TRIP-Br2 promotes oncogenesis in nude mice and is frequently overexpressed in multiple human tumors.

BACKGROUND: Members of the TRIP-Br/SERTAD family of mammalian transcriptional coregulators have recently been implicated in E2F-mediated cell cycle progression and tumorigenesis. We, herein, focus on the detailed functional characterization of the least understood member of the TRIP-Br/SERTAD protein family, TRIP-Br2 (SERTAD2). METHODS: Oncogenic potential of TRIP-Br2 was demonstrated by (1) inoculation of NIH3T3 fibroblasts, which were engineered to stably overexpress ectopic TRIP-Br2, into athymic nude mice for tumor induction and (2) comprehensive immunohistochemical high-throughput screening of TRIP-Br2 protein expression in multiple human tumor cell lines and human tumor tissue microarrays (TMAs). Clinicopathologic analysis was conducted to assess the potential of TRIP-Br2 as a novel prognostic marker of human cancer. RNA interference of TRIP-Br2 expression in HCT-116 colorectal carcinoma cells was performed to determine the potential of TRIP-Br2 as a novel chemotherapeutic drug target. RESULTS: Overexpression of TRIP-Br2 is sufficient to transform murine fibroblasts and promotes tumorigenesis in nude mice. The transformed phenotype is characterized by deregulation of the E2F/DP-transcriptional pathway through upregulation of the key E2F-responsive genes CYCLIN E, CYCLIN A2, CDC6 and DHFR. TRIP-Br2 is frequently overexpressed in both cancer cell lines and multiple human tumors. Clinicopathologic correlation indicates that overexpression of TRIP-Br2 in hepatocellular carcinoma is associated with a worse clinical outcome by Kaplan-Meier survival analysis. Small interfering RNA-mediated (siRNA) knockdown of TRIP-Br2 was sufficient to inhibit cell-autonomous growth of HCT-116 cells in vitro. CONCLUSION: This study identifies TRIP-Br2 as a bona-fide protooncogene and supports the potential for TRIP-Br2 as a novel prognostic marker and a chemotherapeutic drug target in human cancer.

Exploiting the TRIP-Br family of cell cycle regulatory proteins as chemotherapeutic drug targets in human cancer.

TRIP-Br1 and TRIP-Br2 are potent cell growth promoting factors that function as components of the E2F1/DP1 transcription complex to integrate positive growth signals provided by PHD zinc finger- and/or bromodomain-containing transcription factors. TRIP-Br1 has been demonstrated to be an oncogene. We recently reported that antagonism of the TRIP-Br integrator function by synthetic decoy peptides that compete with TRIP-Br for binding to PHD zinc finger- and/or bromodomain-containing proteins elicit an anti-proliferative effect and induces caspase-3-independent sub-diploidization in cancer cells in vitro. We now demonstrate the chemotherapeutic potential of TRIP-Br decoy peptides for the treatment of cutaneous and intracavitary lesions in vitro as well as in vivo in representative human nasopharyngeal cancer (CNE2), cervical cancer (Ca Ski) and melanoma (MeWo) cancer cell lines. In vitro, BrdU incorporation, colony formation assays and cell cycle analysis confirmed that TRIP-Br decoy peptides possess strong anti-proliferative effects and induce nuclear sub-diploidization in cancer cells. In vivo, CNE2, Ca Ski and MeWo-derived chick embryo chorioallantoic membrane (CAM) tumor xenografts were used to evaluate the effect of topically applied TRIP-Br peptides. Confocal microscopy and flow cytometric analysis demonstrated that cells comprising the tumor xenografts efficiently internalized topically applied FITC-labeled peptides. Fifty muM of TRIP-Br1 decoy peptide significantly suppressed the growth of NPC2-derived human nasopharyngeal tumors, while 50 muM of TRIP-Br2 decoy peptide significantly inhibited tumor growth in all three CAM tumor xenograft models. Two hundred muM of TRIP-Br1 decoy peptide significantly inhibited MeWo-derived tumors. These results suggest that the TRIP-Br integrator function may represent a novel chemotherapeutic target for the treatment of human cutaneous and intracavitary proliferative lesions.

The TRIP-Br family of transcriptional regulators is essential for the execution of cyclin E-mediated cell cycle progression.

The G1 D-type cyclins, in conjunction with cyclin-dependent kinases Cdk4 and Cdk6, play key roles in the execution of mitogen-induced cellular proliferation. TRIP-Br1, a member of the TRIP-Br family of transcriptional regulators, has been implicated in the regulation of Cdk4/cyclin D activity. To further elucidate the functional role(s) of the TRIP-Br proteins in mitogenic signaling, we have developed the synthetic DNA enzymes E-Br1 and E-Br2 to specifically knock down the serum-inducible expression of TRIP-Br1 and TRIP-Br2, respectively, in WI-38 human fibroblasts in culture, as well as generated TRIP-Br2 null primary embryonic fibroblasts from a novel TRIP-Br2 knockout mouse model. Both strategies consistently reveal that ablation of TRIP-Br1 or TRIP-Br2 expression disrupts mitogenic signaling in a manner that suppresses serum-induced cyclin E expression, S-phase entry and cellular proliferation. We conclude that both TRIP-Br1 and TRIP-Br2 are required for proper transduction of mitogenic signals and execution of serum-inducible cell cycle progression.

TRIP-Br links E2F to novel functions in the regulation of cyclin E expression during cell cycle progression and in the maintenance of genomic stability.

The TRIP-Br family of transcriptional regulators (TRIP-Br1 and TRIP-Br2) has been proposed to function at E2F-responsive promoters to integrate regulatory signals provided by PHD zinc finger- and/or bromodomain-containing transcription factors. To characterize the TRIP-Br "integrator" function(s), we have employed decoy peptides (*Br1 and *Br2) to antagonize the interaction between TRIP-Br1 or TRIP-Br2 and the PHD zinc finger and/or bromodomain of other transcription factors. Antagonism of the TRIP-Br integrator function elicits anti-proliferative effects through the transcriptional downregulation of a subset of E2F-responsive genes in vivo, and induces aberrant cyclin E accumulation, leading to Geminin deregulation and caspase-3-independent cellular sub-diploidization. The observed cyclin E deregulation is attributed to the downregulation of Fbxw7, which encodes the Fbw7 receptor subunit of the SCF(FBW7) ubiquitin ligase (E3) responsible for targeting cyclin E for proteolysis. Fbxw7 is identified herein as an E2F-responsive and TRIP-Br coregulated gene. Our results demonstrate a physiologic role for TRIP-Br in coupling E2F to novel functions in the regulation of cyclin E expression during cell cycle progression to ensure the proper execution of DNA replication and the maintenance of genomic stability.