Peroxisome proliferator-activated receptor-gamma ligands suppress fibronectin gene expression in human lung carcinoma cells: involvement of both CRE and Sp1

Our plain-English summary of Peroxisome proliferator-activated receptor-gamma ligands suppress fibronectin gene expression in human lung carcinoma cells: involvement of both CRE and Sp1, by S. Han, J.D. Ritzenthaler, H.N. Rivera, et al (American Journal of Physiology. Lung Cellular and Molecular Physiology, 2005).

The study

• Authors: S. Han, J.D. Ritzenthaler, H.N. Rivera, J. Roman
• Journal: American Journal of Physiology. Lung Cellular and Molecular Physiology
• Published: 2005;289(3):L419-28
• Cited by: 37 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Lung carcinoma often occurs in patients with chronic lung disease such as tobacco-related emphysema and asbestos-related pulmonary fibrosis. These diseases are characterized by dramatic alterations in the content and composition of the lung extracellular matrix, and we believe this "altered" matrix has the ability to promote lung carcinoma cell growth. One extracellular matrix molecule shown to be altered in these lung diseases is fibronectin (Fn). We previously reported increased growth and survival of non-small cell lung carcinoma (NSCLC) cells exposed to Fn. Thus Fn may serve as a mitogen/survival factor for NSCLC and therefore represents a novel target for anti-cancer strategies. To this end, we studied the effects of the PPARgamma ligands 15d-PGJ(2), rosiglitazone (BRL49653), and troglitazone on Fn expression in NSCLC cells and found that they were able to inhibit Fn gene transcription. Inhibition of Fn expression by BRL49653 and troglitazone, but not by 15d-PGJ(2), was prevented by the specific PPARgamma antagonist GW-9662 and by PPARgamma small interfering RNA. Working with Fn deletion and mutated promoter constructs, we found that the region between -170 and -50 bp downstream from the transcriptional start site of the promoter was involved in PPARgamma ligand inhibition. PPARgamma ligands also diminished the phosphorylation of CREB, diminished Sp1 nuclear protein expression, and prevented the binding of these transcription factors to CRE and Sp1 sites, respectively, within the Fn promoter. In summary, our results demonstrate that PPARgamma ligands inhibit Fn gene expression in NSCLC cells through PPARgamma-dependent and -independent pathways that affect both CREB and Sp1.

In plain English

This was a laboratory study of human lung cancer cells grown in dishes. It did not study asbestos exposure or people. In their background, the authors noted that lung cancer often occurs with chronic lung diseases such as asbestos-related pulmonary fibrosis, in which a tissue protein called fibronectin is altered. They tested three PPAR-gamma ligands, substances that bind a cell receptor: the natural ligand 15d-PGJ2 and the synthetic ligands rosiglitazone (BRL49653) and troglitazone. They used non-small cell lung carcinoma cell lines, mainly the line H1838. All three ligands lowered fibronectin protein and its messenger RNA. Blocking the receptor, either with the antagonist GW-9662 or by silencing its gene, prevented the effect of rosiglitazone and troglitazone but not that of 15d-PGJ2. Tests on the fibronectin gene's control region pointed to one CRE site and to Sp1 sites. The ligands reduced the binding of the proteins CREB and Sp1 to these sites. Lowering fibronectin by gene silencing reduced cell growth. The authors concluded that their observations suggest a possible role for PPAR-gamma ligands in developing treatments to prevent or inhibit lung cancer progression.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (in vitro) study of cultured human lung carcinoma cell lines. No human subjects, no animals, no asbestos exposure.
• Who was studied: Two commercially obtained human non-small cell lung carcinoma (NSCLC) cell lines, H1838 and H2106. Most experiments were in H1838; the authors reported similar results in H2106 for some tests (data not shown).
• Exposure: No asbestos exposure was studied; asbestos appears only in the background. The cells were treated with PPAR-gamma ligands: 15d-PGJ2 (natural), and rosiglitazone (BRL49653) and troglitazone (synthetic). Doses were printed as 10, 10 and 15 with the unit symbol garbled, apparently micromolar. Some cells also received the PPAR-gamma antagonist GW-9662 or PPAR-gamma small interfering RNA. Treatment generally lasted 24 h.
• Main results:
  • In H1838 cells, BRL49653 and 15d-PGJ2 significantly reduced fibronectin protein in a dose- and time-dependent way. They were most effective at a concentration of 10 for 24 h. Troglitazone gave similar results (not shown).
  • All three ligands, given for 24 h, significantly reduced fibronectin mRNA in H1838 cells compared with untreated cells. This was confirmed by real-time RT-PCR.
  • The fall in fibronectin came before any growth inhibition: fibronectin dropped before 24 h, while growth inhibition was not seen until after 48 h (data not shown).
  • Silencing the cells' own fibronectin with siRNA reduced NSCLC cell proliferation. Adding outside fibronectin restored proliferation to baseline.
  • The antagonist GW-9662 and PPAR-gamma siRNA each prevented the fibronectin-lowering effect of BRL49653 and troglitazone, but not that of 15d-PGJ2.
  • In fibronectin promoter tests, mutating only one of three CRE sites (the 170 bp site) affected the suppressive effect. The authors concluded that CRE and Sp1 elements in the region between 170 and 50 bp were mainly responsible.
  • Treatment with the ligands reduced protein binding to CRE sites and to Sp1 sites in the fibronectin promoter compared with untreated cells.
  • The ligands reduced phosphorylated CREB but not total CREB, and reduced the amount of Sp1 protein in the cell nucleus.
• The authors' conclusion: The authors concluded that PPAR-gamma ligands inhibit fibronectin gene expression in NSCLC cells through receptor-dependent and receptor-independent pathways involving CREB and Sp1. They suggested these ligands may have a role in developing treatments to prevent or inhibit lung carcinoma progression.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Carcinoma, Emphysema, Pulmonary Fibrosis.

Related studies

• Tenascin and fibronectin expression in human mesothelial cells and pleural mesothelioma cell-line cells — V.L. Kinnula, A. Linnala, et al. (1998)
• Fibronectin expression and organization in mesothelial and mesothelioma cells — P.C. Ferriola, W. Stewart (1996)
• Secretion of fibronectin by mineral dust-derived alveolar macrophages and activated peritoneal macrophages — R. Davies, G. Erdogdu (1989)
• Asbestos fibre length-dependent detachment injury to alveolar epithelial cells in vitro: role of a fibronectin-binding receptor — K. Donaldson, B.G. Miller, et al. (1993)
• Fibronectin and procollagen 3 levels in bronchoalveolar lavage of asbestos-exposed human subjects and sheep — R. Bégin, M. Martel, et al. (1986)
• Aggregation of fibronectin by asbestos fibers in the pericellular matrix of cultured human fibroblasts — T. Vartio, I. Virtanen, et al. (1986)

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