Inhibition of AR-mediated transcription by binding of Oct1 to a motif enriched in AR-occupied regions

Search for Novel Diagnostic Biomarkers of Prostate Inflammation-Related Disorders: Role of Transglutaminase Isoforms as Potential Candidates

Investigations on prostate inflammation-related disorders, including acute and chronic prostatitis, chronic pelvic pain syndrome, benign prostate hyperplasia (BPH), and prostate cancer (PCa), are still ongoing to find new, accurate, and noninvasive biomarkers for a differential diagnosis of those pathological conditions sharing some common macroscopic features. Moreover, an ideal biomarker should be useful for risk assessment of prostate inflammation progression to more severe disorders, like BPH or PCa, as well as for monitoring of treatment response and prognosis establishment in carcinoma cases. Recent literature evidence highlighted that changes in the expression of transglutaminases, enzymes that catalyze transamidation reactions leading to posttranslational modifications of soluble proteins, occur in prostate inflammation-related disorders. This review focuses on the role specifically played by transglutaminases 4 (TG4) and 2 (TG2) and suggests that both isoenzymes hold a potential to be included in the list of candidates as novel diagnostic biomarkers for the above-cited prostate pathological conditions.

Chromatin reprogramming as an adaptation mechanism in advanced prostate cancer

Tumor evolution is based on the ability to constantly mutate and activate different pathways under the selective pressure of targeted therapies. Epigenetic alterations including those of the chromatin structure are associated with tumor initiation, progression and drug resistance. Many cancers, including prostate cancer, present enlarged nuclei, and chromatin appears altered and irregular. These phenotypic changes are likely to result from epigenetic dysregulation. High-throughput sequencing applied to bulk samples and now to single cells has made it possible to study these processes in unprecedented detail. It is therefore timely to review the impact of chromatin relaxation and increased DNA accessibility on prostate cancer growth and drug resistance, and their effects on gene expression. In particular, we focus on the contribution of chromatin-associated proteins such as the bromodomain-containing proteins to chromatin relaxation. We discuss the consequence of this for androgen receptor transcriptional activity and briefly summarize wider gain-of-function effects on other oncogenic transcription factors and implications for more effective prostate cancer treatment.

Crosstalk of the Androgen Receptor with Transcriptional Collaborators: Potential Therapeutic Targets for Castration-Resistant Prostate Cancer

Prostate cancer is the second leading cause of death from cancer among males in Western countries. It is also the most commonly diagnosed male cancer in Japan. The progression of prostate cancer is mainly influenced by androgens and the androgen receptor (AR). Androgen deprivation therapy is an established therapy for advanced prostate cancer; however, prostate cancers frequently develop resistance to low testosterone levels and progress to the fatal stage called castration-resistant prostate cancer (CRPC). Surprisingly, AR and the AR signaling pathway are still activated in most CRPC cases. To overcome this problem, abiraterone acetate and enzalutamide were introduced for the treatment of CRPC. Despite the impact of these drugs on prolonged survival, CRPC acquires further resistance to keep the AR pathway activated. Functional molecular studies have shown that some of the AR collaborative transcription factors (TFs), including octamer transcription factor (OCT1), GATA binding protein 2 (GATA2) and forkhead box A1 (FOXA1), still stimulate AR activity in the castration-resistant state. Therefore, elucidating the crosstalk between the AR and collaborative TFs on the AR pathway is critical for developing new strategies for the treatment of CRPC. Recently, many compounds targeting this pathway have been developed for treating CRPC. In this review, we summarize the AR signaling pathway in terms of AR collaborators and focus on pyrrole-imidazole (PI) polyamide as a candidate compound for the treatment of prostate cancer.

Targeting Oct1 genomic function inhibits androgen receptor signaling and castration-resistant prostate cancer growth

Androgen receptor (AR) functions as a ligand-dependent transcription factor to regulate its downstream signaling for prostate cancer progression. AR complex formation by multiple transcription factors is important for enhancer activity and transcriptional regulation. However, the significance of such collaborative transcription factors has not been fully understood. In this study, we show that Oct1, an AR collaborative factor, coordinates genome-wide AR signaling for prostate cancer growth. Using global analysis by chromatin immunoprecipitation sequencing (ChIP-seq), we found that Oct1 is recruited to AR-binding enhancer/promoter regions and facilitates androgen signaling. Moreover, a major target of AR/Oct1 complex, acyl-CoA synthetase 3 (ACSL3), contributes to tumor growth in nude mice, and its high expression is associated with poor prognosis in prostate cancer patients. Next, we examined the therapeutic effects of pyrrole-imidazole polyamides that target the Oct1-binding sequence identified in the center of the ACSL3 AR-binding site. We observed that treatment with Oct1 polyamide severely blocked the Oct1 binding at the ACSL3 enhancer responsible for its transcriptional activity and ACSL3 induction. In addition, Oct1 polyamides suppressed castration-resistant tumor growth and specifically repressed global Oct1 chromatin association and androgen signaling in prostate cancer cells, with few nonspecific effects on basal promoter activity. Thus, targeting Oct1 binding could be a novel therapeutic strategy for AR-activated castration-resistant prostate cancer.

Elevated OCT1 participates in colon tumorigenesis and independently predicts poor prognoses of colorectal cancer patients

Octamer transcription factor 1 (OCT1) was found to influence the genesis and progression of numerous cancers except for colorectal cancer (CRC). This study tried to explore the role of OCT1 in CRC and clarify the association between its expression and patients' clinical outcome. Transcriptional and post-transcriptional expression of OCT1 was detected in CRC cancerous tissues and paired normal mucosae by real-time PCR as well as immunohistochemistry. Moreover, the effect of OCT1 knockdown on CRC cell proliferation was investigated both in vitro and in vivo using Cell Counting Kit-8 assay, colony-forming assay, and mouse tumorigenicity assay. Expression of OCT1 was found to be elevated in CRC. Suppression of OCT1 significantly inhibited CRC cell proliferation both in vitro and in vivo. Furthermore, upregulated level of OCT1 was significantly associated with N stage, M stage, and American Joint Committee on Cancer (AJCC) stage (P = 0.027, 0.014, and 0.002, respectively) as well as differential degree (P = 0.022). By using multivariate Cox hazard model, OCT1 was also shown to be a factor independently predicting overall survival (OS; P = 0.013, hazard ratio = 2.747, 95 % confidence interval 1.125 to 3.715) and disease-free survival (DFS; P = 0.004, hazard ratio = 2.756, 95 % confidence interval 1.191 to 4.589) for CRC patients. Our data indicate that OCT1 carries weight in colorectal carcinogenesis and functions as a novel prognostic indicator and a promising target of anti-cancer therapy for CRC.

High expression of octamer transcription factor 1 in cervical cancer

Cervical carcinoma is the second most prevalent malignancy in females worldwide. The crucial etiologic factors involved in the development of cervical carcinoma include infection with papillomavirus, and the structural or functional mutation of oncogenes and tumor suppressor genes. The abnormal change of octamer transcription factor 1 (OCT1) is associated with tumor progression and a poor patient survival rate. However, little is known regarding the effect of OCT1 in cervical cancer. In the present study, flow cytometry, western blot analysis and quantitative polymerase chain reaction (qPCR) were peformed to identify differentially expressed OCT1 in cervical cancer tissue and adjacent non-cancerous tissues. The normalized OCT1 gene expression in cervical cancer was 5.98 times higher compared with the adjacent non-cancerous tissues. Western blot analysis and flow cytometry assessed the levels of OCT1 protein. The results of these two differential techniques showed that the protein expression level of OCT1 was greater in cervical cancer tissues, which corresponded with the qPCR results. Finally, as OCT1 is a potential target gene for microRNA (miR)-1467, -1185, -4493 and -3919, their expression levels were analyzed in cervical cancer tissues and adjacent non-cancerous tissues; they were downregulated by ~45% in the cervical cancer samples. The results of the present study showed that OCT1 is highly expressed in cervical cancer tissues and indicated that OCT-1 may be significant in cervical cancer.

Genome-wide analysis of androgen receptor targets reveals COUP-TF1 as a novel player in human prostate cancer

Androgen activity plays a key role in prostate cancer progression. Androgen receptor (AR) is the main mediator of androgen activity in the prostate, through its ability to act as a transcription mediator. Here we performed a genome-wide analysis of human AR binding to promoters in the presence of an agonist or antagonist in an androgen dependent prostate cancer cell line. Many of the AR bound promoters are bound in all examined conditions while others are bound only in the presence of an agonist or antagonist. Several motifs are enriched in AR bound promoters, including the AR Response Element (ARE) half-site and recognition elements for the transcription factors OCT1 and SOX9. This suggests that these 3 factors could define a module of co-operating transcription factors in the prostate. Interestingly, AR bound promoters are preferentially located in AT rich genomic regions. Analysis of mRNA expression identified chicken ovalbumin upstream promoter-transcription factor 1 (COUP-TF1) as a direct AR target gene that is downregulated upon binding by the agonist liganded AR. COUP-TF1 immunostaining revealed nucleolar localization of COUP-TF1 in epithelium of human androgen dependent prostate cancer, but not in adjacent benign prostate epithelium. Stromal cells both in human and mouse prostate show nuclear COUP-TF1 staining. We further show that there is an inverse correlation between COUP-TF1 expression in prostate stromal cells and the rising levels of androgen with advancing puberty. This study extends the pool of recognized putative AR targets and identifies a negatively regulated target of AR – COUP-TF1 – which could possibly play a role in human prostate cancer.

Oct1 regulates cell growth of LNCaP cells and is a prognostic factor for prostate cancer

The androgen receptor (AR) plays a critical role in the development and the progression of prostate cancer. Alterations in the expression of AR coregulators lead to AR hypersensitivity, which is one of the mechanisms underlying the progression of prostate cancer into a castrate-resistant state. Octamer transcription factor 1 (Oct1) is a ubiquitous member of the POU-homeodomain family that functions as a coregulator of AR. In our study, the contribution of Oct1 to prostate cancer development was examined. Immunocytochemistry analysis showed that Oct1 is expressed in the nuclei of LNCaP cells. siRNA-mediated silencing of Oct1 expression inhibited LNCaP cell proliferation. Immunohistochemical analysis of Oct1 expression in tumor specimens obtained from 102 patients with prostate cancer showed a positive correlation of Oct1 immunoreactivity with a high Gleason score and AR immunoreactivity (p = 0.0042 and p < 0.0001, respectively). Moreover, patients with high immunoreactivity of Oct1 showed a low cancer-specific survival rate, and those patients with high immunoreactivities of both Oct1 and AR exhibited poorer cancer-specific prognosis. Multivariate hazard analysis revealed a significant correlation between high Oct1 immunoreactivity and poor cancer-specific survival (p = 0.012). These results demonstrate that Oct1 can be a prognostic factor in prostate cancer as a coregulator of AR and may lead to the development of a new therapeutic intervention for prostate cancer.