Ornithine aminotransferase and carbamoyl phosphate synthetase 1 involved in ammonia metabolism serve as novel targets for early stages of gastric cancer

Abstract

Objective: The sensitivity and specificity of current biomarkers for gastric cancer were insufficient. The aim of the present study was to screen novel biomarkers and determine the diagnostic values of ornithine aminotransferase (OAT) and carbamoyl phosphate synthetase 1 (CPS1) for detecting gastric cancer.

Methods: With stable isotope tags, we labelled an initial discovery group of four paired gastric cancer tissue samples and identified with LC-ESI-MS/MS. A validation group of 159 gastric cancer samples and 30 healthy controls were used to validate the candidate targets. GSEA was used to explore the pathways activated in gastric cancer.

Results: Four hundred and thirty one proteins were found differentially expressed in gastric cancer tissues. Of these proteins, OAT and CPS1 were found over-expressed in gastric cancer patients, with sensitivity of 70.4% (95% CI: 63.3%-77.6%) and specificity of 80.5% (95% CI: 74.3%-86.7%) for ornithine aminotransferase, and with sensitivity of 68.6% (95% CI: 61.3%-75.8%) and specificity of 73% (95% CI: 66%-79.9%) for carbamoyl phosphate synthetase 1. The co-expression of OAT and CPS1 in gastric cancer tissues has a sensitivity of 81% (95% CI: 73.2%-88.8%) and specificity of 89% (95% CI: 83%-95%). Furthermore, both OAT and CPS1 were overexpressed in patients with local invasion T3 and T4 stages than those in patients with T1 and T2 stages. The co-expression of OAT and CPS1 was strongly correlated with histological grade I 68% (95% CI: 58.7%-77.3%) and TNM stage I/II 52% (95% CI: 42%-62%). The areas under ROC curves were up to 0.758 for the co-expression of OAT and CPS1 in gastric cancer. GSEA results showed that two gene sets and 30 gene sets were activated in OAT high- and CPS1 high-expression patients with gastric cancer, respectively.

Conclusions: The present findings indicated a tight correlation between the co-expression of OAT and CPS1 and the histological grade, local invasion, and TNM stages of gastric cancer. Therefore, OAT and CPS1 might be predictors for gastric cancer invasion and potential targets for anticancer drug design for gastric cancer.

Keywords: CPS1; OAT; amino metabolism; gastric cancer; iTRAQ.

FIGURE 1

Identification of OAT and CPS1 with iTRAQ based LC‐MS/MS analysis, which showed the representative MS/MS spectrums for OAT (A–D) and CPS1 (E–H).

FIGURE 2

Immunohistochemistry analysis to validate the expression of OAT and CPS1 in gastric cancer tissues. Expression of OAT was predominantly located in the cytoplasm of cancer cells (A, Adjacent tissues; B and C, Gastric cancer tissues). Expression of CPS1 was also predominantly located in cytoplasm of cancer cells (D, Adjacent tissues; E and F, Gastric cancer tissues).

FIGURE 3

Positive rates of OAT (A) and CPS1 (A) and both of the two enzymes (B) in gastric cancer tissues.

FIGURE 4

ROC curve for combined assay of OAT and CPS1. AUC = 0.758, p < 0.001.

FIGURE 5

GSEA was performed to elucidate OAT and CPS1 regulated gene sets in gastric cancer from the GEO database. The TOP two pathways enriched in the OAT‐high expression group were shown in A and B, and TOP four pathways enriched in the CPS1‐high expression group are shown in C–F.

FIGURE 6

The roles of OAT and CPS1 in regulating ammonia metabolism in cancer cells. α‐KG, α‐ketoglutarate; l‐Glu, l‐glutamate; l‐Gln, l‐Glutamine; PLP, pyridoxal 5'‐phosphate; PMP, pyridoxamine phosphate.