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Title: A novel mechanism underlying prostate cancer progression : an investigation into the impact of insulin like growth factors (IGFs), PTEN and IGFBP2 on TMPRSS2:ERG fusion induction
Author: Broadhurst, Jessica
ISNI:       0000 0004 5993 6065
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2014
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Prostate cancer (PC) is the most commonly diagnosed male cancer in the UK. The transmembrane protease serine 2 (TMPRSS2) gene has been found fused to the ETS related gene (ERG), which codes for an oncogenic transcription factor in 50% of PC cases. Fusion puts the coding sequence of ERG under the control of the androgen regulated promoter and enhancer of TMPRSS2, resulting in androgen regulated ERG expression. Androgen is present at high concentrations in the prostate and therefore drives high levels of ERG production, resulting in increase proliferation, metastasis and invasion. Several studies have shown that TMPRSS2:ERG fusion can be achieved in vitro by treating prostate cells with androgen alone or in combination with DNA damaging agents. Here fusion was optimised in LNCaP cells by treatment with the androgen, dihydrotestosterone (DHT) and the double strand break (DSB) inducing agent etoposide and detected at the genomic level using nested PCR. Induction ofTMPRSS2:ERG fusion was shown to be regulated by several different factors. The insulin like growth factor 1 (IGF-I), epidermal growth factor (EGF) and insulin were each found to substantially decrease the rat~ of fusion induction when treatment was combined with DHT and etoposide. Insulin like growth factor binding protein 2 (IGFBP-2) has been shown to function by both sequestering IGFs and by signalling independently of IGF via activation of integrin signalling. IGFBP-2 pre-treatment combined with DHT and etoposide dosing of LN CaP cells, was shown to up regulate the initial expression of the catalytic subunit of the DNA repair protein, DNA protein kinase (DNAPKcs), which was found to be associated with accelerated DSB repair and increased fusion induction. This observation was supported by IGFBP-2 knockdown data, which showed a decrease in the expression of DNAPKcs, associated with a slower rate of DSB repair and decreased fusion induction. These observations suggest that IGFBP-2 increases fusion induction by accelerating DNAPKcs mediated DSB repair. The presence of exogenous IGFBP-2 during fusion induction treatment gave rise to an increase in the expression of the forkhead box protein Al (FOXA1), which functions to open the chromatin allowing enzymes and receptors access to the DNA. This was supported by IGFBP-2 knockdown data, which showed a decrease in FOXAl expression following fusion induction. Previous studies in this laboratory have shown increased IGFBP-2 and FOXAllevels at increased glucose concentrations. Fusion induction was observed to increase at a higher glucose concentration compared to at a physiological glucose concentration, associated with an increase in both FOXAl and IGFBP-2 expression. This suggests that elevated glucose levels triggers increased IGFBP-2 and FOXAl expression resulting in a higher incidence of fusion. Together these data suggest that fusion induction is inhibited by EGF, IGF-I and insulin. Fusion induction is increased by IGFBP-2, potentially mediated by increased levels of FOXAl and accelerated DSB repair.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available