The Molecular Profile of Prostate Tumors in African-American Men

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Previously, we obtained gene expression profiles from primary prostate tumors resected from 33 African-American and 36 European-American men. Analyzing the resulting datasets, we identified gene expression differences that portray the existence of a distinct tumor microenvironment for these two patient groups. Many of the differently expressed genes were immune-regulatory. Perhaps most significant was the presence of a distinct interferon signature in many of the African-American tumors. As now discovered by us, this signature is almost identical with an interferon-related DNA damage resistance signature (IRDS) that predicts resistance to chemotherapy and radiation. The presence of IDRS in African-American tumors may not only affect the response of them to immune-based therapies but may also make them more resistant to standard therapy including radiation therapy. In addition, IDRS has been linked to the pro-metastatic epithelial to mesenchymal transition of cancer cells and is induced by interactions between fibroblasts and tumor cells. Thus, IDRS may also promote the metastatic process. We completed very recently the analysis of two independent datasets with gene expression profiles from African-American and European-American tumors, which showed that IDRS is significantly more common in tumors from the African-American patients than in tumors from European-American patients in both datasets. To explore the origin of IDRS, we interrogated the expression profiles of isolated primary human prostate epithelial cells from 14 African-American patients and 13 European-American patients for the presence of IDRS. This analysis led to the finding that IDRS is present in these cultured cells, thus persisting in cancer cells after being removed from the tumor microenvironment, and was observed in 5 out of 14 (36%) isolates from African-American patients versus 2 out of 13 (15%) isolates from European-American patients. We believe that the heightened prevalence of IDRS in cancer cells from African-American patients could be clinically very significant and warrants further investigations into the origin of this signature, and also how this signature can be targeted. To further understand the possible origin of the detected immunobiological differences in tumors of African-American and European-American prostate cancer patients, we have started with the evaluation of blood-based immune cell profiles of African-American and European-American prostate cancer patients and age-matched population-based controls with a focus of subpopulation that have immune-regulatory functions in cancer biology. It is the hypothesis of this project that immune cell subpopulation that have immune-regulatory functions in cancer biology are different in abundance in these two population groups.The presence of an interferon gene signature in prostate tumors suggests a possible involvement of either a viral infection in disease pathology or the reactivation of endogenous retroviruses in the tumor microenvironment. This hypothesis was further supported by our finding that the interferon signature in prostate tumors coincides with a gene signature of retroviral activation. Thus, we started a project exploring the presence of viral infections and the reactivation of endogenous retroviruses in tumors from African-American and European-American patients. In a pilot study, we investigated tumor samples by immunohistochemistry and peripheral blood mononuclear cell isolates by quantitative PCR for expression of a family of endogenous retroviruses, HERV-K. This project is a collaboration with Dr. Feng Wang-Johanning at MD Anderson. The findings showed that the HERV-K envelope protein can be detected in prostate tumors by immunohistochemistry and is more commonly detected in tumors from African-American men, indicating that HERV-K encoded proteins are expressed in these tumors, and that HERV-K gag expression is elevated blood mononuclear cells from prostate cancer patients when compared with a non-cancer control population. As a next step, we will analyze blood samples from men prospectively recruited into the PLCO study. A pilot study has been approved and will start to analyze 30 blood samples blinded to the case-control status (15/15). These blood samples have been drawn from men that developed prostate cancer and those who did not develop prostate cancer and will be analyzed in collaboration with laboratory of Dr. Sharon Glynn at the National University of Ireland, Galway, to examine whether increased HERV-K can be detected in men who later developed prostate cancer. If the pilot study is successful, a larger study with PLCO samples will be conducted to assess HERV-K as an early detection marker for prostate cancer.The microarray analysis of African-American and European-American prostate tumors identified a two-gene tumor signature that accurately differentiated between African-American and European-American cancer patients. PSPHL is included in this two-gene signature. PSPHL was the most highly up-regulated gene in prostate tumors from African-American patients. Little is known about the function of PSPHL. Interestingly, PSPHL is located on chromosome 7q11.2, a chromosomal region known to have gain of function related to advanced tumor stage in prostate cancer. PSPHL encodes a cysteine-rich small protein of 72 amino acids (predicted size 7.6 kDa). Despite its chromosomal location, there are no studies linking PSPHL expression to cancer progression. In collaboration with Drs. Jun Luo and William Isaacs at Johns Hopkins University, we were examining the genomic region of PSPHL. These studies showed that the PSPHL locus is frequently deleted in European-Americans while present in subjects of African ancestry. The PSPHL gene encodes for two transcripts that are both expressed in prostate cancer cells. Data from siRNA experiments showed that PSPHL may influence endoplasmic reticulum function, protein ubiquitination, O-linked N-acetylglucosamine metabolism and the TGF-beta signaling pathway. A two hybrid screen with PSPHL as bait identified, COPS5, as a candidate binding partner of PSPHL. This protein, also known as CSN5 or JAB1, is a subunit of the COP9 signalosome, a highly conserved protein complex that functions as a regulator in multiple signaling pathways. Future research is needed to clarify whether PSPHL protein indeed specifically interacts with COPS5. Currently, we are testing inducible systems of PSPHL expression to see if induction of PSPHL affects gene expression profiles and xenograft growth of cancer cells, and whether PSPHL is modifier of the stress signaling pathway in tumor cells.Lastly, we started studying the metabolome of prostate tumors comparing African-American and European-American tumors. In a pilot, 12 tumors and 12 non-tumor tissues from African-American patients and the same number of tissues from European-American patients were analyzed. A total of 600 metabolites were identified in the tissues using a proprietary technology of the company, Metabolon. The relative abundance of 113 metabolites was found to be different between all tumors combined and all normal surrounding tissues combined. A relative small number of those (n = 16) were found to be different between African-American and European-American tumors, suggesting that there are either only few differences in the tumor metabolome between these two patient groups or that the sample size of the pilot was too sample. In a follow up study, we increased the number of tumors to n = 24 for each patient group. This project is being continued in collaboration with Dr. Arun Sreekumar from Baylor College of Medicine, leading to the new finding that the tumor metabolome is indicative of certain differences in tumor biology between African-American and European-American patients.