Abstract
Prostate cancer (PCa) is the most common non-cutaneous cancer in men. The androgen receptor (AR), a ligand-activated transcription factor, constitutes the main drug target for advanced cases of the disease. However, a variety of other transcription factors and signaling networks have been shown to be altered in patients and to influence AR activity. Amongst these, the oncogenic transcription factor c-Myc has been studied extensively in multiple malignancies and elevated protein levels of c-Myc are commonly observed in PCa. Its impact on AR activity, however, remains elusive. In this study, we assessed the impact of c-Myc overexpression on AR activity and transcriptional output in a PCa cell line model and validated the antagonistic effect of c-MYC on AR-targets in patient samples. We found that c-Myc overexpression partially reprogrammed AR chromatin occupancy and was associated with altered histone marks distribution, most notably H3K4me1 and H3K27me3. We found c-Myc and the AR co-occupy a substantial number of binding sites and these exhibited enhancer-like characteristics. Interestingly, c-Myc overexpression antagonised clinically relevant AR target genes. Therefore, as an example, we validated the antagonistic relationship between c-Myc and two AR target genes, KLK3 (alias PSA, prostate specific antigen), and Glycine N-Methyltransferase (GNMT), in patient samples. Our findings provide unbiased evidence that MYC overexpression deregulates the AR transcriptional program, which is thought to be a driving force in PCa.
c-MYC and AR share one third of chromatin binding with enhancer-like features.
c-MYC can repress the expression of a subset prostate cancer biomarkers, including PSA.
c-MYC and AR antagonize the expression of, Glycine N-Methyltransferase (GNMT), responsible for sarcosine biosynthesis.
Prostate cancer is a heterogeneous disease. The most frequently used biomarker in clinical setting, a well described androgen receptor target gene, PSA, still performs poorly in stratifying patients at real risk of death due to the disease. Despite this, therapeutic approaches focus on suppressing androgen receptor signaling. However, this is only one of the recurrent alterations found in patients. This study focuses on c-MYC and the effects of its deregulation in advanced prostate cancer. We find that there is an inverse relationship between established biomarkers expression, including PSA. This inverse relationship could be used in clinics to select beneficial therapeutic approaches for a subset of prostate cancer cases.
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