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

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.

Combination of Solamargine and Metformin Strengthens IGFBP1 Gene Expression Through Inactivation of Stat3 and Reciprocal Interaction Between FOXO3a and SP1

“…Although there were important discoveries revealed by other studies indicated multiple signaling pathways and molecular genes or proteins that involved in the anti-tumor responses of solamargine, the in-depth molecular mechanisms by which this agent in inhibition of tumor growth still remained to be elucidated. Consistent with our previous report [21], the current results further confirmed the anti-lung cancer effects of solamargine and suggested a potential therapeutic modality in lung cancer.…”

“…We previous showed that solamargine inhibited growth of human lung cancer A549 cells [21]. In the current study, we further assessed the relative contribution of inhibition affected by solamargine.…”

“…Solamargine reduced the growth of metastatic and primary melanoma cells via disrupting the intrinsic apoptosis pathway [20]. We previously found that s olamargine reduced the proliferation of NSCLC cells through inhibition of prostaglandin E2 (PGE 2 ) receptor EP4, DNA methyltransferase 1 (DNMT1), and c-Jun expressions [21, 22]. However, the detailed mechanisms and potential benefits underlying the effects of solamargine in prevention and treatment of NSCLC still remain to be determined.…”

MicroRNA-19b-3p regulates nasopharyngeal carcinoma radiosensitivity by targeting TNFAIP3/NF-κB axis

“…IR-induced DSBs trigger a DNA damage response with NF-κB activation as the antiapoptotic factor in most cell types [29–32]. Thus, through the inhibition of NF-κB activation, radiosensitivity can be increased [33]. Previous studies have demonstrated that TNFAIP3 acts as a repressor that downregulates NF-κB activity.…”

Anticancer Properties of Solamargine: A Systematic Review

“…Chen et al . () showed that solamargine can inhibit the growth of lung cancer cells through inhibition of prostaglandin E2 receptor EP4. In other study, they indicated that solamargine increased phosphorylation of ERK1/2 and inhibited expression of c‐Jun and DNA methyltransferase 1 (DNMT1) at protein level, which were abrogated in cells transfected with exogenously expressed DNMT1 gene and treated with MEK/ERK1/2 inhibitor, respectively.…”