研究幹細胞與癌細胞中PARP-1輔助KLF4調控端粒酶之表現

Abstract

端粒為染色體末端之特殊基因體構造，對於基因組完整性的調控以及癌細胞的產生息息相關。端粒酶是細胞內延長端粒的酵素，而端粒的長度主要由端粒酶的活性來調控。先前的研究指出轉錄因子Kruppel-like transcription factor 4 (KLF4) 會藉由結合至端粒酶中的活性催化單位，端粒反轉錄酶 (human telomerase reverse transcriptase; hTERT) 之啟動子，並活化端粒反轉錄酶表現。對於維持人類胚胎幹細胞的自我更新能力非常有貢獻。在本篇研究中，我們利用質譜分析確認poly(ADP-ribose) polymerase-1 (PARP-1) 為KLF4之交互作用蛋白。在癌細胞和人類胚胎幹細胞中，負向調控PARP-1會抑制端粒反轉錄酶表現，並使細胞內端粒酶活性下降。PARP-1會幫助KLF4結合到端粒反轉錄酶啟動子上並共同活化其基因表現，而此功能並不需要PARP-1酵素活性參與。本篇論文證明在癌細胞及幹細胞中，PARP-1為KLF4活化端粒反轉錄酶表現之共同調控者，且此發現可能對於幹細胞自我更新能力以及人類再生醫療研究有幫助。

Telomeres are the specialized genomic structures at the ends of chromosomes and implicated in controlling genome integrity and cancer formation. Telomere length is mainly activated by expression of telomerase that elongates telomeres. Previous study has indicated that Kruppel-like transcription factor 4 (KLF4) activates expression of the human telomerase catalytic subunit, human telomerase reverse transcriptase (hTERT), through binding to the hTERT promoter and contributes to maintaining self-renewal in human embryonic stem cells. In this study, we identified poly(ADP-ribose) polymerase-1 (PARP-1) as a novel KLF4-interacting partner by mass spectrometry. Downregulation of PARP-1 reduced hTERT expression and telomerase activity in cancer cells and human embryonic stem cells. PARP-1 but not its catalytic activity is required for KLF4 localizing to the hTERT promoter and transcriptional coactivating gene expression. These results demonstrate that PARP-1 is one of the regulators to turn on telomerase activity in cancerous and stem cells by coactivating KLF4-dependent hTERT expression. Consequently, these findings may be important in stem cell self-renewal and human regenerative therapy.