An initial phase of JNK activation inhibits cell death early in the endoplasmic reticulum stress response.

Accumulation of unfolded proteins in the endoplasmic reticulum (ER) activates the unfolded protein response (UPR). In mammalian cells, UPR signals generated by several ER-membrane-resident proteins, including the bifunctional protein kinase endoribonuclease IRE1α, control cell survival and the decision to execute apoptosis. Processing of XBP1 mRNA by the RNase domain of IRE1α promotes survival of ER stress, whereas activation of the mitogen-activated protein kinase JNK family by IRE1α late in the ER stress response promotes apoptosis. Here, we show that activation of JNK in the ER stress response precedes activation of XBP1. This activation of JNK is dependent on IRE1α and TRAF2 and coincides with JNK-dependent induction of expression of several antiapoptotic genes, including cIap1 (also known as Birc2), cIap2 (also known as Birc3), Xiap and Birc6 ER-stressed Jnk1(-/-) Jnk2(-/-) (Mapk8(-/-) Mapk9(-/-)) mouse embryonic fibroblasts (MEFs) display more pronounced mitochondrial permeability transition and increased caspase 3/7 activity compared to wild-type MEFs. Caspase 3/7 activity is also elevated in ER-stressed cIap1(-/-) cIap2(-/-) and Xiap(-/-) MEFs. These observations suggest that JNK-dependent transcriptional induction of several inhibitors of apoptosis contributes to inhibiting apoptosis early in the ER stress response.

How reliable are sino-nasal cell lines for studying the pathophysiology of chronic rhinosinusitis?

BACKGROUND: Well-characterized cell lines represent useful scientific tools to study the pathophysiology of human disease. Chronic rhinosinusitis (CRS) is a very common condition, though the number of CRS cell lines is limited, as are data showing how closely they resemble primary cells. METHODOLOGY: Searches for available human cell lines were performed using the American Type Culture Collection (ATCC) and European Collection of Cell Cultures (ECACC). Identified cells were cultured and characterized with tinctorial and immunohistochemical staining and ELISA to assess their response to common, disease-relevant inflammatory stimuli. Carefully phenotyped CRS patients were recruited with informed consent. Primary nasal epithelial cell (PNEC) brushings were harvested, cultured, and compared to the available cell lines. RESULTS: Searches identified 1 relevant CRS sino-nasal cell line, RPMI 2650. Cultured PNECs showed strong expression of epithelial markers while being negative for mesenchymal markers. However, RPMI 2650 cells show an atypical mixed epithelial/mesenchymal phenotype. When stimulated by pro-inflammatory ligands, PNECs responded in a dose-dependent manner, whereas RPMI 2650 cells showed limited response. CONCLUSIONS: The number and availability of cell lines to study the pathophysiology of CRS greatly underrepresent the disease burden. Additionally, the sole commercially available cell line appears to have a different phenotype and behavior to primary patient-derived cells. The development of further reproducible cell lines would be beneficial in our understanding of CRS.

MiR-29a reduces TIMP-1 production by dermal fibroblasts via targeting TGF-ß activated kinase 1 binding protein 1, implications for systemic sclerosis.

BACKGROUND: Systemic sclerosis (SSc) is an autoimmune connective tissue disease characterised by skin and internal organs fibrosis due to accumulation of extra cellular matrix (ECM) proteins. Tissue inhibitor of metalloproteinases 1 (TIMP-1) plays a key role in ECM deposition. AIM: To investigate the role of miR-29a in regulation of TAB1-mediated TIMP-1 production in dermal fibroblasts in systemic sclerosis. METHODS: Healthy control (HC) and SSc fibroblasts were cultured from skin biopsies. The expression of TIMP-1, MMP-1 and TGF-ß activated kinase 1 binding protein 1 (TAB1) was measured following miR-29a transfection using ELISA, qRT-PCR, and Western Blotting. The functional effect of miR-29a on dermal fibroblasts was assessed in collagen gel assay. In addition, HeLa cells were transfected with 3'UTR of TAB1 plasmid cloned downstream of firefly luciferase gene to assess TAB1 activity. HC fibroblasts and HeLa cells were also transfected with Target protectors in order to block the endogenous miR-29a activity. RESULTS: We found that TAB1 is a novel target gene of miR-29a, also regulating downstream TIMP-1 production. TAB1 is involved in TGF-ß signal transduction, a key cytokine triggering TIMP-1 production. To confirm that TAB1 is a bona fide target gene of miR-29a, we used a TAB1 3'UTR luciferase assay and Target protector system. We showed that miR-29a not only reduced TIMP-1 secretion via TAB1 repression, but also increased functional MMP-1 production resulting in collagen degradation. Blocking TAB1 activity by pharmacological inhibition or TAB1 knockdown resulted in TIMP-1 reduction, confirming TAB1-dependent TIMP-1 regulation. Enhanced expression of miR-29a was able to reverse the profibrotic phenotype of SSc fibroblasts via downregulation of collagen and TIMP-1. CONCLUSIONS: miR-29a repressed TAB1-mediated TIMP-1 production in dermal fibroblasts, demonstrating that miR-29a may be a therapeutic target in SSc.

Mechanistic differences between phenotypes of chronic lung allograft dysfunction after lung transplantation.

Distinct phenotypes of chronic lung allograft dysfunction (CLAD) after lung transplantation are emerging with lymphocytic bronchiolitis (LB)/azithromycin reversible allograft dysfunction (ARAD), classical or fibrotic bronchiolitis obliterans syndrome (BOS), and restrictive allograft syndrome (RAS) proposed as separate entities. We have additionally identified lung transplant recipients with prior LB, demonstrating persistent airway neutrophilia (PAN) despite azithromycin treatment. The aim of this study was to evaluate differences in the airway microenvironment in different phenotypes of CLAD. Bronchoalveolar lavage (BAL) from recipients identified as stable (control), LB/ARAD, PAN, BOS, and RAS were evaluated for differential cell counts and concentrations of IL-1α, IL-1ß, IL-6, IL-8, and TNF-α. Primary human bronchial epithelial cells were exposed to BAL supernatants from different phenotypes and their viability measured. BOS and RAS showed increased BAL neutrophilia but no change in cytokine concentrations compared with prediagnosis. In both LB/ARAD and PAN, significant increases in IL-1α, IL-1ß, and IL-8 were present. BAL IL-6 and TNF-α concentrations were increased in PAN and only this phenotype demonstrated decreased epithelial cell viability after exposure to BAL fluid. This study demonstrates clear differences in the airway microenvironment between different CLAD phenotypes. Systematic phenotyping of CLAD may help the development of more personalized approaches to treatment.