Nabbi Arash, McClurg Urszula L, Thalappilly Subhash, Almami Amal, Mobahat Mahsa, Bismar Tarek A, Binda Olivier, Riabowol Karl T
Department of Biochemistry & Molecular Biology, Arnie Charbonneau Cancer Institute, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.
Department of Oncology, Arnie Charbonneau Cancer Institute, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.
BMC Med. 2017 May 16;15(1):103. doi: 10.1186/s12916-017-0854-0.
The androgen receptor (AR) is a major driver of prostate cancer, and increased AR levels and co-activators of the receptor promote the development of prostate cancer. INhibitor of Growth (ING) proteins target lysine acetyltransferase or lysine deacetylase complexes to the histone H3K4Me3 mark of active transcription, to affect chromatin structure and gene expression. ING3 is a stoichiometric member of the TIP60 lysine acetyltransferase complex implicated in prostate cancer development.
Biopsies of 265 patients with prostate cancer were stained for ING3, pan-cytokeratin, and DNA. LNCaP and C4-2 androgen-responsive cells were used for in vitro assays including immunoprecipitation, western blotting, Luciferase reporter assay and quantitative polymerase chain reaction. Cell viability and migration assays were performed in prostate cancer cell lines using scrambled siRNA or siRNA targeting ING3.
We find that ING3 levels and AR activity positively correlate in prostate cancer. ING3 potentiates androgen effects, increasing expression of androgen-regulated genes and androgen response element-driven reporters to promote growth and anchorage-independent growth. Conversely, ING3 knockdown inhibits prostate cancer cell growth and invasion. ING3 activates the AR by serving as a scaffold to increase interaction between TIP60 and the AR in the cytoplasm, enhancing receptor acetylation and translocation to the nucleus. Activation is independent of ING3's ability to target the TIP60 complex to H3K4Me3, identifying a previously unknown chromatin-independent cytoplasmic activity for ING3. In agreement with in vitro observations, analysis of The Cancer Genome Atlas (TCGA) data (n = 498) and a prostate cancer tissue microarray (n = 256) show that ING3 levels are higher in aggressive prostate cancers, with high levels of ING3 predicting shorter patient survival in a low AR subgroup. Including ING3 levels with currently used indicators such as the Gleason score provides more accurate prognosis in primary prostate cancer.
In contrast to the majority of previous reports suggesting tumor suppressive functions in other cancers, our observations identify a clear oncogenic role for ING3, which acts as a co-activator of AR in prostate cancer. Data from TCGA and our previous and current tissue microarrays suggest that ING3 levels correlate with AR levels and that in patients with low levels of the receptor, ING3 level could serve as a useful prognostic biomarker.
雄激素受体（AR）是前列腺癌的主要驱动因素，该受体水平的升高及其共激活因子可促进前列腺癌的发展。生长抑制因子（ING）蛋白可将赖氨酸乙酰转移酶或赖氨酸脱乙酰酶复合物靶向到活跃转录的组蛋白H3K4Me3标记上，从而影响染色质结构和基因表达。ING3是TIP60赖氨酸乙酰转移酶复合物的化学计量成员，与前列腺癌的发展有关。
对265例前列腺癌患者的活检组织进行ING3、全细胞角蛋白和DNA染色。使用LNCaP和C4-2雄激素反应性细胞进行体外试验，包括免疫沉淀、蛋白质印迹、荧光素酶报告基因检测和定量聚合酶链反应。使用乱序小干扰RNA（siRNA）或靶向ING3的siRNA在前列腺癌细胞系中进行细胞活力和迁移试验。
我们发现前列腺癌中ING3水平与AR活性呈正相关。ING3增强雄激素作用，增加雄激素调节基因的表达以及雄激素反应元件驱动的报告基因的表达，从而促进生长和非锚定依赖性生长。相反，敲低ING3可抑制前列腺癌细胞的生长和侵袭。ING3通过作为支架增加TIP60与AR在细胞质中的相互作用，增强受体乙酰化并使其易位至细胞核，从而激活AR。激活过程独立于ING3将TIP60复合物靶向H3K4Me3的能力，这确定了ING3以前未知的不依赖染色质的细胞质活性。与体外观察结果一致，对癌症基因组图谱（TCGA）数据（n = 498）和前列腺癌组织芯片（n = 256）的分析表明，侵袭性前列腺癌中ING3水平较高，ING3水平高预示着低AR亚组患者的生存期较短。将ING3水平与目前使用的指标（如Gleason评分）相结合，可为原发性前列腺癌提供更准确的预后评估。
与之前大多数报道表明其在其他癌症中具有肿瘤抑制功能相反，我们的观察结果确定了ING3在前列腺癌中具有明确的致癌作用，它在前列腺癌中作为AR的共激活因子发挥作用。来自TCGA的数据以及我们之前和目前的组织芯片表明，ING3水平与AR水平相关，并且在受体水平较低的患者中，ING3水平可作为一种有用的预后生物标志物。
