The human DEK gene is frequently overexpressed and sometimes amplified in human cancer. Consistent with oncogenic functions, Dek knockout mice are partially resistant to chemically induced papilloma formation. Additionally, DEK knockdown in vitro sensitizes cancer cells to DNA damaging agents and induces cell death via p53-dependent and -independent mechanisms. Here we report that DEK is important for DNA double-strand break repair. DEK depletion in human cancer cell lines and xenografts was sufficient to induce a DNA damage response as assessed by detection of γH2AX and FANCD2. Phosphorylation of H2AX was accompanied by contrasting activation and suppression, respectively, of the ATM and DNA-PK pathways. Similar DNA damage responses were observed in primary Dek knockout mouse embryonic fibroblasts (MEFs), along with increased levels of DNA damage and exaggerated induction of senescence in response to genotoxic stress. Importantly, Dek knockout MEFs exhibited distinct defects in non-homologous end joining (NHEJ) when compared to their wild-type counterparts. Taken together, the data demonstrate new molecular links between DEK and DNA damage response signaling pathways, and suggest that DEK contributes to DNA repair.

The epithelial-to-mesenchymal transition (EMT) is a highly conserved morphogenetic program essential for embryogenesis, regeneration and cancer metastasis. In cancer cells, EMT also triggers cellular reprogramming and chemoresistance, which underlie disease relapse and decreased survival. Hence, identifying compounds that block EMT is essential to prevent or eradicate disseminated tumor cells. Here, we establish a whole-animal-based EMT reporter in zebrafish for rapid drug screening, called Tg(snai1b:GFP), which labels epithelial cells undergoing EMT to produce sox10-positive neural crest (NC) cells. Time-lapse and lineage analysis of Tg(snai1b:GFP) embryos reveal that cranial NC cells delaminate from two regions: an early population delaminates adjacent to the neural plate, whereas a later population delaminates from within the dorsal neural tube. Treating Tg(snai1b:GFP) embryos with candidate small-molecule EMT-inhibiting compounds identified TP-0903, a multi-kinase inhibitor that blocked cranial NC cell delamination in both the lateral and medial populations. RNA sequencing (RNA-Seq) analysis and chemical rescue experiments show that TP-0903 acts through stimulating retinoic acid (RA) biosynthesis and RA-dependent transcription. These studies identify TP-0903 as a new therapeutic for activating RA in vivo and raise the possibility that RA-dependent inhibition of EMT contributes to its prior success in eliminating disseminated cancer cells.

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Expression of the high-risk human papillomavirus (HPV) E6 and E7 oncogenes is essential for the initiationHigh-risk human papillomavirus (hrHPV)-positive cervical cancer cells harbor integrated HPV genomic DNA and are uniquely dependent upon the expression of two viral oncogenes, E6 and E7, for the maintenance of the transformed phenotype (40). hrHPV E6 is best known for its ability to target p53 for proteasomal degradation via its association with the E6-associated protein (E6-AP), a ubiquitin ligase (52,53,64). Additionally, hrHPV E6 activates telomerase to extend the life span of primary human keratinocytes (28,33,58) and binds to and deregulates several PDZ proteins that are known to regulate cell polarity, adhesion, and proliferation (27,32,41,57). This results in deregulation of tumor-suppressive activity and, in so doing, contributes to carcinogenesis. hrHPV E7 binds to and degrades members of the retinoblastoma (Rb) family, resulting in the transcription of E2F target genes such as cyclin E and cyclin A which are responsible for S-phase progression (11, 37). Additional E7 activities include the inhibition of the cyclin-dependent kinase inhibitors p21 CIP1 and p27 KIP1 which activate Rb (22, 24). Together, both hrHPV E6 and E7 contribute to carcinogenesis by suppressing apoptosis and senescence and by stimulating cellular proliferation. Consequently, a number of reports have pioneered various approaches to inhibit E6 and E7 function in HPV-positive cancer cells for the specific induction of cellular growth arrest and death (1,18,48,54). This includes the use of oncogene-specific peptide aptamers (3, 43), antisense technology (59), RNA interference (RNAi) (4,30,45), and the expression of viral E2 protein (7,39,44,56,63). Furthermore, in vivo experiments have provided proof of concept for the therapeutic targeting of E6/E7 in HPV-driven tumors in the presence and absence of conventional treatments (18,25,60).Several laboratories, including ours, have previously described the consequences of virally delivered E2 expression in HPV-positive cervical cancer cells: E6/E7 transcription ceased, followed by the reactivation of Rb and p53 tumor suppressors, cell cycle arrest, and eventually the induction of a synchronized cellular senescence phenotype. This was observed following the expression of bovine papillomavirus type 1 (BPV1) E2 transactivator (E2-TA), but not the transcriptional repressor (E2-TR), in HPV-positive cancer cells (10,17). Similar phenotypes were observed using a temperature-sensitive BPV1 E2 (E2ts) protein that is functional at the permissive temperature of 32°C but not at 37°C and above (8,62). Senescence induction in cervical cancer cells was identified by the typical flat-cell morphology (34), upregulation of senescence markers including senescence-associated ␤-galactosidase (SA-␤-Gal) activity (9), and a transcriptional profile that is reminiscent of replicatively senescent primary cells (23). Rescue of E2-expressing HeLa cells from either E6 or E7 repression further revealed that senescence...