Department of Oncology, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, China.
State Key Laboratory of Proteomics, Beijing Proteome Research Center, National Center for Protein Sciences (Beijing), Beijing Institute of Lifeomics, Beijing, China.
Neoplasia. 2021 Oct;23(10):1037-1047. doi: 10.1016/j.neo.2021.08.002. Epub 2021 Sep 10.
The E3 ubiquitin ligase adaptor Speckle-type POZ protein (SPOP) plays an important tumour suppressor role in prostate cancers (PCa), with mutation rate up to 15%. However, how SPOP mutations regulate prostate tumorigenesis remains elusive. Here, we report the identification of cell division cycle associated 5 (CDCA5) as a SPOP substrate. We found that SPOP interacts with CDCA5 and promotes its polyubiquitin degradation in a degron-dependent manner. This effect was greatly impaired by introducing PCa associated SPOP mutations. Importantly, we found that CDCA5 was essential for PCa cells to survive and proliferate. CDCA5 depletion in PCa cells led to cessation of proliferation, G2M arrest, severe sister chromatid aggregation disturbance, and apoptosis. we also found that CDCA5 knockdown decreased the protein expression of p-GSK3β, increased the activity of caspase-3, caspase-9, and the Bax/Bcl-2 ratio. Besides, we confirmed that CDCA5 interrupted cancer cell behavior via the AKT pathway. In contrast, silencing SPOP or overexpressing CDCA5 increased cell proliferation. Consistently, depleting SPOP along with CDCA5, or overexpressing CDCA5 along with SPOP also caused the growth of cells repressed. Consistent with the functional role of CDCA5, the mRNA and protein levels of CDCA5 were significantly increased in PCa, compared to normal tissues, and its high expression was associated with more severe lymph node metastasis, higher Gleason score, and poorer prognosis. Together, our data showed that SPOP plays a crucial role in inhibiting tumorigenesis and partly achieved this by promoting the degradation of oncoprotein CDCA5.
E3 泛素连接酶衔接子 Speckle-type POZ 蛋白（SPOP）在前列腺癌（PCa）中发挥着重要的肿瘤抑制作用，其突变率高达 15%。然而，SPOP 突变如何调节前列腺肿瘤发生仍不清楚。在这里，我们报告鉴定出细胞分裂周期相关蛋白 5（CDCA5）是 SPOP 的底物。我们发现 SPOP 与 CDCA5 相互作用，并以依赖降解基序的方式促进其多泛素化降解。这一效应在引入与 PCa 相关的 SPOP 突变时受到严重损害。重要的是，我们发现 CDCA5 对于 PCa 细胞的存活和增殖是必需的。在 PCa 细胞中敲除 CDCA5 会导致增殖停止、G2M 期阻滞、严重的姐妹染色单体聚集干扰和细胞凋亡。我们还发现，CDCA5 敲低会降低 p-GSK3β 的蛋白表达，增加 caspase-3、caspase-9 和 Bax/Bcl-2 比值的活性。此外，我们证实 CDCA5 通过 AKT 通路干扰癌细胞行为。相反，沉默 SPOP 或过表达 CDCA5 会增加细胞增殖。一致地，敲除 SPOP 并同时敲低 CDCA5，或过表达 CDCA5 并同时过表达 SPOP，也会导致细胞生长受到抑制。与 CDCA5 的功能作用一致，与正常组织相比，CDCA5 的 mRNA 和蛋白水平在 PCa 中显著升高，其高表达与更严重的淋巴结转移、更高的 Gleason 评分和更差的预后相关。总之，我们的数据表明 SPOP 在抑制肿瘤发生中起着至关重要的作用，部分通过促进癌蛋白 CDCA5 的降解来实现这一作用。
