Epigenetic modification facilitates proline synthase PYCR1 aberrant expression in gastric cancer

Pyrroline-5-carboxylate reductase 1 (PYCR1) upregulation contributes to the progression of gastric cancer (GC) and indicates poor survival. However, PYCR1 expression profile in GC subtypes and the mechanism behind its upregulation are not well-studied.

PYCR1 expression profiles in GC subtypes and different stages of gastric carcinogenesis were assessed in different GC cohorts. Genetic alterations and epigenetic modulation in PYCR1 regulation were further investigated using bioinformatics analysis and in vitro experiments.

PYCR1 expression was significantly higher in intestinal-type GC and associated molecular subtypes in TCGA and ACRG GC cohorts. During the cascade of intestinal-type GC, PYCR1 was continuously increased from normal gastric tissues through to atrophic gastritis, to intraepithelial neoplasia, and to GC. Copy number alterations in PYCR1 were associated with PYCR1 transcript expression. One CpG island was observed in PYCR1 promoter region, and the hypomethylation occurred at this region could contribute to PYCR1 transcriptional activation in GC. Besides, H3K27ac combination was found in PYCR1 promoter, and acetyltransferase p300 induced H3K27ac could promote PYCR1 expression in GC.

PYCR1 expression varies across GC subtypes, with intestinal-type GC and associated molecular subtypes having the highest expression. Hypomethylation at CpG sites and p300-induced H3K27ac modification within PYCR1 promoter could contribute to maintaining PYCR1 overexpression in GC. These results provide us with a new insight into epigenetic modulation in mitochondrial proline metabolism.