ATF2 promotes urothelial cancer outgrowth via cooperation with androgen receptor signaling

Abstract

We investigated the functional role of ATF2, a transcription factor normally activated via its phosphorylation in response to phospho-ERK/MAPK signals, in the outgrowth of urothelial cancer. In both neoplastic and non-neoplastic urothelial cells, the expression levels of androgen receptor (AR) correlated with those of phospho-ATF2. Dihydrotestosterone treatment in AR-positive bladder cancer cells also induced the expression of phospho-ATF2 and phospho-ERK as well as nuclear translocation and transcriptional activity of ATF2. Meanwhile, ATF2 knockdown via shRNA resulted in significant decreases in cell viability, migration and invasion of AR-positive bladder cancer lines, but not AR-negative lines, as well as significant increases and decreases in apoptosis or G0/G1 cell cycle phase and S or G2/M phase, respectively. Additionally, the growth of AR-positive tumors expressing ATF2-shRNA in xenograft-bearing mice was retarded, compared with that of control tumors. ATF2 knockdown also resulted in significant inhibition of neoplastic transformation induced by a chemical carcinogen 3-methylcholanthrene, as well as the expression of Bcl-2/cyclin-A2/cyclin-D1/JUN/MMP-2, in immortalized human normal urothelial SVHUC cells stably expressing AR, but not AR-negative SVHUC cells. Finally, immunohistochemistry in surgical specimens demonstrated significant elevation of ATF2/phospho-ATF2/phospho-ERK expression in bladder tumors, compared with non-neoplastic urothelial tissues. Multivariate analysis further showed that moderate/strong ATF2 expression and phospho-ATF2 positivity were independent predictors for recurrence of low-grade tumors (hazard ratio (HR) = 2.956, P = 0.045) and cancer-specific mortality of muscle-invasive tumors (HR = 5.317, P = 0.012), respectively. Thus, ATF2 appears to be activated in urothelial cells through the AR pathway and promotes the development and progression of urothelial cancer.

The Role of Steroid Hormone Receptors in Urothelial Tumorigenesis

“…The activity of ATF2 is normally regulated via its phosphorylation through ERK/MAPK signals. Similar to the findings in ELK1, we demonstrated prevention of the neoplastic transformation of MCA-SVHUC-AR cells by ATF2 knockdown [79]. Immunohistochemistry in transurethral resection specimens also showed significant elevation of the expression of ATF2, phospho-ATF2 and phospho-ERK in bladder tumors, compared with non-neoplastic urothelial tissues [79].…”

“…The expression levels of ATF2 and phospho-ATF2 were considerably higher in SVHUC-AR than in AR-negative SVHUC [79]. In AR-positive bladder cancer cells, DHT induced the expression of phospho-ATF2 and phospho-ERK as well as nuclear translocation and transcriptional activity of ATF2.…”

Extracellular-Signal Regulated Kinase: A Central Molecule Driving Epithelial–Mesenchymal Transition in Cancer

“…Previous reports show that the phosphorylation levels of RAF, MEK, and ERK were significantly upregulated in samples from laryngeal cancer patients and contributed to tumor progression [163]. On the other hand, SHP2 promotes laryngeal cancer growth through the RAS/RAF/MEK/ERK pathway and serves as a prognostic indicator for laryngeal cancer [164]. In hepatocellular carcinoma patients, p-ERK was localized to the nucleus of tumor cells and higher levels of p-ERK were associated with increased progression time.…”

The activating transcription factor 2: an influencer of cancer progression

“…The oncogenic duality of ATF2 was further studied in bladder cancer where ATF2 activation was shown to be dependent on the androgen receptor (AR) with ATF2 activity being positively correlated to AR-induced urothelial tumorigenesis. Androgen was demonstrated to induce phosphorylation of ERK, an upstream kinase of ATF2, leading to the phosphorylation of ATF2 at Thr71 and its nuclear translocation (114). Moreover, Atf2 was shown to be indispensable for mouse skin tumour growth and progression since its downstream targets lead to cell proliferation and tumour progression(115,116).…”