Abstract 5193: Conditional knockout of histone chaperone FACT in mice: Consequences for normal tissues

Histone chaperone FAcilitates Chromatin Transcription (FACT) is, a complex of SSRP1 and SPT16, involved in chromatin remodeling during transcription, replication, and DNA repair. FACT is selectively expressed during early stages of development and later exclusively present in the stem cell niches in adult normal tissues. It is expressed in undifferentiated aggressive tumors with poor prognosis.¹ FACT inhibition is not tolerated by most tumor, unlike normal cells. This vulnerability of tumor cells upon FACT inactivation suggests evaluating FACT inhibition as an antitumor therapeutic approach.¹ Since FACT knockout (KO) is embryonically lethal (E3.5),² study of FACT’s function in different non-tumor cells of mammalian organisms was not possible and was mostly studied in single cell organisms and in tumor cell lines. Therefore, to assess the safety of FACT inhibition as an anticancer approach, by understanding its role in normal physiology, we generated a conditional KO of Ssrp1 mouse model using CreERT2-LoxP system.³ We harvested stem cells of different lineages to better understand the role of FACT in normal mouse physiology. Using the hematopoietic stem cells (HSCs) from the bone marrow (BM), we performed BM colony formation assay. We found that FACT inactivation significantly decreased the number of colonies of HSCs. Furthermore, inhibiting FACT significantly increased caspase 3 expression in mouse adipose stem cells (ASCs), resulting in apoptosis and decreased survival. These results prompted us to comprehensively evaluate roles of FACT in stem cell development and survival. To this end, fibroblasts in a conditional knockout mouse were reprogrammed by retroviral vector encoding four pluripotency transcription factors (Oct3/4, Klf4, Sox2 and c-Myc). We have found successful generation of induced pluripotent stem (iPS) cells 14 days after reprogramming. In conclusion, FACT associates with development and/or survival of mouse HSCs and ASCs. Further evaluation using iPS cells is expected to delineate roles of FACT in various stages of stem cell development and thus normal physiology. 1. Garcia H, et al. Cell Rep, 2013 4(1) 2. Cao S, et al. Mol Cel Bio. 2003 23(15) 3. Sandlesh P et al. PLOS ONE. 2018 13(6) Citation Format: Masaki A. Ito, Poorva Sandlesh, Imon Goswami, Laura A. Prendergast, Katerina Gurova. Conditional knockout of histone chaperone FACT in mice: Consequences for normal tissues [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5193.