Clinical proteomics in lung diseases.

Proteomics is a relatively new approach for understanding the pathology and pathogenesis of various diseases. It has also been used for characterizing the modifications in protein expression during the development of interstitial lung diseases, in lung tumors, or following exposure to exogenous stress signals. We compared the protein composition of primary human lung fibroblasts derived from patients with lung fibrosis and control fibroblasts of unaffected lung tissues. We found a predominant modulation in proteins related to the cytoskeleton, including decreased expression of vimentin and lamin A/C, and increased expression of moesin. Furthermore, we observed lower levels of components of the antioxidative system, such as omega class glutathione S-transferase and an up-regulation of an intracellular chloride channel. In fibroblasts obtained from fibrotic lungs, the expression of a major histocompatibility complex class I C was decreased, and so was the expression of tripeptidyl-peptidase-I-precursor, a collagen-degrading exopeptidase. Our results and the studies reviewed in this paper represent just the beginning of detailed studies that should unravel the relevance and the functional consequences of differential protein expressions in the diseased lung.

Increased carcinogenic potential of myeloid tumor cells induced by aberrant TGF-beta1-signaling and upregulation of cathepsin B.

The TGF-beta signaling pathways are implicated in cancer. Cysteine cathepsins can contribute to the carcinogenic potential of tumor cells. The aim of this study was to investigate the regulation of cysteine cathepsin expression by TGF-beta1 and the functional implications in tumor cells. We found an upregulation of cathepsin B (CathB, 2- to 5-fold) in different myeloid tumor cells (THP-1, MonoMac-1, MonoMac-6) after incubation with TGF-beta1. No upregulation was found in monocytes, and there was suppression of CathB expression in epithelial tumor cells (A549). Increased cathepsin B activity led to enhanced carcinogenic potential, which was reflected by increased migration and invasion of the cells and resistance to inhibitor-induced apoptosis. Analysis of the TGF-beta signaling pathways showed no alterations in TGF-beta/BMP receptor expression or SMAD2/3 phosphorylation, and no influence of MAP kinase pathways. However, a reduction in SMAD1 expression was detected. The lack of BMP action on cysteine cathepsin expression in myeloid tumor cells, but not in epithelial tumor cells, suggests a defect in the Smad1/Smad5 pathway. We located a related TGF-beta1-responsive element within the first intron of the CathB gene. In conclusion, alterations in the TGF-beta1 signaling pathway lead to upregulation of CathB, which contributes to the carcinogenic potential of tumor cells.

Functional consequences of cathepsin L deficiency in human lung epithelial cells.

Cathepsin L is a cysteine protease of the papain family. Lung epithelial cells play an important role in host defence. The aim of the present study was to investigate the functional role of cathepsin L in the human lung carcinoma cell line A549. Cathepsin L-deficient A549 clones were generated. They showed a significant lower proliferation and secreted 5- to 8-fold more IL-8 than the control cells. The production of IL-6, IL-18, and TGF-beta1/2 was not affected significantly. It was shown that the cells upregulate IL-8 transcription and that IL-8 in the culture supernatant is necessary for the containment of cellular proliferation. In conclusion, the data show that suppression of cathepsin L expression in A549 cells leads to a growth inhibition which is partially compensated by an upregulation of IL-8 production.

Cathepsin L is involved in cathepsin D processing and regulation of apoptosis in A549 human lung epithelial cells.

Cathepsins are implicated in a multitude of physiological and pathophysiological processes. The aim of the present study was to investigate the function of cathepsin L (catL) in the proteolytic network of human lung epithelial cells and its role in the regulation of apoptosis. We found that catL-deficient A549 cells as well as lung tissue extracts of catL(-/-) mice express increased amounts of single-chain cathepsin D (catD). Degradation experiments indicate that catL specifically degrades the single-chain isoform of catD. Furthermore, we found that catL-deficient cells showed increased sensitivity to apoptosis. Finally, we demonstrate that the inhibition of catD activity by pepstatin A decreased the number of apoptotic cells in catL-deficient A549 cells after anti-Fas treatment. In conclusion, catL is involved in catD processing and the accumulation of catD isoforms in catL-deficient cells is associated with increased rates of spontaneous and anti-Fas-induced apoptosis.