Abstract 2559: Loss of AKT2 correlates with activation of β-catenin signaling in immortalized mouse hepatocytes

Abstract

Abstract Background: Primary liver cancer is the second most common cause of cancer-related mortality. Abnormal activation of the phosphatidylinositol 3-kinase (PI3K)/AKT and Wnt/β-catenin signaling pathways, which act as key regulators in cell proliferation and growth, is frequently observed in liver cancer. This study investigated the role of AKT2, the major AKT isoform expressed in the liver, on the activation of β-catenin signaling in immortalized mouse hepatocytes. Methods: Regulation of β-catenin signaling by AKT2 was examined in hepatocytes lacking the negative regulator of PI3K/AKT signaling, PTEN (phosphatase and tensin homolog deleted on chromosome 10). Immortalized hepatocytes were established from mice with liver specific deletions of Pten alone (PtenloxP/loxP; albumin [Alb]-Cre+) or in combination with Akt2 (PtenloxP/loxP; Akt2-/-; Alb-Cre+). Control mice were PtenloxP/loxP; Alb-Cre-. Immunoblotting was used to assess protein expression of AKT and β-catenin. Gene expression of β-catenin targets cyclin D1, CD44, and Jag1 was determined with quantitative PCR. Cell growth was evaluated with hemacytometer count. Results: Pharmacological inhibition of PI3K using LY294002 resulted in decreased phosphorylation levels of AKT (Ser473 and Thr308) and β-catenin (Ser552), suggesting crosstalk between the PI3K/AKT and β-catenin pathways. When compared to wild-type hepatocytes, Pten null and Pten;Akt2 double mutant (DM) expressed significantly higher protein levels of β-catenin (p≤0.0327), with no difference observed in Pten null vs. Pten;Akt2 double mutant groups (p>0.05). Phosphorylation of β-catenin at Ser552, a residue that has been previously shown to be phosphorylated by AKT, was also significantly enhanced in both Pten null and Pten;Akt2 double mutant groups, when compared to wild-type cells. Enhanced phosphorylation of β-catenin in these groups correlated with increased expression of β-catenin transcriptional targets CD44 and Jag1 (p≤0.0041), with no significant difference in mRNA levels of these targets observed in Pten null vs. DM group (p>0.05). Activation of the β-catenin signaling pathway in Pten null and DM groups correlated with enhanced cell growth and significantly increased mRNA levels of cyclin D1 (p<0.0001). Interestingly, when compared to the control group, DM group showed enhanced expression of Akt1 and total phosphorylated AKT. Conclusions: Pten loss alone or accompanied with Akt2 deletion resulted in enhanced activation of β-catenin signaling and cell proliferation. These changes correlated with increased expression of AKT1 and total phosphorylated AKT in the Pten;Akt2 DM group. These findings suggest the need to further evaluate the role of AKT isoforms in the PI3K/AKT/β-catenin signaling axis and a promise for evaluation of isoform-specific inhibitors targeted at AKT to block tumor growth. Citation Format: Ielyzaveta Slarve, Bangyan Stiles, Lina He. Loss of AKT2 correlates with activation of β-catenin signaling in immortalized mouse hepatocytes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2559.