Бузук Георгий Николаевич

юбилеиученыеВРАЧ

The role of androgen in prostate cancer cell invasion

p>Prostate cancer (PCa) is the most commonly diagnosed cancer in men in developed countries. Androgen deprivation therapy (ADT) is the mainstay treatment for patient diagnosed with PCa. However, the cancer will eventually relapse with metastatic cancer and become resistant to the treatment. Since mortality in PCa is due to our inability to manage metastatic cancer, there is a great need for a better understanding of the cancer progression to develop novel therapeutic principles. As reflected by the therapeutic effects of (ADT) for PCa, it has become clear that intact androgen receptor signaling is necessary for the development of the disease. Previous works in our group have focused on studies of androgen regulated genes in a systematic and high-throughput manner using microarray technology. In those studies, several androgen-regulated genes were identified, some of which could be important in the regulation of PCa cell invasion. The aim of this thesis was to characterize a set of androgen-regulated genes in PCa and investigate the role of androgen on PCa cell invasion and the mode of actions of those selected genes in the invasion process. In this thesis, we demonstrate that androgen stimulation of the androgen sensitive PCa cell line, LNCaP-FGC up-regulate those selected genes at both mRNA and protein levels. For the first time, we also demonstrated that androgen induces the invasiveness of LNCaP-FGC through matrigel. This process was mediated by Ezrin, one of our selected genes. Androgen treatment phosphorylates ezrin in Thr-567 and Tyr-353 in a sequential manner and can also induce ezrin gene expression. The phosphorylation event was mediated by protein kinase C alpha and Src tyrosine kinase, respectively. Androgen furthermore induces the translocation of both protein kinase C alpha and ezrin to the cell membrane and their association. Inhibition of ezrin using short interference RNA or the overexpression of T567A and Y353F-ezrin mutants significantly reduces androgen-induced Matrigel invasion but does not affect cell proliferation or cell adhesion. We also demonstrate that androgens also increase gene expression of ezrin in LNCaP-FGC cell, through a mechanism involving the transcription factor c-Myc. Our finding that c-Myc binds to an E-Box in Ezrin promoter region leads us to suggest that androgen induction of ezrin is indirect and mediated by c-Myc. In addition, androgen treatment prolonged the half-life of c-Myc protein in LNCaP-FGC. We propose that this effect is achieved through changes in Ezrin phosphorylation, which leads to activation of downstream Akt and downregulation of GSK-3β signaling resulting in the inhibition of the degradation of c-Myc protein. Ezrin protein expression and cell invasion in two other androgen insensitive cell lines, LNCaP-R and PC3 are also depend on c-Myc. In conclusion, we have shown that androgen can induce PCa cell invasion that mediated through two distinct proteins c-Myc and ezrin. Ezrin also acts as a key modulator of c-Myc induced tumorigenesis in PCa cell

Performance appraisal in banks in Singapore

This final year report presents a survey of the performance appraisal practices in banks in Singapore. The report incorporates the findings from a survey on twenty-six banks and discusses the results in the light of literature reviewed on this topic. The survey touched on areas such as the purpose of the performance appraisal as well as the types of performance appraisal techniques used. The results show that most of the practices and attitudes of appraisers such as managers and human resource managers for the banks surveyed do not differ significantly from those found in the literature. Given the recent interest in performance reward schemes in both the public and private sectors, performance appraisal practice in Singapore is thus timely.ACCOUNTANC

OTUB1 de-ubiquitinating enzyme promotes prostate cancer cell invasion in vitro and tumorigenesis in vivo

Background: Ubiquitination is a highly dynamic and reversible process with a central role in cell homeostasis. Deregulation of several deubiquitinating enzymes has been linked to tumor development but their specific role in prostate cancer progression remains unexplored. Methods: RNAi screening was used to investigate the role of the ovarian tumor proteases (OTU) family of deubiquitinating enzymes on the proliferation and invasion capacity of prostate cancer cells. RhoA activity was measured in relation with OTUB1 effects on prostate cancer cell invasion. Tumor xenograft mouse model with stable OTUB1 knockdown was used to investigate OTUB1 influence in tumor growth. Results: Our RNAi screening identified OTUB1 as an important regulator of prostate cancer cell invasion through the modulation of RhoA activation. The effect of OTUB1 on RhoA activation is important for androgen-induced repression of p53 expression in prostate cancer cells. In localized prostate cancer tumors OTUB1 was found overexpressed as compared to normal prostatic epithelial cells. Prostate cancer xenografts expressing reduced levels of OTUB1 exhibit reduced tumor growth and reduced metastatic dissemination in vivo. Conclusions: OTUB1 mediates prostate cancer cell invasion through RhoA activation and promotes tumorigenesis in vivo. Our results suggest that drugs targeting the catalytic activity of OTUB1 could potentially be used as therapeutics for metastatic prostate cancer

SOCS2 mediates the cross talk between androgen and growth hormone signaling in prostate cancer

Anabolic signals such as androgens and the growth hormone/insulin-like growth factor 1 (GH/IGF-1) axis play an essential role in the normal development of the prostate but also in its malignant transformation. In this study, we investigated the role of suppressor of cytokine signaling 2 (SOCS2) as mediator of the cross talk between androgens and GH signals in the prostate and its potential role as tumor suppressor in prostate cancer (PCa). We observed that SOCS2 protein levels assayed by immunohistochemistry are elevated in hormone therapy-naive localized prostatic adenocarcinoma in comparison with benign tissue. In contrast, however, castration-resistant bone metastases exhibit reduced levels of SOCS2 in comparison with localized or hormone naive, untreated metastatic tumors. In PCa cells, SOCS2 expression is induced by androgens through a mechanism that requires signal transducer and activator of transcription 5 protein (STAT5) and androgen receptor-dependent transcription. Consequentially, SOCS2 inhibits GH activation of Janus kinase 2, Src and STAT5 as well as both cell invasion and cell proliferation in vitro. In vivo, SOCS2 limits proliferation and production of IGF-1 in the prostate in response to GH. Our results suggest that the use of GH-signaling inhibitors could be of value as a complementary treatment for castration-resistant PCa. Summary: Androgen induced SOCS2 ubiquitin ligase expression and inhibited GH signaling as well as cell proliferation and invasion in PCa, whereas reduced SOCS2 was present in castration-resistant cases. GH-signaling inhibitors might be a complementary therapeutic option for advanced PCa

REST mediates androgen receptor actions on gene repression and predicts early recurrence of prostate cancer

The androgen receptor (AR) is a key regulator of prostate tumorgenesis through actions that are not fully understood. We identified the repressor element (RE)-1 silencing transcription factor (REST) as a mediator of AR actions on gene repression. Chromatin immunoprecipitation showed that AR binds chromatin regions containing well-characterized cis-elements known to mediate REST transcriptional repression, while cell imaging studies confirmed that REST and AR closely co-localize in vivo. Androgen-induced gene repression also involves modulation of REST protein turnover through actions on the ubiquitin ligase β-TRCP. Androgen deprivation or AR blockage with inhibitor MDV3100 (Enzalutamide) leads to neuroendocrine (NE) differentiation, a phenomenon that is mimicked by REST inactivation. Gene expression profiling revealed that REST not only acts to repress neuronal genes but also genes involved in cell cycle progression, including Aurora Kinase A, that has previously been implicated in the growth of NE-like castration-resistant tumors. The analysis of prostate cancer tissue microarrays revealed that tumors with reduced expression of REST have higher probability of early recurrence, independently of their Gleason score. The demonstration that REST modulates AR actions in prostate epithelia and that REST expression is negatively correlated with disease recurrence after prostatectomy, invite a deeper characterization of its role in prostate carcinogenesis