Doctoral candidate, University of Minnesota
ER stress and chemoresistance in pancreatic cancer
Endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) have been shown to correlate with advanced stage, shorter survival, and chemoresistance in multiple cancers, including pancreatic cancer. The UPR is a homeostatic mechanism that allows cells to ameliorate stress-inducing conditions, which can result in cell survival. The activation and inactivation of UPR is regulated by glucose regulatory protein (GRP78). Our studies and others have shown that GRP78 is overexpressed in pancreatic cancer, and my work studies how.
Abstract: Every year, nearly 300,000 people are diagnosed with pancreatic cancer worldwide, and an equivalent number succumb to this disease. One of the major challenges of pancreatic cancer that contributes to its poor survival rates is the development of resistance to the standard chemotherapy. Heterogeneity of the tumor, the dense fibroblastic stroma, and the aggressive biology of the tumor all contribute to the chemoresistant phenotype. In addition, the acellular components of the tumor microenvironment like hypoxia, stress pathways in the stromal cells, and the cytokines that are secreted by the immune cells, have a definitive role in orchestrating the chemoresistant property of the tumor. In this review, we systematically focus on the role played by the different microenvironmental components in determining chemoresistance of pancreatic tumors.
Pub.: 31 Dec '16, Pinned: 06 Jul '17
Abstract: Endoplasmic reticulum (ER) stress initiates an important mechanism for cell adaptation and survival, named the unfolded protein response (UPR). Severe or chronic/prolonged UPR can breach the threshold for survival and lead to cell death. There is a fundamental gap in knowledge on the molecular mechanism of how chronic ER stress is stimulated and leads to cell death in pancreatic ductal adenocarcinoma (PDAC). Our study shows that downregulating specificity protein 1 (Sp1), a transcription factor that is overexpressed in pancreatic cancer, activates UPR and results in chronic ER stress. In addition, downregulation of Sp1 results in its decreased binding to the ER stress response element present in the promoter region of Grp78, the master regulator of ER stress, thereby preventing homeostasis. We further show that inhibition of Sp1, as well as induction of ER stress, leads to lysosomal membrane permeabilization (LMP), a sustained accumulation of cytosolic calcium, and eventually cell death in pancreatic cancer.
Pub.: 10 May '17, Pinned: 06 Jul '17
Abstract: Hepatocellular carcinoma (HCC) has an annual worldwide incidence of 626 000 cases and causes 550 000 deaths per year. Although the mainstay of treatment is surgical resection, for inoperable or metastatic disease, chemotherapy may be offered. The primary agent used is doxorubicin, but response rates are poor (<20%). The unfolded protein response (UPR) is a cytoprotective cellular stress response that enables cells to survive periods of hypoxia and nutrient deprivation. The UPR may confer resistance to anticancer agents and contribute to treatment failure. This study has investigated whether the UPR is activated in HCC and whether this may contribute to doxorubicin resistance.Eighty-six human HCCs were immunohistochemically stained for glucose regulated protein 78, the key marker of UPR activation. An in-vitro model of UPR activation in HepG2 HCC cells was developed by glucose deprived culture. UPR activation was confirmed with western blotting and PCR to show overexpression of glucose regulated protein 78. The relative efficacy of doxorubicin chemotherapy on UPR-activated HepG2 cells was compared with normal HepG2 cells by use of an thiazolyl blue tetrazolium bromide colorimetric assay.Expression of glucose regulated protein 78 was shown in 100% of the HCC samples with 66% showing strong staining. In-vitro UPR activation was achieved with glucose deprivation. UPR activation induced significant resistance to doxorubicin: 34% survival under standard culture conditions versus 58% and 63% for UPR-activated cells in 0.5 and 1 mmol glucose respectively (P=0.00928).The UPR is activated in HCCs and confers resistance to chemotherapy in vitro. UPR activation may contribute to HCC chemoresistance.
Pub.: 24 Feb '10, Pinned: 06 Jul '17
Abstract: Pancreatic cancer is a devastating disease with a survival rate of <5%. Moreover, pancreatic cancer aggressiveness is closely related to high levels of prosurvival mediators, which can ultimately lead to rapid disease progression. One of the mechanisms that enables tumor cells to evade cellular stress and promote unhindered proliferation is the endoplasmic reticulum (ER) stress response. Disturbances in the normal functions of the ER lead to an evolutionarily conserved cell stress response, the unfolded protein response (UPR). The UPR initially compensates for damage, but it eventually triggers cell death if ER dysfunction is severe or prolonged. Triptolide, a diterpene triepoxide, has been shown to be an effective compound against pancreatic cancer. Our results show that triptolide induces the UPR by activating the PKR-like ER kinase-eukaryotic initiation factor 2α axis and the inositol-requiring enzyme 1α-X-box-binding protein 1 axis of the UPR and leads to chronic ER stress in pancreatic cancer. Our results further show that glucose-regulated protein 78 (GRP78), one of the major regulators of ER stress, is downregulated by triptolide, leading to cell death by apoptosis in MIA PaCa-2 cells and autophagy in S2-VP10 cells.
Pub.: 05 Apr '14, Pinned: 06 Jul '17
Abstract: Nuclear factor (erythroid-derived-2)-like 2 is one of the most efficient cytoprotective rheostats against exogenous or endogenous oxidative insults. At present, the modulation of the Nrf2 pathway represents an interesting and highly explored strategy in the oncological area. Area covered: In this review, we present and discuss the different modulation of the Nrf2 pathway by some natural compounds with a well demonstrated anticancer activity, and critically analyze the challenges associated with the development of an Nrf2-based anticancer strategy. Expert opinion: Many natural compounds with a well-defined anticancer activity are able to modulate this pathway. Both Nrf2 inducers and inhibitors can be useful as anticancer strategy. However, since Nrf2 modulates many networks potentially involved in the detoxification process of anticancer drugs, its activation in cancer cells could lead to chemoresistance. The switch between a beneficial or detrimental role of Nrf2 in cancer cells essentially depends on the tight control of its activity, the specific conditions of tumor microenvironment, and cell type. In line with the paucity of clear data related to the mechanisms underpinning the role of Nrf2 in cancer development and chemoresistance, discovery and development of Nrf2-based strategies is one of the most critical and challenging assignments for fighting cancers.
Pub.: 05 Jul '17, Pinned: 06 Jul '17