Dynamic chromatin accessibility licenses STAT5- and STAT6-dependent innate-like function of TH9 cells to promote allergic inflammation

Allergic diseases are a major global health issue. Interleukin (IL)-9-producing helper T (TH9) cells promote allergic inflammation, yet TH9 cell effector functions are incompletely understood because their lineage instability makes them challenging to study. Here we found that resting TH9 cells produced IL-9 independently of T cell receptor (TCR) restimulation, due to STAT5- and STAT6-dependent bystander activation. This mechanism was seen in circulating cells from allergic patients and was restricted to recently activated cells. STAT5-dependent Il9/IL9 regulatory elements underwent remodeling over time, inactivating the locus. A broader 'allergic TH9' transcriptomic and epigenomic program was also unstable. In vivo, TH9 cells induced airway inflammation via TCR-independent, STAT-dependent mechanisms. In allergic patients, TH9 cell expansion was associated with responsiveness to JAK inhibitors. These findings suggest that TH9 cell instability is a negative checkpoint on bystander activation that breaks down in allergy and that JAK inhibitors should be considered for allergic patients with TH9 cell expansion.

Dynamic modulation of cortical actin at the immunological synapse controls lytic granule secretion in cytotoxic T lymphocytes

CD8+ cytotoxic T lymphocytes (CTLs) are critical for eliminating virally infected cells. Upon target recognition, CTLs reorganize their actin cytoskeleton to facilitate the polarized secretion of specialized granules containing lytic proteins that kill cells. Because a single CTL can kill multiple targets, granule secretion must be tightly regulated, ensuring only appropriate cells are killed, and preserving granules for serial killing. However, how CTLs regulate secretion remains unclear. Here, we used live confocal and TIRF microscopy to evaluate how cortical actin affects granule secretion at the membrane. While previous work has shown that clearance of actin at the synapse precedes granule secretion, we find that after granule fusion, cortical actin recovers and no further secretion is observed. Depolymerization of recovered actin led to resumed granule fusion, suggesting that recovered actin acts as a barrier to prevent further lytic granule secretion. We further show that CTLs from mice unable to secrete granules due to a Rab27a mutation that prevents granule fusion, failed to recover cortical actin at the synapse. This suggests that granule fusion itself triggers actin recovery in CTLs. Thus, cortical actin both regulates, and is regulated by, secretion. Finally, using fluorescent reporters, we correlated the clearance and recovery of actin with PIP2. PIP2 binds numerous actin regulatory proteins, suggesting phosphatidylinositol distribution in the membrane as a potential mechanism through which CTLs regulate the density of cortical actin during killing. Our work provides insight into actin-related mechanisms regulating CTL secretion that may serial killing capacity during immune responses.

The Tec family kinase Itk is required for Th9 cell differentiation (LYM8P.642)

One of the main functions of the adaptive immune system is to mount specific responses to pathogens. These effector CD4 T helper cells, include Th1, Th2, Th9 and Th17 cells, produce distinct cytokines important in the eradication of different infectious pathogens--however excessive activation of these cells can be harmful to the host, contributing to immunopathology, including autoimmunity and asthma. ITK-deficient mice exhibit reduced responses in models of allergic asthma, a disease attributed to increased Th2 responses. Polymorphisms in the Itk promoter in humans have also been linked to increased asthma incidence. Th9 cells are a recently appreciated T helper cell population that produce IL-9, a cytokine implicated in allergic asthma, responses to microbial infections, inflammatory gut diseases and autoimmunity. However, the factors contributing to IL-9 regulation are still poorly understood. We have found that ITK-deficient CD4 cells completely fail to produce IL-9 in culture. This defect is one of the most profound phenotypes we have observed for Itk-/- cells to date, and is associate with reduced levels of IRF4 during Th9 differentiation. Furthermore, in preliminary experiments, we found decreased IL-9 and IL-13 expression in vivo using a papain hypersensitivity model. Our studies demonstrate important roles for Itk in Th9 differentiation, suggesting Itk as a therapeutic candidate for treatment of diseases involving Th9-mediated inflammation.

Investigating the role of inducible T cell kinase in CD8+ T-lymphocyte cytolytic effector function (HUM8P.343)

CD8+ cytotoxic T lymphocytes (CTLs) are critical for eliminating virally infected cells, and defects in CTL responses are implicated in lymphoproliferative diseases. Patients with mutations in inducible T cell kinase (Itk), a tyrosine kinase that serves as an amplifier of T cell receptor (TCR) signaling, develop lymphoproliferative disease associated with ineffective responses against EBV, a virus that infects B cells. This phenotype is similar to X-linked lymphoproliferative syndrome, where mutations in the adaptor SAP lead to fatal EBV infections associated with specific defects in B cell cytolysis. Unlike SAP-deficient CTLs however, we found CTLs from Itk-deficient mice exhibit impaired killing of multiple targets, suggesting Itk-deficiency leads to global defects in cytolysis. Killing by CTLs begins when TCR signaling triggers adherence to targets, centrosome polarization, and release of secretory granules inducing cytolysis of targets. Although early events such as adhesion, actin ring formation, and polarization of lytic machinery were intact in Itk-deficient murine CTLs, we found defects in granule secretion suggesting Itk may play an unappreciated role in the final stages of killing. Exploration of the role of Itk in CTL function may provide new insight into the contribution of early TCR signaling to late stages of cytolysis, and why mutations in Itk lead to lymphoproliferative diseases.

Cross-talk between T cell receptor and cytokine signaling is mediated by Itk: implications for the balance between Th17 and regulatory T cells (P1141)

A proper balance between Th17 and T regulatory cells (Tregs) is critical for the generation of immune protective immune responses while minimizing autoimmunity. We show that the Tec family kinase Itk influences the balance between Th17 and T regulatory cells by regulating crosstalk between T Cell Receptor (TCR) and cytokine signaling. Under both Th17 and Tregs differentiation conditions, Itk-/- CD4 T cells develop higher percentages of functional Foxp3+ cells, associated with increased responsiveness to IL-2. Itk-deficient CD4 cells show reduced TCR-induced phosphorylation of mTOR targets, including ribosomal S6 and AKT, accompanied by changes in metabolic signatures that are affected by mTOR pathways. Surprisingly, iTreg Itk-/- cells also show reduced IL-2-induced mTOR pathways, despite increased STAT5 phosphorylation. We find that TCR stimulation in WT CD4+ T cells leads to a dose-dependent repression of expression of Pten; however, at low TCR stimulation or in the absence of Itk, Pten is not effectively repressed, thereby uncoupling STAT5 phosphorylation and PI3K/mTOR pathways and increasing Foxp3 expression. Functional studies show that naïve Itk-/- CD4 T cells also preferentially develop into Tregs in an in vivo colitis model. Furthermore Itk-deficient Tregs are capable to inhibit the development of colitis demonstrating that Treg function is independent of Itk. Our results suggest that Itk is a potential target for altering the balance between Th17 and Treg cells.

Ly108 enhances PLZF expression in developing thymocytes (P4452)

Promyelocytic zinc finger transcription factor (PLZF) is an important transcription factor expressed by natural killer T (NKT) cells and a variety of other innate T cells. Development of these PLZF positive cells require the adaptor molecule SLAM- associated protein (SAP) and the interaction of the signaling lymphocyte activation molecule (SLAM) family member receptors in addition to TCR stimulation. However, it remains unclear how these interactions influence the development of innate thymocytes. We have found that costimulation of pre-selection double positive (PS-DP) thymocytes with an agonist to the SLAM family receptor Ly108 greatly enhances PLZF expression compared to TCR stimulation alone. Furthermore, PLZF expressing cells were reduced in Ly108 deficient mice and increased in transgenic mice expressing a hyperactive Ly108 isoform. Costimulaiton with Ly108 also increased the expression of Egr-2 and the binding of Egr-2 to the PLZF (Zbtb16) promoter. Surprisingly costimulation with CD28 was unable to enhance Egr-2 nor PLZF expression in vitro suggesting that Ly108 has a unique role in PLZF expression. This work provides a novel mechanism by which innate thymocyte development is regulated via Ly108 and possibly other SLAM family receptor interactions.

Cellular and molecular profiling of CD8 T cell differentiation with respect to positive and negative selection in vitro reveals a role for Notch signaling (111.45)

Differentiation of functionally mature CD8 single positive (SP) T cells is predicated by the ability of lymphocyte progenitors to integrate multiple signaling cues provided by the thymic microenvironment. In thymus, signaling through Notch receptors directs T cell progenitors to commit to the T cell lineage, undergo early T cell differentiation, and progress to the CD4+CD8+ (DP) stage of T cell development. However, it is still unclear whether Notch signals are prerequisite for differentiation or commitment of DP cells to CD8 SP stage of T cell development. Here, we demonstrate that ectopic expression of the Notch-ligand by OP9 stromal cells allows for efficient differentiation of conventional effector CD8 T cells from SAP-/- bone marrow (BM)-derived hematopoietic stem cells (HSCs). We also prove that OP9-DL1 stromal cells restrict differentiation of innate CD8 T cells but allow for differentiation of IL17-producing CD8 T cells from BM-HSCs isolated from Itk-/-Rlk-/- (DKO) mice. We further reveal that the process of positive and negative selection in vitro is constrained by peptide-MHC (pMHC) class I expressed by the OP9 stromal cells. Finally, using a T cell receptor (TCR) transgenic model we disclose that the commitment of DP precursors to the CD8 T cell lineage is facilitated by Notch signaling. Our findings further establish the requirement for Notch receptor-ligand interactions throughout intrathymic T cell differentiation.

Investigating signaling downstream of SLAM family members CD84 and Ly108 in thymocytes and activated T cells (99.4)

The SLAM family consists of 6 immunoregulatory receptors including CD84 and Ly108. SLAM receptors are expressed on T, B, NKT cells, DCs and macrophages and are self ligands that have intracellular binding sites for the adaptor molecule SAP. SAP recruits and activates the FynT kinase, resulting in signaling leading to cytokine production, cytotoxicity, enhanced cellular interactions and thereby immune regulation. Defective SAP expression is associated with the disease XLP, characterized by dysregulated hyperimmune response to EBV infection and impaired humoral responses. Both CD84 and Ly108 are highly expressed on developing thymocytes and activated T cells, including Tfh cells, which are important for germinal center responses. We have found that CD84 affects GC formation and that CD84 and Ly108 participate in T:B cell interactions. SAP and Ly108 signaling is also implicated in development of innate T cells, like NKTs. We find that Ly108 phosphorylation varies in different genotypes of mice. While thymi of SAP-/- mice, that lack NKT cells, demonstrate reduced pLy108, thymi from Itk-/- mice that develop increased numbers of innate T cells, demonstrate increased pLy108. As development of this increased innate T cell population in Itk-/- mice requires SAP, we hypothesize that SAP-associated Ly108 may be contributing to their development. We are further characterizing biochemical and cellular properties of these receptors, given their roles in these important T cell lineages.

Humoral responses require a multi-stage T:B lymphocyte interaction process (99.5)

X-linked lymphoproliferative (XLP) disease is an immune disorder caused by mutations encoding SLAM-associated protein (SAP, Sh2d1a), an adaptor that facilitates Fyn recruitment to SLAM family of receptors, including 2B4, Ly9, SLAM, CD84 and Ly108. SAP-/- CD4 T cells exhibit a selective impairment in adhesion to antigen presenting B cells but not dendritic cells (DC), resulting in defective germinal centre (GC) formation. However, the nature of this selective adhesion defect is unclear. We provide evidence that while T:DC interactions are primarily integrin-dependent, T:B cell interactions have an early integrin-dependent component and a sustained phase that also requires SAP. We further demonstrate that T cells adhere to the SLAM family members, CD84 and Ly108, in a SAP-dependent manner. Both CD84 and Ly108 are highly expressed on T follicular helper (TFH) cells, a specialized subset of CD4 T cells that reside within GCs and are critical for their formation. Cd84-/- mice exhibit a partial defect in GC responses to T-dependent antigens. This defect correlated with impaired cognate T:B cell conjugate pairing observed in vivo by dynamic imaging as well as reduced TFH cell differentiation and function. Strikingly, the combined loss of CD84 and Ly108 markedly reduced T:B conjugate pairing in vitro. Thus, our results identify SLAM family members as critical receptors involved in the dynamic regulation of sustained T:B cell interactions.

Partial rescue of Itk-/- iNKT cell development by Txk/Rlk reveals a unique role for Itk in the survival of iNKT cells. (50.40)

Invariant natural killer T (iNKT) cells are a distinct population of innate T lymphocytes that play important role in the immune response. Itk and Txk/Rlk are Tec family kinases that are expressed in iNKT cells, with the expression level of Itk about 7-fold higher than that of Txk. It has been reported that the Itk null mice have reduced iNKT cell frequency and numbers, as well as defects in iNKT cell development and cytokine secretion, all of which are exacerbated in the Itk/Txk DKO mice. By contrast, the phenotype of iNKT cells in Txk null mice is similar to that from WT mice. In order to determine whether Itk and Txk plays distinct roles in iNKT cell development and function, we examined the iNKT cells in Tg(Lck-Txk)/Itk-/- mice, which over express Txk in T cells to the similar level as Itk. Over expression of Txk rescues the maturation and cytokine secretion of iNKT cells in Itk null mice. It also rescues the altered expression of transcription factor T-bet, eomesodermin and PLZF. By contrast, over expression of Txk does not rescue the reduced iNKT cell numbers in Itk null mice, which is due to the failure to rescue the increased apoptosis observed in Itk-/- iNKT cells. These data suggest that Txk plays an overlapping role with Itk in iNKT cell development and function, but that Itk also has a unique function in the survival of iNKT cells.

SLAM-associated protein (SAP)-deficiency impedes the function of T follicular helper cells in germinal center formation (99.3)

Mutations affecting SAP lead to XLP, an immune disorder with impaired antibody responses. SAP-/- mice show defective formation of germinal centers (GC), due to a defect in T:B cell interactions. T follicular helper cells (Tfh) are important for providing help to B cells and GC formation. To investigate the role of SAP in Tfh cells for GC formation, we have developed a modified protocol to generate “Tfh-like” cells in vitro, resulting in IL-21 producing cells with elevated expression of hallmark Tfh markers CXCR5, ICOS, PD-1, BTLA, and SLAM family receptors CD84 and Ly108, along with enhanced levels of Bcl6 transcripts. Cell transfer of control Tfh-like cells into SAP-/- hosts can rescue GC formation upon immunization significantly better than polarized Th1, Th2 or Th17 cells, suggesting these cells act as functional Tfh cells in vivo. In vitro differentiation of SAP-/- cells is similar to control cells, yet, upon cell transfer, SAP-/- Tfh-like cells are unable to support GC formation. Interestingly, differentiation of Tfh-like cells is not terminal, as they can be repolarized to produce other distinct Th cell cytokines. Similarly, other Th cell populations can be repolarized to Tfh-like cells. Analyses of epigenetic modifications of transcription factors also supports plasticity between these Th cell lineages. These findings provide further insight into Tfh cell biology and suggest that SAP is critical for Tfh cell function in GC formation and immune homeostasis.

Differential expression of IL-17A and IL-17F is coupled to TCR signaling via Itk-mediated regulation of NFATc1 (139.4)

Th17 CD4+ effector T cells play important roles in autoimmunity and responses to bacterial infections. The roles of cytokines in regulating the transcription factors STAT3 and RORγT in Th17 differentiation have been extensively studied. However, the role of T cell receptor (TCR) signaling in Th17 differentiation is less appreciated. To examine this issue, we evaluated IL17 production from T cells lacking Itk, a tyrosine kinase required for full TCR-induced activation of PLC-γ and downstream pathways. We find that Itk-/- CD4+T cells exhibit specific defects in the expression of IL-17A despite relatively normal expression of RORγT, RORα and the other Th17 cytokines, including the closely related IL-17F. Defects in IL-17A expression and differential regulation of IL-17A and IL-17F were also observed in vivo in Itk-/- mice challenged with an allergic asthma model. Although Itk-deficient cells have slightly depressed phosphorylation of STAT-3 in response to IL-6, expression of constitutively activated STAT-3 failed to rescue their IL-17A production. In contrast, expression of IL-17A could be rescued by pharmacologically-induced Ca2+ influx or by a constitutively active NFATc1. The effects of Itk on transcriptional complexes and chromatin at the IL-17 locus are under further investigation. Our results suggest that Itk specifically couples TCR signaling strength to IL-17A expression through NFATc1 and that TCR signaling pathways differentially influence Th17 cytokine production.

Transcriptional regulation of innate αβ CD8+ T cell development in Itk deficient mice (36.35)

Inducible T cell kinase (Itk) deficient mice develop a large population of αβ CD8+ innate-like T cells that possess a memory-like phenotype and are dependent on IL-15. Similar to other innate T cell lineages, these cells are positively selected by hematopoietic cells instead of thymic stroma in a SAP dependent manner that involves the interaction of signaling activation molecule (SLAM) family members. While much work has been done to characterize these cells, very little is known about the molecular pathways that prevent (Wt) or initiate (Itk-/-) the expansion of innate CD8+ T cells. One clue came from work examining mice with a T-cell specific deletion of CREB binding protein (CBP) driven from the Lck proximal promoter. These mice revealed a similar expansion of CD8 T cells with an innate phenotype. CBP is a transcriptional co-activator, which possesses histone acetyl transferase (HAT) activity and is known to associate with a wide range of transcription factors, most notably the cAMP response element binding protein (CREB). We find that TCR stimulation induces robust phosphorylation of CREB that is impaired in Itk-deficient T cells. We are currently further evaluating how Itk-deficiency affects CREB/CBP activation, and the impact of these pathways on transcriptional programs leading to innate T cell development.

Antigen-specific responses and ANA production in B6.Sle1b mice: a role for SAP

B6.Sle1b mice, which contain the Sle1b gene interval derived from lupus prone NZM2410 mice on a C57BL/6 background, present with gender-biased, highly penetrant anti-nuclear antibody (ANA) production. To obtain some insight into the possible induction mechanism of autoantibodies in these mice we compared antigen-specific T dependent (TD) and T independent (TI-II) responses between B6.Sle1b and B6 mice before the development of high ANA titers. Our results show that B6.Sle1b mice mount enhanced responses to a TI-II antigen. Additionally, the memory T cell response generated by a TD antigen also increased. This enhancement correlates with the greater ability of B cells from B6.Sle1b mice to present antigen to T cells. The SLAM Associated Protein (SAP) is critical for signaling of many of the molecules encoded by the SLAM/CD2 gene cluster, candidates for mediating the Sle1b phenotype; therefore, we also investigated the effect of sap deletion in these strains on the TD and TI-II responses as well as on ANA production. The results of these studies of responses to non-self-antigens provide further insight into the mechanism by which responses to self-antigens might be initiated in the context of specific genetic alterations.

Cytohesin binder and regulator (cybr) is not essential for T- and dendritic-cell activation and differentiation

Cybr (also known as Cytip, CASP, and PSCDBP) is an interleukin-12-induced gene expressed exclusively in hematopoietic cells and tissues that associates with Arf guanine nucleotide exchange factors known as cytohesins. Cybr levels are dynamically regulated during T-cell development in the thymus and upon activation of peripheral T cells. In addition, Cybr is induced in activated dendritic cells and has been reported to regulate dendritic cell (DC)-T-cell adhesion. Here we report the generation and characterization of Cybr-deficient mice. Despite the selective expression in hematopoietic cells, there was no intrinsic defect in T- or B-cell development or function in Cybr-deficient mice. The adoptive transfer of Cybr-deficient DCs showed that they migrated efficiently and stimulated proliferation and cytokine production by T cells in vivo. However, competitive stem cell repopulation experiments showed a defect in the abilities of Cybr-deficient T cells to develop in the presence of wild-type precursors. These data suggest that Cybr is not absolutely required for hematopoietic cell development or function, but stem cells lacking Cybr are at a developmental disadvantage compared to wild-type cells. Collectively, these data demonstrate that despite its selective expression in hematopoietic cells, the role of Cybr is limited or largely redundant. Previous in vitro studies using overexpression or short interfering RNA inhibition of the levels of Cybr protein appear to have overestimated its immunological role.

B cell induction of IL-13 expression in NK cells: role of CD244 and SLAM-associated protein

NK cells are an important component of the innate immune system that can also interact with B cells in a mutually productive manner. We have previously shown that activated B cells can induce NK cells to up-regulate their secretion of IFN-gamma. In this study, we show that B cells, and, particularly, marginal zone B cells, can, in addition, induce NK cells via direct cell-cell interactions to express mRNA encoding the Th2 cytokine IL-13. The induction of NK cell IL-13 mRNA expression requires the ligation of the CD244 receptor by the CD48 ligand on B cells via signaling pathways that depend upon expression of the X-linked lymphoproliferative disease gene product, SH2D1A/DSHP/SAP (SLAM-associated protein, or SAP) in NK cells. Thus, the positive signals attributed to the B cell activation of CD244 on murine NK cells appears to be more similar to the activity of CD244 on human cells. The induction of IL-13 mRNA by B cells may account for the effect of NK cells on the generation of Th2-type responses in the presence of some adjuvants.

Enhanced levels of Staphylococcus aureus stress protein GroEL and DnaK homologs early in infection of human epithelial cells

Antibodies to Staphylococcus aureus heat shock proteins (Hsps) are present in the sera of patients with S. aureus endocarditis (M. W. Qoronfleh, W. Weraarchakul, and B. J. Wilkinson, Infect. Immun. 61:1567-1570, 1993). Although these proteins are immunogenic, their role in infection has not been established. We developed a cell culture system as a model to examine the potential involvement of staphylococcal Hsps in the initial events of infection. This study supports a model in which a clinical endocarditis isolate responds to host cell signals by selectively regulating the synthesis of numerous proteins, including the stress proteins Hsp60 (GroEL homolog) and Hsp70 (DnaK homolog) and a unique 58-kDa protein.

Immune responses in mice deficient in Ly-GDI, a lymphoid-specific regulator of Rho GTPases

Ly-GDI (lymphoid-specific guanosine diphosphate (GDP) dissociation inhibitor), also called D4-GDI, is preferentially expressed in hematopoietic tissues including bone marrow, thymus, spleen and lymph nodes. It binds to the small guanosine triphosphate (GTP)-binding protein Rho and inhibits GDP dissociation from Rho proteins. To explore the function of Ly-GDI in lymphocytes, we have generated Ly-GDI-deficient mice by gene targeting. These mice showed no striking abnormalities of lymphoid development or thymocyte selection. The mice also exhibited, for the most part, normal immune responses including lymphocyte proliferation, IL-2 production, cytotoxic T lymphocyte activity, antibody production, antigen processing and presentation, immune cell aggregation and migration, and protection against an intracellular protozoan. However, Ly-GDI-deficient mice exhibited deregulated T and B cell interactions after in vitro cultivation of mixed lymphocyte populations in concanavalin A (Con A) leading to overexpansion of B lymphocytes. Further studies revealed that Ly-GDI deficiency decreased IL-2 withdrawal apoptosis of lymph node cells while dexamethasone- and T cell receptor-induced apoptosis remained intact. These data implicate the regulation of the Rho GTPase by Ly-GDI in lymphocyte survival and responsiveness, but suggest that these functions may be partially complemented by other Rho regulatory proteins when the Ly-GDI protein is deficient.

A randomized controlled trial of salmon calcitonin to prevent bone loss in corticosteroid-treated temporal arteritis and polymyalgia rheumatica

Patients treated with high-dose or long-term corticosteroids are at risk of accelerated osteoporosis and spontaneous vertebral and traumatic fractures. To assess the efficacy of salmon calcitonin in preventing corticosteroid- induced osteoporosis, 48 patients with newly diagnosed polymyalgia rheumatica, temporal arteritis, and other vasculitides were enrolled in a 2-year, double-blind, randomized, controlled trial. Patients were randomized to receive subcutaneous injections t.i.w. of either 100 IU of salmon calcitonin (25 patients) or placebo (23 patients). After 2 years, 19 and 21 patients, respectively, were evaluable. All patients also received supplemental calcium carbonate (1500 mg daily in divided doses) and vitamin D3 (400 IU daily). Baseline and serial radiologic assessments included dual-energy X-ray absorptiometry (DXA) of the lumbar spine and hip, and spine radiographs to detect vertebral fractures. There were no significant baseline differences between the two study groups. The mean within-subject percentage change in DXA lumbar spine density in the two groups over the 2-year period of the study was only -0.1% (calcitonin plus calcium) versus -0.2% (placebo plus calcium) a nonsignificant difference despite the high mean cumulative corticosteroid doses of 5371 mg and 4680 mg, respectively (NS). The incidence of vertebral fracture was 12.5% (calcitonin plus calcium: 11%, versus placebo plus calcium: 14%, NS), with four fractures in the first year and one fracture in the second year. Higher cumulative cortico-steroid dose was associated with a greater loss in bone density. In rheumatic disease patients starting high-dose, long-term corticosteroids, salmon calcitonin with calcium and vitamin D3 provided no greater bone preservation than that observed with calcium and vitamin D3 alone.

Clinical reproducibility of dual energy x-ray absorptiometry

Dual energy x-ray absorptiometry is a technique advocated for the measurement of bone mass throughout the skeleton, and recently it has been used to measure changes in periprosthetic bone mass after joint replacement. The accuracy and precision of the method in clinical patient populations have not been firmly established. This study sought to establish the short-term reproducibility of measurements made with dual energy x-ray absorptiometry of multiple sites in a large sample of elderly patients with rheumatic disease. Reproducibility was assessed in the lumbar spine and in three femoral sites in 69 patients participating in a longitudinal clinical trial. In each patient, absorptiometry was performed twice in the same day at as many as five time points over a 2-year period. The mean (+/- SD) baseline bone density was 0.783 +/- 0.128 g/cm2 for the femoral neck and 1.015 +/- 0.218 g/cm2 for the lumbar spine. The correlations between the duplicate baseline measurements of the spine were excellent (r = 0.9936, p < 0.001) and were stable over the 2-year period; the mean difference between the duplicate baseline measurements was 1.82 +/- 1.54% and the mean coefficient of variation was 1.29%. Measurements in the femur were much less precise; these values were 3.61 +/- 3.14% and 2.55% in the femoral neck, 3.66 +/- 4.35% and 2.59% in the greater trochanter, and 5.28 +/- 5.61% and 3.73% in Ward's triangle. This study evaluated the short-term reproducibility of dual energy x-ray absorptiometry in a clinical population.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of mutations in the integration function of Moloney murine leukemia virus: effects on DNA binding and cutting

The 3' terminus of the pol gene of Moloney murine leukemia virus encodes the integration (IN) protein, required for the establishment of the integrated provirus. A series of six linker insertion mutations and two single-base substitutions were generated within the region encoding the IN protein. Mutations were initially generated within an Escherichia coli plasmid expressing the IN protein, and the resulting variants were assayed for DNA-binding activity. Mutations which altered conserved cysteine residues within a potential DNA finger-binding motif resulted in lower or variable DNA binding, which appeared to be the result of variable protein folding. Upon renaturation, these proteins were able to nonspecifically bind DNA in a manner similar to that of the other mutant IN proteins and the parent. When reconstructed back into full-length virus, seven of the eight mutations were lethal. All mutants produced a stable IN protein in virions and mediated normal conversion of the retroviral RNA to its three DNA forms. Fine-structure analysis of the linear double-stranded viral DNA indicated that all seven lethal alterations within the IN protein blocked the formation of the 3' recessed termini that normally precedes integration.

Null mutations in the SNF3 gene of Saccharomyces cerevisiae cause a different phenotype than do previously isolated missense mutations

Missense mutations in the SNF3 gene of Saccharomyces cerevisiae were previously found to cause defects in both glucose repression and derepression of the SUC2 (invertase) gene. In addition, the growth properties of snf3 mutants suggested that they were defective in uptake of glucose and fructose. We have cloned the SNF3 gene by complementation and demonstrated linkage of the cloned DNA to the chromosomal SNF3 locus. The gene encodes a 3-kilobase poly(A)-containing RNA, which was fivefold more abundant in cells deprived of glucose. The SNF3 gene was disrupted at its chromosomal locus by several methods to create null mutations. Disruption resulted in growth phenotypes consistent with a defect in glucose uptake. Surprisingly, gene disruption did not cause aberrant regulation of SUC2 expression. We discuss possible mechanisms by which abnormal SNF3 gene products encoded by missense alleles could perturb regulatory functions.

Point mutations in the P30 domain of the gag gene of Moloney murine leukemia virus

A series of point mutations in the P30 domain of the Moloney murine leukemia virus gag gene was generated by bisulfite treatment of heteroduplex DNAs containing a single-stranded region in the gag gene. One virus bearing such a mutation exhibited a coordinate defect in gag and pol function, and was similar to previously described deletion mutants with alterations in this gene. One mutant virus displayed a different phenotype: it could assemble virion particles and provide pol function, but the particles were defective in the early stages of infection. The continued concordance of the mutants' failure or ability to both assemble virions and provide pol lends further support to the proposal that similar parts of the gag gene are required for these two processes.

Construction and analysis of deletion mutations in the pol gene of Moloney murine leukemia virus: a new viral function required for productive infection

We have used in vitro mutagenesis to explore the functions of the gene products encoded by the pol gene of Moloney murine leukemia virus (M-MuLV). Deletions were constructed at a variety of positions in the gene, and the altered DNA copies of the viral genome were introduced into mouse cells by cotransformation. The mutants could be divided into two classes depending on the phenotype and map position of the deletion within the pol gene. Mutants with deletions mapping in the 5' portion of the gene were found to be completely deficient in reverse transcriptase activity. Mutants mapping in the 3' portion of the gene, however, assembled and released virions with normal levels of reverse transcriptase and RNAase H activities. When applied to permissive cells, these virions directed the synthesis of all three forms of unintegrated viral DNA: full-length, double-stranded linear DNA and the two circular forms with one and two copies of the long terminal repeat sequences. The infection was arrested at this point and the infected cells did not become producers of virus. Thus the 3' portion of the pol gene encodes a polypeptide with a function distinct from that of reverse transcriptase, which is not required for synthesis of viral DNA but is essential for establishment of that DNA in a stable, active form in the infected cell. We suggest that this function may be the integration of the proviral DNA.

Mutations in the gag gene of Moloney murine leukemia virus: effects on production of virions and reverse transcriptase

We have constructed a series of deletion mutations in the p30 and p10 domains of the gag gene of Moloney murine leukemia virus. Mutants with deletions in P30 were completely defective in virion particle production even though an altered gag precursor protein is synthesized. This domain is apparently critical for particle formation. A mutant in P10 was able to release virion particles into the medium, and low levels of reverse transcriptase activity could be detected in these virions. To explore the effects of these mutations on the utilization of the gag-pol precursor, we have introduced these mutants into cells already releasing defective particles from an endogenous provirus which directs the synthesis of gag gene products and not pol gene products. The P10 mutant was capable of providing pol function as judged by the incorporation of high levels of reverse transcriptase into the particles and complete complementation for XC plaque formation. In contrast, the mutants in P30 were negative in this complementation test. Thus, those gag mutants which were unable on their own to assemble virion particles were also unable to contribute the gag-pol precursor to these particles. These mutations are the first to be mapped to the gag region which affect pol function, suggesting that the gag-pol precursor must be assembled before pol is functionally separated from the gag domain. The concordance of the effects of different mutations on both particle formation and gag-pol utilization suggests that similar domains of gag (namely, domains in the P30 region) are needed for these two processes.

Deletion mutants of Moloney murine leukemia virus which lack glycosylated gag protein are replication competent

A series of deletion mutations localized near the 5' end of the Moloney murine leukemia virus genome was generated by site-specific mutagenesis of cloned viral DNA. The mutants recovered from such deleted DNAs failed to synthesize the normal glycosylated gag protein gPr80gag. Two of the mutants made no detectable protein, and a third mutant, containing a 66-base pair deletion, synthesized an altered gag protein which was not glycosylated. All the mutants made normal amounts of the internal Pr65gag protein. The viruses were XC positive and replicated normally in NIH/3T3 cells as well as in lymphoid cell lines. These results indicate that the additional peptides of the glycosylated gag protein are encoded near the 5' end, that the glycosylated and internal gag proteins are synthesized independently, and that the glycosylated gag protein is not required during the normal replication cycle. In addition, the region deleted in these mutants apparently encodes no cis-acting function needed for replication. Thus, all essential sequences, including those for packaging viral RNA, must lie outside this area.