Hedgehog signaling enables repair of ribosomal DNA double-strand breaks

Ribosomal DNA (rDNA) consists of highly repeated sequences that are prone to incurring damage. Delays or failure of rDNA double-strand break (DSB) repair are deleterious, and can lead to rDNA transcriptional arrest, chromosomal translocations, genomic losses, and cell death. Here, we show that the zinc-finger transcription factor GLI1, a terminal effector of the Hedgehog (Hh) pathway, is required for the repair of rDNA DSBs. We found that GLI1 is activated in triple-negative breast cancer cells in response to ionizing radiation (IR) and localizes to rDNA sequences in response to both global DSBs generated by IR and site-specific DSBs in rDNA. Inhibiting GLI1 interferes with rDNA DSB repair and impacts RNA polymerase I activity and cell viability. Our findings tie Hh signaling to rDNA repair and this heretofore unknown function may be critically important in proliferating cancer cells.

The Pros and Cons of Incorporating Transcriptomics in the Age of Precision Oncology

The treatment of cancer continues to evolve toward personalized therapies based on individual patient and tumor characteristics. Our successes and failures in adopting a precision-oncology approach have demonstrated the utmost importance in identifying the proper predictive biomarkers of response. Until recently, most biomarkers were identified using immunohistochemistry for protein expression or single-gene analysis to identify targetable alterations. With the rapid propagation of next-generation sequencing to evaluate tumor tissue and "liquid biopsies," identification of genomic biomarkers is now standard, particularly in non-small cell lung cancer, for which there is now an extensive catalog of biomarker-directed therapies with more anticipated to come. Despite these great strides, it has also become apparent that using genomic biomarkers alone will be insufficient, as it has been consistently shown that at least one-half of patients who undergo tumor genomic profiling have no actionable alteration. This is perhaps to be expected given the remarkable breadth of nongenetic factors that contribute to tumor initiation and progression. Some have proposed that the next logical step is to use transcriptome profiling to define new biomarkers of response to targeted agents. Recently, results from the WINTHER trial were published, specifically investigating the use of transcriptomics to improve match rates over genomic next-generation sequencing alone. In this review, we discuss the complexities of precision-oncology efforts and appraise the available evidence supporting the incorporation of transcriptomic data into the precision-oncology framework in the historical context of the development of biomarkers for directing cancer therapy.

First-Line Treatment of Widely Metastatic BRAF-Mutated Salivary Duct Carcinoma With Combined BRAF and MEK Inhibition

Salivary duct carcinoma (SDC) is a rare and aggressive malignancy for which limited data exist to guide treatment decisions. With the advent of advanced molecular testing and tumor genomic profiling, clinicians now have the ability to identify potential therapeutic targets in difficult-to-treat cancers such as SDC. This report presents a male patient with widely metastatic SDC found on targeted next-generation sequencing to have a BRAF p.V600E mutation. He experienced a prolonged and robust response to first-line systemic chemotherapy with dabrafenib and trametinib. During his response interval, new data emerged to justify subsequent treatment with both an immune checkpoint inhibitor and androgen blockade after his disease progressed. To our knowledge, this is the first report of frontline BRAF-directed therapy eliciting a response in metastatic SDC.

Developing Cures: Targeting Ontogenesis in Cancer

Cancer has long been known to histologically resemble developing embryonic tissue. Since this early observation, a mounting body of evidence suggests that cancer mimics or co-opts developmental processes to facilitate tumor initiation and progression. Programs important in both normal ontogenesis and cancer progression broadly fall into three domains: the lineage commitment of pluripotent stem cells, the appropriation of primordial mechanisms of cell motility and invasion, and the influence of multiple aspects of the microenvironment on the parenchyma. In this review we discuss how derangements in these developmental pathways drive cancer progression with a particular focus on how they have emerged as targets of novel treatment strategies.

Abstract POSTER-BIOL-1333: TRIP6 regulates p27KIP1 to promote ovarian tumorigenesis

Although the nuclear p27KIP1 functions as a negative regulator of G1/S cell cycle progression by binding to and inhibiting cyclin-CDK complexes, the cytosolic p27KIP1 has been shown to promote adhesion disassembly and tumor invasion. Loss of nuclear p27KIP1 and cytosolic mislocalization of p27KIP1 are frequently found during cancer progression, and these events correlate with poor clinical outcome in many types of cancers, including ovarian cancer. However, the mechanisms underlying this dysregulation are not yet fully understood.

TRIP6 is an adaptor protein that is highly expressed in ovarian serous cystadenocarcinoma. It serves as a platform to recruit a number of molecules, such as NF-κB p65, c-Src, p130cas, Crk, LPA2 and Fas/CD95 receptors, to promote cell motility and antiapoptotic signaling. Using an ovarian cancer xenograft mouse model, we find that TRIP6 knockdown significantly reduces ovarian tumor proliferation. We determine that this effect is in part through the regulation of p27KIP1. Our data show that TRIP6 serves as a bridge to promote the recruitment of p27KIP1 to AKT in the cytosol. TRIP6 regulates the membrane translocation and activation of AKT, and facilitates AKT-mediated recognition and phosphorylation of p27KIP1 specifically at T157, thereby promoting the cytosolic mislocalization of p27KIP1. This is required for p27KIP1 to enhance LPA-induced ovarian cancer cell migration. TRIP6 also promotes serum-induced reduction of nuclear p27KIP1 expression through Skp2-dependent and -independent mechanisms. Consequently, knockdown of TRIP6 in ovarian cancer xenografts restores nuclear p27KIP1 expression and impairs tumor proliferation. Since the expression of TRIP6 and the activity of AKT are significantly higher in ovarian cancer, restoring the expression of nuclear p27KIP1 and inhibiting the migratory effect of phospho-T157-p27KIP1 by targeting TRIP6 may prove to be an effective approach to reduce ovarian cancer progression.

Citation Format: Fang-Tsyr Lin, Victor T. G. Lin, Vivian Y. Lin, Yun-Ju Lai, Chen-Shan Chen, Kang Liu, Weei-Chin Lin. TRIP6 regulates p27KIP1 to promote ovarian tumorigenesis [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-BIOL-1333.

TRIP6: an adaptor protein that regulates cell motility, antiapoptotic signaling and transcriptional activity

Thyroid hormone receptor interacting protein 6 (TRIP6), also known as zyxin-related protein-1 (ZRP-1), is an adaptor protein that belongs to the zyxin family of LIM proteins. TRIP6 is primarily localized in the cytosol or focal adhesion plaques, and may associate with the actin cytoskeleton. Additionally, it is capable of shuttling to the nucleus to serve as a transcriptional coregulator. Structural and functional analyses have revealed that through multidomain-mediated protein-protein interactions, TRIP6 serves as a platform for the recruitment of a wide variety of signaling molecules involved in diverse cellular responses, such as actin cytoskeletal reorganization, cell adhesion and migration, antiapoptotic signaling, osteoclast sealing zone formation and transcriptional control. Although the physiological functions of TRIP6 remain largely unknown, it has been implicated in cancer progression and telomere protection. Together, these studies suggest that TRIP6 plays multifunctional roles in different cellular responses, and thus may represent a novel target for therapeutic intervention.