Human rhinovirus (RV) is the major cause of common cold, and it also plays a significant role in asthma and asthma exacerbation. Airway epithelium is the primary site of RV infection and production. In contrast, monocytic cells (e.g. monocytes and macrophages) are believed to be non-permissive for RV replication. Instead, RV has been shown to modulate inflammatory gene expressions in these cells via a replication-independent mechanism. In the present study, RV16 (a major-group RV) replication was found to be significantly enhanced in monocytes when co-cultivated with airway epithelial cells. This effect appeared to be mediated by secretory components from epithelial cells, which stimulated RV16 replication and significantly elevated the expression of a number of proinflammatory cytokines. The lack of such effect on RV1A, a minor-group RV that enters the cell by a different receptor, suggests that ICAM1, the receptor for major-group RVs, may be involved. Indeed, conditioned media from epithelial cells significantly increased ICAM1 expression in monocytes. Consistently, ICAM1 overexpression and ICAM1 knockdown enhanced and blocked RV production, respectively, confirming the role of ICAM1 in this process. Thus, this is the first report demonstrating that airway epithelial cells direct significant RV16 replication in monocytic cells via an ICAM1-dependent mechanism. This finding will open a new venue for the study of RV infection in airway disease and its exacerbation.
PMID: 11713095;Abstract:
Human mucin (MUC) 5B gene expression in human airway epithelium was studied in both tissue sections and cultures of tracheobronchial epithelial (TBE) cells. In situ hybridization demonstrated that MUC5B message was expressed mainly in the mucous cells of submucosal glands of normal human airway tissues. Nevertheless, an elevated MUC5B message level could be seen in surface goblet cells from patients with airway diseases and inflammation. Regardless of the airway tissue sources, MUC5B message was regulated by all-trans-retinoic acid (RA) and culture conditions in both primary and passage-1 cultures of TBE cells. MUC5B message, to a lesser extent, was also found in the immortalized epithelial cell line HBE1, but not in BEAS-2B cells. To elucidate the molecular mechanism of MUC5B gene expression, a genomic clone was obtained and sequenced for the amino terminal and the 5′-flanking region of MUC5B gene. A luciferase reporter construct containing 4,169 base pairs of the 5′-flanking region of MUC5B gene demonstrated a cell type-specific basal promoter activity in transfection studies. Both RA and the air-liquid interface culture condition further enhanced this promoter activity. These results suggest that the 5′-flanking region of MUC5B gene contains cis-elements that are potentially involved in the regulation of MUC5B gene expression.
In the context of the human airway, interleukin-17A (IL-17A) signaling is associated with severe inflammation, as well as protection against pathogenic infection, particularly at mucosal surfaces such as the airway. The intracellular molecule Act1 has been demonstrated to be an essential mediator of IL-17A signaling. In the cytoplasm, it serves as an adaptor protein, binding to both the intracellular domain of the IL-17 receptor as well as members of the canonical nuclear factor kappa B (NF-κB) pathway. It also has enzymatic activity, and serves as an E3 ubiquitin ligase. In the context of airway epithelial cells, we demonstrate for the first time that Act1 is also present in the nucleus, especially after IL-17A stimulation. Ectopic Act1 expression can also increase the nuclear localization of Act1. Act1 can up-regulate the expression and promoter activity of a subset of IL-17A target genes in the absence of IL-17A signaling in a manner that is dependent on its N- and C-terminal domains, but is NF-κB independent. Finally, we show that nuclear Act1 can bind to both distal and proximal promoter regions of DEFB4, one of the IL-17A responsive genes. This transcriptional regulatory activity represents a novel function for Act1. Taken together, this is the first report to describe a non-adaptor function of Act1 by directly binding to the promoter region of IL-17A responsive genes and directly regulate their transcription.
PMID: 11694445;Abstract:
The effects of extracellular nucleotide triphosphates on the stimulation of mucin production by airway epithelial cells were examined. The order of potency in stimulating mucin secretion in primary cultures of human tracheobronchial epithelial cells is: uridine 5′-triphosphate (UTP) ≈ adenosine 5′-triphosphate (ATP) ≈ ATP-γ-S > uridine 5′-diphosphate ≈ adenosine 5′-diphosphate > α,β-methylene ATP >> adenosine. However, only UTP can increase mucin gene (MUC5AC, MUC5B) expression; ATP and other analogues have no stimulatory effect. The stimulation of MUC5AC and MUC5B expression by UTP is time- and dose-dependent. A similar effect on the elevation of mucous cell population in mouse airway epithelium can be demonstrated in vivo by an intratracheal instillation of UTP-saline solution. The stimulatory effect of UTP or ATP on mucin secretion was inhibited by pertussis toxin, U73122, and Calphostin C, but not by PD98059, suggesting a G-protein/phospholipase (PL) C/protein kinase (PK) C-dependent and mitogen-activated protein kinase (MAPK)-independent signaling pathway. However, the stimulatory effect of UTP on mucin gene expression was sensitive to pertussis toxin and PD98059, but not to Calphostin C and U73122, suggesting a G-protein/MAPK-dependent and PLC/PKC-independent signaling pathway. These findings are the first demonstration that UTP, a pyrimidine nucleotide triphosphate, can enhance both mucin secretion and mucin gene expression through different signaling pathways.
