Prostacyclin reverses the cigarette smoke-induced decrease in pulmonary Frizzled 9 expression through miR-31

Abstract

Half of lung cancers are diagnosed in former smokers, leading to a significant treatment burden in this population. Chemoprevention in former smokers using the prostacyclin analogue iloprost reduces endobronchial dysplasia, a premalignant lung lesion. Iloprost requires the presence of the WNT receptor Frizzled 9 (Fzd9) for inhibition of transformed growth in vitro. To investigate the relationship between iloprost, cigarette smoke, and Fzd9 expression, we used human samples, mouse models, and in vitro studies. Fzd9 expression was low in human lung tumors and in progressive dysplasias. In mouse models and in vitro studies, tobacco smoke carcinogens reduced expression of Fzd9 while prostacyclin maintained or increased expression. Expression of miR-31 repressed Fzd9 expression, which was abrogated by prostacyclin. We propose a model where cigarette smoke exposure increases miR-31 expression, which leads to decreased Fzd9 expression and prevents response to iloprost. When smoke is removed miR-31 is reduced, prostacyclin can increase Fzd9 expression, and progression of dysplasia is inhibited. Fzd9 and miR-31 are candidate biomarkers for precision application of iloprost and monitoring of treatment progress. As we continue to investigate the mechanisms of prostacyclin chemoprevention and identify biomarkers for its use, we will facilitate clinical trials and speed implementation of this valuable prevention approach.

Prostacyclin and EMT Pathway Markers for Monitoring Response to Lung Cancer Chemoprevention

“…Early stages of lung premalignancy are also regulated by miRNA, making them potentially relevant to prostacyclin chemoprevention (8,13). While very little is known about prostacyclin or PPARγ and miRNA, we demonstrated that reduction of miR-31 occurs with prostacyclin treatment and may be linked to expression of the presumed iloprost receptor in the lung epithelium (14,15).…”

“…In the one-week smoke exposed model, mice are harvested after one week of smoke exposure or ambient air. After one week of smoke, FVB mice have early gene expression changes associated with lung cancer but do not yet have lesions (14). With smoke exposure, Snail, Vimentin, and COX-2 increase, while Ecadherin, CRB3, and PPARγ, decrease (Fig.…”

“…We investigated miR-34c and miR-221 as potential markers of iloprost activity based on our initial screens and previous studies linking their dysregulation to lung cancer (14,25–29). In HBEC treated for two weeks, miR-34c expression increased with iloprost but did not change with CSC (Fig.…”

“…The prostacyclin analogue iloprost is an agent with strong potential as lung cancer chemoprevention. Significant preclinical data supported moving this agent to clinical trials (4,5,14,15,31). Former smokers treated with iloprost in a phase II clinical trial had improved endobronchial dysplasia, a premalignant lesion linked with development of squamous cell carcinoma (6,30).…”

“…In lung epithelial cells, PPARγ is activated by WNT7a binding to its receptor Fzd9, leading to decreased transformed growth, a pathway also stimulated by iloprost (15,22). Fzd9 is the presumed receptor for iloprost in the lung epithelium and its expression is reduced in HBEC by one week of CSC exposure (14,15). We identified Fzd9 as a potential marker for predicting response to iloprost in high-risk subjects and are investigating its role in the mechanism of iloprost activity (14,15).…”