| Summary: | 博士 === 高雄醫學大學 === 醫學研究所 === 97 === Cancer has been described as disorganized organogenesis, since a wealth of studies point out the similarity between carcinogenesis and organogenesis. The close link underlying the two seemingly different events is suggested to be tissue stem cells. Therefore, it is important to understand what tissue stem cells are and how they behave under different conditions, which may help to unravel the mystery of carcinogenesis.
Gastric epithelium is a high turn-over tissue, in which stem cells are assumed to be robust. Accordingly, it is an ideal tissue for stem cell study. From histology study, the undifferentiated cells resided in the gastric corpal isthmus were suggested to be the putative gastric stem/progenitor cells, also called pluripotent mini-granule cells. As the study how the putative human gastric stem/progenitor cells may contribute to gastric carcinogenesis, an in vitro model of cultured gastric stem/progenitor cells would be a useful model for further dissection. In my study, I used the gastric specimens obtained by endoscopic biopsy to isolate gastric stem/ progenitor cells. From 56 human specimens, 118 cell clones were isolated. Among them, KMU-GI2 (GI2) showed many characteristics of gastric stem cells, including a high cumulative population doubling level (CPDL=37), a capacity to give rise to cells with different morphology, including epithelial cells, glial cells and neuron cells, and expression of Oct-4. In addition, we isolated a spontaneously transformed subclone, named GI2CS- (KMU-CSN; CSN). After long-term culture (CPDL=132), a subclone, named KMU-CS12 (CS12), in CSN cell was tumorigenic and showed an abnormality in chromosome 12 by karyotyping. With both of normal and transformed gastric epithelial cell clones at hand (GI2, CSN, CS12), it is possible to study how the specific genetic abnormality can contribute to gastric carcinogenesis.
My thesis is comprised of 3 parts. The first part is to show how I isolated and cultured the gastric stem/progenitor cell like-cell clones (KMU-GI2) from human gastric specimens and my approach to characterize their gastric stem/progenitor cells properties, including cumulative population doubling level (cpdl), cell morphology and immunocytochemistry. The second part is to show how this GI2 interacts with carcinogenic environmental cues, like N-methyl-N’-nitro -N- nitrosoguanidine (MNNG) and Helicobacter pylori (Hp), and evaluate their responses. This study was assumed to simulate how stem cells would behave under similar conditions. We found telomerase in the study cells was highly activated under these noxious stimuli, and this increment was correlated with human clinical findings. The third part is to evaluate how transformed gastric stem/progenitor cells can recapitulate carcinogenesis. By Spectral karyotyping (SKY), we confirmed there was an extra fragment, replicated from the short arm of chromosome 7, on chromosome 12 in CS12 clone, which appeared to be tumorigenic in nude mice. There were 1145 genes up-regulated and 890 gene down-regulated by this genetic abnormality, detected by microarray. According to the array data, the HOXA genes, located in chromosome 7, were focused. Further analysis revealed HOXA 4, 5, 7, 9, 13 were significantly over-expressed and this effect might be attributed to the tumorigenecity we observed.
With the creation of in vitro gastric stem/progenitor cell line, a model to approach carcinogenesis and built a preclinical system to test the possible anti-cancer therapy has been established. This study also alludes gastric cancer may derive from transformed gastric stem cells and provides a great chance to further increase our understanding of gastric cancer stem cells.
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