Mutation of the APC gene occurs in a high percentage of colorectal tumors and is a central event driving tumor initiation in the large intestine. The APC protein performs multiple tumor suppressor functions including negative regulation of the canonical WNT signaling pathway by both cytoplasmic and nuclear mechanisms. Published reports that APC interacts with β-catenin in the chromatin fraction to repress WNT-activated targets have raised the possibility that chromatin-associated APC participates more broadly in mechanisms of transcriptional control. This screening study has used chromatin immunoprecipitation and next-generation sequencing to identify APC-associated genomic regions in colon cancer cell lines. Initial target selection was performed by comparison and statistical analysis of 3,985 genomic regions associated with the APC protein to whole transcriptome sequencing data from APC-deficient and APC-wild-type colon cancer cells, and two types of murine colon adenomas characterized by activated Wnt signaling.289 transcripts altered in expression following APC loss in human cells were linked to APC-associated genomic regions. High-confidence targets additionally validated in mouse adenomas included 16 increased and 9 decreased in expression following APC loss, indicating that chromatin-associated APC may antagonize canonical WNT signaling at both WNT-activated and WNT-repressed targets. Motif analysis and comparison to ChIP-seq datasets for other transcription factors identified a prevalence of binding sites for the TCF7L2 and AP-1 transcription factors in APC-associated genomic regions. Our results indicate that canonical WNT signaling can collaborate with or antagonize the AP-1 transcription factor to fine-tune the expression of shared target genes in the colorectal epithelium. Future therapeutic strategies for APC-deficient colorectal cancers might be expanded to include agents targeting the AP-1 pathway.

Floor cleaning and disinfection are essential components of maintaining animal health status and meeting regulatory requirements in research vivaria. However, best practices for method, frequency, and evaluation techniques have not been established. Reuse of cotton string mop and bucket systems has been implicated in spreading contamination in the human hospital setting. We evaluated 4 different combinations of disinfectant and mop systems commonly used in rodent vivaria. Eight housing rooms were mopped a total of 4 times using one of the following methods: quaternary ammonium compound (QUAT) and cotton string mop (QC), QUAT and microfiber mop (QM), hydrogen peroxide disinfectant (HPD) and cotton string mop (HC), or HPD and microfiber mop (HM). ATP and RODAC samples of the floor were taken before and after mopping. The time to mop each room, floor drying time, and the amount of disinfectant used were recorded. The QC method was associated with significantly more bacterial contamination while all other methods significantly reduced bacterial contamination. The QC method performed significantly worse in reducing bacterial contamination as compared with all other methods when cotton mop heads were reused. All methods except QC significantly reduced ATP levels, with the HC and HM methods being significantly more effective at reducing ATP levels than the QC and QM methods. Costs were similar for the QC, QM, and HM methods. The results of this study indicate that reuse of cotton string mop heads with QUAT increases floor contamination while HPD is effective for up to 3 reuses. Single use microfiber mops were effective with both QUAT and HPD but did not result in more effective cleaning or disinfection than cotton string mops.

Bloom's syndrome (BS) is a recessive human chromosome breakage disorder caused by mutations in the recQ-like helicase BLM, sometimes known as RECQL2. Its clinical phenotype invariably includes male infertility, dwarfism, cancer susceptibility, and growth defects related to now characterized biochemical functions in DNA repair and rDNA transcription. The BLM protein includes two serines within a highly conserved carboxy-terminal nuclear localization sequence (NLS) that are critical for dynamic nucleolar trafficking of BLM where it facilitates rRNA transcription through direct interactions with RNA polymerase I and topoisomerase 1. CRISPR/Cas9-directed gene editing techniques generated homozygous murine models with these two conserved amino acids substituted by aspartic acids or alanines, and Blm proteins that were invariably excluded (DD) or constitutively localized (AA) within the nucleolus. Both protein isoforms retain biochemical functions and nuclear localization; BLM-/- cells transfected with the DD transgene display increases in nucleolar DNA damage compared to those transfected with the wild-type gene. BlmDD/DD mice with excluded Blm, but not BlmAA/AA mice, are smaller than their wild-type littermates at 8, 12, and 16 weeks of age; BlmDD/DD mice develop significantly more adenomas than littermates when crossed to the ApcMin/+ model of intestinal tumor formation. Finally, BlmDD/DD mice, but not their wild-type littermates, display signs of premature aging by one year of age, with weight loss, changes in coat color and quality, and spontaneous tumor formation. Our studies demonstrate functions for dynamic Blm nucleolar localization in maintaining stability of both the nucleolar and non-nucleolar genomes. A role for Blm/BLM in the prevention of aging is also exposed by these mouse models as only RecqL4 (RECQL4 mutations lead to Rothmund-Thomson syndrome in the human), but not Wrn/RecqL3 (WRN mutations lead to Werner's syndrome in the human), localizes to the murine nucleolus. Both Werner's syndrome and Rothmund-Thomson syndrome are associated with DNA repair deficiency, tumor susceptibility, and premature aging in the human. Our murine models also permit the definition of amino acid sequences and mechanisms that target or exclude proteins from the nucleolus. This abstract is also being presented as Poster A30. Citation Format: Michael McIlhatton, Max Fernandez, Samir Acharya, Vincenzo Coppola, Joanna L. Groden. Altered nucleolar trafficking of the Blm helicase in the mouse reduces size, increases DNA damage and tumor susceptibility, and facilitates premature aging [abstract]. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr PR08.