The Role of BRK in Gastric Cancer

Abstract

In 2020, gastric cancer proved to be an important health issue by not only being the 6th most diagnosed cancer, but also the 3rd most common cause of cancer-related deaths, after lung and liver cancer. Helicobacter pylori (H. pylori) is the main risk factor for gastric cancer incidences as it accounts for over 90% of all gastric cancer cases. H. pylori infection can either be cytotoxic- associated gene A (cagA)-positive or cagA-negative. cagA-positive H. pylori infection results in higher incidence, and more aggressive gastric cancers. Infection consequences in the administration of its respective oncogenic protein, CagA, which upon phosphorylation by a Src family kinase initiates a chain of molecular events leading to carcinogenesis. Protein tyrosine kinases (PTKs) are a multigene family with functions including cell to cell signaling regarding growth, differentiation, adhesion, motility, and cell death. PTKs have been implicated in many human diseases, including cancer. There are 32 non-receptor PTKs (NRTKs) including the Breast Tumour Kinase (BRK) Family Kinases (BFKs) consisting of BRK, Fyn-Related Kinase (FRK), and Src-Related Kinase Lacking C-Terminal Regulatory Tyrosine and N-Terminal Myristylation Sites (SRMS). BRK has been previously characterized as an oncogene in many cancers, namely breast, where breast cancer patients show unfavourable prognoses when BRK is overexpressed. Similarly, BRK has also been found to be implicated in gastric cancer, demonstrating the same unfavourable prognosis when overexpressed in gastric cancer patients. The BRK gene has been shown to have positive selection in East Asian populations, revealing a strong correlation with gastric cancer as it is highly endemic in Eastern Asia. In addition, a recent study indicated that BRK transcript and protein levels were significantly high in metastatic gastric cancer patients irrespective of tumor stage, suggesting that BRK could be a potential biomarker and therapeutic target for metastatic gastric cancer patients. This project characterizes BFKs in gastric cancer, as well as explores BRK’s presence and potential role as an oncogene in gastric cancer. Here we discover that BRK is present in AGS and NCIN87 gastric cancer cell lines, that it localizes in a cyto-nuclear pattern in AGS gastric cancer cells, and that BRK is indeed in its active form in both AGS and NCIN87 gastric cancer cell lines. In addition, BRK knockout (BRK-/-) AGS gastric cancer cells, generated using the CRISPR/Cas-9 genome editing system, showed that BRK-/- AGS cells proliferated, migrated, and invaded at a significantly slower rate than parental AGS gastric cancer cells, indicating that BRK does play a significant role in these processes in gastric cancer.