Peter N. Kao

Immunosuppressant PG490 (Triptolide) Inhibits T-cell Interleukin-2 Expression at the Level of Purine-box/Nuclear Factor of Activated T-cells and NF-κB Transcriptional Activation

PG490 (triptolide) is a diterpene triepoxide with potent immunosuppressive and antiinflammatory properties. PG490 inhibits interleukin(IL)-2 expression by normal human peripheral blood lymphocytes stimulated with phorbol 12-myristate 13-acetate (PMA) and antibody to CD3 (IC50 of 10 ng/ml), and with PMA and ionomycin (Iono, IC50 of 40 ng/ml). In Jurkat T-cells, PG490 inhibits PMA/Iono-stimulated IL-2 transcription. PG490 inhibits the induction of DNA binding activity at the purine-box/antigen receptor response element (ARRE)/nuclear factor of activated T-cells (NF-AT) target sequence but not at the NF-κB site. PG490 can completely inhibit transcriptional activation at the purine-box/ARRE/NF-AT and NF-κB target DNA sequences triggered by all stimuli examined (PMA, PMA/Iono, tumor necrosis factor-α). PG490 also inhibits PMA-stimulated activation of a chimeric transcription factor in which the C-terminal TA1 transactivation domain of NF-κB p65 is fused to the DNA binding domain of GAL4. In 16HBE human bronchial epithelial cells, IL-8 expression is regulated predominantly by NF-κB, and PG490 but not cyclosporin A can completely inhibit expression of IL-8. The mechanism of PG490 inhibition of cytokine gene expression differs from cyclosporin A and involves nuclear inhibition of transcriptional activation of NF-κB and the purine-box regulator operating at the ARRE/NF-AT site at a step after specific DNA binding.

Immunosuppressive and Anti-Inflammatory Mechanisms of Triptolide, the Principal Active Diterpenoid from the Chinese Medicinal Herb Tripterygium wilfordii Hook. f.

Extracts of Tripterygium wilfordii hook. f. (leigong teng, Thundergod vine) are effective in traditional Chinese medicine for treatment of immune inflammatory diseases including rheumatoid arthritis, systemic lupus erythematosus, nephritis and asthma. Characterisation of the terpenoids present in extracts of Tripterygium identified triptolide, a diterpenoid triepoxide, as responsible for most of the immunosuppressive, anti-inflammatory and antiproliferative effects observed in vitro. Triptolide inhibits lymphocyte activation and T-cell expression of interleukin-2 at the level of transcription. In all cell types examined, triptolide inhibits nuclear factor-κB transcriptional activation at a unique step in the nucleus after binding to DNA. Further characterisation of the molecular mechanisms of triptolide action will serve to elucidate pathways of immune system regulation.

Simvastatin Rescues Rats From Fatal Pulmonary Hypertension by Inducing Apoptosis of Neointimal Smooth Muscle Cells

Background—Pulmonary vascular injury by toxins can induce neointimal formation, pulmonary arterial hypertension (PAH), right ventricular failure, and death. We showed previously that simvastatin attenuates smooth muscle neointimal proliferation and pulmonary hypertension in pneumonectomized rats injected with the alkaloid toxin monocrotaline. The present study was undertaken to investigate the efficacy of simvastatin and its mechanism of reversing established neointimal vascular occlusion and pulmonary hypertension. Methods and Results—Pneumonectomized rats injected with monocrotaline at 4 weeks demonstrated severe PAH at 11 weeks (mean pulmonary artery pressure [mPAP]=42 versus 17 mm Hg in normal rats) and death by 15 weeks. When rats with severe PAH received simvastatin (2 mg · kg−1 · d−1 by gavage) from week 11, there was 100% survival and reversal of PAH after 2 weeks (mPAP=36 mm Hg) and 6 weeks (mPAP=24 mm Hg) of therapy. Simvastatin treatment reduced right ventricular hypertrophy and reduced proliferation and increased apoptosis of pathological smooth muscle cells in the neointima and medial walls of pulmonary arteries. Longitudinal transcriptional profiling revealed that simvastatin downregulated the inflammatory genes fos, jun, and tumor necrosis factor-&agr; and upregulated the cell cycle inhibitor p27Kip1, endothelial nitric oxide synthase, and bone morphogenetic protein receptor type 1a. Conclusions—Simvastatin reverses pulmonary arterial neointimal formation and PAH after toxic injury.

Radiation pneumonitis in mice: A severe injury model for pneumocyte engraftment from bone marrow

OBJECTIVE To better understand the process by which pneumocytes can be derived from bone marrow cells, we investigated the in vivo kinetics of such engraftment following lethal irradiation. METHODS A cohort of lethally irradiated B6D2F1 female mice received whole bone marrow transplants (BMT) from age-matched male donors and were sacrificed at days 1, 3, 5, and 7 and months 2, 4, and 6 post-BMT (n = 3 for each time point). Additionally, 2 female mice who had received 200 male fluorescence-activated cell sorter (FACS)-sorted CD34(+)lin(-) cells were sacrificed 8 months post-BMT. RESULTS Lethal irradiation caused histologic evidence of pneumonitis including alveolar breakdown and hemorrhage beginning at day 3. To identify male-derived pneumocytes, simultaneous fluorescence in situ hybridization (FISH) for Y-chromosome and surfactant B messenger RNA was performed on lung tissue. Y(+) type II pneumocytes were engrafted as early as day 5 posttransplant, and eventually from 2 to 14% of the pneumocytes were donor derived in individual mice. Co-staining for epithelial-specific cytokeratins demonstrated that by 2 months, marrow-derived pneumocytes could comprise entire alveoli, suggesting that type I cells derived from type II pneumocytes. CONCLUSIONS We conclude that alveolar lining cells derive from bone marrow cells immediately after acute injury. Also, the CD34(+)lin(-) subpopulation is capable of such pulmonary engraftment.

PG490 (triptolide) cooperates with tumor necrosis factor-alpha to induce apoptosis in tumor cells.

Progress in the treatment of solid tumors has been slow and sporadic. The efficacy of conventional chemotherapy in solid tumors is limited because tumors frequently have mutations in the p53 gene. Also, chemotherapy only kills rapidly dividing cells. Members of the tumor necrosis factor (TNF) family, however, induce apoptosis regardless of the p53 phenotype. Unfortunately, the cytotoxicity of TNF-α is limited by its activation of NF-κB and activation of NF-κB is proinflammatory. We have identified a compound called PG490, that is composed of purified triptolide, which induces apoptosis in tumor cells and sensitizes tumor cells to TNF-α-induced apoptosis. PG490 potently inhibited TNF-α-induced activation of NF-κB. PG490 also blocked TNF-α-mediated induction of c-IAP2 (hiap-1) and c-IAP1 (hiap-2), members of the inhibitor of apoptosis (IAP) family. Interestingly, PG490 did not block DNA binding of NF-κB, but it blocked transactivation of NF-κB. Our identification of a compound that blocks TNF-α-induced activation of NF-κB may enhance the cytotoxicity of TNF-α on tumors in vivo and limit its proinflammatory effects.

Members of the NF90/NFAR protein group are involved in the life cycle of a positive-strand RNA virus

A major issue of current virology concerns the characterization of cellular proteins that operate as functional components of the viral multiplication process. Here we describe a group of host factors designated as ‘NFAR proteins’ that are recruited by the replication machinery of bovine viral diarrhea virus, a close relative of the human pathogen hepatitis C virus. The NFAR proteins associate specifically with both the termini of the viral RNA genome involving regulatory elements in the 5′ and 3′ non‐translated regions. Modification of the protein interaction sites in the 3′ non‐translated region yielded viral RNAs that were replication deficient. Viral replication was also inhibited by RNAi approaches that reduced the concentration of RNA helicase A, a member of the NFAR group, in the host cells cytoplasm. Further experimental data suggest that NFAR proteins mediate a circular conformation of the viral genome that may be important for the coordination of translation and replication. Because NFAR proteins are presumed components of the antiviral response, we suspect that viral recruitment may also serve to weaken cellular defense mechanisms.

Simvastatin Treatment of Pulmonary Hypertension: An Observational Case Series

BACKGROUND Statins confer cardiovascular benefits beyond the reduction of serum cholesterol through antiproliferative and antiinflammatory mechanisms and induction of endothelial nitric oxide expression. In pneumonectomized rats injected with monocrotaline, simvastatin reversed established pulmonary hypertension and conferred a 100% survival advantage. STUDY OBJECTIVES To evaluate the safety and efficacy of simvastatin for treatment of patients with pulmonary arterial hypertension (PAH). DESIGN Open-label observational study performed at Stanford University Medical Center. Sixteen patients with primary and secondary causes of PAH, World Health Organization (WHO) classes I (n = 2), II (n = 4), III (n = 3), IV (n = 7), are described. Simvastatin was prescribed at 20 to 80 mg/d and continued in the absence of adverse effects. MEASUREMENTS AND RESULTS Serial measurements of 6-min walk (6MW) performance, hemodynamics, and echocardiographic estimates of right ventricular systolic pressures (RVSPs) were recorded on each patient. Simvastatin treatment was not associated with hepatic dysfunction, muscle necrosis, or other adverse events. Individual patients demonstrated improvements in 6MW performance, improvements in cardiac output, or decreases in RVSP that may be attributable to simvastatin treatment. Overall, the rate of disease progression appeared to be attenuated, and WHO class IV patients demonstrated improved survival. CONCLUSIONS Simvastatin treatment appears safe in patients with PAH.

Pulmonary Arterial Hypertension Future Directions: Report of a National Heart, Lung and Blood Institute/Office of Rare Diseases Workshop

Pulmonary arterial hypertension (PAH) is characterized by vascular obstruction and the variable presence of vasoconstriction, leading to increased pulmonary vascular resistance and right-sided heart failure. PAH can present in an idiopathic form, usually called primary pulmonary hypertension (PPH), and PAH is also associated with the scleroderma spectrum of diseases, HIV infection, portal hypertension with or without cirrhosis, and anorectic drug ingestion. Idiopathic PAH occurs in women more often than men (>2:1), has a mean age at diagnosis of 36 years, and is usually fatal within 3 years if untreated. Modern treatment has markedly improved physical function and has extended survival, and the 5-year mortality rate is ≈50%. We still do not understand what initiates the disease or what allows it to progress. New studies of the pathogenetic basis of PAH will lead to targeted therapies for PAH. The National Heart, Lung and Blood Institute (NHLBI) and the Office of Rare Diseases (ORD), National Institutes of Health, convened a workshop to bring together investigators with various interests in vascular biology and pulmonary hypertension to identify new research directions. Discussion included genetics of PAH, receptor function, mediators, ion channels, extracellular matrix, signaling, and potential clinical approaches. Molecular genetic studies have demonstrated mutations in a receptor in the transforming growth factor (TGF-β) superfamily, called bone morphogenetic protein receptor 2 (BMPR2), in most cases of familial pulmonary hypertension.1,2 Less common mutations associated with PAH occur in Alk1, a TGF receptor that also causes hereditary hemorrhagic telangectasia.3 Because only ≈10% to 20% of persons with a BMPR2 mutation develop PAH, it is likely that other genes, genetic polymorphisms, and environmental factors are necessary to initiate the pathological sequence that leads to disease.4 Most cases of PAH are not associated with known inherited genetic mutations.5 Thus, external stimuli coupled with as-yet-undefined genetic …

DNA-dependent Protein Kinase Interacts with Antigen Receptor Response Element Binding Proteins NF90 and NF45

The DNA-dependent protein kinase (DNA-PK) is composed of a large catalytic subunit of approximately 470 kDa (DNA-PKcs) and the DNA-binding protein, Ku. Absence of DNA-PK activity confers sensitivity to x-rays and defects in both DNA double-strand break repair and V(D)J recombination. However, the precise function of DNA-PK in DNA double-strand break repair is not known. Here we show, using electrophoretic mobility shift assays, that polypeptides in a fraction purified from human cells interact with DNA-PK and stabilize the formation of a complex containing DNA-PKcs-Ku and DNA. Five polypeptides in this fraction have been identified by amino-terminal sequence analysis and/or immunoblotting. These proteins are NF90 and NF45, which are the 90- and 45-kDa subunits of a protein known to bind specifically to the antigen receptor response element of the interleukin 2 promoter, and the α, β, and γ subunits of eukaryotic translation initiation factor eIF-2. We also show that NF90, NF45, and eIF-2β are substrates for DNA-PK in vitro. In addition, recombinant NF90 promotes formation of a complex between DNA-PKcs, Ku, and DNA, and antibodies to recombinant NF90 or recombinant NF45 immunoprecipitate DNA-PKcs in vitro. Together, our data suggest that NF90, in complex with NF45, interacts with DNA-PKcs and Ku on DNA and that NF90 and NF45 may be important for the function of DNA-PK.

NF90 regulates cell cycle exit and terminal myogenic differentiation by direct binding to the 3'-untranslated region of MyoD and p21WAF1/CIP1 mRNAs.

NF90 and splice variant NF110/ILF3/NFAR are double-stranded RNA-binding proteins that regulate gene expression. Mice with targeted disruption of NF90 were engineered. NF90(–/–) mice were born small and weak and succumbed to perinatal death within 12 h because of neuromuscular respiratory failure. Lung inflation and morphology were normal in NF90(–/–) mice. The diaphragm and other skeletal muscles in NF90(–/–) mice demonstrated disorganized arrangement and paucity of myofibers, evidence of myocyte degeneration and increased apoptosis. The expression of myogenic regulators, MyoD, myogenin, and p21WAF1/CIP1, was severely decreased in NF90(–/–) mice. These myogenic transcription factors and cell cycle inhibitors are regulated in part through post-transcriptional mRNA stabilization. Northwestern blotting revealed that NF90 is the principal and specific p21WAF1/CIP1 and MyoD 3′-untranslated region RNA-binding protein in developing skeletal muscles. NF90 regulates transcription factors and a cell cycle inhibitor essential for skeletal muscle differentiation and for survival.