John H. Kehrl, M.D.Building 10, Room 11N21410 Center DriveBethesda, MD 20892-1876Phone: 301-443-6907Fax: firstname.lastname@example.org
Chief, B-Cell Molecular Immunology Section, LIR
Extracellular signals modulate and regulate the function of cells that participate in immune responses. Some of these signals activate pathways that utilize heterotrimeric G proteins to transduce signals. The importance of chemokine receptor signaling in the orchestration and coordination of immune cell trafficking is but one example of the importance of heterotrimeric G-protein-mediated signaling in immune function. Our goals are to understand how G-protein-coupled receptors (GPCR) transduce signals to downstream effectors in immune cells, to discern the mechanisms that control these responses, and to determine the physiologic consequences of G-protein activation for lymphocyte function. To do so, we are using genetic modified mice that have disruption of key genes in the chemokine receptor signaling pathway and sophisticated imaging techniques including intravital two-photon laser scanning microscopy (TP-LSM). As an extension of these studies, we are also characterizing the functional roles of G-proteins, their regulators in a non-canonical G-protein signaling pathway, which employs alternative activators and effectors. Finally, we are investigating some aspects of the signaling pathway that triggers autophagy in macrophages. Autophagy is a process that delivers cytoplasmic constituents to autolysosomes and has been linked to both innate and adaptive immunity.
A major accomplishment of BCMIS was the identification of a family of proteins that regulate heterotrimeric G-protein signaling, which have been termed RGS proteins. RGS proteins are GTPase-activating proteins (GAPs) for Gα subunits of heterotrimeric G proteins. By shortening the duration that a Gα subunit is GTP bound, the RGS proteins curtail both Gα and Gβ µ signaling. Mice lacking various RGS proteins, as well as mice lacking specific GPCRs or other components in the GPCR signaling pathway, are currently being studied. In addition, mice with GFP knock-in to either the Rgs13 or Rgs19 locus are being characterized. These later mice have proven useful to assess the cell types in which Rgs13 and Rgs19 are expressed, as well as for imaging studies.
To facilitate our studies of chemokine receptor signaling in immune cells, we have employed intravital TP-LSM to study the interactions of lymphocytes with high endothelial venules and the lymphatic endothelium and to examine the positioning and motility of lymphocytes in various regions within the lymph node. Using both normal and gene-targeted B cells, we have shown 1) how changes in chemokine and sphingosine-1 phosphate receptor (S1PR) expression and signaling coordinate the homeostatic trafficking of B cells through lymph nodes; 2) the importance of Rgs1 and Gαi2 in regulating B-lymphocyte chemotaxis and cell motility within the lymph node; 3) the existence of efferent lymphatics close to the lymph node follicle that support B-lymphocyte lymph node egress; 4) how lymph node remodeling along with cell-intrinsic factors facilitate and coordinate the trafficking of B cells into lymph node follicles, the retention of activated B cells in germinal centers, and the egress of non-antigen-activated and effector B cells. These studies are being complemented by in vitro studies examining B-lymphocyte migration in chemotaxis chambers, as well as on endothelial cell lines. Much of the focus of the in vitro studies is to understand how Gαi and its associated Gβγ subunits trigger lymphocyte chemotaxis and migration.
Studies in model organisms uncovered a new G-protein signaling pathway, where the GPCR is replaced by an intracellular G-protein activator, which triggers Gα nucleotide exchange. One such protein, called Ric-8, has been functionally implicated in embryonic cell divisions in model organisms. A mammalian homolog also called Ric-8 exists, but little is known about its roles in mammalian cells. We are using a combination of gene silencing, gene overexpression, and FRET probes and sensors to examine the functional role of Ric-8 and Gα subunits in mammalian cell division and in lymphocyte function, which express significant levels of Ric-8A. These studies have implicated Ric-8 and Gαi in helping to orient the mitotic spindle during cell division.
TLRs play an instructive role in innate and adaptive immunity by recognizing specific molecular patterns from pathogens. Engagement of several different TLR family members triggers autophagy in macrophages. Two key molecules in the TLR signaling pathway interact with Beclin 1, an essential factor in autophagosome formation. TLR signaling enhances these interactions and reduces the known binding of Beclin 1 to Bcl-2, an inhibitor of autophagy. Both interleukin 1 and TLR signaling cause the E3 ligase Traf6 to ubiquitinate Beclin 1, which has two Traf6 binding sites. A lysine residue in Beclin 1 strategically located in the Beclin 1 BH3 domain serves as a major site for ubiquitination. A20, a known deubiquitinating enzyme, reduces Beclin ubiquitination and limits the induction of autophagy following TLR signaling. These results indicate that the status of Beclin 1 K63-linked ubiquitination plays a key role in regulating autophagy during inflammatory responses. Recently, inflammasomes have been shown to undergo ubiquitination and autophagic destruction, which can limit inflammasome mediated IL-1b secretion.
Dr. Kehrl graduated from Wayne State Medical School, completed his medical residency in internal medicine at Yale New Haven Hospital, and held fellowships in both infectious diseases and allergy-immunology in the Laboratory of Immunoregulation. Dr. Kehrl is currently a tenured senior investigator and a member of the research officers group in the Commissioned Corps of the U.S. Public Health Service. Dr. Kehrl was appointed chief of the LIR B-Cell Molecular Immunology Section (BCMIS) in 1993. Under his supervision, his laboratory has gained international recognition for its studies of human and murine B lymphocytes and the function and regulation of heterotrimeric G-protein signaling in lymphocytes and other cell types.
Chong-Shan Shi, Kathleen Harrison, Ning-Na Huang, Chung Park, Il-Young Hwang, Cedric Boularan, Olena Kamenyeva, Ali Vural, and Yolanda Williams-Bey
Shi CS, Shenderov K, Huang NN, Kabat J, Abu-Asab M, Fitzgerald KA, Sher A, Kehrl JH. Activation of autophagy by inflammatory signals limits IL-1β production by targeting ubiquitinated inflammasomes for destruction. Nat Immunol. 2012 Jan 29;13(3):255-63.
Park C, Hwang IY, Sinha RK, Kamenyeva O, Davis MD, Kehrl JH. Lymph node B lymphocyte trafficking is constrained by anatomy and highly dependent upon chemoattractant desensitization. Blood. 2012 Jan 26;119(4):978-89.
Sinha RK, Pack C, Hwang IY, Davis MD, Kehrl JH. B lymphocytes exit lymph nodes through cortical lymphatic sinusoids by a mechanism independent of sphingosine-1-phosphate-mediated chemotaxis. Immunity. 2009 Mar 20;30(3):434-46.
Cho H, Kehrl JH. Localization of Gi alpha proteins in the centrosomes and at the midbody: implication for their role in cell division. J Cell Biol. 2007 Jul 16;178(2):245-55.
Sinnarajah S, Dessauer CW, Srikumar D, Chen J, Yuen J, Yilma S, Dennis JC, Morrison EE, Vodyanoy V, Kehrl JH. RGS2 regulates signal transduction in olfactory neurons by attenuating activation of adenylyl cyclase III. Nature. 2001 Feb 22;409(6823):1051-5.
Druey KM, Blumer KJ, Kang VH, Kehrl JH. Inhibition of G-protein-mediated MAP kinase activation by a new mammalian gene family. Nature. 1996 Feb 22;379(6567):742-6.
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Last Updated September 14, 2012