No abstract

The Ets family of transcription factors control a myriad of cellular processes and contribute to the underlying genetic loss of cellular homeostasis resulting in cancer. PDEF (prostate-derived Ets factor) has been under investigation for its role in tumor development and progression. However, the role of PDEF in cancer development has been controversial. Some reports link PDEF to tumor promoter, and others show tumor-suppressing functions in various systems under different conditions. So far, there has been no conclusive evidence from in vivo experiments to prove the role of PDEF. We have used both in vitro and in vivo systems to provide a conclusive role of PDEF in the progression process. PDEF-expressing cells block the cell growth rate, and this retardation was reversible when PDEF expression was silenced with PDEF-specific small interfering RNA. When these PDEF-expressing cells were orthotopically implanted into the mouse mammary gland, tumor incidence and growth rate were significantly retarded. Cell cycle analysis revealed that PDEF expression partially blocked cell cycle progression at G 1 /S without an effect on apoptosis. PDEF overexpression resulted in an increase in p21/CIP1 at both the mRNA and protein levels, resulting in decreased Cdk2 activity. Promoter deletion analysis, electrophoresis mobility shift assays, and chromatin immunoprecipitation studies identified the functional Ets DNA binding site at ؊2118 bp of the p21/CIP1 gene promoter. This site is capable of binding and responding to PDEF. Furthermore, we silenced p21/CIP1 expression in PDEFoverexpressing cells by small interfering RNA. p21-silenced PDEF cells exhibited significantly increased cell growth in vitro and in vivo, demonstrating the p21 regulation by PDEF as a key player. These experiments identified PDEF as a new transcription factor that directly regulates p21/CIP1 expression under non-stressed conditions. This study conclusively proves that PDEF is a breast tumor suppressor for the first time using both in vitro and in vivo systems. PDEF can be further developed as a target for designing therapeutic intervention of breast cancer.

Angiocidin, a tumor-secreted protein, was measured in serum of 27 healthy volunteers and 33 hepatocellular carcinoma (HCC) patients. Healthy controls either hepatitis B surface antigen (HBsAg) positive or negative showed undetectable levels. Patients had levels of angiocidin ranging from 15.09-195.73 pg/ml. Patients with stages III-IV had higher levels of angiocidin (97±13 pg/ml, n=17) compared to those with stages I-II (63±37 pg/ml, n=16), p<0.043. Patients with microsatellite tumor nodules had higher average levels (98±55 pg/ml, n=17) compared to those without microsatellite nodules (51± 27 pg/ml, n=20), p<0.032. Our studies suggest that angiocidin predicts advanced stage and intra-hepatic metastasis.

We recently cloned the full-length cDNA of a tumour-associated protein. The recombinant protein expressed in bacteria and referred to as angiocidin has potent antitumour activity in vivo and in vitro. Angiocidin inhibits tumour growth and angiogenesis by inducing apoptosis in endothelial cells. Based on the sequence similarity of angiocidin to S5a, one of the major polyubiquitin recognition proteins in eukaryotic cells, we postulated that the antiendothelial activity of angiocidin could be due in part to its polyubiquitin binding activity. In support of this hypothesis, we show that angiocidin binds polyubiquitin in vivo with high affinity and colocalises with ubiquitinated proteins on the surface of endothelial cells. Binding is blocked with an antiubiquitin antibody. Angiocidin treatment of endothelial cells transfected with a proteasome fluorescent reporter protein showed a dose-dependent inhibition of proteasome activity and accumulation of polyubiquitinated proteins. Full-length angiocidin bound polyubiquitin while three angiocidin recombinant proteins whose putative polyubiquitin binding sites were mutated either failed to bind polyubiquitin or had significantly diminished binding activity. The in vitro apoptotic activity of these mutants correlated with their polyubiquitin binding activity. These data strongly argue that the apoptotic activity of angiocidin is dependent on its polyubiquitin binding activity.

Abstract. The Ets proteins are a family of transcription factors characterized by an evolutionarily conserved DNA binding domain that controls key cellular processes. Prostate-derived Ets transcription factor (PDEF), a member of the Ets family, is reported to be present in tissues with high epithelial content, notably breast and prostate. However, the role of PDEF in cancer development is not fully understood. To gain insight into the molecular mechanisms associated with prostate cancer progression, we employed iTRAQ labeling followed by mass spectrometric (MS) analysis to identify candidate proteins that are differentially expressed in prostate cancer cells with or without PDEF. To this end, we overexpressed PDEF in PC3 human prostate cells using a tetracycline inducible system (Tet-On). Many differentially expressed proteins which play important roles in various cellular and biological processes were identified. Among them, stathmin (STMN), which is a microtubule (MT)-destabilizing protein, was found to be downregulated in multiple analyses. We demonstrated that re-expression of STMN reversed the antitumor properties of PDEF in PDEF-overexpressing PC3 cells. Using in vitro functional assays, we showed that STMN overexpression counteracted PDEF's effects against cell proliferation, colony formation and tumor migration. Similar results were further confirmed with the prostate cancer cell line CWR22rv1. In conclusion, many differentially expressed proteins were identified and STMN was found to be downregulated by PDEF.These results suggest that PDEF may inhibit prostate cancer progression by transcriptional downregulation of oncogenic STMN expression. Analyzing the association among differentially expressed proteins may provide a basis to better understand the molecular mechanisms underlying the process of cancer progression and development and further aid in designing therapeutics in the future. IntroductionProstate cancer is the most common cancer diagnosed among men and the second leading cause of death in American men, behind only lung cancer. The American Cancer Society (ACS) estimates about 1 man in 36 will die of prostate cancer (1). Although screening for prostate cancer, based on prostate specific antigen (PSA) has revolutionized early detection and diagnosis of the disease, the challenge that clinicians face are to determine which patients progress to aggressive disease (2,3). In order to determine the possibility of disease progression and ability to manage patient outcomes, it is necessary to better understand the molecular processes underlying the disease development and progression. Gene regulation is an important process in maintaining the integrity of cells for their proper growth and survival. Improper regulation of genes can lead to various diseases like cancer. The Ets family of transcription factors has been long investigated for their role in genetic loss of cellular homeostasis which results in development of various cancers. So far, 25 human and 26 murine Ets family members have been report...