TIP60 represses telomerase expression by inhibiting Sp1 binding to the <i>TERT</i> promoter

HIV1-TAT interactive protein (TIP60) is a haploinsufficient tumor suppressor. However, the potential mechanisms endowing its tumor suppressor ability remain incompletely understood. It plays a vital role in virus-induced cancers where TIP60 down-regulates the expression of human papillomavirus (HPV) oncoprotein E6 which in turn destabilizes TIP60. This intrigued us to identify the role of TIP60, in the context of a viral infection, where it is targeted by oncoproteins. Through an array of molecular biology techniques such as Chromatin immunoprecipitation, expression analysis and mass spectrometry, we establish the hitherto unknown role of TIP60 in repressing the expression of the catalytic subunit of the human telomerase complex, TERT, a key driver for immortalization. TIP60 acetylates Sp1 at K639, thus inhibiting Sp1 binding to the TERT promoter. We identified that TIP60-mediated growth suppression of HPV-induced cervical cancer is mediated in part due to TERT repression through Sp1 acetylation. In summary, our study has identified a novel substrate for TIP60 catalytic activity and a unique repressive mechanism acting at the TERT promoter in virus-induced malignancies.HIV-1 TAT相互作用蛋白（TIP60）是一类单倍剂量不足型肿瘤抑制因子。然而，介导其肿瘤抑制功能的潜在分子机制仍未完全明确。该蛋白在病毒诱导型癌症中发挥关键调控作用：在此类癌症中，TIP60可下调人乳头瘤病毒（HPV）癌蛋白E6的表达，而E6又会反过来降低TIP60的稳定性。这一现象引发了我们的研究兴趣，旨在探究病毒感染背景下TIP60的功能角色——此时TIP60会被癌蛋白靶向调控。通过染色质免疫沉淀（Chromatin immunoprecipitation）、表达分析及质谱分析等一系列分子生物学技术，我们证实了TIP60此前未被报道的功能：它可抑制人端粒酶复合物的催化亚基TERT的表达，而TERT是细胞永生化的关键驱动因子。TIP60在K639位点对Sp1进行乙酰化修饰，进而阻断Sp1与TERT启动子的结合。我们发现，TIP60介导的HPV诱导型宫颈癌生长抑制，有一部分是通过Sp1乙酰化实现TERT抑制来完成的。综上，本研究鉴定出了TIP60催化活性的新型底物，同时揭示了病毒诱导型恶性肿瘤中作用于TERT启动子的独特抑制机制。