Inactivation of PI3-K/Akt and reduction of SP1 and p65 expression increase the effect of solamargine on suppressing EP4 expression in human lung cancer cells.

YuQing Chen,Qing Tang,Swei Sunny Hann,LiJun Yang,Fang Zheng,JingJing Wu

doi:10.1186/s13046-015-0272-0

Abstract

BackgroundLung cancer is the most common cause of cancer-related deaths worldwide. Natural phytochemicals from traditional medicinal plants such as solamargine have been shown to have anticancer properties. The prostaglandin E2 receptor EP4 is highly expressed in human cancer, however, the functional role of EP4 in the occurrence and progression of non small cell lung cancer (NSCLC) remained to be elucidated.MethodsCell viability was measured by MTT assays. Western blot was performed to measure the phosphorylation and protein expression of PI3-K downstream effector Akt, transcription factors SP1, p65, and EP4. Quantitative real-time PCR (qRT-PCR) was used to examine the mRNA levels of EP4 gene. Exogenous expression of SP1, p65, and EP4 genes was carried out by transient transfection assays. EP4 promoter activity was measured by Dual Luciferase Reporter Kit.ResultsWe showed that solamargine inhibited the growth of lung cancer cells. Mechanistically, we found that solamargine decreased the phosphorylation of Akt, the protein, mRNA expression, and promoter activity of EP4. Moreover, solamargine inhibited protein expression of SP1 and NF-κB subunit p65, all of which were abrogated in cells transfected with exogenous expressed Akt. Intriguingly, exogenous expressed SP1 overcame the effect of solamargine on inhibition of p65 protein expression, and EP4 protein expression and promoter activity. Finally, exogenous expressed EP4 feedback reversed the effect of solamargine on phosphorylation of Akt and cell growth inhibition.ConclusionOur results show that solamargine inhibits the growth of human lung cancer cells through inactivation of Akt signaling, followed by reduction of SP1 and p65 protein expression. This results in the inhibition of EP4 gene expression. The cross-talk between SP1 and p65, and the positive feedback regulatory loop of PI3-K/Akt signaling by EP4 contribute to the overall responses of solamargine in this process. This study unveils a novel mechanism by which solamargine inhibits growth of human lung cancer cells.

Highlights

Lung cancer is the most common cause of cancer-related deaths worldwide
We showed that solamargine inhibited the growth of H1299 and A549 lung cancer cells in the dose-dependent manner with the most significant effect observed at 6 μM for up to 72 h (Fig. 1a)
Our results found that, compared with the untreated control cells, solamargine significantly increased the proportion of cells at G0/G1 phase, while the proportion of cells at S phase were reduced at the 6 μM solamargine (Fig. 1b) suggesting that solamargine induced cell cycle arrest in G0/G1 phase in lung cancer cells

Summary

Introduction

Lung cancer is the most common cause of cancer-related deaths worldwide. The prostaglandin E2 receptor EP4 is highly expressed in human cancer, the functional role of EP4 in the occurrence and progression of non small cell lung cancer (NSCLC) remained to be elucidated. Lung cancer is the most common cancer and the leading cause of cancer mortality worldwide for both men and women [1]. Most patients present with incurable advanced or metastatic disease with poor 5-year survival rate. The choice of treatment for patients with advanced disease remains dilemma and challenge, which dependent on the histological types, tumor characteristics, stages, co-morbidities and prior therapies history. Inspire of the advance in understanding the molecular mechanism and treatment options, the poor patient survival still remain no changes and the caused debilitating symptoms seriously affect the quality of life of patients. Searching for more effective alternative treatment strategies in order to strengthen the therapeutic efficacy with negligible side effects is urgently needed

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Conclusion