Abstract
Gastric cancer is extremely common in New Zealand, with the general New Zealand population having better health outcomes than Māori and Pacific populations. Previous studies have shown that proteasomal protein PA28β is involved gastric cancer cell invasiveness. PA28 is an intracellular protein comprised of two subunits, ⍺ and β, which form a complex with the immunoproteasome to increase its activity. Our research group has identified a new alternative isoform of PA28β, with no previous information on its function or role in gastric cancer.
This project investigates the role of the new PA28β isoform in gastric cancer by quantifying its expression under the inflammatory stimulus of interferon gamma (IFNγ). Quantification of expression levels was undertaken using quantitative real-time polymerase chain reaction and western blotting.
Findings from this research show that in SNU-1 diffuse gastric cancer cells, the new isoform is present along with the canonical isoform. This new isoform is upregulated approximately 5-fold in response to IFNγ compared to unstimulated cells, with two specific primer sets to quantify the expression of this isoform. These primer sets showed an average upregulation of 5.93 ± 0.78 SD (P = 0.0004) and 5.68 ± 0.80 SD (P = 0.0005), respectively. In comparison, the primer set for the canonical isoform showed an average upregulation of 6.97 ± 0.54 SD (P < 0.0001). We found expression of the new PA28β isoform in three other gastric cancer cell lines - MKN-45 (diffuse type), MKN-74 (intestinal type), and AGS, but did not observe as notable response to IFNγ stimulation.
These findings lay the foundation for additional research to further establish the role this new PA28β isoform plays in gastric cancer. The next steps include investigating the effect the new isoform has on the growth kinetics of SNU-1 gastric cancer cells compared to growth kinetics with the canonical isoform.