Intriguingly, although the correlation between autophagy and tumorigenesis is well established, controversy about its pro-death or pro-survival role still exists . of cell death in some pancreatic cancer cell lines . Although triptolide is shown to be a very effective compound and and data suggesting that triptolide leads to an increase in miR-204 levels and decreased Mcl-1 levels, miR-204 expression was significantly increased (20C40 fold) in Minnelide treated vs. control tumors (Figure? 6B). Our data, taken together, suggests that triptolide induces pancreatic cancer cell death via down-regulation of Mcl-1 and increased expression of miR-204. Open in a separate window Figure 6 Minnelide treatment leads to loss of Mcl-1 expression and increase of miR-204 in vivo. A. Minnelide treatment decreases Mcl-1 levels in patient tumors transplanted into SCID mice. B. Minnelide treatment increases miR-204 levels in patient tumors transplanted into SCID mice. Discussion Resistance to conventional chemotherapy remains a significant obstacle in long-term survival of pancreatic cancer patients, and the mechanisms of recurrence and resistance remain poorly understood. Recent genome-wide research suggests that Mcl-1 is subject to increased gene copy number across more than two dozen cancer types Beta-Cortol Beta-Cortol . Exploiting drug regimens targeting pathways that down-regulate Mcl-1 expression is therefore a current strategy in cancer therapy . Increase in levels of Mcl-1 has been associated with advanced staging in breast, colon and lung cancers, but its status in pancreatic tumors remained poorly understood. Mcl-1 also protects cancer cells against cell death and is known to contribute to chemoresistance. Our results show Mcl-1 is up-regulated in pancreatic tumors but not in the adjacent normal tissue (Figure? 1). Here we show that while Mcl-1 levels correlate with TNM staging and advanced stage of disease (Figure? 1). Peddabonina et al. have recently shown that siRNA mediated loss of Mcl-1 results in decrease in cell viability in colon and lung cancers, and loss of chemoresistance . In agreement with these studies, we show that loss of Mcl-1 by Mcl-1 specific siRNA results in Rabbit Polyclonal to KITH_HHV1 cell death in both MIA PACA-2 and S2-VP10 pancreatic cancer cells (Figure? 2). MicroRNA based regulation of several pro-survival pathways have recently gained considerable interest. The function of miR-204, to date, is still unclear, although some mRNA targets that are important for normal cell development have been identified. miR-204 is reported to act as a tumor suppressor in a variety of cancers through different mechanisms including down-regulation of Bcl-2, NTRK2 in neuroblastoma cancer and suppression of invasion in endometrial cancer mediated by FOXC1 regulation [31,32]. Loss of miR-204 has recently been shown to promote cancer cell migration via increased expression of brain derived neurotrophic factor or its receptor, TrkB. Importantly, loss of miR-204 has been associated with a stem cell-like phenotype in gliomas, and its over-expression results in reduced tumorigenicity and loss of Beta-Cortol the stemness transcription factor, SOX4 . Loss of miR-204 expression in gastric cancer has been associated with poor prognosis due to an increase in the anti-apoptotic protein, Bcl-2. In agreement with these studies, we have shown that miR-204 is down-regulated in pancreatic cancer cells, and over-expression of miR-204 induces loss of pancreatic cancer cell viability (Figure? 3). While the role of miR-204 as a tumor suppressor is well established, its ability to regulate Mcl-1 expression was not known prior to this study. Our previously published data has shown that triptolide-mediated cell death is cell-type dependent. While MIA PaCa-2 cells undergo apoptosis, S2-VP10 cells die via autophagy. Intriguingly, although the correlation between autophagy and tumorigenesis is well established, controversy about its pro-death or pro-survival role still exists . In support of the role of autophagy as a cell death mechanism, caspase inhibition of L929 cells results in non-apoptotic, non-necrotic cell death. Additionally, knock down of Atg7 or Beclin-1 in these cells abrogates cell death. In the current study, we find that loss of Mcl-1 mimics triptolide mediated cell death; while MIA PaCa-2 cells undergo PARP cleavage, a hallmark of apoptosis, S2-VP10 cells show the presence of LC3-II, representing formation of autophagosomes (Figure? 2). Previous studies have shown that high Mcl-1 level is an important factor for cancers to escape apoptosis . However, little is known about Mcl-1 mediated protection against autophagy. A recent study has shown that cortical neuron-specific Mcl-1 deleted animals undergo autophagy, suggesting that Mcl-1 plays a role in both apoptosis and autophagy. However, the role of Mcl-1 in autophagic response of cancer cells is unclear. While there is some evidence to show that compounds that inhibit Mcl-1.