In summary, the present work is the first demonstration of the prognostic value of SIK2 for patients with GC and of the suppression of GC tumorigenesis by SIK2 and progression by activation of mTORC1 to inhibit autophagic degradation of protein phosphatases PP2A and PHLPP2, thus increasing dephosphorylation and inactivation of AKT/GSK3β/β‐catenin signaling. Here, GSK3B is linked to gastric cancer.