Scott Snapper Laboratory


Lab Members:

David Adamovich - webpage
Parool Meelu - webpage
Deanna Nguyen, M.D. - webpage
Lisa Westerberg, Ph.D. - webpage

Address:

Massachusetts General Hospital
Jackson
55 Fruit St.
Boston, MA 02114
Phone: 617-72
Laboratory Members Projects

Our Mission

Our laboratory is broadly interested in cell signaling pathways that regulate immune cells and epithelial cells in health and disease and the role of host: microbial cytoskeletal interactions in microbial pathogenesis.

We have focused on the Wiskott-Aldrich syndrome protein (WASP) family of signaling molecules. These proteins are expressed in the cytosol of all cell types and act as molecular scaffolds integrating incoming cell surface signals to the actin cytoskeleton. Recently, WASP-family proteins have been shown to bind to a number of signaling molecules (WIP, nck, Cdc42, profillin, PIP2) and can also bind and activate the Arp2/3 complex leading directly to actin polymerization. By regulating the actin cytoskeleton, WASP family members regulate cell movement by controlling membrane surface structures (i.e., filopodia, lamellipodia), vesicular trafficking, and apical/basal polarity. In addition, in the immune system, WASP family members are important for immune synapse formation and T-cell signaling. Interestingly, a number of infectious microbes (Salmonella, Shigella, vaccinia, EPEC) usurp the host actin cytoskeleton machinery and bind WASP family members to permit invasion of cells and movement within cells. In this context, our laboratory has been investigating the host:signaling pathways activated by enteric pathogens for their pathogenesis. Our laboratory has also shown that WASP family members play an important role in vivo in controlling mucosal immune homeostasis. WASP-deficiency in mice leads to severe inflammatory bowel disease. We are defining the role that WASP-family proteins play in regulating immune cell signaling and the contol of autoimmunity.

Elucidating the role of WASP-family members in Leukocyte Signaling and Trafficking

We are interested in signaling pathways that regulate lymphoid activation and leukocyte trafficking. We have recently focused on the WASP (Wiskott-Aldrich syndrome protein) family of proteins that integrate incoming cell surface signals to cytoskeletal changes in leukocytes and epithelial cells. Coordination of cell shape through cytoskeletal changes is required for such diverse properties as lymphocyte activation, homing as well as mucosal repair. The Wiskott-Aldrich syndrome is an X-linked primary immunodeficiency characterized by bloody diarrhea, B- and T cell immunodeficiency, lymphoreticular malignancies, and thrombocytopenia. Lymphocytes and platelets from these patients fail to proliferate and activate normally and have aberrant shapes. The protein defective in these patients (WASP) was recently discovered and is a cytoplasmic protein that when activated by Rho-family GTPases (Cdc42) and phosphoinositides directly binds to the Arp2/3 complex and drives actin assembly.

We have employed gene-targeting approaches in mice to generate a murine model of the Wiskott-Aldrich syndrome. Like human WAS patients, WASP-deficient mice are thrombocytopenic, and despite normal lymphoid development, are lymphopenic. Murine lymphocytes devoid of WASP fail to proliferate normally to antigen receptor stimulation and have abnormal cytoskeletal organization. Interestingly, the majority of WASP-deficient mice develop chronic colitis. We have recently demonstrated in vivo and in vitro that WASP-deficient dendritic cells, neutrophils and lymphocytes have marked trafficking abnormalities. Using various approaches with the aid of numerous collaborators, we are further defining hematopoietic signaling pathways regulated by WASP and to elucidate potential defects in cytoskeletal architecture and actin reorganization resulting from WASP deficiency. (Collaborators: Laboratories of Dr. Frederick Alt, Children's Hospital; Raif Geha, Children's Hospital; Dr. Ulrich Von Andrian, Center for Blood Research; and Dr. John Hartwig, Brigham & Women's Hospital).

The Role of WASP Family Members in Cytoskeletal Regulation in Health and Disease.

WASP-family proteins are known to regulate the actin cytoskeleton in all cells and likely play a role in maintaining the structural integrity and locale of epithelial cells. We have used gene-targeting approaches to define the role of N-WASP in embryonic development, intracellular signaling and cellular function. We have targeted the N-WASP gene in embryonic stem cells and have transmitted this mutation to the germline. N-WASP deficiency results in embryonic lethality at an early stage of development. We have demonstrated that this protein is essential for neural tube and cardiac development and is required for some but not all actin containing structures.

We are also employing inducible and tissue-specific gene targeting approaches using the Cre-loxP system to define the role of N-WASP specifically in lymphocytes and various epithelial tissues. We have generated ES cells and mice that have a specific targeting of N-WASP that allow for conditional/inducible deletion of the gene using the Cre-loxP system. These mice are being mated with a variety of mice expressing the Cre recombinase under the control of different promoters. These studies aim to determine in vivo the role of N-WASP in settings of health and neoplasia (Collaborators: Laboratories of Dr. Frederick Alt, Children's Hospital; Dr. John Brugge, Harvard Medical School).

The Role Of The Host-Signaling Machinery In Microbial Pathogenesis

Many intracellular pathogens utilize the host's intracellular actin-based machinery to invade cells and to move within and between cells. Many of these pathogens have surface proteins that interact and stimulate host proteins resulting in the activation of a complicated signaling cascade resulting in directed actin polymerization. Shigella, Salmonella, Listeria, and Vaccinia are examples of intracellular pathogens that depend on the host-actin cytoskeletal machinery for their pathogenicity. Recently N-WASP has been implicated in the actin-based motility of Shigella and vaccinia. We have demonstrated the absolute requirement for N-WASP, but not Cdc42, in the actin-based motility of vaccinia, Shigella, and enteropathogenic E. coli. We continue to investigate mechanistically the role of N-WASP and other host proteins in the pathogenesis of these and other pathogens (Collaborators: Laboratory of Dr. Marcia Goldberg, MGH).

Innate and Adaptive Immune Mechanisms for Regulating Mucosal Homeostasis

Crohn's disease and ulcerative colitis are chronic inflammatory disorders of the gastrointestinal tract that are associated with significant morbidity and mortality. Recent genetic models of such disorders have included those with either dysregulation of the immune system or disrupted mucosal epithelial barrier function. These models have demonstrated: the requirement of bacteria or bacterial products, the involvement of altered T cells, especially CD4+ T cells with an exaggerated Th1 response, and the role of disrupted mucosal integrity in the development of intestinal mucosal inflammation. We are characterizing the etiology of the severe colitis in WASP-KO mice. We have recently determined that unlike most models of IBD, the colitis in WASP-deficiency is associated with a Th2 cytokine profile. Lymphocytes from WASP-deficient mice are essential and sufficient to transfer IBD in RAG-2 recipient mice. We are currently addressing whether regulatory T cells are uniquely sensitive to WASP-deficiency. Finally, we are assessing the role of microbial infection in the development of chronic colitis. (Collaborator: Laboratories of Dr. Atul Bhan, MGH; Dr. Cathryn Nagler, MGH; Dr. James Fox, MIT)


Recent Publications

  • Snapper SB, Meelu P, Nguyen D, Stockton BM, Bozza P, Alt FW, Rosen FS, von Andrian UH, Klein C. WASP deficiency leads to global defects of directed leukocyte migration in vitro and in vivo. J Leukoc Biol. 2005 Jun;77(6):993-8.

  • Manchanda N, Lyubimova A, Ho HY, James MF, Gusella JF, Ramesh N, Snapper SB, Ramesh V. The NF2 tumor suppressor Merlin and the ERM proteins interact with N-WASP and regulate its actin polymerization function. J Biol Chem. 2005 Apr 1;280(13):12517-22.

  • Cotta-de-Almeida V, Schonhoff S, Shibata T, Leiter A, Snapper SB. A new method for rapidly generating gene-targeting vectors by engineering BACs through homologous recombination in bacteria. Genome Res. 2003 Sep;13(9):2190-4.

  • Shibata T, Takeshima F, Chen F, Alt FW, Snapper SB. Cdc42 facilitates invasion but not the actin-based motility of Shigella. Curr Biol. 2002 Feb 19;12(4):341-5.

Past Lab Members

  • Jose Abad
  • Vinicius Almeida, Ph.D.
  • Irun Bhan
  • Archana Kapoor, Ph.D.
  • Dilek Onaldi, M.D.
  • Tomoyuki Shibata, M.D., Ph.D.