During ascent to high altitude and pulmonary edema, the alveolar epithelial cells (AEC) are exposed to hypoxic conditions. Hypoxia inhibits alveolar fluid reabsorption and decreases Na,K-ATPase activity in AEC. We report here that exposure of AEC to hypoxia induced a time-dependent decrease of Na,K-ATPase activity and a parallel decrease in the number of Na,K-ATPase α1 subunits at the basolateral membrane (BLM), without changing its total cell protein abundance. These effects were reversible upon reoxygenation and specific, because the plasma membrane protein GLUT1 did not decrease in response to hypoxia. Hypoxia caused an increase in mitochondrial reactive oxygen species (ROS) levels that was inhibited by antioxidants. Antioxidants prevented the hypoxia-mediated decrease in Na,K-ATPase activity and protein abundance at the BLM. Hypoxia-treated AEC deficient in mitochondrial DNA (ρ0 cells) did not have increased levels of ROS, nor was the Na,K-ATPase activity inhibited. Na,K-ATPase α1 subunit was phosphorylated by PKC in hypoxia-treated AEC. In AEC treated with a PKC-ζ antagonist peptide or with the Na,K-ATPase α1 subunit lacking the PKC phosphorylation site (Ser-18), hypoxia failed to decrease Na,K-ATPase abundance and function. Accordingly, we provide evidence that hypoxia decreases Na,K-ATPase activity in AEC by triggering its endocytosis through mitochondrial ROS and PKC-ζ–mediated phosphorylation of the Na,K-ATPase α1 subunit.
Laura A. Dada, Navdeep S. Chandel, Karen M. Ridge, Carlos Pedemonte, Alejandro M. Bertorello, Jacob I. Sznajder
Among infectious agents, measles virus (MV) remains a scourge responsible for 1 million deaths per year and is a leading cause of childhood deaths in developing countries. Although MV infection itself is not commonly lethal, MV-induced suppression of the immune system results in a greatly increased susceptibility to opportunistic bacterial infections that are largely responsible for the morbidity and mortality associated with this disease. Despite its clinical importance, the underlying mechanisms of MV-induced immunosuppression remain unresolved. To begin to understand the basis of increased susceptibility to bacterial infections during MV infection, we inoculated transgenic mice expressing the MV receptor, CD46, with MV and Listeria monocytogenes. We found that MV-infected mice were more susceptible to infection with Listeria and that this corresponded with significantly decreased numbers of macrophages and neutrophils in the spleen and substantial defects in IFN-γ production by CD4+ T cells. The reduction in CD11b+ macrophages and IFN-γ–producing T cells was due to reduced proliferative expansion and not to enhanced apoptosis or to altered distribution of these cells between spleen, blood, and the lymphatic system. These results document that MV infection can suppress both innate and adaptive immune responses and lead to increased susceptibility to bacterial infection.
Mark K. Slifka, Dirk Homann, Antoinette Tishon, Robb Pagarigan, Michael B.A. Oldstone
We have shown that cytotoxic T lymphocytes specific for PR1, an HLA-A2–restricted nonopeptide derived from proteinase 3, kill leukemia cells and may contribute to the elimination of chronic myelogenous leukemia (CML) after treatment with IFN or allogeneic bone marrow transplant. Some patients with persistent disease also have circulating PR1-specific T cells, however, suggesting the likelihood of immune tolerance. Here we show that both high- and low-avidity PR1-specific T cells from the peripheral blood of healthy donors can be identified and selectively expanded in vitro. Although high-avidity PR1-specific T cells killed CML more effectively than low-avidity T cells, only high-avidity T cells underwent apoptosis when stimulated with high PR1 peptide concentration or when exposed to leukemia that overexpressed proteinase 3. No high-avidity PR1-specific T cells could be identified or expanded from newly diagnosed leukemia patients, whereas low-avidity T cells were readily expanded. Circulating high-avidity PR1-specific T cells were identified in IFN-sensitive patients in cytogenetic remission, however. These results provide evidence that CML shapes the host immune response and that leukemia outgrowth may result in part from leukemia-induced selective deletion of high-avidity PR1-specific T cells.
Jeffrey J. Molldrem, Peter P. Lee, Shreya Kant, Eric Wieder, Weidong Jiang, Sijie Lu, Changqing Wang, Mark M. Davis
Stat3 is the most pleiotropic member of the signal transducer and activator of transcription (STAT) family of transcription factors and mediates pivotal responses for the cytokine family. In resting cells, STATs, including Stat3, reside largely in the cytoplasm. Upon cytokine stimulation, they rapidly translocate to the nucleus, where they promote the expression of target genes. During the subsequent period of signal decay they are re-exported back to the cytoplasm in preparation for the next round of signaling. This process of nuclear export can be blocked by the fungal toxin leptomycin B (LMB). In contrast to what appears to be the case for Stat1, LMB treatment not only blocks the poststimulation export of Stat3 from the nucleus back to the cytoplasm, but also promotes the nuclear accumulation of Stat3 in resting cells. Remarkably, the LMB-dependent nuclear accumulation of Stat3 in resting cells is independent of tyrosine phosphorylation, highlighting the existence of a “basal” signaling pathway. Subsequent studies identified three nuclear export signal (NES) elements. Two of these elements, Stat3306–318 and Stat3404–414, corresponded to those recently identified in Stat1, and a third, Stat3524–535, is novel. Stat3306–318 appears to be important in the rapid nuclear export seen after stimulation (poststimulation export), whereas the Stat3404–414 and Stat3524–535 play a more important role in regulating basal nuclear export. In summary, these studies indicate that the process of Stat3 nuclear export is dependent on multiple NES elements.
Samita Bhattacharya, Christian Schindler
A pathogenic hallmark of rheumatoid arthritis (RA) is persistent activation of self-reactive CD4+ T cells. The cause of this aberrant activity remains elusive. We report here detection of autoantibodies against B7-H1, a recently described member of the B7 family, in 29% of patients with RA versus 4% of healthy donors. High-level expression of cell surface B7-H1 are found on activated human CD4+, CD8+, and CD45RO+ T cells. Immobilized autoantibodies to B7-H1 are capable of costimulating the proliferation of CD4+ T cells in vitro, and the presence of these autoantibodies correlates with active disease status. Using immobilized B7-H1 mAb’s and programmed death 1Ig, we demonstrate that engagement of B7-H1 on CD4+ T cells costimulates proliferation and secretion of IL-10, and subsequently leads to programmed cell death, accompanied with upregulated expression of TNF-related apoptosis–inducing ligand and activation of caspase-3. Taken together with our previous findings, these data indicate a bidirectional signaling role of B7-H1 in T cell costimulation and apoptosis and implicate B7-H1 autoantibodies as contributing to the progression of RA by inducing aberrant T cell responses.
Haidong Dong, Scott E. Strome, Eric L. Matteson, Kevin G. Moder, Dallas B. Flies, Gefeng Zhu, Hideto Tamura, Colin L.W. Driscoll, Lieping Chen
We have previously described the identification of Artemis, a factor involved in the nonhomologous end joining (NHEJ) phase of V(D)J recombination of T and B cell receptor genes. Null mutations of the Artemis gene result in a complete absence of T and B lymphocytes that is associated with increased cell radiosensitivity, causing the radiosensitive T–B– SCID (RS-SCID) condition. We presently report the occurrence of hypomorphic mutations of the Artemis gene in four patients from two kindreds. Partially preserved in vivo activity of Artemis is associated with the presence of polyclonal T and B lymphocyte populations, albeit in reduced numbers, along with chromosomal instability and development of EBV-associated lymphoma in two of four patients. This syndrome emphasizes the role of Artemis in the NHEJ pathway of DNA repair and suggests that other, yet ill-defined, conditions associating immunodeficiency and lymphoma could be caused by mutations in genes encoding NHEJ factors.
Despina Moshous, Christophe Pannetier, Régina de Chasseval, Françoise le Deist, Marina Cavazzana-Calvo, Serge Romana, Elizabeth Macintyre, Danielle Canioni, Nicole Brousse, Alain Fischer, Jean-Laurent Casanova, Jean-Pierre de Villartay
Christian F. Krieglstein, Wolfgang H. Cerwinka, Andrew G. Sprague, F. Stephen Laroux, Matthew B. Grisham, Victor E. Koteliansky, Norbert Senninger, D. Neil Granger, Antonin R. de Fougerolles
Valérie Dutoit, Robert N. Taub, Kyriakos P. Papadopoulos, Susan Talbot, Mary-Louise Keohan, Michelle Brehm, Sacha Gnjatic, Paul E. Harris, Brygida Bisikirska, Philippe Guillaume, Jean-Charles Cerottini, Charles S. Hesdorffer, Lloyd J. Old, Danila Valmori
Soon H. Kim, Mary M. Cleary, Howard S. Fox, David Chantry, Nora Sarvetnick
Kurt Redlich, Silvia Hayer, Romeo Ricci, Jean-Pierre David, Makiyeh Tohidast-Akrad, George Kollias, Günter Steiner, Josef S. Smolen, Erwin F. Wagner, Georg Schett