Kawahara Takashi, Shareef Hasanain Khaleel, Aljarah Ali Kadhim, Ide Hiroki, Li Yi, Kashiwagi Eiji, Netto George J, Zheng Yichun, Miyamoto Hiroshi
Departments of Pathology and Urology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, NY, USA.
Oncotarget. 2015 Oct 6;6(30):29860-76. doi: 10.18632/oncotarget.5007.
Little is known about biological significance of ELK1, a transcriptional factor that activates downstream targets including c-fos proto-oncogene, in bladder cancer. Recent preclinical evidence also suggests the involvement of androgen receptor (AR) signaling in bladder cancer progression. In this study, we aim to investigate the functions of ELK1 in bladder cancer growth and their regulation by AR signals. Immunohistochemistry in bladder tumor specimens showed that the levels of phospho-ELK1 (p-ELK1) expression were significantly elevated in urothelial neoplasms, compared with non-neoplastic urothelium tissues, and were also correlated with AR positivity. Patients with p-ELK1-positive non-muscle-invasive and muscle-invasive tumors had significantly higher risks for tumor recurrence and progression, respectively. In AR-positive bladder cancer cell lines, dihydrotestosterone treatment increased ELK1 expression (mRNA, protein) and its nuclear translocation, ELK1 transcriptional activity, and c-fos expression, which was restored by an anti-androgen hydroxyflutamide. ELK1 silencing via short hairpin RNA (shRNA) resulted in decreases in cell viability/colony formation, and cell migration/invasion as well as an increase in apoptosis. Importantly, ELK1 appears to require activated AR to regulate bladder cancer cell proliferation, but not cell migration. Androgen also failed to significantly induce AR transactivation in ELK1-knockdown cells. In accordance with our in vitro findings, ELK1-shRNA expression considerably retarded tumor formation as well as its growth in xenograft-bearing male mice. Our results suggest that ELK1 plays an important role in bladder tumorigenesis and cancer progression, which is further induced by AR activation. Accordingly, ELK1 inhibition, together with AR inactivation, has the potential of being a therapeutic approach for bladder cancer.
关于ELK1（一种激活包括c-fos原癌基因在内的下游靶点的转录因子）在膀胱癌中的生物学意义，人们所知甚少。最近的临床前证据也表明雄激素受体（AR）信号传导参与了膀胱癌的进展。在本研究中，我们旨在研究ELK1在膀胱癌生长中的功能及其受AR信号的调控。膀胱肿瘤标本的免疫组织化学显示，与非肿瘤性尿路上皮组织相比，磷酸化ELK1（p-ELK1）在尿路上皮肿瘤中的表达水平显著升高，且与AR阳性相关。p-ELK1阳性的非肌层浸润性和肌层浸润性肿瘤患者分别具有显著更高的肿瘤复发和进展风险。在AR阳性的膀胱癌细胞系中，双氢睾酮处理增加了ELK1的表达（mRNA、蛋白质）及其核转位、ELK1转录活性和c-fos表达，而抗雄激素药物氟他胺可使其恢复。通过短发夹RNA（shRNA）沉默ELK1导致细胞活力/集落形成、细胞迁移/侵袭减少以及细胞凋亡增加。重要的是，ELK1似乎需要激活的AR来调节膀胱癌细胞增殖，但不调节细胞迁移。雄激素也未能在ELK1敲低的细胞中显著诱导AR反式激活。与我们的体外研究结果一致，ELK1-shRNA表达在携带异种移植瘤的雄性小鼠中显著延缓了肿瘤形成及其生长。我们的结果表明，ELK1在膀胱肿瘤发生和癌症进展中起重要作用，AR激活可进一步诱导其作用。因此，抑制ELK1以及使AR失活有可能成为膀胱癌的一种治疗方法。
