Constitutive and inducible nitric oxide synthase gene expression, regulation, and activity in human lung epithelial cells.

Abstract

Histochemical activity and immunoreactivt of nitric oxide synthase (NOS, EC 1.14.13.39) have been recently demonstrated in human lung epithelium. However, the molecular nature of NOS and the regulation and function of the enzyme(s) in the airway is not known. A549 cells (human alveolar type I epithelium-like), BEAS 2B cells (transformed human bronchial epithelial cells), and primary cultures of human bronchial epithelial cells all exhibited constitutive NOS activity that was calcium dependent and inhibitable by the NOS inhibitor NG-monomethyl-L-arginine. Nitric oxide production by epithelial cells was enhanced by culture in the presence of interferon y, interleukin 1p, tumor necrosis factor a, and lipopolysaccharide; the NOS activity expressed under these conditions showed less dependence on calcium, reminiscent of other inducible forms of NOS. Two distinct NOS mRNA species, homologous to previously identified constitutive brain (type I) and inducible hepatic (type II) NOS, were demonstrated by reverse transcription-polymerase chain reaction in all cell lines. Northern analysis confirmed the expression of inducible NOS mRNA. Cell culture with epidermal growth factor, a principal regulator of epithelial cell function, decreased inducible NOS activity by posttranscriptional action but did not affect constitutive NOS activity. The coexistence of constitutive and inducible NOS in human alveolar and bronchial epithelial cells is consistent with a complex mechanism evolved by epithelial cells to protect the host from microbial assault at the air/surface interface while shielding the host from the induction of airway hyperreactivity.In addition to its role in regulating airway tone (1-4), the airway epithelium is an important interface between higher organisms and their extracellular environments. Once considered a simple physical barrier to noxious agents, it is now well appreciated that the epithelium has evolved complex metabolic mechanisms to deal with constant assault by viruses, bacteria, inflammatory stimuli, and environmental pollutants. Thus, epithelial cells transport antibodies, rapidly proliferate in response to injury, actively propel a protective layer of mucus with their surface cilia, and can exhibit selected activities of immunologically active macrophages, including the expression and/or secretion of several cytokines, growth factors, and adhesion molecules (5-11). Epidermal growth factor (EGF) has been implicated as a principal regulator of these physiological responses through its control of epithelial cell proliferation, differentiation, and inflammatory responses (12, 13).The divergent roles of nitric oxide (NO) as a servoregulator of smooth muscle tone and cytotoxin important in host defense (14) make it an attractive candidate to regulate the multifaceted cellular biology of the airway epithelium. The diverse actions of NO have been explained by the differential expression and activity of enzymes involved in its synthesis, their regulation, and its chemistry in different biological milie...

Cell-Specific Nitric Oxide Synthase-Isoenzyme Expression and Regulation in Response to Endotoxin in Intact Rat Lungs

“…This was anticipated for the constitutive isoforms bNOS and eNOS (Asano et al, 1994;Kobzik et al, 1993;Shaul et al, 1994;Steudel et al, 1999), although an entire profile of cellular localization of both isoforms in lung tissue has so far not been shown. A recent study reported eNOS expression in epithelial cells, endothelial cells, and VSMC in normal rat lung tissue, which corresponds well with the data presented in this study.…”

Differential expression of nitric oxide synthase in human stomach cancer

“…Concomitant expression of TNF-a and iNOS may indicate that TNF-a might contribute to induction of NOS in human stomach cancer. The induction of NOS in several tumor cell lines by various exogenous cytokines and cytokines released from themselves has been reported [6,24].…”

Bronchial obstruction and exhaled nitric oxide response during exercise in cold air

“…Endogenous NO is produced in the lung by a family of NO synthases [9][10][11]. This NO is thought to be an important modulator of vascular tone and airway function in normal airways.…”

“…According to some authors, normal subjects do not develop measurable obstruction in response to airway cooling [1][2][3], whereas other authors claim that they respond by developing measurable obstruction when the stimulus is sufficiently great [4,5]. Under these conditions, the origin and mechanisms involved in the development of bronchial obstruction are still under debate [6][7][8].Endogenous NO is produced in the lung by a family of NO synthases [9][10][11]. This NO is thought to be an important modulator of vascular tone and airway function in normal airways.…”