The Prostate Cancer Foundation Scholar-in-Training Awards recognize promising young cancer researchers presenting outstanding proffered papers relating to advanced prostate cancer at the AACR Annual Meeting. The Prostate Cancer Foundation is one of 13 organizations sponsoring this highly competitive awards program in conjunction with the AACR. The 2015 AACR Annual Meeting will be held from April 18 – 22, 2015, at the Pennsylvania Convention Center in Philadelphia, PA.
Yanfei Gao, PhD
Beth Israel Deaconess Medical Center/Harvard Medical School
Boston, MA, United States
“Androgen receptor transcriptionally represses genes mediating DNA synthesis and repair in prostate cancer”
Abstract: In the U.S., prostate cancer (PCa) ranked second for cancer related deaths for men. It has been well established that androgen receptor (AR) plays an essential role in the development of primary PCa and its activity is restored in castration resistant prostate cancers (CRPC). While AR has been extensively characterized as a transcriptional activator, it can also function by direct or indirect mechanisms to suppress gene expression. Despite the critical role AR plays in PCa, mechanisms by which it functions as a transcriptional repressor are poorly understood. Using VCaP and VCaP derived CRPC cell lines, we have reported that androgen-repressed genes were functionally enriched for DNA synthesis and repair, while AR stimulated genes were associated with lipid/sterol synthesis and other aspects of cellular metabolism. Significantly, a subset of the genes that were androgen-repressed in VCaP cells were consistently increased in CRPC clinical samples, and this 53-gene subset was also highly enriched for genes mediating DNA synthesis and repair. Using AR ChIP-seq and transcriptome profiling in VCaP cells, we found that the majority of this AR-suppressed gene subset (39/53) have one or more AR binding sites within the gene locus. The expression level of these direct AR-suppressed genes is associated with poor survival of disease in clinical cohorts. Interestingly, although the suppression activity of AR on this subset of genes is direct, in other PCa cell lines such as LNCaP, there is a secondary mechanism that allows AR to indirectly stimulate the expression of these genes. Importantly, the direct AR mediated repression of these genes is enhanced in PCa cells expressing higher levels of AR, and overexpression of AR in LNCaP cells resulted in increased and more persistent AR binding to these genes, and also enhanced the direct AR repression of this gene subset.
Mechanistically, we found that the indirect activation of these DNA synthesis genes by AR is mediated through transcriptionally stimulating lipid synthesis, which could subsequently drive the G1/S cell cycle progression and RB1 phosphorylation. Indeed, this indirect stimulatory effect of AR on these genes could be suppressed by cyclin dependent kinase inhibition or by preventing the AR stimulation of mTOR (rapamycin) or sterol synthesis (statins). Taken together, these findings indicate that the ability of AR to repress this gene set mediating DNA synthesis may persist in CRPC, and may be exploited therapeutically by combination therapies that stimulate AR while repressing its metabolic functions.
This abstract will be presented in a Poster Session entitled Molecular Endocrinology of Cancer, located in Section 36, on Monday, April 20, 2015, 8:00 a.m.-12:00 p.m.
Claire M. Faltermeier, BA
University of California, Los Angeles
Los Angeles, CA, United States
“Identification and characterization of wild type kinases driving prostate cancer metastasis”
Abstract: Despite numerous oncogenic alterations implicated in metastatic prostate cancer, mutations or DNA amplifications of kinases are rare. We previously demonstrated that 1) expression of wild type (wt) Src in combination with the androgen receptor synergizes to produce aggressive prostate adenocarcinoma, 2) tyrosine phosphorylation increases with prostate cancer stage, and 3) the phosphoproteomic profile of metastatic prostate cancer is different from localized disease. However, the question still remains as to whether wt kinases can drive prostate cancer metastasis and should be regarded as therapeutic targets. To identify wt kinases driving prostate cancer metastasis, we performed phospho-tyrosine, threonine and serine peptide enrichment and quantitative mass spectrometry on metastatic prostate cancer tissues obtained at rapid autopsy. Analysis of this phosphoproteomic dataset combined with bioinformatic analyses of genomic datasets identified ~140 kinases differentially expressed or activated in prostate cancer metastases. To determine which of these kinases function to promote prostate cancer metastasis, we developed an in vitro and in vivo metastasis screen. Out of 140 kinases, 20 kinases promote resistance to anoikis in vitro and metastatic colonization in vivo. Positive kinases include Src, Lyn, and EGFR which have been previously reported to be important in prostate cancer metastasis and thus provide strength to the validity of our screen. In addition we identified kinases with uncharacterized roles in prostate cancer metastasis and of particular interest, several of these kinases promote bone metastasis. We expect our findings will improve our understanding of the mechanistic role of kinase activation in prostate cancer and identify promising new therapeutic targets for metastatic disease.
This abstract will be presented in a Poster Session entitled Predicting, Profiling, and Imaging Prospective and Established Metastases, located in Section 18, on Wednesday, April 22, 2015, 8:00 a.m.-12:00 p.m.
Udit Singhal, BSc
University of Michigan
Ann Arbor, MI, United States
“SChLAP1 mediated epigenetic modifications in prostate cancer”
Abstract: Prostate cancer is the leading cancer diagnosis in men, but only a subset of patients die from the disease. Understanding the molecular basis of aggressive prostate cancer remains elusive and few genomic biomarkers exist to guide clinical management. Long non-coding RNAs (lncRNAs) have emerged as a class of regulatory genes that play a role in several biological and disease processes, including cancer.
Recently, we identified SChLAP1, a novel, prognostic lncRNA expressed in a subset of prostate tumors. Mechanistically, SChLAP1 interacts with and inhibits genome-wide binding of the SWI/SNF nucleosome-remodeling complex. Additionally, SWI/SNF plays a key role in the epigenetic control of gene expression and has been shown to have tumor suppressive ability. Given the emerging role of SChLAP1 in the pathogenesis of aggressive prostate cancer and its interaction with the tumor suppressive SWI/SNF complex, exploring the detailed mechanism of action of SChLAP1 warranted further investigation.
To identify the regions of SChLAP1 necessary for its function, we created 250 base pair deletion constructs of SChLAP1 and measured RNA-enrichment following SWI/SNF pull-down as well as cell invasion using a Boyden chamber matrigel assay. To investigate whether SChLAP1 preferentially interacts with specific components of the SWI/SNF complex, we performed RNA immunoprecipitation assays using antibodies targeting various enzymatic subunits of SWI/SNF. SChLAP1 enrichment was measured by qPCR.
Our results indicate that there is a 250bp region of SChLAP1 that mediates its interaction with SWI/SNF and promotes an invasive phenotype. Furthermore, SChLAP1 shows binding specificity for certain SWI/SNF subunits. Future studies to elucidate the details of this interaction will provide a more comprehensive understanding of the biological and therapeutic consequences of SChLAP1 in prostate cancer progression.
This abstract will be presented in a Minisymposium Session entitled Non-coding RNAs in Cancer Biology 2 on Monday, April 20, 2015, Terrace Ballroom I (400 Level), 3:00 p.m.-5:00 p.m.