Previously, we obtained gene expression profiles of primary prostate tumors resected from 33 African-American and 36 European-American patients. Analyzing the resulting datasets, we identified gene expression differences between African-American and European-American patients 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 (EMT) of cancer cells and is induced by interactions between fibroblasts and tumor cells. Thus, IDRS may also promote the metastatic process and its increased presence in African-American tumors (in 22 out of 33 African-American tumors versus 12 out of 36 European-American tumors, as tested) could be causatively linked to the heightened aggressiveness of these tumors. To further understand 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 the signature and how this signature can be reversed/targeted. The presence of an interferon gene signature in a tumor suggests a possible involvement of viral infections in disease pathology. 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. Previously, we completed a study that used a proprietary microarray chip that can detect all known mammalian viruses (650) in total RNA preparations. We analyzed tumors from African-American (n = 26) and European-American patients (n = 37), and benign prostate hyperplasia tissue (n = 9). We detected a number of viral sequences that were enriched in prostate tumors but were not present in benign prostate hyperplasia resections. Some of these sequences refer to viruses that one would not expect in the human prostate (e.g., bovine popular stomatitis virus, equine rhinitis B virus, Ljungan virus), while others point to the presence of either known human viruses (e.g., herpesvirus 1, 2, 7) or human endogenous retroviral sequences (e.g., ERV9, HERV 4-1) in the tissues. One surprising finding was the presence of spleen focus forming virus sequences in these prostate samples. Consultation with Frank Ruscetti at the NCI revealed that these sequences are likely indicative of xenotropic murine leukemia virus-related virus (XMRV), a closely related virus, and in collaboration with Frank Ruscetti we are currently studying whether XMRV is indeed presence in these tumors and whether there is a different infection rate for African-American and European-American patients. Future experiments are planned if test results are positive, and will include the screening of blood samples for XMRV seroprevalence in our case control study of prostate cancer in the context of race/ethnicity when a suitable screening test for this virus becomes available. Such a test is in development at Frank Ruscettis laboratory. In another approach, 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, who has described HERV-K expression in human breast tumors. Preliminary results show that the HERV-K envelope protein can be detected in prostate tumors, 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. These observations are further pursued but suggest that HERV-K is reactivated and expressed in human prostate tumors. 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 are 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. To study the function of these transcripts in prostate cancer, we generated isogenic cell line pairs with PSPHL knockdown (shRNA) and PSPHL overexpession (transgene), and co-expression of a luciferase reporter gene, using lentiviral constructs. Cell lines with altered PSPHL expression have been injected into nude mice to study tumor growth and metastasis. These studies are ongoing. Previous 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. 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 will increase the number of tumors to n = 24 for each patient group.
Showing the most recent 10 out of 18 publications
