p53 modulates the effect of ribosomal protein S6 kinase1 (S6K1) on cisplatin toxicity in chronic myeloid leukemia cells

Aescin Protects Neuron from Ischemia-Reperfusion Injury via Regulating the PRAS40/mTOR Signaling Pathway

Ischemic stroke is one of the major causes of disability; widely use of endovascular thrombectomy or intravenous thrombolysis leads to more attention on ischemia-reperfusion injury (I/R injury). Aescin, a natural compound isolated from the seed of the horse chestnut, has been demonstrated anti-inflammatory and antiedematous effects previously. This study was aimed at determining whether aescin could induce protective effects against ischemia-reperfusion injury and exploring the underlying mechanisms in vitro. Primary cultured neurons were subjected to 2 hours of oxygen-glucose deprivation (OGD) followed by 24 hours of simulated reperfusion. Aescin, which worked in a dose-dependent manner, could significantly attenuate neuronal death and reduce lactate dehydrogenase (LDH) release after OGD and simulated reperfusion. Aescin treatment at a concentration of 50 μg/ml provided protection with fewer side effects. Results showed that aescin upregulated the phosphorylation level of PRAS40 and proteins in the mTOR signaling pathway, including S6K and 4E-BP1. However, PRAS40 knockdown or rapamycin treatment was able to undermine and even abolish the protective effects of aescin; meanwhile, the levels of phosphorylation PRAS40 and proteins in the mTOR signaling pathway were obviously decreased. Hence, our study demonstrated that aescin provided neuronal protective effects against I/R injury through the PRAS40/mTOR signaling pathway in vitro. These results might contribute to the potential clinical application of aescin and provide a therapeutic target on subsequent cerebral I/R injury.

PACT cessation overcomes ovarian cancer cell chemoresistance to cisplatin by enhancing p53-mediated apoptotic pathway

Ovarian cancer ranks as a lethal gynecological malignancy, and development of resistance to chemotherapy agents constitutes a major clinical challenge in ovarian carcinoma management. P53-associated cellular protein-testes derived (PACT) is recently proven to be expressed aberrantly in several cancers, and exerts a critical roles in cell proliferation, apoptosis and migration. Up to now, its function in chemoresistance of ovarian cancer remains poorly defined. In the present study, elevated expression of PACT was detected in cisplatin-resistant A2780/CP cells relative to cisplatin-sensitive A2780 cells. Moreover, exposure to cisplatin also increased PACT expression in A2780 cells. Functional assay confirmed that knockdown of PACT further aggravated the inhibitory effects of cisplatin on A2780 cell viability and enhanced cell apoptosis and caspase-3 activity in cisplatin-treated A2780 cells, indicating that PACT cessation elevates cell sensitivity to cisplatin in A2780 cells. Whilst, deletion of PACT affords little effects on cisplatin resistance in p53-defective SKOV3 cells. Mechanistic analysis corroborated that depression of PACT notably enhanced cisplatin-induced p53 expression, concomitant with the increases in p53-downstream Bax, p21 expression and decrease in Bcl-2 expression. Intriguingly, blocking the p53 pathway notably reversed PACT inhibition-increased cell sensitivity to cisplatin in A2780 cells by elevating cell viability and depressing cell apoptosis. Additionally, abrogation of p53 signaling also blunts PACT suppression-overcomed chemotherapy resistance to cisplatin in A2780/CP cells. Together, these findings confirm that targeting PACT may antagonize ovarian cancer cell resistance to cisplatin, supporting a promising therapeutic strategy to overcome the chemotherapy resistance in the treatment of ovarian cancer.

The pregnane X receptor (PXR) and the nuclear receptor corepressor 2 (NCoR2) modulate cell growth in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is the sixth most frequent cancer worldwide. The pregnane X receptor (PXR) is a nuclear receptor regulating several target genes associated with cancer malignancy. We here demonstrated a significant effect of PXR on HNSCC cell growth, as evidenced in PXR knock-down experiments. PXR transcriptional activity is more importantly regulated by the presence of coactivators and corepressors than by PXR protein expression. To date, there is scarce information on the regulation of PXR in HNSCC and on its role in the pathogenesis of this disease. Coactivator and corepressor expression was screened through qRT-PCR in 8 HNSCC cell lines and correlated to PXR activity, determined by using a reporter gene assay. All cell lines considerably expressed all the cofactors assessed. PXR activity negatively correlated with nuclear receptor corepressor 2 (NCoR2) expression, indicating a major role of this corepressor in PXR modulation and suggesting its potential as a surrogate for PXR activity in HNSCC. To test the association of NCoR2 with the malignant phenotype, a subset of three cell lines was transfected with an over-expression plasmid for this corepressor. Subsequently, cell growth and chemoresistance assays were performed. To elucidate the mechanisms underlying NCoR2 effects on cell growth, caspase 3/7 activity and protein levels of cleaved caspase 3 and PARP were evaluated. In HNO97 cells, NCoR2 over-expression decreased cell growth, chemoresistance and increased cleaved caspase 3 levels, caspase activity and cleaved PARP levels. On the contrary, in HNO124 and HNO210 cells, NCoR2 over-expression increased cell growth, drug resistance and decreased cleaved caspase 3 levels, caspase activity and cleaved PARP levels. In conclusion, we demonstrated a role of PXR and NCoR2 in the modulation of cell growth in HNSCC. This may contribute to a better understanding of the highly variable HNSCC therapeutic response.