Abstract 5532: Functional role of Friend Leukemia Integration-1 (FLI1) in gastric carcinogenesis
Authors: Portillo Armando Del , Komissarova Elena V. , Gonzalez Anne Koehne de , Bokhari Aqiba , Remotti Helen , Sepulveda Jorge , Sepulveda Antonia 
Published: July 2017

Abstract
Gastric adenocarcinoma (GC) is the 5th most common cancer worldwide but is the 3rd leading cause of cancer death. FLI1 (Friend leukemia integration-1) is an ETS family transcription factor that regulates genes involved in proliferation and differentiation. FLI1 is implicated in tumorigenesis, such as in Ewing’s sarcoma where a translocation creates an EWS-FLI1 oncogenic fusion protein. However, few studies have examined the role of FLI1 in carcinomas. In human breast cancer, overexpression of FLI1 led to inhibition of apoptosis, thereby promoting survival and malignant potential. In functional studies in a murine breast cancer model, however, downregulation of FLI1 increased malignant potential. In human GCs, we recently reported that FLI1 expression is inversely correlated with its promoter CpG methylation of the FLI1.
To determine if decreased expression occurs in GC epithelial cells or background non-epithelial cells, we analyzed 91 human GC tumors by immunohistochemistry (IHC) for FLI1 and compared them to normal gastric mucosa and intestinal metaplasia (IM) using an IHC composite scoring system accounting for intensity and percentage of epithelial cells expressing FLI1. We found that FLI1 is strongly expressed in normal gastric glandular epithelium and in IM, and that decreased expression was seen in most human GCs (P &lt; 1x10-17 vs normal, P &lt; 1x10-26 vs IM). These findings suggest that FLI1 acts as a tumor suppressor gene in GC. To test this hypothesis, we used an invasion assay and the human GC cell lines NUGC3 and SNU638, which have little to no FLI1 expression, respectively. Cultured GC cells were transduced to overexpress FLI1 or control, along with an eGFP reporter from an IRES (Lv203, Genecopoeia). After selection by puromycin, these GC cells were plated in serum-free media in the upper chamber on a Matrigel coated 8µm pore opaque membrane. Complete media with 10% fetal calf serum was plated in the lower chamber. Images were obtained of the lower membrane with an inverted fluorescent microscope and cellSens imaging software. Overexpression of FLI1 significantly decreased invasion by NUGC3 cells at 24 hours (P = 0.013) but not at 48 hours (P = 0.268) as compared to control. Overexpression of FLI1 significantly decreased invasion by SNU638 cells at both 24 and 48 hours (P = 0.027 and 0.012, respectively) as compared to control. Since NUGC3 cells have low FLI1 expression, we knocked down FLI1 by using a FLI1 shRNA lentiviral system with mCherry from an IRES as a reporter (LvRU6MP, Genecopoeia). Using the same invasion assay, knockdown of FLI1 trended towards a significant increase in invasion as compared to control at 48 hrs (P = 0.14), but not at 24 hrs (P = 0.73).
In summary, the combined observations in human GC tissue samples and the functional analyses in GC cells support a tumor suppressor role for FLI1 in human GC and also suggest that FLI1 and/or its target genes may be involved in regulatory mechanisms driving invasive properties of GC.
Citation Format: Armando Del Portillo, Elena V. Komissarova, Anne Koehne de Gonzalez, Aqiba Bokhari, Helen Remotti, Jorge Sepulveda, Antonia Sepulveda. Functional role of Friend Leukemia Integration-1 (FLI1) in gastric carcinogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5532. doi:10.1158/1538-7445.AM2017-5532