title: 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.
abstract: BACKGROUND
  Lung 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.
  
  
  METHODS
  Cell 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.
  
  
  RESULTS
  We 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.
  
  
  CONCLUSIONS
  Our 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.
authors.affiliation: Laboratory of Tumor Biology, Department of Medical Oncology, Guangdong Provincial Hospital of Chinese Medicine, The Second Clinical Medical Collage, University of Guangzhou Traditional Chinese Medicine, Guangzhou, Guangdong Province, 510120, China. yuqing900@163.com.
authors.forename: YuQing
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Laboratory of Tumor Biology, Department of Medical Oncology, Guangdong Provincial Hospital of Chinese Medicine, The Second Clinical Medical Collage, University of Guangzhou Traditional Chinese Medicine, Guangzhou, Guangdong Province, 510120, China. tangqingyanjiu@163.com.
authors.forename: Qing
authors.initials: Q
authors.lastname: Tang
authors.affiliation: Laboratory of Tumor Biology, Department of Medical Oncology, Guangdong Provincial Hospital of Chinese Medicine, The Second Clinical Medical Collage, University of Guangzhou Traditional Chinese Medicine, Guangzhou, Guangdong Province, 510120, China. star8677@163.com.
authors.forename: JingJing
authors.initials: J
authors.lastname: Wu
authors.affiliation: Laboratory of Tumor Biology, Department of Medical Oncology, Guangdong Provincial Hospital of Chinese Medicine, The Second Clinical Medical Collage, University of Guangzhou Traditional Chinese Medicine, Guangzhou, Guangdong Province, 510120, China. zhenfang_123@163.com.
authors.forename: Fang
authors.initials: F
authors.lastname: Zheng
authors.affiliation: Laboratory of Tumor Biology, Department of Medical Oncology, Guangdong Provincial Hospital of Chinese Medicine, The Second Clinical Medical Collage, University of Guangzhou Traditional Chinese Medicine, Guangzhou, Guangdong Province, 510120, China. 813901541@qq.com.
authors.forename: LiJun
authors.initials: L
authors.lastname: Yang
authors.affiliation: Laboratory of Tumor Biology, Department of Medical Oncology, Guangdong Provincial Hospital of Chinese Medicine, The Second Clinical Medical Collage, University of Guangzhou Traditional Chinese Medicine, Guangzhou, Guangdong Province, 510120, China. swhan2010@live.com.|Higher Education Mega Center, No. 55, Neihuan West Road, Panyu District, Guangzhou, Guangdong Province, 510006, PR China. swhan2010@live.com.
authors.forename: Swei Sunny
authors.initials: SS
authors.lastname: Hann
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D051058:Oncogene Protein v-akt / Q000096:biosynthesis* / Q000235:genetics; D019869:Phosphatidylinositol 3-Kinases / Q000096:biosynthesis / Q000235:genetics; D010766:Phosphorylation / Q000187:drug effects; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis; D058309:Receptors, Prostaglandin E, EP4 Subtype / Q000096:biosynthesis* / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects; D012991:Solanaceous Alkaloids / Q000008:administration & dosage*; D016329:Sp1 Transcription Factor / Q000096:biosynthesis* / Q000235:genetics; D051996:Transcription Factor RelA / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D012333:RNA, Messenger; D058309:Receptors, Prostaglandin E, EP4 Subtype; D012991:Solanaceous Alkaloids; D016329:Sp1 Transcription Factor; C108209:SP1 protein, human; D051996:Transcription Factor RelA; C026609:beta-solamarine; D019869:Phosphatidylinositol 3-Kinases; D051058:Oncogene Protein v-akt