Matrilysin-1 mediates bronchiolization of alveoli, a potential premalignant change in lung cancer

The NANCI-Nkx2.1 gene duplex buffers Nkx2.1 expression to maintain lung development and homeostasis

A subset of long noncoding RNAs (lncRNAs) is spatially correlated with transcription factors (TFs) across the genome, but how these lncRNA–TF gene duplexes regulate tissue development and homeostasis is unclear. Here, Herriges et al. identified a feedback loop within the NANCI–Nkx2.1 gene duplex that is essential for buffering Nkx2.1 expression, lung epithelial cell identity, and tissue homeostasis.

A subset of long noncoding RNAs (lncRNAs) is spatially correlated with transcription factors (TFs) across the genome, but how these lncRNA–TF gene duplexes regulate tissue development and homeostasis is unclear. We identified a feedback loop within the NANCI (Nkx2.1-associated noncoding intergenic RNA)–Nkx2.1 gene duplex that is essential for buffering Nkx2.1 expression, lung epithelial cell identity, and tissue homeostasis. Within this locus, Nkx2.1 directly inhibits NANCI, while NANCI acts in cis to promote Nkx2.1 transcription. Although loss of NANCI alone does not adversely affect lung development, concurrent heterozygous mutations in both NANCI and Nkx2.1 leads to persistent Nkx2.1 deficiency and reprogramming of lung epithelial cells to a posterior endoderm fate. This disruption in the NANCI–Nkx2.1 gene duplex results in a defective perinatal innate immune response, tissue damage, and progressive degeneration of the adult lung. These data point to a mechanism in which lncRNAs act as rheostats within lncRNA–TF gene duplex loci that buffer TF expression, thereby maintaining tissue-specific cellular identity during development and postnatal homeostasis.

Matrilysin (MMP-7) catalytic activity regulates β-catenin localization and signaling activation in lung epithelial cells

Matrix metalloproteinase-7 (matrilysin, MMP-7) expression is increased in epithelium by bacterial infection, inflammation, fibrosis, and in a myriad of carcinomas. It functions to degrade extracellular matrix and other pericellular substrates including the adherens junction protein E-cadherin to promote wound healing and tissue remodeling. β-catenin functions as both a structural component of adherens junctions and as an intracellular signaling molecule. To assess if matrilysin-mediated disassembly of adherens junctions regulates β-catenin function, we assessed effects of matrilysin catalytic activity on β-catenin localization and signaling activity in A549 cells and in bleomycin-induced lung injury in mice. We determined that matrilysin activity releases β-catenin from the cell membrane after which it is degraded in the cytosol. However, in the presence of a β-catenin stabilizing Wnt signal, β-catenin accumulated in the cytosol and activated a β-catenin luciferase promoter. Furthermore, β-catenin nuclear translocation and activation was impaired in matrilysin-null mice when compared to wild-type mice after bleomycin-induced lung injury. These results show identify matrilysin as a regulator of β-catenin function in injured lung epithelium and may link extracellular proteolytic activity to cell junction disassembly and intracellular signaling.

Receptor interacting protein-2 plays a critical role in human lung epithelial cells survival in response to Fas-induced cell-death

Lung epithelial cell death is critical to the lung injury that occurs in the acute respiratory distress syndrome. It is known that FasL plays a prominent role in this lung cell death pathway and may work in part through activation of the receptor interacting protein-2 (RIP2). RIP2 is serine/threonine kinase with a C-terminal caspase activation and recruitment domain (CARD). This CARD contains a highly conserved, predicted tyrosine phosphorylation site. Thus, involvement of tyrosine phosphorylation in the CARD domain of RIP2 may play a critical role in Fas-mediated apoptosis in the human lung immune system. To test this hypothesis, human lung epithelial cells (BEAS-2B) were induced to undergo cell death in response to the Fas agonist antibody CH11 with and without manipulation of endogenous RIP2 concentrations. We show that CH11 increases lung epithelial cell death in a dose-dependent manner as determined by LDH release and nuclear condensation. Fas-induced LDH release was inhibited by RIP2 knock-down. Reduced levels of RIP2 in BEAS-2B cells after treatment with RIP2 siRNA were confirmed by immunoblot. Overexpression of RIP2 in BEAS-2B cells synergized with Fas ligand-induced LDH release in a dose-dependent manner. Finally, mutation of the tyrosine phosphorylation site in CARD of RIP2 protected BEAS-2B cells from Fas ligand induced cell death. Thus RIP2's CARD tyrosine phosphorylation may represent a new therapeutic target to promote the survival of human lung epithelial cells in disorders that lead to acute lung injury and ARDS.

MMP-7 is upregulated by COX-2 and promotes proliferation and invasion of lung adenocarcinoma cells

Matrix metalloproteinases (MMPs) have been implicated in a variety of pathophysiological conditions, of which MMP-7 is expressed by tumor cells of epithelial and mesenchymal origin. However, the function of MMP-7 in human lung adenocarcinoma (LAC) is unclear. In the present study the expression of MMP-7 in LAC was examined by immunohistochemical assay using a tissue microarray procedure. A loss-of-function experiment was performed to explore the effects and molecular mechanisms of lentiviral vector-mediated MMP-7 siRNA (siMMP-7) on cell proliferation and invasive potential in LAC A549 cells, measured by MTT and Transwell assays, respectively. It was found that, the expression of MMP-7 protein in LAC was significantly increased compared with that in adjacent non-cancerous tissues (ANCT) (76.0% vs 44.0%, P<0.001), and positively correlated with lymph node metastases of the tumor (P=0.014). Furthermore, targeted inhibition of cyclooxygenase-2 (COX-2) by siRNA downregulated the expression of MMP-7 and inhibited invasion of LAC cells, and knockdown of MMP-7 suppressed tumor proliferation and invasion in LAC cells. Taken together, our findings indicate that increased expression of MMP-7 is associated with lymph node metastasis and upregulated by COX-2, and promotes the tumorigenesis of LAC, suggesting that MMP-7 may be a potential therapeutic target for the treatment of cancer.

Achaete-scute complex homolog-1 promotes DNA repair in the lung carcinogenesis through matrix metalloproteinase-7 and O(6)-methylguanine-DNA methyltransferase

Lung cancer is the leading cause of cancer-related deaths in the world. Achaete-scute complex homolog-1 (Ascl1) is a member of the basic helix-loop-helix (bHLH) transcription factor family that has multiple functions in the normal and neoplastic lung such as the regulation of neuroendocrine differentiation, prevention of apoptosis and promotion of tumor-initiating cells. We now show that Ascl1 directly regulates matrix metalloproteinase-7 (MMP-7) and O(6)-methylguanine-DNA methyltransferase (MGMT). Loss- and gain-of-function experiments in human bronchial epithelial and lung carcinoma cell lines revealed that Ascl1, MMP-7 and MGMT are able to protect cells from the tobacco-specific nitrosamine NNK-induced DNA damage and the alkylating agent cisplatin-induced apoptosis. We also examined the role of Ascl1 in NNK-induced lung tumorigenesis in vivo. Using transgenic mice which constitutively expressed human Ascl1 in airway lining cells, we found that there was a delay in lung tumorigenesis. We conclude that Ascl1 potentially enhances DNA repair through activation of MMP-7 and MGMT which may impact lung carcinogenesis and chemoresistance. The study has uncovered a novel and unexpected function of Ascl1 which will contribute to better understanding of lung carcinogenesis and the broad implications of transcription factors in tobacco-related carcinogenesis.

Achaete-scute homologue-1 (ASH1) stimulates migration of lung cancer cells through Cdk5/p35 pathway

Cyclin-dependent kinase 5 (Cdk5) activity is important for the migration and invasion of cancer cells. Our results indicate that in the lung one of the mechanisms that hASH1 regulates—migration—takes place through induction of Cdk5 activity. Our data suggest that Cdk5 and its activator p35 promote lung cancer cell migration through hASH1-mediated signaling.

Our previous data suggested that the human basic helix–loop–helix transcription factor achaete-scute homologue-1 (hASH1) may stimulate both proliferation and migration in the lung. In the CNS, cyclin-dependent kinase 5 (Cdk5) and its activator p35 are important for neuronal migration that is regulated by basic helix–loop–helix transcription factors. Cdk5/p35 may also play a role in carcinogenesis. In this study, we found that the neuronal activator p35 was commonly expressed in primary human lung cancers. Cdk5 and p35 were also expressed by several human lung cancer cell lines and coupled with migration and invasion. When the kinase activity was inhibited by the Cdk5 inhibitor roscovitine or dominant-negative (dn) Cdk5, the migration of lung cancer cells was reduced. In neuroendocrine cells expressing hASH1, such as a pulmonary carcinoid cell line, knocking down the gene expression by short hairpin RNA reduced the levels of Cdk5/p35, nuclear p35 protein, and migration. Furthermore, expression of hASH1 in lung adenocarcinoma cells normally lacking hASH1 increased p35/Cdk5 activity and enhanced cellular migration. We were also able to show that p35 was a direct target for hASH1. In conclusion, induction of Cdk5 activity is a novel mechanism through which hASH1 may regulate migration in lung carcinogenesis.

The role of catalase in pulmonary fibrosis

BACKGROUND

Catalase is preferentially expressed in bronchiolar and alveolar epithelial cells, and acts as an endogenous antioxidant enzyme in normal lungs. We thus postulated epithelial damage would be associated with a functional deficiency of catalase during the development of lung fibrosis.

METHODS

The present study evaluates the expression of catalase mRNA and protein in human interstitial pneumonias and in mouse bleomycin-induced lung injury. We examined the degree of bleomycin-induced inflammation and fibrosis in the mice with lowered catalase activity.

RESULTS

In humans, catalase was decreased at the levels of activity, protein content and mRNA expression in fibrotic lungs (n = 12) compared to control lungs (n = 10). Immunohistochemistry revealed a decrease in catalase in bronchiolar epithelium and abnormal re-epithelialization in fibrotic areas. In C57BL/6J mice, catalase activity was suppressed along with downregulation of catalase mRNA in whole lung homogenates after bleomycin administration. In acatalasemic mice, neutrophilic inflammation was prolonged until 14 days, and there was a higher degree of lung fibrosis in association with a higher level of transforming growth factor-β expression and total collagen content following bleomycin treatment compared to wild-type mice.

CONCLUSIONS

Taken together, these findings demonstrate diminished catalase expression and activity in human pulmonary fibrosis and suggest the protective role of catalase against bleomycin-induced inflammation and subsequent fibrosis.