Bexarotene Inhibits The Viability Of Non-small Cell Lung Cancer Cells Via Slc10a2/PPAR?/PTEN/mTOR Signaling Pathway

Retinoids play critical roles in normal development and physiology by modulating cell growth,division,reproduction,differentiation,and immune function.They are capable of inhibiting cell growth,inducing differentiation,and inducing apoptosis in a variety of tumor cell lines.The retinoids have been investigated extensively for their utility in cancer chemoprevention and treatment.Bexarotene is a novel synthetic retinoid analog which exerts its action through retinoic X receptor?RXR?subclass of receptors?RXR?,RXR?and RXR??.In clinical practice,bexarotene has a wide range of dermatologic indications including for psoriasis,acneiform and keratinization disorders and been approved for the treatment of cutaneous T-cell lymphoma by the American Food and Drug Adiministration?FDA?.A known side-effect of retinoid therapy is the elevation of serum lipids.The molecular mechanism underlying the rexinoid-induced hypertriglyceridemia remains largely unknown.Bexarotene was evaluated with or without standard chemotherapy as a first-line therapy in treating advanced non-small-cell lung cancer?NSCLC?in two large phase III trials?SPIRIT I and SPIRIT II?.Although a significant survival benefit was not observed for the overall bexarotene-treated population,a third of bexarotene-treated patients who developed NCI grade 3 or higher hypertriglyceridemia exhibited significantly longer survival compared to the patients in the control arm and to the patients with low-grade hypertriglyceridemia.Similar correlations between survival and triglyceride level induced by bexarotene were also revealed by retrospective analysis in other bexarotene cancer trials.In order to identify genomic polymorphisms that could serve as potential predictive biomarkers for response and improved survival by bexarotene treatment in NSCLC patients,Meglasson et al used Affymetrix 500K whole genome SNP arrays and Sequenom i PLEX^TM arrays to genotype DNA samples extracted from plasma archieved from 403 patients who were enrolled into SPIRIT I and SPIRIT II trials.They identified that solute carrier family 10,member 2?SLC10A2?was an attractive candidate that might be involved in bexarotene induced hypertriglyceridemia,implicating its potential in predicting bexarotene-improved survival response.SLC10A2 is known to be regulated by RXR at transcriptional level,probably through forming a heterodimer with PPAR,a nuclear receptor known to participate in lipid metabolism.These intriguing results provide a new hypothesis for bexarotene induced hypertriglyceridemia and its antitumor action.They warrant confirmation and further exploration.So we designed the two-step experiments in vitro to explore the cellular mechanism which may involve in this process.We constructed slc10a2overexpressed A549 cells and H1299 cells as cell models,normal A549 cells and H1299cells as control.Then we explored the effects of slc10a2 on A549 cells and H1299 cells behaviors,including proliferation,invasion and apoptosis.The expression of apoptotic related genes and anti-cancer genes was also be detected.We found that the proliferation and migration were inhibited and the apoptosis of NSCLC cells was accelerated by bexarotene.In addition,overexpressed slc10a2 in NSCLC cells can further suppress the proliferation and migration,and promote apoptosis under the treatment of bexarotene.On the contrary,the opposite results were obtained after slc10a2 gene was silenced in NSCLC cells treated with bexarotene.Moreover,the expression of caspase 3,caspase 7,PTEN,P21,P53,LKB1,TSC2 were increased and the expression of Bcl-2,cyclin D1,c-FLIP were declined in NSCLC cells and slc10a2 overexpressed NSCLC cells with the treatment of bexarotene,and the opposite situations were seen after slc10a2 gene was silenced in NSCLC cells.We further explored how could slc10a2 affect in this process.We found that GW9662?an selective PPAR?antagonist?could shorten the proliferative inhibition effects of bexarotene.The expression of caspase 3,caspase 7,PTEN,P21,P53,LKB1 and TSC2 were declined and the expression of Bcl-2,cyclin D1,c-FLIP were increased when A549 cells,H1299 cells or slc10a2 overexpressed A549 cells and H1299cells were co-treated with bexarotene and GW9662.In addition the western blotting and RT-PCR showed the expression of slc10a2 and PPAR?were gradually enhanced with the increase of bexarotene's concentrations from 1 m M to 10m M.The expression of PTEN was inhibited when A549 cell was co-treated with bexarotene and GW9662.On the contrary,the expression of m TOR peroxisome proliferator-activated receptor??PPAR??,then up-regulated PTEN expression and down-regulated m TOR expression.These results suggest that bexarotene inhibits the viability of lung cancer cells via slc10a2/PPAR?/PTEN/m TOR signaling pathway.