Genetics and Molecular Mechanisms of Prostate Cancer

Division Of Basic Sciences - Nci

Investigators

Linked publications & trials

Abstract

We have conducted translational research to understand the genetic and molecular mechanism that govern prostate cancer development and progression, to identify novel pathways for drug development, and investigate mechanisms of resistance to treatment paradigms. Prostate cancer has entered into the era of precision medicine with the recent approvals of targeted therapeutics. The presence of germline variants has important hereditary cancer implications for patients with prostate cancer, and germline testing is increasingly important in cancer screening, risk assessment, and the overall treatment and management of the disease. We are interested in understanding variants associated with inherited predisposition, prostate cancer risk and outcomes. Understanding the role of germline (heritable) mutations that affect prostate cancer biology and risk as well as the subsequent effect of these alterations on potential therapies is critical as the treatment paradigm shifts towards precision medicine. Towards this end, the NIH All of Us Research Program (AoURP) is a longitudinal cohort study aimed to capture at least one million individuals across the US population to accelerate biomedical research and improve human health. The All of Us Research Hub contains a publicly accessible Data Browser for exploration of summary phenotypic and clinical grade genomic data (e.g., whole-genome sequencing and genotyping data). We are using the AoURP dataset to investigate whether treatment usage, disease progression, and genomic research participation vary across demographic factors among participants with prostate cancer. As we move into the era of precision medicine, the growing relevance of genetic alterations to prostate cancer (PCa) development and treatment demonstrates the importance of characterizing preclinical models at the genomic level. Our study investigated the genomic characterization of eight PCa cell lines to understand which models are clinically relevant. We designed a custom AmpliSeq DNA gene panel that encompassed key molecular pathways targeting AR signaling, apoptosis, DNA damage repair, and PI3K/AKT/PTEN, in addition to tumor suppressor genes. We examined the relationship between cell line genomic alterations and therapeutic response. In addition, using DepMap's Celligner tool, we identified which preclinical models are most representative of specific prostate cancer patient populations on cBioPortal. These data will help investigators understand the genetic differences in preclinical models of PCa and determine which ones are relevant for use in their translational research. We have a longstanding interest in understanding the molecular mechanisms of androgen transport. The organic anion transporter OATP1B3, encoded by the SLCO1B3 gene, is involved in the transport of steroid hormones. We have shown that prostate cancer overexpresses OATP1B3 compared to normal or benign hyperplastic tissue, and the common SLCO1B3 GG/AA haplotype is associated with impaired testosterone transport and improved survival in patients with PCa. We found that a polymorphism in this transporter increases testosterone import is associated with a shorter time to androgen independence in patients with PCa who are treated with ADT. We have conducted studies to ascertain the androgen uptake kinetics, functional, and clinical relevance of de novo expression of OATP1B3. We found that de novo OATP1B3 expression in prostate cancer drives greater androgen uptake and is consistent with previous observations that greater OATP1B3 activity results in the development of androgen deprivation therapy resistance and shorter overall survival. Studies are ongoing to characterize the molecular mechanisms of SLCO1B3 transcription including transcription factor complexes that assemble at distinct regulatory elements in the SLCO1B3 promoter for driving tissue-specific expression of OATP1B3 in prostate cancer. We have recently evaluated the role of extracellular vesicles (EV)-based liquid biopsy tumor markers for CRPC disease progression. EVs provide a minimally invasive liquid biopsy source of tumor-specific markers for patients who have already undergone prostatectomies. Our laboratory has previously demonstrated enrichment of the cancer-type solute carrier organic anion transporter family 1B3 (ct-SLCO1B3) and the ATP Binding Cassette Subfamily Member C (ABCC3) in castration-resistant cell lines. However, their expression in EVs has yet to be explored. Our study demonstrated that ct-SLCO1B3 and ABCC3 are highly detectable in CRPC cell line-derived EVs. We also showed that ct-SLCO1B3 and ABCC3 were detectable in a CRPC xenograft mouse model, both intratumorally and in plasma-derived EVs. Our results provide evidence for EV-contained ct-SLCO1B3 and ABCC3 as novel, EV-based tumor markers for prostate cancer progression. Studies are ongoing to characterize the functional role of ct-SLCO1B3 in prostate cancer using CRISPR-Cas9 technology. Hypoxia is a common feature of many solid tumors and is associated with poor prognosis and therapeutic resistance. The main regulator of cellular responses to hypoxia is the transcription factor HIF. Additionally, several histone lysine demethylases require oxygen for their activity. Therefore, the activity of these enzymes is inhibited by hypoxia and global histone hypermethylation results. Histone methylation can be associated with both gene activation and repression, and it remains unclear how the balance of these widespread changes regulates locus-specific expression. Furthermore, previous attempts to analyze histone methylation by ChIP-seq in hypoxia have not employed normalization methods that consider global changes in histone modification. We performed ChIP-seq analysis of histone trimethylation (H3K4me3, H3K9me3, H3K27me3, H3K36me3) in PC3 prostate cancer cells incubated in normoxia or (16hrs, 0.5%) hypoxia. We then examined the effects of the HIF-transcriptional pathway on these marks using the same cell line following deletion of HIF-1b to block the HIF response. We employed a spike-in with drosophila chromatin to provide a normalization control. We then related our findings to changes in gene expression using RNA-seq analysis, again normalized to a spike-in. We observed that hypoxia increases all four histone modifications across the genome. The hypoxic induction of 'active' histone marks H3K4me3 and H3K36me3 positively correlated with changes in expression, while induction of 'repressive' marks H3K9me3 and H3K27me3 did not. These findings question the model that changes in histone modification instruct changes in transcription and suggest that the overall impact of histone trimethylation is a more subtle balance of competing effects. Interestingly, in wild-type PC3 cells, HIF target genes were enriched amongst genes at which H3K4me3 and H3K36me3 increase most. While HIF was not required for the global hypoxic induction of histone methylation, deletion of HIF-1b revealed that HIF activity is essential for a locus-specific and pronounced effect observed at HIF target genes.