Constitutive activation of an epithelial signal transducer and activator of transcription (STAT) pathway in asthma
Deepak Sampath, Mario Castro, Dwight C. Look, Michael J. Holtzman
Deepak Sampath, Mario Castro, Dwight C. Look, Michael J. Holtzman
View: Text | PDF
Article

Constitutive activation of an epithelial signal transducer and activator of transcription (STAT) pathway in asthma

Abstract

Cytokine effects on immunity and inflammation often depend on the transcription factors termed signal transducers and activators of transcription (STATs), so STAT signaling pathways are candidates for influencing inflammatory disease. We reasoned that selective IFN responsiveness of the first STAT family member (Stat1) and Stat1-dependent immune-response genes such as intercellular adhesion molecule-1 (ICAM-1), IFN regulatory factor-1 (IRF-1), and Stat1 itself in airway epithelial cells provides a basis for detecting cytokine signaling abnormalities in inflammatory airway disease. On the basis of nuclear localization and phosphorylation, we found that epithelial Stat1 (but not other control transcription factors) was invariably activated in asthmatic compared with normal control or chronic bronchitis subjects. Furthermore, epithelial levels of activated Stat1 correlated with levels of expression for epithelial ICAM-1, IRF-1, and Stat1, and in turn, ICAM-1 levels correlated with T-cell accumulation in tissue. However, only low levels of IFN-γ or IFN-γ–producing cells were detected in airway tissue in all subjects. The results therefore provide initial evidence linking abnormal behavior of STAT pathways for cytokine signaling to the development of an inflammatory disease. In that context, the results also change the current scheme for asthma pathogenesis to one that must include a localized gain in transcriptional signal ordinarily used for a T helper 1–type cytokine (IFN-γ) in combination with allergy-driven overproduction of T helper 2–type cytokines.

Authors

Deepak Sampath, Mario Castro, Dwight C. Look, Michael J. Holtzman

×

Figure 5

Options: View larger image (or click on image) Download as PowerPoint
Increased levels of T cells with normal levels of IFN-γ expression in as...
Increased levels of T cells with normal levels of IFN-γ expression in asthma. (a–f) Representative photomicrographs of endobronchial biopsy sections from a representative control (a, d, and e) and asthma (b, c, and f) subject after immunostaining with anti-CD3 mAb (a and b) and after in situ hybridization with 35S-labeled IFN-γ cRNA using unstimulated (c and d) or PMA/ionomycin–stimulated (e and f) biopsies. In all cases, hybridization with 35S-labeled IFN-γ RNA (sense probe) gave no detectable signal above background (not shown). Arrowheads indicate cells expressing IFN-γ mRNA. Scale bar: 15 μM. (g and h) Representative results of RT-PCR from endobronchial tissue (lanes 1–6) and from PMA/ionomycin–stimulated PMBCs (lane 7) using oligonucleotide primers for IFN-γ, IL-4, and β-actin. PCR products were subjected to agarose gel electrophoresis and then detected using ethidium bromide staining (g) or subsequent Southern blotting with 32P-labeled cDNA probes (h).