Induction of Gastric Cancer by Successive Oncogenic Activation in the Corpus.

Background & Aims: Metaplasia and dysplasia in the corpus are reportedly derived from de-differentiation of chief cells. However, the cellular origin of metaplasia and cancer remained uncertain. Therefore, we investigated whether pepsinogen C (PGC) transcript-expressing cells represent the cellular origin of metaplasia and cancer using a novel Pgc-specific CreERT2 recombinase mouse model.

Methods: We generated a Pgc-mCherry-IRES-CreERT2 (Pgc-CreERT2) knock-in mouse model. Pgc-CreERT2/ and Rosa-EYFP mice were crossed to generate Pgc-CreERT2/Rosa-EYFP (Pgc-CreERT2/YFP) mice. Gastric tissues were collected, followed by lineage-tracing experiments and histologic and immunofluorescence staining. We further established Pgc-CreERT2;Kras mice and investigated whether PGC transcript-expressing cells are responsible for the precancerous state in gastric glands. To investigate cancer development from PGC transcript-expressing cells with activated Kras, inactivated Apc, and Trp53 signaling pathways, we crossed Pgc-CreERT2/ mice with conditional Kras, Apc, Trp53 mice.

Results: Expectedly, mCherry mainly labeled chief cells in the Pgc-CreERT2 mice. However, mCherry was also detected throughout the neck cell and isthmal stem/progenitor regions, albeit at lower levels. In the Pgc-CreERT2;Kras mice, PGC transcript-expressing cells with Kras mutation presented pseudopyloric metaplasia. The early induction of proliferation at the isthmus may reflect the ability of isthmal progenitors to react rapidly to Pgc-driven Kras oncogenic mutation. Furthermore, Pgc-CreERT2;Kras;Apc mice presented intramucosal dysplasia/carcinoma and Pgc-CreERT2;Kras;Apc;Trp53 mice presented invasive and metastatic gastric carcinoma.

Conclusions: The Pgc-CreERT2 knock-in mouse is an invaluable tool to study the effects of successive oncogenic activation in the mouse corpus. Time-course observations can be made regarding the responses of isthmal and chief cells to oncogenic insults. We can observe stomach-specific tumorigenesis from the beginning to metastatic development.