| Summary: | 碩士 === 國立成功大學 === 生物資訊與訊息傳遞研究所 === 100 === Ribosome is composed of rRNAs, ribosomal proteins, and many non-ribosomal factors to conduct the translation function. Traditionally, ribosomal proteins were considered as co-factors to execute the protein translation. But, numerous studies have demonstrated that ribosomal proteins not only play as co-factors of translational complex but also regulate the protein synthesis of specific mRNAs. RPL19 is a component of ribosome large subunit which belonged to the L-19E super-family and conserved among eukaryotes. In previous study, RPL19 was reported to have an impact on cyclin D1 protein expression but not on other cell cycle regulators, which indicated RPL19 may be a regulator of specific cell cycle regulators. During cell cycle progression, internal ribosome entry site (IRES) was reported to mediate the translational regulation of many cell cycle regulators. Since cyclin D1 expression was reported to be regulated by RPL19 and the 5’UTR of cyclin D1 mRNA carries a potential IRES element, the hypothesis was reported that RPL19 may regulate the expression of cyclin D1 through IRES. To address it, cells were synchronized and following experiments were conducted. First, western blot analysis showed that RPL19 expression level remained unchanged during cell cycle progression. However, RNA-IP showed that RPL19 interacted with cyclin D1 mRNAs at G1/S boundary. Bicistronic reporter assay showed that the 5’UTR of cyclin D1 had strong IRES activity and was regulated by RPL19. IRES-mediated translation regulation is often facilitated with the help of IRES trans-acting factors (ITAFs). RPL19 cooperated with a known ITAF, hnRNP A1, to regulate the IRES activity of cyclin D1. Furthermore, we observed that down-regulation of RPL19 significantly decreased the proliferation rate of HeLa cells. To sum up, we identified that RPL19, a ribosomal protein, can cooperate with hnRNPA1 to regulate cell cycle progression through regulating the IRES activity of cyclin D1.
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