Expression And Clinicopathological Significance Of RSK4 In Primary Pancreatic Carcinoma

PurposePancreatic cancinoma (PC) is one of digestive system malignant tumors, its incidence trends to rise in recent ten years in the world, but it is after ten on ranking list, however, its high mortality makes it become the seventh leading cause of cancer-related deaths both in the world and in China. RSK4, a member of the Ribosomal S6 kinases (RSK) family, is expressed in abundance in brain, renal, heart and skeletal muscle and has an impotant role in tissue development. RSK4 was down-regulated in a variety of malignant tumors, suggested that it might participat in the tumor development and progression as a cancer suppressor gene. It has not been reported about the expression of RSK4 mRNA in human PC tissues and the relationship between RSK4 mRNA expression level and prognosis of PC. Therefore, we detected RSK4 protein in three PC cell lines and one human immortal pancreatic duct epithelial cell line by immunohistochemistry (IHC) and detected RSK4 mRNA and protein in human PC tissues and adjacent non-neoplastic pancreatic (ANP) tissues by reverse transcription and quantitative real-time polymerase chain reaction (RT-qPCR) and IHC, respectively. Furthermore, we analyzed the relationship between the expression of RSK4 mRNA and protein and clinicopathological parameters and prognosis of PC.Methods(1) Three human PC cell lines and one human immortal pancreatic duct epithelial cell line were constructed into blocks, and then we detected the expression of RSK4 protein by IHC.(2)We collected the formalin-fixed, paraffin-embedded specimens of fifty cases of PC tissues and thirty cases of ANP tissues from the Department of Pathology of the First Affiliated Hospital of GuangXi Medical University between January,2010 and June,2013, and the clinicopathological and follow-up data.(3) RT-qPCR and IHC were performed to detect the expression of RSK4 mRNA and protein in fifty cases of PC tissues and thirty cases of ANP tissues, respectively. Receiver operator characteristic (ROC) curve was employed to identify the diagnostic value of RSK4 mRNA. The relationship between the expression level of RSK4 mRNA and protein and clinicopathological parameters were analyzed by chi-square test and spearman correlation analysis.(4)The prognostic factors were predicted by Kaplan-Meier univariate analysis and COX proportional hazards mode.Results(1) There was no expression of RSK4 protein in PC cell lines or in human immortal pancreatic duct epithelial cell line.(2) The relative transcript levels of RSK4 mRNA in PC tissues and ANP tissues were 0.634±0.2315 and 1.080±0.3423, respetivly. The expression of RSK4 mRNA in PC tissues was significantly lower than that in ANP tissues (P<0.05). The area under ROC curve of RSK4 mRNA was 0.695(95%CI 0.540-0.853, P<0.05). The cut-off value was 0.12 and the sensitivity and specificity were 64% and 43.3%, respectively. The expression of RSK4 mRNA was reversely related to distant metastasis (r=-0.364, P<0.05), however, no statistically significant correlation was found between the expression of RSK4 mRNA and gender, age, smoking history, drinking history, diabetes mellitus(DM) history, carbohydrate antigen 199(CA199), carcino embryonie antigen (CEA), tumor position, tumor size, tumor differentiation, neural infiltration, lymphatic metastasis or Tumor-node-metastasis (TNM) clinical stages (P>0.05).(3) The RSK4 protein positive rates in PC tissues and ANP tissues were 28% (14/50) and 50%(15/30), respectively. The expression of RSK4 proein in PC tissues was significantly lower than that in ANP tissues (P<0.05). The expression of RSK4 protein was reversely related to CA199 (r=-0.288, P<0.05), however no correlation was found between the expression of RSK4 protein and gender, age, smoking history, drinking history, DM history, CEA, tumor position, tumor size, tumor differentiation, neural infiltration, lymphatic metastasis, distant metastasis or TNM clinical stages(P>0.05).(4)The expression of RSK4 mRNA was correlated to RSK4 protein (P<0.05).(5)The median survival time of the group of positive expression of RSK4 mRNA (19 months) was longer than the negative one (8 months, P<0.05), however, RSK4 protein expression had no effect on the suvival of PC(P>0.05). RSK4 mRNA, tumor differentiation and TNM clinical stages were the independent prognostic factors of PC.Conclusion(1) RSK4 protein can not be detected either in PC cell lines or in human immortal pancreatic duct epithelial cell line, however, the RSK4 mRNA and protein is found down-regulated in PC tissues, particularly with the distant metastasis and CA199 high level tissues. The above findings suggest that RSK4 may participate in the regulation of development and metastasis of PC.(2)The diagnostic value of RSK4 mRNA is moderate, however it can affect the survival time of PC. Down-regulation of RSK4 mRNA is related to poor prognosis, suggesting it may be considered as a potential prognostic indicator.