Kaempferol induces autophagy through AMPK and AKT signaling molecules and causes G2/M arrest via downregulation of CDK1/cyclin B in SK-HEP-1 human hepatic cancer cells.

Kaempferol belongs to the flavonoid family and has been used in traditional folk medicine. Here, we investigated the antitumor effects of kaempferol on cell cycle arrest and autophagic cell death in SK-HEP-1 human hepatic cancer cells. Kaempferol decreased cell viability as determined by MTT assays and induced a G2/M phase cell cycle arrest in a concentration-dependent manner. Kaempferol did not induce DNA fragmentation, apoptotic bodies or caspase-3 activity in SK-HEP-1 cells as determined by DNA gel electrophoresis, DAPI staining and caspase-3 activity assays, respectively. In contrast, kaempferol is involved in the autophagic process. Double-membrane vacuoles, lysosomal compartments, acidic vesicular organelles and cleavage of microtubule-associated protein 1 light chain 3 (LC3) were observed by transmission electron microscopy, LysoΤracker red staining, GFP-fluorescent LC3 assays and acridine orange staining, respectively. In SK-HEP-1 cells, kaempferol increased the protein levels of p-AMPK, LC3-II, Atg 5, Atg 7, Atg 12 and beclin 1 as well as inhibited the protein levels of CDK1, cyclin B, p-AKT and p-mTOR. Taken together, CDK1/cyclin B expression and the AMPK and AKT signaling pathways contributed to kaempferol-induced G2/M cell cycle arrest and autophagic cell death in SK-HEP-1 human hepatic cancer cells. These results suggest that kaempferol may be useful for long-term cancer prevention.

AKT serine/threonine protein kinase modulates baicalin-triggered autophagy in human bladder cancer T24 cells.

Baicalin is one of the major compounds in the traditional Chinese medicinal herb from Scutellaria baicalensis Georgi. We investigated the molecular mechanisms of cell autophagy induced by baicalin in human bladder cancer T24 cells. Baicalin inhibited cell survival as shown by MTT assay and increased cell death by trypan blue exclusion assay in a concentration-dependent manner. Baicalin did not induce apoptotic cell death in T24 cells by TUNEL and caspase-3 activity assay. Baicalin induced the acidic vesicular organelle cell autophagy marker, manifested by acridine orange (AO) and monodansylcadaverine (MDC) staining and cleavage of microtubule-associated protein 1 light chain 3 (LC3). The protein expression levels of the Atg 5, Atg 7, Atg 12, Beclin-1 and LC3-II were upregulated in T24 cells after baicalin treatment. Inhibition of autophagy by 3-methyl-adenine (an inhibitor of class III phosphatidylinositol-3 kinase; 3-MA) reduced the cleavage of LC3 in T24 cells after baicalin treatment. Furthermore, protein expression levels of phospho-AKT (Ser473) and enzyme activity of AKT were downregulated in T24 cells after baicalin treatment. In conclusion, baicalin triggered cell autophagy through the AKT signaling pathway in T24 cells.

Bufalin increases sensitivity to AKT/mTOR-induced autophagic cell death in SK-HEP-1 human hepatocellular carcinoma cells.

Bufalin is the major component of Chan-Su (a traditional Chinese medicine, TCM) extracts from the venom of Bufo bufo gargarizan. In the present study, we investigated the pharmacological mechanisms of cell cycle arrest and autophagic cell death induced by bufalin in SK-HEP-1 human hepatocellular carcinoma cells in vitro. Bufalin inhibited cell survival by MTT assay and increased cell death by trypan blue exclusion assay in a concentration-dependent manner. In addition, bufalin induced G2/M phase arrest by reducing CDK1 activity. Bufalin triggered DNA fragmentation and apoptotic cell death in SK-HEP-1 cells by DNA gel electrophoresis, TUNEL and caspase-3 activity assay, while bufalin induced autophagic cell death by double-membrane vacuoles (transmission electron microscopy, TEM), acidic vesicular organelles (acridine orange staining) and cleavage of microtubule-associated protein 1 light chain 3 (LC3). Protein expression levels of cyclin A and B, CDK1, phospho-CDK1 (Thr161), Cdc25c, phospho-Cdc25c (Ser198), phospho-AKT (Thr308), phospho-AKT (Ser473), phospho­mTOR (Ser2481) were downregulated. In contrast, protein expression levels of the Chk1, Wee1, LC3-II, Beclin-1, Atg 5, Atg 7 and Atg 12 were upregulated in SK-HEP-1 cells after bufalin treatment. Inhibition of autophagy by 3-methyladenine (an inhibitor of class III phosphatidylinositol-3 kinase; 3-MA) or bafilomycin A1 (an inhibitor of the vacuolar proton pump of lysosomes and endosomes) reduced the effect of bufalin on cell viability and enhanced the effect of bufalin on apoptosis. In conclusion, bufalin triggered autophagic cell death and G2/M phase arrest through the AKT/mTOR signaling pathway in SK-HEP-1 cells. Our findings showed that bufalin may be potentially efficacious in the treatment of human hepatocellular carcinoma.

Interactions between SIRT1 and AP-1 reveal a mechanistic insight into the growth promoting properties of alumina (Al2O3) nanoparticles in mouse skin epithelial cells.

The physicochemical properties of nanomaterials differ from those of the bulk material of the same composition. However, little is known about the underlying effects of these particles in carcinogenesis. The purpose of this study was to determine the mechanisms involved in the carcinogenic properties of nanoparticles using aluminum oxide (Al(2)O(3)/alumina) nanoparticles as the prototype. Well-established mouse epithelial JB6 cells, sensitive to neoplastic transformation, were used as the experimental model. We demonstrate that alumina was internalized and maintained its physicochemical composition inside the cells. Alumina increased cell proliferation (53%), proliferating cell nuclear antigen (PCNA) levels, cell viability and growth in soft agar. The level of manganese superoxide dismutase, a key mitochondrial antioxidant enzyme, was elevated, suggesting a redox signaling event. In addition, the levels of reactive oxygen species and the activities of the redox sensitive transcription factor activator protein-1 (AP-1) and a longevity-related protein, sirtuin 1 (SIRT1), were increased. SIRT1 knockdown reduces DNA synthesis, cell viability, PCNA levels, AP-1 transcriptional activity and protein levels of its targets, JunD, c-Jun and BcL-xl, more than controls do. Immunoprecipitation studies revealed that SIRT1 interacts with the AP-1 components c-Jun and JunD but not with c-Fos. The results identify SIRT1 as an AP-1 modulator and suggest a novel mechanism by which alumina nanoparticles may function as a potential carcinogen.