Liver Tumor의 발암과정에서 단백질 네트워크에 관한 연구

Abstract

Liver cancer is the third most common cause of cancer-related mortality worldwide. Liver tumors consist of hepatocellular carcinoma (HCC), cholangiocarcinoma (CC), hepatocellular adenoma, and hepatoblastoma. Among them, HCC accounts for 85-90% of all primary liver cancer. CC is the second common primary liver malignancy. Liver tumors including HCC and CC are not single disease but a group of neoplasms with diverse genetic abnormalities and variable responses to treatment. Therefore, identifying molecular factors which contribute the carcinogenesis and progression of liver cancer and targeting for those factors are essential to improve outcome of patients with liver tumors.Firstly, we investigated the roles of renal tumor antigen (RAGE) in the progression and clinical outcome of HCC using patient samples. Although RAGE was investigated as a potential target for cancer-specific immunotherapy, the possible prognostic role and the functional role of RAGE have not been assessed. We investigated RAGE mRNA levels in 350 cases of HCC using quantitative real-time reverse transcription-PCR and analyzed the relationship of RAGE mRNA level with clinicopathologic parameters and clinical outcome. To identify the possible role of RAGE on cellular invasion, we performed in vitro analyses using small interfering RNAs (siRNAs). RAGE mRNA level was significantly higher in HCC than in non-cancerous hepatic tissues (P < 0.001). Overexpression of RAGE was significantly correlated with the presence of multiple tumors (P = 0.021), high AFP level (P = 0.042), and advanced tumor stage (P = 0.016). Higher levels of RAGE expression were associated with significantly shorter overall survival time (P = 0.029). Knockdown of RAGE expression by siRNAs suppressed the invasive ability of HCC cells and the expression and secretion of matrix metalloproteinase-9 (MMP-9). We found that RAGE and MMP-9 expressions were correlated in HCCs and furthermore, the combination of RAGE and MMP-9 expression was associated with the survival of patients (P = 0.0066). Our results suggest that RAGE may be important in tumor invasion and could be a potential predictor for the prognosis of HCC patients.Secondly, we investigated the antitumor effects of ZD1839, an epidermal growth factor receptor (EGFR) inhibitor, in combination with rapamycin, an mTOR inhibitor, in CC. Expression and activation of effector molecules on EGFR and mTOR pathways were investigated for distinctly differentiated CC cells and tissues by immunoblot and immunohistochemical analyses. Antitumor effects by ZD1839 and/or rapamycin were investigated in CC cells and in xenograft models of mice. EGFR and mTOR pathways were found to be activated differentially in differentiated and dedifferentiated CC cells, respectively. The responsiveness of CC cells to ZD1839 was proportional to the EGFR expression and dedifferentiated CC cells were resistant to the inhibitor. ZD1839 efficiently induced cellular apoptosis in differentiated CC, and exhibited synergistically apoptogenic effects when combined with rapamycin. However, rapamycin mainly induced the G1 cell cycle arrest, rather than apoptotic cell death by modulating p27, cdk2, and cdk4 expressions in dedifferentiated CC. In the xenograft models, combined treatments of ZD1839 and rapamycin synergistically inhibited tumor growth in differentiated CC and exhibited better antitumor effects than either inhibitor alone. The enhanced antitumor effect of the combination therapy was also found in dedifferentiated CC. Interestingly, rapamycin alone exhibited almost complete suppression of the tumor growth like the combination treatment in dedifferentiated CC. ZD1839 combined with rapamycin could overcome the insensitivity to the EGFR inhibition, suggesting that dual targeting of EGFR and mTOR pathways could be a promising approach for CC chemotherapy.