Influence of gossypol acetic acid on the growth of human adenoid cystic carcinoma ACC-M cells and the expression of DNA methyltransferase 1

Dual effects of gossypol on human hepatocellular carcinoma via endoplasmic reticulum stress and autophagy

Treatment outcomes for hepatocellular carcinoma (HCC) remain unsatisfactory, and effective new therapeutic methods are urgently needed. Gossypol has been shown to have an anti-HCC effect, but the underlying mechanism requires further study. In this study, we found gossypol inhibited HCC cells in vitro and in vivo. Typical apoptosis was induced in HCC cells. Dilated ER and autophagosomes were observed by electron microscopy, and the activation of the unfolded protein response and autophagy markers suggested that gossypol induced both ER stress and autophagy. C/EBP homologous protein was the key factor that led to apoptotic cell death, whereas inositol-requiring enzyme 1α and eukaryotic initiation factor 2α played a protective role. Autophagy protected the cells from ER stress-related apoptosis. Both in vitro and in vivo studies indicated that inhibition of autophagy enhanced the anti-HCC effect of gossypol. Taken together, ER stress is the molecular mechanism underlying gossypol-induced apoptosis and autophagy. Gossypol exhibits anti-HCC activity primarily through the activation of apoptosis. However, gossypol-induced autophagy protects HCC cells from ER stress. Therefore, a combination therapy of gossypol and autophagy inhibitors may lead to an enhanced anti-HCC effect.

Targeting EP4 downstream c-Jun through ERK1/2-mediated reduction of DNMT1 reveals novel mechanism of solamargine-inhibited growth of lung cancer cells

Lung cancer is the most common cancer and the leading cause of cancer deaths worldwide. We previously showed that solamargine, one natural phytochemicals from traditional plants, inhibited the growth of lung cancer cells through inhibition of prostaglandin E2 (PGE₂ ) receptor EP4. However, the potential downstream effectors of EP4 involving in the anti-lung cancer effects of solamargine still remained to be determined. In this study, we further verified that solamargine inhibited growth of non-small-cell lung cancer (NSCLC) cells in multiple cell lines. Mechanistically, solamargine increased phosphorylation of ERK1/2. Moreover, solamargine inhibited the protein expression of DNA methyltransferase 1 (DNMT1) and c-Jun, which were abrogated in cells treated with MEK/ERK1/2 inhibitor (PD98059) and transfected with exogenously expressed DNMT1 gene, respectively. Interestingly, overexpressed DNMT1 gene antagonized the effect of solamargine on c-Jun protein expression. Intriguingly, overexpressed c-Jun blocked solamargine-inhibited lung cancer cell growth, and feedback resisted the solamargine-induced phosphorylation of ERK1/2. A nude mouse xenograft model implanted with lung cancer cells in vivo confirmed the results in vitro. Collectively, our results show that solamargine inhibits the growth of human lung cancer cells through reduction of EP4 protein expression, followed by increasing ERK1/2 phosphorylation. This results in decrease in DNMT1 and c-Jun protein expressions. The inter-correlations between EP4, DNMT1 and c-Jun and feedback regulation of ERK1/2 by c-Jun contribute to the overall responses of solamargine in this process. This study uncovers an additional novel mechanism by which solamargine inhibits growth of human lung cancer cells.