, the product of the sevenless gene of Drosophila melanogaster. The activation of the sevenless PTK serves as a switch that causes a single cell within each unit of the Drosophila compound eye to develop as a photoreceptor rather than as a lens-secreting cell. Our approach is to identify essential components of the sevenless signaling pathway by isolating and characterizing mutations that attenuate signaling by the sevenless PTK. These studies have led to the identification of seven genetic loci (called Enhancers of sevenless) that are candidates to encode proteins that act in sevenless signaling pathway. We have molecularly identified two of the Enhancer of sevenless genes. One, Rasl, is the Drosophila homologue of the H-ras gene of vertebrates. The other, Son of Sevenless (Sos), encodes a putative guanine nucleotide exchange factor whose role may be to activate the Rasl protein. Our subsequent studies have demonstrated that the activation of the Rasl protein can bypass the requirement for sevenless activity and have therefore suggested that the activation of the Rasl protein may be the sole essential action of the sevenless PTK. The goal of the proposed research is to further characterize the sevenless signaling pathway by: 1) molecularly characterizing additional Enhancer of sevenless genes, 2) asking whether the Sos protein is an activator of nucleotide exchange by the Rasl protein, and if so, whether Sos protein activity is regulated by the sevenless PTK, and 3) genetically identifying and molecular characterizing loci that encode components of the Rasl effector pathway. The ability of PTKs to regulate crucial cell processes suggests that an understanding of PTK signal transduction pathways will provide insight into the basic control mechanisms that regulate cell division, metabolism and differentiation. Furthermore, the well-documented involvement of PTKs and ras proteins in the etiology of cancer suggests that understanding the pathways that PTKs and ras proteins use to regulate cellular events will shed light on how inappropnate activation of these proteins can contribute to neoplastic transformation.
|
1 |
1993 — 1999 |
Simon, Michael [⬀] |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Nsf Young Investigator
9357009 Simon Protein tyrosine kinases (PTKs) are important regulatory molecules that control many aspects of cellular growth, differentiation and metabolism. This work is directed toward understanding the mechanisms by which these proteins, particularly those which span the plasma membrane and are controlled by extracellular ligands, regulate intracellular events. The PI has focused his studies on the action of a particular transmembrane PTK that is encoded by the sevenless gene of Drosphilia melanogaster. Mutations that inactivate the sevenless protein (Sev) lead to a single known defect in the fly. Seven Enhancer of sevenless loci were identified. Mutations in four of the Enhancer of sevenless loci also affect signaling by other receptor PTKs. The PI has concentrated on the analysis of these four loci in hopes that they would encode components of a general PTK signaling pathway. One locus, Ras1, encodes a ras protein. ras proteins are known to be molecular switches that control many aspects of cellular activity. How Ras1 is activated has therefore become the crucial question which will be a major focus of this work. %%% This work explores a complex signal transduction system that functions in cellular and organizational development and growth control. Since the components of this system are highly conserved during evolution, it is likely that this knowledge gained will apply to all PTK signalling systems.
|
0.915 |
1998 — 2001 |
Simon, Michael A |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Molecular Genetic of Tyrosine Kinase and Ras Function
Receptor Tyrosine Kinases (RTKs) are transmembrane proteins that transduce hormonal signals from the exterior to the interior of cells. The activation of RTKs can control many aspects of cellular metabolism, growth, and differentiation. Inadequate or inappropriate RTK signaling can result in diseases such as diabetes (inadequate insulin receptor signaling), certain forms of cancer (such as familial medullary thyroid carcinoma caused by overly active signaling by the RET RTK), and developmental abnormalities (such as Hirschsprung's disease caused by inadequate signaling by the RET RTK). The aim of the proposed research is to investigate how RTKs biochemically control cellular functions. We are addressing this issue by studying the action of a particular RTK, the product of the sevenless gene of Drosophila. We have chosen to study sevenless because of the ability to perform genetic and biochemical studies that are either difficult or impossible to conduct in vertebrate organisms. The activation of the sevenless RTK serves as a switch that causes a single cell within each subunit of the Drosophila eye to develop as a photoreceptor cell. Our approach is to identify components of the sevenless signaling pathway by characterizing mutations which attenuate sevenless signaling. We have shown that the activity of three proteins (corkscrew, daughter of sevenless and disabled) are essential for sevenless to efficiently induce photoreceptor development. Our results have shown that disabled is a probable substrate for the kinase activity of sevenless. Corkscrew encodes a protein tyrosine phosphatase which we have shown to function by dephosphorylating the daughter of sevenless protein. The goals of the proposed research are to further characterize the sevenless signaling pathway by: 1) biochemical and genetic investigations of the regulation and role of daughter of sevenless during sevenless signaling, 2) molecular characterization of further genes whose products collaborate with corkscrew and daughter of sevenless during sevenless signaling, and 3) biochemical investigation of disabled function. Since the biochemical pathways downstream of RTKs are highly conserved between flies and humans, we hope that a fuller understanding of sevenless signaling will provide the basis for understanding important aspects of human RTK signaling.
|
1 |
2000 — 2004 |
Simon, Michael A |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Cytoskeletal Regulation by Src64/Tec29 Kinases
Members of the SRC family of non-receptor protein tyrosine kinases (SFKs) play crucial roles in the regulation of cellular growth, differentiation, and morphology. Studies in vertebrates have shown that inappropriate activation of SFKs can lead to oncogenic transformation of cells, while the absence of SFKs has been associated with defects in signaling by the B and T cell antigen receptors and with defects in bone resorption (osteopetrosis). Among the important cellular consequences of altered SFK function are defects in the cellular actin cytoskeleton. The aim of the proposed research is to investigate how SFKs participate in cytoskeletal regulation. We are addressing this issue by studying the action of a particular SFK, the product of the Drosophila Src64 gene. We have chosen to study Src64 because of the ability to perform genetic studies that would be either difficult or impossible to conduct in vertebrate organisms. Our goal is to combine these genetic studies with extensive biochemical analysis in order to understand Src64 function. In our previous work, we identified mutations that inactivated the Src64 gene. We showed that the lack of Src64 function has a surprisingly specific phenotype: Src64 mutant animals are fully viable, but the females are partially sterile. Our analysis of this phenotype revealed that it is associated with defects in the morphogenesis of specialized actin cytoskeletal structures, called ring canals, that form at the cytoplasmic bridges connecting the developing oocyte and its adjacent cluster of nurse cells. We then genetically identified the Tec29 protein as a major target of SRC64 action. ThC29 is a member of a family of tyrosine kinases that includes vertebrate proteins such as Bruton's tyrosine kinase, whose absence in humans leads to X-linked agammaglobulinemia. We showed that TEC29 is essential for normal ring canal morphogenesis and is recruited to the growing ring canals in response to SRC64 activity. The goals of the proposed research are to further characterize the role of SRC64 and TBC29 in actin cytoskeletal regulation by: 1) investigating the role of SRC64 and ThC29 using domain specific mutagenesis, 2) investigating the biochemical basis for SRC64 regulation of TEC29, 3) identifying and characterizing substrates of TEC29, 4) cloning and analyzing E(Src64)2B, another potential target of SRC64, and 5) conducting further genetic screens to identify additional components of the SRC64/TEC29 pathway.
|
1 |
2004 — 2007 |
Simon, Michael A |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Cadherin Regulation of Tissue Polarity and Growth
[unreadable] DESCRIPTION (provided by applicant): Epithelial planar cell polarity (PCP) is present when the cells of a tissue are all polarized along a uniform axis lying in the plane of the epithelium. Physiologically important examples of PCP are found in many vertebrate tissues including the respiratory system, where ciliated cells must be polarized in a uniform direction for their beating to drive mucus from the lungs, and the ear, where the sensory hair cells must be polarized in a uniform direction so that their stereocilia are correctly arrayed to respond to sound. Among the most important questions regarding PCP is how individual cells sense the proper direction in which to polarize. Previous studies in Drosophila have provided a partial answer to this question by showing that cells respond to Frizzled, a transmembrane receptor protein, whose activity is present in a gradient across the tissue. However, Frizzled is not itself expressed in a graded fashion and the mechanisms used to establish the Frizzled signaling gradients are poorly understood. In a recent study of PCP in the Drosophila eye, we demonstrated that Fat, a protocadherin protein, is essential for establishing the Frizzled activity gradient that directs PCP. We also showed that Fat is regulated during this process by Dachsous (another protocadherin) and Four-jointed (a transmembrane protein). We further suggested that Fat, Dachsous and Four-jointed may form an evolutionarily conserved signaling cassette that is used to control PCP in many tissues. Fat is also a negative regulator of epithelial cell proliferation. Cells lacking Fat exhibit hyperplasic growth. Despite this critical role, little is known about the Fat regulation or function during growth control. We propose to study the role of Fat by: 1) examining the roles of graded Four-jointed, Dachsous and Fat activity in specifying the direction of PCP, 2) examining the ability of Four-jointed and Dachsous to regulate Fat during the control of cell proliferation, 3) identifying the downstream pathways used by Fat to control PCP and proliferation and 4) determining how Fat is regulated by Four-jointed and Dachsous. These experiments should yield new insights into PCP and growth control as well as into the function of protocadherins, which have been implicated in the Usher Syndrome hearing disorders and as tumor suppressors in liver and colon carcinomas. [unreadable] [unreadable]
|
1 |