This association can also promote proteasomal degradation of MCL1 to enhance the mitochondrial apoptosis [21]. Chemotherapy has been reported to induce ER stress response in cancer cells [22]. ER stress is usually caused by accumulation of misfolded or unfolded proteins in the ER lumen. When those proteins are not resolved, ER stress is prolonged to induce apoptosis [23, 24].There are several mechanisms linking ER stress to apoptosis such as cleavage and activation of pro-CASP12 and activation of ASK1 [25]. Many TSA HDAC studies have focused on the ER stress effector DDIT3,

which is a downstream target of ATF4 [26]. DDIT3 is a bZIP-containing transcription factor that can target several apoptotic genes including GW572016 TNFRSF10B and PMAIP1 [27]. The molecular mechanisms of ER stress-induced apoptosis still require further study. Cancer stem cells have many similar PF-3084014 clinical trial aspects with stem cells. Those cells have the ability of self-renewal and differentiation, express typical markers of stem cells [28]. They are also considered to be the origin

of cancer cells and are rather resistant to active drugs. Many reports have indicated that cancer stem cells are correlated with poor clinical prognosis [29, 30]. So, targeting cancer stem cell may be a promising strategy for cancer therapy. PTL could preferentially inhibit cancer stem cells, but the molecular mechanism was still unclear. In our study, we explored the mechanism signaling pathways involved in PTL-induced apoptosis in non-small cell lung cancer (NSCLC) cells and the role of ER stress in this process. We also found a potential mechanism why PTL would selectively eradicate cancer stem-like cells, which may have clinical Sirolimus in vitro implications in eradicating cancer stem cells eventually. Methods Antibodies and reagents Parthenolide and PMAIP1 antibody were purchased

from Calbiochem (Darmstadt, Germany). Briefly, parthenolide was dissolved in dimethyl sulfoxide (DMSO) at a concentration of 10 mmol/L, and the aliquots were stored at -20°C. Stock solutions were diluted to the desired concentrations with growth medium before use. The antibodies of TNFRSF10B and ACTB were purchased from Sigma-Aldrich (St. Louis, MO, USA). CDH1 and CFLAR antibodies were obtained from BD Biosciences (San Jose, CA, USA) and Alexis (San Diego, CA) respectively. Anti-CASP8, CASP9, HSPA5, MCL1, p-EIF2A, and PARP1 antibodies were purchased from Cell Signaling Technology (Danvers, MA, USA). CASP3 anti-body was obtained from Imgenex (San Diego, CA, USA). Antibodies of ATF4, DDIT3 were obtained from Santa Cruz (Santa Cruz, CA). Cell lines and cell culture Human lung cancer cell lines were obtained from the American Type Culture Collection (Manassas, VA). Cells were gown in monolayer culture with RPMI 1640 medium containing 5% new born calf serum at 37°C in a humidified atmosphere consisting of 5% CO2 and 95% air.