The normal cellular prion protein (PrPC) is a GPI-anchored membrane protein present on many cell types. While the expression of PrPC is critical for a group of fatal neurodegenerative conditions, known as prion diseases, the normal functions of PrPC remain an enigma. We screened for PrPC expression in a panel of human tumor cell lines, and found that human pancreatic tumor cell lines consistently express high levels of PrPC and produce high amounts of PrPC in their culture supernatants. These findings lead us to investigate whether PrPC is up regulated in human pancreatic ductal adenocarcinoma (Pan-DAC) tissues by immunohistochemical staining with anti- PrPC monoclonal antibodies (Mabs). Tissues from patients with chronic pancreatitis and pre-cancerous conditions, such as pancreatic intraepithelial neoplasia (PanIN-1, 2, 3) were included as controls. PrPC is not detected in normal ductal cells, in chronic pancreatitis, in PanIN-1 or in PanIN-2 tissues. Only four cases (14%) of PanIN-3 express low levels of PrPC. PrPC expression is uniquely up regulated in 41% of Pan-ADCs. Furthermore, PrPC expression is associated with poorer prognosis. Patients with PrPC expression in carcinoma had a much shorter median survival time of 360 days compared to >1,000 days for patients without PrPC expression (P<0.001). In addition, siRNA down regulation of PrPC expression in a Pan-DAC cell line, BXPC-3 reduces the proliferation of BxPC-3 cells. These results suggest that PrPC expression may be important in the genesis of human Pan-DAC. This hypothesis was supported by studies using a transgenic mouse line, which had an activated K-ras, with deleted TGF2 receptor 2, under the control of a pancreatic specific promoter, Ptfia, (Ptf1acre/+;K-rasG12D/+; Tgfbr2flox/flox). This transgenic mouse line develops Pan-ADC with features reminiscent of human Pan-DAC. PrPC expression was detected in Pan-DAC but not in ductal cells, Pan-IN tissues or normal pancreatic ductal cells in this transgenic mouse line. We hypothesize that PrPC is involved in carcinogenesis of a subgroup of Pan-ADCs, either through its ligand-receptor activation or dysfunctional apoptosis cascade. We proposed three specific aims, using in vitro cell models, transgenic animal models and additional human tissues to further investigate the role PrPC plays in the genesis of human Pan-DAC. Results from these studies will provide new insights into the pathogenesis and may also identify new targets for therapeutic intervention of this deadly disease.
Pancreatic ductal adenocarcinoma (Pan DAC) is the fourth leading cancer causing deaths in the United States with more than 30,000 deaths per year. The overall median survival for all Pan-DAC is 6 months and the 5-year survival rate is less than 10%. At present, the underlying mechanisms that cause Pan-DAC are still poorly understood. We found that a subset (41%) of human Pan-DAC has increased expression of the normal cellular prion protein, PrPC, and identified that such an increase in PrPC expression is associated with poor clinical outcome (P>0.001). We also found that human Pan-DAC cell lines that express more PrPC have a higher proliferative rate in vitro. In addition, in a transgenic mouse model of Pan-DAC, we found that PrPC is also up regulated in the tumors but not in the precancerous lesions. Therefore, our findings in human Pan-DAC are recapitulated in vitro in a cell model and in an animal model. We propose to further investigate the role PrPC plays in Pan-DAC development using in vitro cell models, additional patient tissues and a transgenic mouse model. Results from these studies will provide new insights into the pathogenesis of human Pan-DAC and may also identify new targets for therapeutic intervention of this deadly disease. ? ? ? ?
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