CDC25A suppression of apoptosis in cutaneous squamous cell carcinoma depends on 14-3-3 epsilon

Cytoplasmic relocalization of the dual-specificity phosphatase, CDC25A, occurs during nonmelanoma skin cancer development and progression, leading to suppression of cell death. Cytoplasmic CDC25A is phosphorylated at Ser178, which allows for its association with 14-3-3e. 14-3-3e is a member of the 14-3-3 family of proteins that bind phosphoserine/threonine-containing proteins and are involved in various processes including scaffolding, nuclear transport, protein degradation, cell cycle regulation, apoptosis and cell signaling. We hypothesized that CDC25A9s antiapoptotic function depends upon 14-3-3e binding to trigger activation of prosurvival signaling pathways in SCC cells. Co-immunoprecipitation of CDC25A from the SCC cell line SCC12B.2 followed by immunoblotting for 14-3-3e confirmed an association between CDC25A and14-3-3e. CDC25A over-expression in SCC12B.2 cells reduced apoptosis by approximately 50%, as assessed by a caspase 3/7 glo assay. However, inhibition of 14-3-3e with the peptide R18, or silencing of 14-3-3e, blocked the anti-apoptotic effect of CDC25A in SCC cells. Treatment with serial dilutions of R18 increased cell death with an IC50 of 8.9 μM in SCC12B.2 cells. Interestingly, over-expression of CDC25A significantly increased P-Akt (p=0.011), P-BAD (p=0.034) and Survivin (p=0.036) when compared to control. Consistent with our hypothesis that 14-3-3e facilitates CDC25A9s antiapoptotic activity, silencing of 14-3-3e decreased P-Akt (p=0.044), P-BAD (p=0.034) and Survivin (p=0.008). Taken together, these results indicate that cytoplasmic CDC25A and 14-3-3e interact in skin carcinomas to suppress apoptosis through a mechanism involving activation of Akt/BAD/Survivin signaling, rendering SCC cells sensitive to 14-3-3e or CDC25A inhibition, a mechanism that requires further study. Citation Format: Thomas R. Holmes, Jenan Al-Matouq, Brianna Hammiller, Yawah T. Nicholson, Matti J. Holmes, Laura A. Hansen. CDC25A suppression of apoptosis in cutaneous squamous cell carcinoma depends on 14-3-3e [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-190.