Faculty Bibliography

To efficiently bud off from infected cells, HIV and other enveloped viruses hijack the host cellular machinery that is normally involved in vacuolar protein sorting and multivesicular body (MVB) biogenesis. The HIV Gag protein mimics hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs), a modular adaptor protein that links membrane cargo recognition to its degradation after delivery to MVBs. In contrast to T cells, where HIV budding occurs at the plasma membrane, virus buds into vacuoles of macrophages, a process that may facilitate its spread within the infected host

Ligation of antigen receptors (TCR, BCR) on T and B lymphocytes leads to the activation of new transcriptional programs and cell cycle progression. Antigen receptor-mediated activation of NF-kappa B, required for proliferation of B and T cells, is disrupted in T cells lacking PKC theta and in B and T cells lacking Bcl10, a caspase recruitment domain (CARD)-containing adaptor protein. CARMA1 (also called CARD11 and Bimp3), the only lymphocyte-specific member in a family of membrane-associated guanylate kinase (MAGUK) scaffolding proteins that interact with Bcl10 by way of CARD-CARD interactions, is required for TCR-induced NF-kappa B activation in Jurkat T lymphoma cells. Here we show that T cells from mice lacking CARMA1 expression were defective in recruitment of Bcl10 to clustered TCR complexes and lipid rafts, in activation of NF-kappa B, and in induction of IL-2 production. Development of CD5(+) peritoneal B cells was disrupted in these mice, as was B cell proliferation in response to both BCR and CD40 ligation. Serum immunoglobulin levels were also markedly reduced in the mutant mice. Together, these results show that CARMA1 has a central role in antigen receptor signaling that results in activation and proliferation of both B and T lymphocytes

Peripheral blood monocytes are a heterogeneous population of circulating leukocytes. Using a murine adoptive transfer system to probe monocyte homing and differentiation in vivo, we identified two functional subsets among murine blood monocytes: a short-lived CX(3)CR1(lo)CCR2(+)Gr1(+) subset that is actively recruited to inflamed tissues and a CX(3)CR1(hi)CCR2(-)Gr1(-) subset characterized by CX(3)CR1-dependent recruitment to noninflamed tissues. Both subsets have the potential to differentiate into dendritic cells in vivo. The level of CX(3)CR1 expression also defines the two major human monocyte subsets, the CD14(+)CD16(-) and CD14(lo)CD16(+) monocytes, which share phenotype and homing potential with the mouse subsets. These findings raise the potential for novel therapeutic strategies in inflammatory diseases

The chemokine receptor CXCR4 is expressed in the embryonic and mature CNS, yet its normal physiological function in neurons remains obscure. Here, we show that its cognate chemokine, stromal cell-derived factor-1 (SDF-1), promotes the survival of cultured embryonic retinal ganglion cell neurons even in the absence of other neurotrophic factors. This survival effect is mediated primarily through a cAMP-dependent pathway that acts through protein kinase A and MAP kinase. Addition of SDF-1 to a human neuronal cell line induces phosphorylation of p44/p42 MAP kinase and GSK3beta. Mouse embryos lacking the CXCR4 receptor have a reduced number of retinal ganglion cells. The ligand of CXCR4, SDF-1, may therefore provide generalized trophic support to neurons during their development and maturation

Altering the concentrations of cyclic nucleotides within nerve cells can dramatically change their responses to axonal guidance cues, but the physiological signals that might induce such alterations are unknown. Here we show that the chemokine stromal cell-derived factor 1 (SDF-1) reduces the repellent activities of slit-2 on cultured retinal ganglion cell axons, of semaphorin 3A on dorsal root ganglion sensory axons, and of semaphorin 3C on sympathetic axons. This is a modulatory effect because SDF-1 has no detectable attractive or repellent effects on retinal or DRG axons by itself. This modulation is mediated through CXCR4, the receptor of SDF-1, and a pertussis toxin-sensitive G-protein-coupled signaling pathway that induces an elevation of cAMP. The spinal cords of CXCR4 mutant mice contain hyperfasciculated and aberrantly projecting axons. These results suggest that SDF-1 plays an essential role in modulating axonal responsiveness to various known guidance cues through a cyclic nucleotide-dependent signaling pathway

We studied whether circulating activated platelets and platelet-leukocyte aggregates cause the development of atherosclerotic lesions in apolipoprotein-E-deficient (Apoe(-/-)) mice. Circulating activated platelets bound to leukocytes, preferentially monocytes, to form platelet-monocyte/leukocyte aggregates. Activated platelets and platelet-leukocyte aggregates interacted with atherosclerotic lesions. The interactions of activated platelets with monocytes and atherosclerotic arteries led to delivery of the platelet-derived chemokines CCL5 (regulated on activation, normal T cell expressed and secreted, RANTES) and CXCL4 (platelet factor 4) to the monocyte surface and endothelium of atherosclerotic arteries. The presence of activated platelets promoted leukocyte binding of vascular cell adhesion molecule-1 (VCAM-1) and increased their adhesiveness to inflamed or atherosclerotic endothelium. Injection of activated wild-type, but not P-selectin-deficient, platelets increased monocyte arrest on the surface of atherosclerotic lesions and the size of atherosclerotic lesions in Apoe(-/-) mice. Our results indicate that circulating activated platelets and platelet-leukocyte/monocyte aggregates promote formation of atherosclerotic lesions. This role of activated platelets in atherosclerosis is attributed to platelet P-selectin-mediated delivery of platelet-derived proinflammatory factors to monocytes/leukocytes and the vessel wall

T lymphocytes differentiate in discrete stages within the thymus. Immature thymocytes lacking CD4 and CD8 coreceptors differentiate into double-positive cells (CD4(+)CD8(+)), which are selected to become either CD4(+)CD8(-)helper cells or CD4(-)CD8(+) cytotoxic cells. A stage-specific transcriptional silencer regulates expression of CD4 in both immature and CD4(-)CD8(+) thymocytes. We show here that binding sites for Runt domain transcription factors are essential for CD4 silencer function at both stages, and that different Runx family members are required to fulfill unique functions at each stage. Runx1 is required for active repression in CD4(-)CD8(-) thymocytes whereas Runx3 is required for establishing epigenetic silencing in cytotoxic lineage thymocytes. Runx3-deficient cytotoxic T cells, but not helper cells, have defective responses to antigen, suggesting that Runx proteins have critical functions in lineage specification and homeostasis of CD8-lineage T lymphocytes

An intronic silencer within the CD4 gene is the critical cis regulatory element for T cell subset-specific expression of CD4. We have combined transfection studies with gene targeting in mice to identify several key sequences within the silencer core that are required for gene silencing during thymocyte development. In mice, mutations in individual sites resulted in variegated, but heritable, derepression of CD4 in mature CD8(+) T lymphocytes, whereas compound mutations resulted in full derepression. These results indicate that there is partial redundancy in recruiting a chromatin remodeling machinery that results in epigenetic silencing. Mutations in single sites also resulted in partial derepression of CD4 in immature double-negative thymocytes, but there was no apparent variegation. These findings suggest two distinct modes of CD4 silencer function at different developmental stages: active repression in CD4(-)CD8(-) thymocytes, in which silencing must be reversible, and epigenetic gene silencing upon differentiation to the CD8(+) cytotoxic T cell lineage