| Purpose:The aim of this study was to search for new valuable molecular biomarkers for liver cancer,also investigate the protein expression and promoter methylation status of PCDH8 in liver cancer and evaluate the association between PCDH8 methylation and the clinicopathological features.Design:(1)The methylation status of PCDH8,HIN1 and RAR-?2 in 42 hepatocellular carcinoma(HCC),8 Cholangiocarcinoma(CC)and 50 normal liver tissues were examined using methylation-specific PCR(MSP).(2)The protein expression of PCDH8 was detected in live cancer and normal liver tissues by immunohistochemistry(IHC).(3)The relationships between PCDH8 methylation and clinicopathological features were evaluated in patients with liver cancer.(4)Univariate and Multivariate Cox proportional analysis were performed to determine which markers can act as an independent prognostic factor for liver cancer.The relationships between PCDH8 promotor methylation,AFP level,tumor size,tumor differentiation and the total survival time of patients with liver cancer were evaluated.Results:(1)Compare with normal liver tissues,PCDH8 promotor has a higher rate of methylation in liver cancer.PCDH8 promoter methylation was present in 37/42 HCC(88.1%)and 7/8(87.5%)CC,whereas 16/50(32%)of the normal liver tissues.The difference was statistically significant(P<0.001).However,there was no significant difference in the methylation rates of HINM and RAR-P2 in HCC and normal liver tissues.(2)The protein expression of PCDH8 was reduced in liver cancer.The protein expression of PCDH8 was strongly positive in the majority of normal liver tissues(43/50,86%),but in most cases,the protein expression of PCDH8 was loss in most liver cancer patients(35/42HCC,83.3%;7/8 CC cases,87.5%).(3)PCDH8 promoter methylation was significantly correlated with protein expression.In the normal liver tissue sections,PCDH8 protein was detected in 43/50 cases.However,there was 42 cases lost their protein expression in all the 50cases of liver cancer tissues,and among the 42 PCDH8 negative cases,40 cases occurred PCDH8 promoter methylation.Therefore,PCDH8 protein expression was lost in most of the cases with promoter methylation,which indicated a significant correlation between promoter hypermethylation and transcriptional silencing(P = 0.004).(4)The aberrant methylation status ofPCDH8 in liver cancer tissues was significantly associated with alpha fetoprotein(AFP)level(P = 0.008),while there were no statistically significant associations between PCDH8 promoter methylation and the other clinicopathological parameters such as age,gender,tumor size,or tumor differentiation(P>0.05).(5)The overall median survival of patients with methylated PCDH8 in HCC was 15 months.On the other hand,those without methylated PCDH8 tended to have a longer survival(all are alive at the end of follow up,P = 0.041).Moreover,tumor size,tumor differentiation and AFP level were also found to be associated with the overall survival(OS)of liver cancer.COX analysis showed the PCDH8 methylation could not act as an independent predictor(P>0.05).Similar results were obtained from tumor size and tumor differentiation.Multivariate Cox proportional analysis revealed that only AFP level could serve as an independent prognostic factor.Conclusions:PCDH8 has a higher methylation rate in liver cancer.It is often inactivated by promoter methylation and its protein expression is regulated by promoter methylation in liver cancer.PCDH8 gene promoter methylation plays an important role in the development and progression of liver cancer.PCDH8 gene can serve as a valuable diagnostic biomarker for early detection of liver cancer and might be useful to predict an unfavorable clinical feature.The aberrant methylation status of PCDH8 in liver cancer tissues was significantly associated with AFP level.The patients without methylated PCDH8 tended to have a longer survival,but PCDH8 methylation could not act as an independent predictor in liver cancer.Only AFP level could serve as an independent prognostic factor. |
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