细胞衰老抑制蛋白Rsl1d1在结直肠癌细胞中的功能挖掘及其负调控p53的分子机制研究

Ribosomal L1 domain-containing protein 1 not only inhibits cellular senescence, but also promotes tumor growth, and plays a key role in tumorigenesis. Previously, we have identified Rsl1d1 as a potential target for colorectal cancer therapy. Our unpublished data show that Rsl1d1 is overexpressed in human colorectal cancer cells, interacts with tumor suppressor p53, and its knockdown results in a reduced intranuclear level of MDM2, p53 activation, G1/S arrest, accelerated senescence, apoptosis, in vitro and in vivo cancer cell growth inhibition. Accordingly, we supposed that Rsl1d1 cooperates with MDM2 to negatively regulate p53, thus to regulate p53 downstream genes to promote cancer cell growth. However, the involved molecular mechanism remains unclear. In this proposal, we plan to carry out the following studies: (1) functional exploration of Rsl1d1 in colorectal cancer cells/tissues, and the confirmation of Rsl1d1 knockdown to accelerated cell aging as an effective anti-colorectal cancer strategy; (2) identification of the interaction between Rsl1d1 and p53; (3) elucidation of the negative regulation mechanism on p53 by Rsl1d1. The goals of this proposal are to elucidate the negative regulation of p53 by Rsl1d1 and thus the molecular mechanism for the tumor promoting function of Rsl1d1, and in the end, to provide a new strategy and target for human colorectal cancer treatment.

Rsl1d1不仅抑制细胞衰老，也能促进肿瘤生长，在肿瘤发生发展中起着重要作用。我们新近发现，Rsl1d1在结直肠癌细胞中高表达，并能与肿瘤抑制蛋白p53相互作用，Rsl1d1敲低导致细胞核内MDM2蛋白水平下调、p53活化、细胞G1/S期阻滞、衰老加速、细胞凋亡、癌细胞体内外生长抑制。我们推测，Rsl1d1可能与MDM2共同负调控p53，进而调控下游p53靶基因，促进肿瘤生长。为此本项目拟进行如下研究：①在体内外研究Rsl1d1在结直肠癌细胞/组织中的功能，确证敲低Rsl1d1加速细胞衰老是一种可行的抗结直肠肿瘤策略; ②明确Rsl1d1与p53的相互作用；③深入解析Rsl1d1对p53的负调控分子机制。本项目旨在研究Rsl1d1与p53之间的关系，并阐明Rsl1d1促肿瘤生长的分子机制，为结直肠肿瘤治疗提供新策略和新靶点。

细胞衰老抑制基因（Rsl1d1, CSIG）是一种核仁蛋白，主要定位于核仁，具有促进细胞增殖的功能，与肿瘤的发生发展密切相关。据报道，RSL1D1在核仁应激条件下释放至核浆，能够与HDM2相互作用，通过抑制p53负调控者HDM2的活性提升肺癌细胞和骨肉瘤细胞中p53蛋白水平。但我们依托该项目的研究表明，RSL1D1在结直肠细胞中对p53-HDM2信号通路的调节与之前的报道恰恰相反，其亚细胞定位不仅仅局限于核仁中，而是在正常条件下就散布于整个细胞核中。RSL1D1在HCT116结直肠癌细胞中，不仅能够通过提升HDM2的mRNA稳定性上调后者蛋白水平，还能够直接与p53和HDM2相互作用，通过形成三联复合体促进HDM2对p53的泛素化降解作用。体内外研究数据表明，RSL1D1敲低能够通过激活p53信号通路，抑制结直肠癌细胞在体内外的生长，揭示了RSL1D1是一种潜在的结直肠癌治疗靶点，利用不同手段抑制RSL1D1-p53、RSL1D1-HDM2相互作用是一种极具潜力的结直肠肿瘤治疗方案。