Ki67交互作用之蛋白NIFK在細胞週期運行、p53訊息傳遞與核醣體生成的功能

對細胞增生來說，連結的細胞生長與分裂十分重要。逐漸有研究指出，核醣體生成途徑的完整性為調控細胞生長與分裂所需，然而其調節異常時會發生人類疾病，其中包括癌症與核醣體缺乏疾病。核醣體之生成控制蛋白質合成。NIFK為一個核醣體生成的關鍵調控因子 c-Myc 正向轉錄之蛋白。已知 NIFK 除了與Ki-67 及 NPM1 蛋白有交互作用之外，其生物功能尚未完整的建立。我們在此報導NIFK為細胞週期運行時所需，與其藉RNA辨識區域 (RRM) 參與生成核醣體。我們的結果指出，當以基因沉默方式降低 NIFK表現時，可能因引發RPL5/RPL11調控之核仁壓力，而活化可逆的p53路徑將細胞週期停留在 G1，進而抑制細胞增生。在機制上，這是由於內轉錄空白子1 (ITS1) 之切割─前驅核醣體分離為小與大次級單位之關鍵步驟─效率不佳，因而破壞28S與5.8S rRNA之成熟所導致。將突變之NIFK補回NIFK基因沉默之細胞的結果顯示，RRM的RNA結合能力為前驅rRNA (pre-rRNA) 後製與細胞間期運行所需。更明確地，我們證實RRM可能以依存 RNA 序列與二級結構的方式，選擇結合於ITS2 rRNA 5’端的位置。我們的結果顯示NIFK是如何藉由RRM依存的pre-rRNA成熟途徑而調控細胞週期之運行，除了可以增加我們對於NIFK在細胞增生功能上的了解，還可觸及對癌症與核醣體缺失疾病的認識。

關鍵字

Ki-67 ； NIFK ；細胞週期；核醣體RNA後製；核仁壓力；核醣體生成； RNA辨識區域

並列摘要

Coupled cell growth and division is critical for cell proliferation. Emerging studies suggest that the integrity of ribosome biogenesis is essential for the coordination of cell growth and division, while its dysregulation is associated with human diseases including cancer and ribosomopathies. Ribosome biogenesis governs protein synthesis. NIFK is transactivated by c-Myc, the key regulator of ribosome biogenesis. The biological function of human NIFK is not well established, except that it has been shown to interact with Ki-67 and NPM1. Here we report that NIFK is required for cell cycle progression and participates in the ribosome biogenesis via its RNA recognition motif (RRM). We show that silencing of NIFK inhibits cell proliferation through a reversible p53-dependent G1 arrest, possibly by induction of the RPL5/RPL11-mediated nucleolar stress. Mechanistically it is the consequence of impaired maturation of 28S and 5.8S rRNA resulting from inefficient cleavage of internal transcribed spacer (ITS) 1, a critical step in the separation of pre-ribosome to small and large subunits. Complementation of NIFK silencing by mutants shows that RNA-binding ability of RRM is essential for the pre-rRNA processing and G1 progression. More specifically, we validate that the RRM of NIFK preferentially binds to the position in the 5’-end of ITS2 rRNA, likely in both sequence specific and secondary structure dependent manners. Our results show how NIFK is involved in cell cycle progression through RRM-dependent pre-rRNA maturation, which could enhance our understanding of the function of NIFK in cell proliferation, and potentially also cancer and ribosomopathies.

並列關鍵字

Ki-67 ； NIFK ； cell cycle ； rRNA processing ； nucleolar stress ； ribosome biogenesis ； RNA recognition motif (RRM)

參考文獻

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Ki67交互作用之蛋白NIFK在細胞週期運行、p53訊息傳遞與核醣體生成的功能

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