THE EXPRESSION OF ANGIOGENIN IN ORAL CANCER AND ITS FUNCTIONS

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Objectives : Angiogenin is an angiogenic protein that undergoes nuclear translocation in endothelial cells where it accumulates in the nucleolus and stimulates ribosomal RNA transcription, a rate-limiting step in ribosome biogenesis, protein translation, and cell growth. Recently, besides its angiogenic activity, it is revealed that angiogenin also plays a role in cancer cell proliferation through ribosomal RNA transcription. In the current study, we examined the expression of angiogenin in oral cancer and its functions by RNA interference (RNAi).Methods : 1. The expression of angiogenin in biopsy specimens obtained from patients with oral squamous cell carcinoma was examined by immunohistochemistry. 2. Secreted levels of angiogenin and VEGF in various oral cancer cell lines were measured by ELISA. HSC-2 cell that secreted high levels of angiogenin and VEGF was transfected with angiogenin RNAi construct. Then, stable angiogenin RNAi transfectants were selected by puromycin resistance. 3. Vector control and angiogenin RNAi transfectants (RNAi-2, RNAi-3), 1X10^6 cells per mouse, were subcutaneously injected into each mouse. 4. Mice were sacrificed on day 15, and the tumor tissues were formalin-fixed, paraffin-embedded and examined by immunohistochemistry.Results : 1. The expression of angiogenin in oral squamous cell carcinomas was observed in the nuclei or cytoplasms, but not in normal epithelia. 2. Secreted levels of angiogenin and VEGF in various oral cancer cell lines had a wide range of their secretions, and HSC-2 cell secreted high levels of angiogenin and VEGF. 3. Angiogenin RNAi HSC-2 transfectants have decreased tumor volume in athymic mice. 4. Angiogenesis in the tumor tissues of angiogenin RNAi HSC-2 transfectants was inhibited in athymic mice, and moreover, the expression of PCNA also decreased.Conclusion : Angiogenin may play a key role in not only tumor angiogenesis but also cell proliferation in oral cancer.