Conclusion
We found that patients who overexpressed PHLPP1 showed low recurrence and good prognosis. PHLPP1 was found to work by lowering the activity of AKT Ser473 in gastric cancer. Additionally, we found a clue regarding the mechanism of chemotherapeutic drug resistance in a cell line of signet ring cell origin and will uncover this mechanism in the future.
Methods
Surgically resected gastric cancer tissue specimens were obtained from 309 patients who underwent gastrectomy, and PHLPP1 expression was validated by tissue microarray analysis with immunohistochemistry. We assessed whether PHLPP1 selectively dephosphorylates Ser473 of AKT in an in-vitro study.
Results
We found that the PHLPP1 overexpression (OE) group showed significantly greater proportions of differentiated subtype samples and early T stage samples, lower lymph node metastasis, and lower TNM stage than the PHLPP1 underexpression (UE) group. The overall survival of the PHLPP1-OE group was significantly higher (53.39 ± 0.96 months) than that of the PHLPP1-UE group (47.82 ± 2.57 months) (P = .01). In vitro analysis, we found that the PHLPP1-OE group showed a significant decrease in relative AKT S-473 levels in both cell lines (MKN-74 and KATO-III). We found that treatment with chemotherapy drugs decreased the activity of Ser473 in the MKN-74 cell line with PHLPP1 OE, but it did not affect the activity of Ser473 in KATO-III cells.