An integrated functional genomic analysis identifies the antitumorigenic mechanism of action for PPARγ in lung cancer cells

Hormonal modulation of ESR1 mutant metastasis

Estrogen receptor alpha gene (ESR1) mutations occur frequently in ER-positive metastatic breast cancer, and confer clinical resistance to aromatase inhibitors. Expression of the ESR1 Y537S mutation induced an epithelial-mesenchymal transition (EMT) with cells exhibiting enhanced migration and invasion potential in vitro. When small subpopulations of Y537S ESR1 mutant cells were injected along with WT parental cells, tumor growth was enhanced with mutant cells becoming the predominant population in distant metastases. Y537S mutant primary xenograft tumors were resistant to the antiestrogen tamoxifen (Tam) as well as to estradiol (E2) withdrawal. Y537S ESR1 mutant primary tumors metastasized efficiently in the absence of E2; however, Tam treatment significantly inhibited metastasis to distant sites. We identified a nine-gene expression signature, which predicted clinical outcomes of ER-positive breast cancer patients, as well as breast cancer metastasis to the lung. Androgen receptor (AR) protein levels were increased in mutant models, and the AR agonist dihydrotestosterone significantly inhibited estrogen-regulated gene expression, EMT, and distant metastasis in vivo, suggesting that AR may play a role in distant metastatic progression of ESR1 mutant tumors.

5-HT induces PPAR γ reduction and proliferation of pulmonary artery smooth muscle cells via modulating GSK-3β/β-catenin pathway

Studies have shown that peroxisome proliferator-activated receptor γ (PPAR γ) is down-regulated in pulmonary vascular lesions of patients with pulmonary hypertension (PH) and animal models of PH. Yet, the detailed molecular mechanisms underlying this alteration are not fully defined; the aim of this study is to address this issue. 5-HT dose- and time-dependently reduced PPAR γ expression and promoted pulmonary artery smooth muscle cells (PASMCs) proliferation; this was accompanied with the phosphorylation of Akt, inactivation of GSK-3β and up-regulation of β-catenin. Importantly, pre-treatment of cells with PI3K inhibitor (Ly294002) or prior silencing of β-catenin with siRNA blocked 5-HT-induced PPAR γ reduction and PASMCs proliferation. In addition, inactivation or lack of GSK-3β or inhibition of proteasome function up-regulated β-catenin protein without affecting its mRNA level and reduced PPAR γ protein expression. Taken together, our study indicates that 5-HT suppresses PPAR γ expression and stimulates PASMCs proliferation by modulating GSK-3β/β-catenin axis, and suggests that targeting this pathway might have potential value in the management of PH.

MicroRNA-27a/b mediates endothelin-1-induced PPARγ reduction and proliferation of pulmonary artery smooth muscle cells

The down-regulation of peroxisome proliferator-activated receptor γ (PPARγ) expression has been found to correlate with the proliferation of pulmonary artery smooth muscle cells (PASMC), pulmonary vascular remodeling and pulmonary hypertension, while the molecular mechanisms underlying PPARγ reduction in PASMC remain largely unclear. The aim of the current study is to address this issue. Endothelin-1 (ET-1) dose- and time-dependently resulted in PPARγ reduction and proliferation of primary cultured rat PASMC, which was accompanied by the activation of nuclear factor-kappaB (NF-κB) and subsequent induction of microRNA-27a/b (miR-27a/b) expression. Chromatin immunoprecipitation assay revealed that NF-κB directly bound to the promoter regions of miR-27a/b. Luciferase reporter assay identified that miR-27a/b directly regulates the expression of PPARγ in PASMC. Further study indicated that the presence of either NF-κB inhibitor pyrrolidinedithiocarbamate or prior silencing miR-27a/b with anti-miRNA oligonucleotides suppressed ET-1-induced PPARγ reduction and proliferation of PASMC, while overexpression of miR-27a/b reduced PPARγ expression and enhanced PASMC proliferation. Taken together, our study demonstrates that ET-1 stimulates miR-27a/b expression by activation of the NF-κB pathway, which in turn results in PPARγ reduction and contributes to ET-1-induced PASMC proliferation.