Atf3 deficiency promotes genome instability and spontaneous tumorigenesis in mice

Mice lacking genes involving in the DNA damage response (DDR) are often tumor prone owing to genome instability caused by oncogenic challenges. Previous studies demonstrate that activating transcription factor 3 (ATF3), a common stress sensor, can activate the tumor suppressor p53 and regulate expression of p53 target genes upon DNA damage. However, whether ATF3 contributes to the maintenance of genome stability and tumor suppression remains unknown. Here we report that Atf3-deficient (Atf3^-/-) mice developed spontaneous tumors, and died significantly earlier than wild-type (Atf3^+/+) mice. Consistent with these results, Atf3^-/- mouse embryonic fibroblasts (MEFs) had more aberrant chromosomes and micronuclei, and were genetically unstable. Whereas we demonstrated that ATF3 activated p53 and promoted its pro-apoptotic activity in mouse thymi and small intestines, the chromosomal instability caused by Atf3 deficiency was largely dependent on the regulation of p53 by ATF3. Interestingly, loss of Atf3 also promoted spontaneous tumorigenesis in Trp53^+/- mice, but did not affect tumor formation in Trp53^-/- mice. Our results thus provide the first genetic evidence linking ATF3 to the suppression of the early development of cancer, and underscore the importance of ATF3 in the maintenance of genome integrity.

Abstract P5-07-12: RAD51AP1 is a novel prognostic marker and therapeutic target for breast cancer

Background: Ionizing radiation is one of the most effective therapeutic strategies for the treatment of breast cancer and is considered as a more appropriate therapy for patients with high-risk of recurrence. Despite substantial benefits are achievable with this treatment, especially for ductal carcinoma and early invasive cancer, the critical barrier in using this treatment strategy is that tumor cells develop radioresistance, which in turn progress into advanced invasive cancer. Breast cancer stem cells (BCSCs), a subpopulation of cells within the tumor with a characteristic feature of self-renewal, play a critical role radioresistance and treatment failure. BCSCs exhibit increased DNA repair activity by increasing RAD51AP1 for their prolonged survival and to evade from the radiation therapy. We explored the expression profile of RAD51AP1 in BCSCs, human normal and various subtypes of breast tumor tissues and cell lines and response to chemo- and radiation- therapy.

Methods: Gene expression (RNA and protein) profile was assessed using semi-quantitative and real-time PCR (qPCR) and western blot analyses. RAD51AP1 expression and its prognostic value in large cohort of human samples were analyzed by TCGA, GOBO, and Kaplan-Meier plotter integrative bioinformatics interface analyses. Breast cancer stem cell (BCSC) status was analyzed by FACS using CD24 and CD49f cell surface marker. Cell death was analyzed by propidium iodide (PI) stained cell cycle analysis.

Results: We found that tumor propagating CD49f+CD24+ cells activate RAD51AP1 more promptly than non-tumorigenic CD49f-CD24- cells and confer chemo- and radiation- therapy resistance. RAD51AP1 inactivation facilitates chemo- and radiation- therapy response by depleting CD49f+CD24+ cells with significant activation of apoptotic cell death signaling. RAD51AP1 expression was significantly higher in BC, especially in the basal triple-negative and HER2-positive BC subtype, than in normal mammary tissue. Further, RAD51AP1 expression is highest in grade III histological tumor types and negatively associated to overall disease-free survival. RAD51AP1 levels across different BC cell lines showed that triple-negative breast cancer (TNBC) cell lines expressed highest level of this gene than other sub types.

Conclusion:Overall, our findings provide evidence that BCSCs utilize DNA repair signaling for their self-renewal and RAD51AP1 play a critical role in BCSC self-renewal and maintenance. Further, RAD51AP1 expression profile can be used as a prognostic marker to monitor disease progression and chemotherapy response.

Citation Format: Thangaraju M, Kolhe RB, Pathania R. RAD51AP1 is a novel prognostic marker and therapeutic target for breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P5-07-12.

An essential role of Ffar2 (Gpr43) in dietary fibre-mediated promotion of healthy composition of gut microbiota and suppression of intestinal carcinogenesis

Composition of the gut microbiota has profound effects on intestinal carcinogenesis. Diet and host genetics play critical roles in shaping the composition of gut microbiota. Whether diet and host genes interact with each other to bring specific changes in gut microbiota that affect intestinal carcinogenesis is unknown. Ability of dietary fibre to specifically increase beneficial gut microbiota at the expense of pathogenic bacteria in vivo via unknown mechanism is an important process that suppresses intestinal inflammation and carcinogenesis. Free fatty acid receptor 2 (FFAR2 or GPR43) is a receptor for short-chain fatty acids (acetate, propionate and butyrate), metabolites of dietary fibre fermentation by gut microbiota. Here, we show FFAR2 is down modulated in human colon cancers than matched adjacent healthy tissue. Consistent with this, Ffar2(-/-) mice are hypersusceptible to development of intestinal carcinogenesis. Dietary fibre suppressed colon carcinogenesis in an Ffar2-dependent manner. Ffar2 played an essential role in dietary fibre-mediated promotion of beneficial gut microbiota, Bifidobacterium species (spp) and suppression of Helicobacter hepaticus and Prevotellaceae. Moreover, numbers of Bifidobacterium is reduced, whereas those of Prevotellaceae are increased in human colon cancers than matched adjacent normal tissue. Administration of Bifidobacterium mitigated intestinal inflammation and carcinogenesis in Ffar2(-/-) mice. Taken together, these findings suggest that interplay between dietary fibre and Ffar2 play a key role in promoting healthy composition of gut microbiota that stimulates intestinal health.

Utility and impact of early t(15;17) identification by Fluorescence In Situ Hybridization (FISH) in clinical decision making for patients in Acute Promyelocytic Leukemia (APL)

INTRODUCTION

Acute Promyelocytic Leukemia (APL) is a curable malignancy with studies showing above 90% survival. However, population-based studies looking at survival suggest that approximately 30% of patients with APL die during induction. Early demonstration of t(15;17) will lead to accurate decision making regarding treatment. The aim of this project was to validate earlier time frames for the Abbott Molecular Vysis LSI promyelocytic leukemia (PML)/ retinoic acid receptor alpha (RARA) fluorescence in situ hybridization (FISH) probe (ASR 6-16 h).

METHODS

Twenty patients (15 APL cases and five non-APL cases) were selected for validating various hybridization times for the FISH probe. Expected normal signal pattern was two red and two green signals (2R2G), and the most common expected abnormal signal pattern was two fusion (yellow) signals, one red and one green (2F1R1G) and/or one fusion, one red and one green (1F1R1G).

RESULTS

The specificity of the probe ranged from 84% at 2 h, 86% at 4 h, 84% at 6 h, and 87% for overnight hybridization. The sensitivity increased from 79% at 2 h, 80% at 4 h, 81% at 6 h to 87% for overnight hybridization.

CONCLUSION

Based on the validation studies, we recommend reading of FISH results at the 4-h incubation mark for a preliminary diagnosis and confirmation with overnight hybridization.