Study On The Fuction Of Prostaglandin E2 Biosynthesis Pathway In Oral Carcinogenesis

PGE2 is a kind of important factors in rgulating cell growth.And it plays an essential role in carcinogenesis with its receptors.It may promote cell proliferation and differentiation.Further more,it can inhibit cell apoptosis and promote blood supply of tumor,cPLA2 and COX-2 are two key enzymes in PGE2 biosynthesis.Recent findings support the notion that it is the coordinated up-regulation of cPLA2 and COX-2 which constitutes a critical step in the transition of normal epithelium to carcinoma,in a variety of human cancer types,including head and neck cancers.In spite of this,there has been little focus on elucidating the dual role of these enzymes in the process of oral carcinogenesis.In the first part of this study,we evaluated the expression of cPLA2 and COX-2 in normal oral mucosa,dysplastic oral mucosa and squamous carcinoma(SCC)using immunohistochemistry.And analyzed the correlation between cPLA2 and COX-2.mRNA levels of cPLA2,COX-2, COX-1,mPGES-1 and mPGES-2 in three tissues were also evaluated.In the second part,we used NS-398,a selective inhibitor of COX-2,to inhibit the enzymatic activity of COX-2 in Tca8113 oral cancer cells and KB oral cancer cells.The inhibition of cell proliferation was assessed using MTT,and the changes of cell cycle and cell apoptosis were tested using flow cytometry.The levels of cPLA2 and COX-2 expression among the cancer cells were followed and compared to control cultures not exposed to the NS-398.Finally,we assessed the production of PGE2 in our culture medium and compared it to samples obtained from controls, and to the samples exposed to differing durations of treatment.Through these experiments,we try to elucidate the function of PGE2 biosynthesis pathway in oral carcinogenesis. Purpose:To investigate the expression of cPLA2 and COX-2 in normal oral mucosa,dysplastic oral mucosa and squamous carcinoma, and to analyze the correlation between cPLA2 and COX-2.mRNA levels of cPLA2,COX-2,COX-1,mPGES-1 and mPGES-2 in three tissues.Materials and methods:9 tissue samples of normal oral epithelium, 37 cases of oral dysplasia and 53 cases of oral SCC were collected.The expressions of cPLA2 and COX-2 in these tissues were analyzed by Immuno histological chemistry.And mRNA levels of cPLA2,COX-2, COX-1,mPGES-1 and mPGES-2 in three tissues were also evaluated by using RT-PCR.Results:cPLA2 and COX-2 were expressed much higher in oral dyslasia and oral SCC(p＜0.01).The difference of cPLA2 expression between oral dysplasias and SCCs was not found to be statistically significant(p＞0.05).Among the oral dysplasia cases,cPLA2 expression in mild dysplasia was found to be significantly lower than in moderate and severe dysplasia(p＜0.01).There was no statistically significant relationship established between cPLA2 expression and the pathological grade assessed to the 53 cases of OSCC(p＞0.05).The pattern of staining of COX-2 was similar to cPLA2 in normal oral epithelia,oral dysplasias and SCCs.there was no statistically significant relationship established between the COX-2 expression and the pathological grade assessed to the oral dysplasia and SCC groups(p＞0.05).Within each sample,a significant correlation was revealed between cPLA2 expression and COX-2 expression(p＜0.01).The mRNA levels of cPLA2,COX-2 and mPGES-1 were much higher in oral dysplasias and SCCs than in normal oral epithelia(p＜0.01).On the other hand,there was no difference of COX-1 and mPGES-2 expression among normal oral epithelia,oral dysplasias and oral SCCs(p＞0.05).Conclusions:Our findings revealed that cPLA2 and COX-2,key factors in PGE2 biosynthesis,work in concert to promote the progression of normal oral epithelium toward oral carcinoma,cPLA2-COX-2-mPGES-1 signal pathway may play an essential role in promoting oral carcinogenesis. Purpose:To investigate the function of cPLA2 and COX-2 in the process of NS-398 induced oral cancer cell apoptosis.Materials and methods:25,50,75,100 and 200μmol/L NS-398(a selective inhibitor of COX-2)were used to treat on Tca8113 cell line for varying time intervals:24,48,72 and 96 hours.The effect of cell growth inhibition was evaluated by using MTT method.Then Tca8113 oral cancer cells and KB oral cancer cells were treated with 50μmol/L NS-398 for varying time intervals:6,12,24,48 and 72 hours.The cell cycle and the rate of cell apoptosis was analyzed by flow cytometry.The protein levels of cPLA2,COX-2,Bcl-2 and Caspase 3 were evaluated by western blot and PGE2 production was analyzed by radioimmunoassay(RIA).Results:MTT assay showed that NS-398 significantly reduced the proliferation of Tca8113 cells in a dose- and time-dependent manner(p＜0.01).At a concentration of 50μM,NS-398 had the minimal cytotoxicity and could nicely inhibit the cell growth in Tca8113 oral cancer cells.After the treatment of 50μM NS-398,the cell apoptosis rates of Tca8113 and KB cell line were both gradually increased.And the ratio of G1 cells was significantly increased compared with the cells which were not treated with NS-398 when the ratio of S cells was significantly reduced.Moreover,the enzymatic activity of cPLA2 and COX-2 in Tca8113 cells and KB cells were gradually down-regulated(p＜0.01)with longer durations of treatment with NS-398, as demonstrated by a reduction in the amount of PGE2 production over time(p＜0.01).And the protein level of caspase 3 was gradually up-regulated.But Bcl-2 expression was not changed.Conclusion:Our data suggest that the coordinated activity of cPLA2 and COX-2 contribute to the process of oral cancer cell cycle arrest and cell apoptosis,and is related to the activity of caspase 3,thus identifying cPLA2 as a potential target for the prevention and treatment of oral cancers.