Islam Khan

Apoptosis Regulators Bim and Fas Function Concurrently to Control Autoimmunity and CD8+ T Cell Contraction

Throughout most of adult life, lymphocyte number remains constant because of a balance of proliferation and apoptosis. Mutation of Bim, a proapoptotic protein in the intrinsic death pathway, or Fas, a tumor necrosis factor receptor (TNFR) superfamily member of the extrinsic pathway, results in late-onset autoimmunity and increased antigen-specific CD8(+) T cell responses during viral infection. However, virus-specific immune responses eventually return to amounts comparable to those for nonmutant mice. Here, we show that loss of both Bim and Fas function resulted in a synergistic disruption of lymphoid homeostasis, rapid-onset autoimmunity, and organ-specific blocks on contraction of antiviral immune responses. When lymphocytic choriomeningitis virus (LCMV)-specific immune responses were quantitated, double-mutant mice had 100-fold more antigen-specific memory CD8(+) T cells in their lymph nodes than wild-type mice. Our results demonstrate that multiple death pathways function concurrently to prevent autoimmunity and downsize T cell responses.

Deficient type I protein kinase A isozyme activity in systemic lupus erythematosus T lymphocytes.

Systemic lupus erythematosus (SLE) is an autoimmune disorder of indeterminate etiology characterized by a dysfunctional cellular immune response. We have previously identified a metabolic disorder of the adenylate cyclase/cAMP/protein kinase A (AC/cAMP/PKA) pathway characterized by impaired cAMP-inducible, PKA-catalyzed protein phosphorylation in intact T lymphocytes from subjects with severe SLE disease activity. Because this metabolic disorder may contribute to abnormal T cell immune effector functions, we tested the hypothesis that impaired PKA-dependent protein phosphorylation is the result of a PKA isozyme deficiency in SLE T lymphocytes. Compared with healthy and rheumatoid arthritis (RA) controls, subjects with severe SLE activity exhibited reduced PKA-catalyzed phosphorylation of proteins in the T lymphocyte plasma membrane where the type I isozyme of PKA (PKA-I) is predominantly localized. Both silver staining and biosynthetic labeling of membrane-associated proteins with [35S]methionine demonstrated that reduced protein phosphorylation was not due to either an altered distribution of or absence of proteins. Moreover, phosphorylation of SLE membrane-associated proteins with the PKA catalytic (C) subunit showed a similar distribution and extent of phosphorylation compared with membrane proteins from healthy T cells, suggesting that SLE T cell membrane proteins could be phosphorylated. Sequential column chromatography of the type I and type II isozymes of PKA (PKA-I, PKA-II) demonstrated a deficiency of PKA-I isozyme activity. Compared with a ratio of PKA-I to PKA-II activity of 4.2:1 in healthy T cells, the activity ratio in T cells from subjects with severe SLE disease activity was 0.99:1 (P = 0.01, SLE versus healthy controls for PKA-I). The deficient PKA-I activity was associated with a significant increase of free C-subunit activity (P = 0.04, SLE versus healthy controls for C-subunit). T cells from subjects with mild/moderate SLE disease activity also exhibited diminished PKA-I activity, yielding a ratio of PKA-I to PKA-II activity of 2.4:1. By contrast, T cells from RA controls possessed increased PKA-I, PKA-II, and free C-subunit activities compared with healthy controls, resulting in a ratio of PKA-I to PKA-II activity of 3.6:1. We conclude that the reduced PKA-catalyzed protein phosphorylation in the plasma membrane of SLE T cells is the result of deficient PKA-I isozyme activity. This is the first identification of a deficiency of PKA activity in SLE T lymphocytes; the deficiency, resulting in diminished protein phosphorylation, may alter cellular homeostasis, contributing to the cellular immune dysfunctions observed in SLE.

Protein Kinase A RIβ Subunit Deficiency in Lupus T Lymphocytes: Bypassing a Block in RIβ Translation Reconstitutes Protein Kinase A Activity and Augments IL-2 Production

A profound deficiency of type I protein kinase A (PKA-I or RIα/β2C2) phosphotransferase activity occurs in the T lymphocytes of 80% of subjects with systemic lupus erythematosus (SLE), an autoimmune disorder of unknown etiology. This isozyme deficiency is predominantly the product of reduced or absent β isoform of the type I regulatory subunit (RIβ). Transient transfection of RIβ cDNAs from SLE subjects into autologous T cells that do not synthesize the RIβ subunit bypassed the block, resulting in RIβ subunit synthesis and restoration of the PKA-Iβ (RIβ2C2) holoenzyme. Transfected T cells activated via the T cell surface receptor complex revealed a significant increase of cAMP-activatable PKA activity that was associated with a significant increase in IL-2 production. These data demonstrate that a disorder of RIβ translation exists, and that correction of the PKA-I deficiency may enhance T lymphocyte effector functions in SLE.

Diabetes-induced suppression of IGF-1 and its receptor mRNA levels in rat superior cervical ganglia

Insulin-like growth factor-I (IGF-I) is implicated in the development, survival and maintenance of function of sympathetic and sensory neurons. These neurons are affected at an early stage during the course of diabetes. Reverse transcriptase polymerase chain reaction (RT-PCR) based assay revealed that rat superior cervical ganglia (SCG) express mRNA transcripts for IGF-I and its receptor. Moreover, specific membrane protein binding sites for IGF-I within the SCG have also been demonstrated using competition-inhibition and affinity cross-linking techniques. An induction of diabetes with streptozotocin (STZ, 55 mg/kg, i.v.) produced a marked decrease in the SCG levels of mRNA transcripts for IGF-I and its receptor. Concentrations of circulating IGF-I and its receptor protein within the SCG were also reduced in this disease state. Insulin treatment partially prevented diabetes-related alterations in circulating IGF-I and the SCG-IGF-I system. Overall, the data described in this study may be of value in understanding the pathogenetic mechanism(s) responsible for the development of diabetic sympathetic neuropathy.

Role of Na+/H+ exchanger isoform-1 in human inflammatory bowel disease.

BACKGROUND Na+/H+ exchanger (NHE) is responsible for a net uptake of sodium chloride and water from the gastrointestinal tract and maintains electrolyte and water homeostasis. However, its status in human inflammatory bowel disease such as ulcerative colitis (UC) and Crohns disease (CD) remains poorly understood. OBJECTIVES To investigate the role of NHE-1 isoform in human CD and UC. METHODS Expression of NHE-1 protein and messenger ribonucleic acid and sodium pump activity were examined in the colonic biopsy samples taken from UC (n=11) and CD (n=13) patients using enhanced chemiluminescence-Western blot analysis, reverse transcription polymerase chain reaction and spectrophotometry. Subjects presenting with abdominal pain and endoscopically normal colon served as normal controls (n=11). Myeloperoxidase (MPO) activity and histology were performed to confirm tissue inflammation. RESULTS MPO activity increased significantly (P<0.05) in both UC and CD patients compared with the normal controls. Parallel to MPO activity profile, there was also a significantly higher infiltration of inflammatory cells in both cases. P-nitrophenylphosphatase activity, a marker of the sodium pump, remained unchanged in CD but increased significantly (P<0.05) in UC compared with the normal controls. On the contrary, the level of NHE-1 protein and messenger ribonucleic acid was significantly decreased (P<0.05) in both cases, whereas the internal control, a-actin remained unaltered. CONCLUSIONS These findings demonstrate a transcriptionally regulated suppression of NHE-1 in both UC and CD. This NHE-1 suppression may reduce an uptake of sodium chloride and water from the inflamed colonic lumen and thus contribute to diarrhea and neuromuscular alterations in these conditions.

Association of Deficient Type II Protein Kinase A Activity with Aberrant Nuclear Translocation of the RIIβ Subunit in Systemic Lupus Erythematosus T Lymphocytes

Systemic lupus erythematosus (SLE) is an autoimmune disorder of indeterminate etiology characterized by abnormal T cell signal transduction and altered T cell effector functions. We have previously observed a profound deficiency of total protein kinase A (PKA) phosphotransferase activity in SLE T cells. Here we examined whether reduced total PKA activity in SLE T cells is in part the result of deficient type II PKA (PKA-II) isozyme activity. The mean PKA-II activity in SLE T cells was 61% of normal control T cells. The prevalence of deficient PKA-II activity in 35 SLE subjects was 37%. Deficient isozyme activity was persistent over time and was unrelated to SLE disease activity. Reduced PKA-II activity was associated with spontaneous dissociation of the cytosolic RIIβ2C2 holoenzyme and translocation of the regulatory (RIIβ) subunit from the cytosol to the nucleus. Confocal immunofluorescence microscopy revealed that the RIIβ subunit was present in ∼60% of SLE T cell nuclei compared with only 2–3% of normal and disease controls. Quantification of nuclear RIIβ subunit protein content by immunoprecipitation and immunoblotting demonstrated a 54% increase over normal T cell nuclei. Moreover, the RIIβ subunit was retained in SLE T cell nuclei, failed to relocate to the cytosol, and was associated with a persistent deficiency of PKA-II activity. In conclusion, we describe a novel mechanism of deficient PKA-II isozyme activity due to aberrant nuclear translocation of the RIIβ subunit and its retention in the nucleus in SLE T cells. Deficient PKA-II activity may contribute to impaired signaling in SLE T cells.

A Multiplex Polymerase Chain Reaction Assay for the Detection of Mycobacterium paratuberculosis DNA in Crohn's Disease Tissue

BACKGROUND Mycobacterium paratuberculosis is implicated as a possible cause of Crohns disease. However, due to lack of an appropriate diagnostic method, this has been a subject of significant controversy. Our aim was therefore to develop a multiplex polymerase chain reaction (MPCR) for the detection of M. paratuberculosis DNA in Crohns disease tissue. METHODS Biopsy samples were collected by endoscopic forceps from terminal ileum, and genomic DNA was isolated. M. paratuberculosis-specific marker genes were amplified by using the present MPCR method. RESULTS Here we report a new MPCR for detection of M. paratuberculosis DNA in Crohns disease tissue. In this technique two genetic markers, IS900 and a newly described specific marker of MP2, were amplified in a single tube simultaneously. The method was evaluated using biopsy specimens from 10 Crohns disease patients, 6 ulcerative colitis patients, and 21 irritable bowel syndrome patients. The patients were characterized by using standard clinical and histologic observations. The present MPCR method could not detect M. paratuberculosis DNA in the biopsy specimens. However, the marker genes were amplified from the samples that were spiked with M. paratuberculosis before DNA extraction. The marker genes were also not detected in 10 closely related mycobacterial strains and human genomic DNA. CONCLUSIONS The present MPCR method is highly specific and can detect M. paratuberculosis DNA more reliably. These findings do not support an aetiologic role of M. paratuberculosis in Crohns disease.

Signal transduction mechanisms involved in cardiac preconditioning: role of Ras-GTPase, Ca2+/calmodulin-dependent protein kinase II and epidermal growth factor receptor.

It is well established that brief episodes of ischemia/reperfusion (I/R) [preconditioning (PC)] protect the myocardium from the damage induced by subsequent more prolonged I/R. However, the signaling pathways activated during PC or I/R are not well characterized. In this study, the role of Ras-GTPase, tyrosine kinases (TKs), epidermal growth factor receptor (EGFR) and Ca2 +/calmodulin-dependent protein kinase II (CaMK II) in mediating PC in a perfused rat heart model was investigated. A 40-min episode of global ischemia in perfused rat hearts produced significantly impaired cardiac function, measured as left ventricular developed pressure (Pmax) and left ventricular end-diastolic pressure (LVEDP), and impaired coronary hemodynamics, measured as coronary flow (CF) and coronary vascular resistance (CVR). PC significantly enhanced cardiac recovery after I/R. Combination of PC and FPT III (Ras-GTPase inhibitor FPT III; 232 ng/min for 6 days) treatment did not produce any additive benefits as compared to PC alone. In contrast, PC-induced improvements in cardiac function after I/R were significantly attenuated by pretreatment with genistein (1mg/kg/day for 6 days), a broad-spectrum inhibitor of TKs, or AG1478 (1mg/kg/day for 6 days), a specific inhibitor of EGFR tyrosine kinase or KN-93 (578 ng/min for 6 days), a CaMK II inhibitor, before PC. These observations suggest that PC and FPT III pretreatment may produce cardioprotection via similar mechanisms. Present results also indicate that activation of TKs and specifically activation of EGFR-mediated TKs and CaMK II-mediated regulation of calcium homeostasis are part of the PC mechanisms that improve recovery after I/R. (Mol Cell Biochem 268: 175–183, 2005)

Transcript mutations of the α regulatory subunit of protein kinase A and up-regulation of the RNA-editing gene transcript in lupus T lymphocytes

BACKGROUND Systemic lupus erythematosus (SLE) is an autoimmune disorder characterised by diverse dysfunctions of immune effector cells, including proliferation and cytotoxicity. In T cells from patients with SLE, activity of type 1 protein kinase A isozymes is greatly reduced because of decreased expression of the alpha and beta regulatory subunits (RI alpha and RI beta). We aimed to identify a molecular mechanism or mechanisms for this isozyme deficiency by assessing occurrence of mutations in transcripts of the RI alpha subunit in patients with SLE. METHODS We cloned and sequenced cDNA of RI alpha and corresponding genomic DNA of the coding region to detect sequence changes from eight patients with SLE and six healthy controls. Because transcript editing is regulated by adenosine deaminases that act on RNA (ADAR), we quantified expression of ADAR1 transcripts in SLE and control T cells by competitive PCR. FINDINGS Sequence analyses of cDNA showed heterogeneous transcript mutations, including deletions, transitions, and transversions. We identified 1.22 x 10(-3)/bp transcript mutations in SLE T cells-a frequency 7.5 times higher than that in control T cells. By contrast, we identified no genomic mutations. Two hotspots were identified in the RI alpha subunit transcripts from SLE T cells, one located adjacent to a pseudosubstrate site of the RI alpha subunit and the other a component of the cAMP binding A domain. ADAR1 mRNA content was 3.5 times higher in SLE cells than in control T cells (p=0.001). INTERPRETATION An RNA-editing enzyme could be converting adenosine to inosine within double-stranded regions of RNA, resulting in transcript mutations. This process could be one mechanism resulting in mutations in the RI alpha subunit of type 1 protein kinase A.

Suppression of Na+/H+ exchanger isoform-3 in human inflammatory bowel disease: Lack of reversal by 5′-aminosalicylate treatment

Objective. Na+/H+ exchanger isoform 3 (NHE-3) is responsible for net uptake of NaCl and water from the gastrointestinal (GI) tract. However, its status in human inflammatory bowel diseases (IBDs) such as ulcerative colitis (UC) and Crohns disease (CD) remains poorly understood. The aim of this study was to investigate the underlying mechanism of NHE-3 isoform expression and its modulation by 5′-aminosalicylate in human CD and UC. Material and methods. Subjects were divided into three groups: 1) controls; 2) untreated/new IBD cases (n=13) and 3) 5′- aminosalicylate-treated IBD patients (n_13). Subjects presenting with abdominal pain but with endoscopically normal colons served as normal controls. Inflammation was confirmed by the level of myeloperoxidase (MPO) activity, malondialdehyde (MDA) concentrations and by histologic evaluation. Expressions of NHE-3 protein and mRNA, sodium pump activity and IL-1β and TNF-α mRNA were estimated in the colonic biopsies using ECL-Western blot analysis, reverse transcription-polymerase chain reaction (RT-PCR) and enzyme assays. Results. The level of NHE-3 protein and sodium pump activity was reduced (p<0.05) in both the untreated and treated CD and UC patients. NHE-3 mRNA was reduced only in CD patients but not in those with UC. The treatment reversed the symptoms, but levels of MPO activity, MDA concentration, IL-1β, TNF-α and infiltration of inflammatory cells remained high with the exception of IL-1β mRNA in the treated patients. Conclusions. NHE-3 suppression is regulated differentially in CD and UC, which together with suppression of sodium pump activity will reduce NaCl and water uptake from the colonic lumen. These findings suggest a role of TNF-α in the regulation of NHE-3 expression in IBD.