Abstract

Gastric cancer is the third leading cause of cancer-related death worldwide and, in Chile, one of the leading causes of death. Gastric cancer is a multifactorial disease, with infectious, host-related factors and a variety of environmental conditions associated with its development. Chronic infection, mostly by H. pylori and occasionally by Epstein-Barr virus (EBV), is related to a large number of cases. The multistep cascade of gastric cancer hypothesizes that a specific sequence of lesions, as a consequence of H. pylori infection, leads to gastric cancer. These lesions include: multifocal atrophic gastritis (MAG), intestinal metaplasia (IM), dysplasia (DY) and gastric carcinoma (GC). However, the risk of progression of this cascade has not yet been defined. Epigenetic processes, such as DNA methylation or microRNAs (miRNAs), offer a new study field for the evaluation of the multistep cascade of gastric cancer. Our previous FONDECYT grants (#1030130, #1080563, #1111014) from the Government of Chile, led us to identify overexpression of p73, associated with loss of DNA methylation, as a key player in the risk assessment of the multistep cascade. Additionally, we discovered circulating methylated Reprimo DNA in plasma from gastric cancer patients. These findings opened the concept that epigenetic processes offer, not only the possibility to study the pathogenesis of gastric cancer, but also an opportunity for non-invasive detection of this malignancy. Preliminary data from our laboratory identified four upregulated miRNAs previously undescribed in gastric cancer (miR-505, -552, -592 and -597). These miRNA may contribute to the risk assessment of the multistep cascade of this malignancy. We hypothesize that “Upregulation of microRNAs miR-505, - 552, -592, and -597 contributes to the progression of the multistep cascade of gastric cancer”. To demonstrate this hypothesis, we will first evaluate the predictive role of these miRNA candidates through qPCR array analysis of tissue samples (30 MAG, 30 IM, 30 DY and 30 GC). Then, we will evaluate binding of these miRNAs to their predictive cancer-related targeted genes (FOXO3, TSC1, ACVR2, CREB3L3, ASF/SF2 and ATM) through reporter assays. Next, their effect on expression of these genes will assessed by Western blot in gastric cancer cell lines and by immunohistochemistry in Tissue Microarray (TMA) representing all the stages of the multistep cascade of gastric cancer. Subsequently, we will evaluate the tumorigenic effect of miR-505, -552, -592, and -597 in gastric cancer in-vitro models by functional assays (cell cycle, proliferation and apoptosis). Finally, we will correlate levels of miRNA candidates in paired tissue and plasma samples, and will determine their predictive role as a novel approach for the non-invasive detection of this malignancy. Our expected results will be to observe that upregulation of miR-505, -552, -592, and -597 drives the progression of the multistep cascade of gastric cancer through downregulation of targeted genes involved in cell cycle, proliferation and apoptosis. Furthermore, we expect to detect these miRNAs in plasma and determine their role in non-invasive detection of gastric cancer. In conclusion, we believe that miRNAs-505, -552, -592 and -597 may play an important role in the epigenetic processes that drive the multistep cascade of gastric cancer. This project represents a further step to understanding epigenetic processes affecting gastric cancer pathogenesis and may contribute to predict and detect early lesions of this disease.