| Research Abstract |
This study evaluated the mechanisms of biological malignant potential, i.e., apoptosis resistance, growth potential, activity of invasion and metastasis, in pancreatic cancer cells. We first focused on epidermal growth factor receptor expression and mutasion in pancreatic cancer cell lines such as Panc-1, MIA PaCa-2, Capan-1, Capan-2 and BxPC-3. We did not find positive correction between apoptosis resistance and EGFR expression levels. In addition, we did not find specific EGFR mutation that correlates apoptosis resistance in all the pancreatic cancer cell lines used in this study. Therefore, we next focused on heterogeneity of the cells within each cell line. We identified both side population(SP), an apoptosis resistant fraction, and main population(MP), a relatively sensitive population to chemotherapy-induced apoptosis in some pancreatic cancer cell line. By comparative analysis of SP cells and MP cells, SP cells were resistant to a variety of apoptosis-including stimuli, i.e., tu
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mor necrosis factor-related ligand(TRAIL), 4-fluorouracil(5-FU) and cisplatin(CDDP). In addition, SP cells displayed greater in vitro colony forming activity and in vivo tumor forming capacity, suggesting that SP cells have so-called cancer stem cell-like properties. In an isolated SP cell culture, the cells rapidly expressed and upregulated E-cadherin, an epithelial phenotypic marker, and the cells grew up forming tightly contained cell cluster, which is a representative epithelial phenotypic appearance. When the SP cells were incubated in the presence of TGF-beta, the SP cells changed their shape into mesenchymal-like appearance including spindle shaped assembly. This alteration was concordant with significant reduction of E-cadherin protein expression level. TGF-beta induced EMT-associated gene alteration such as reduction of E-cadherin mRNA and induction of Snail mRNA and matrixmetalloproteinase (MMP)-2 mRNA. SP cells appears to respond TGF-b-signaling more, as TGF activin responsive element (TARE)-based luciferase reporter assay revealed superior response to TGF-beta treatment in SP cells as compared to MP cells. Finally, SP cells exerted notable matrigel invasion activity in response to TGF-beta, while MP cells did not respond to TGF-beta-mediated invasion. Because SP fraction is known as cancer stem cell-enriched fraction, we conclude that SP cells play a major role in apoptosis resistance in pancreatic cancer cells. SP cells also play a important roles in pancreatic cancer invasion and metastasis. Thus, SP cells appears to be a target to prevent cancer development. Less
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