O -GlcNAcylation of the Tumor Suppressor FOXO3 Triggers Aberrant Cancer Cell Growth.

Posttranslational modifications of tumor suppressors can induce abnormal cell growth. Here, we identify site-specific O -GlcNAcylation as a critical block of FOXO3 that may abrogate a part of the p53 pathway, resulting in aberrant cancer cell growth. Of seven O -GlcNAcylation sites identified within the FOXO3 transactivation domain, we found that changes in O -GlcNAcylation at Ser284 modulated p21-mediated cancer cell growth. Overexpression of either O -GlcNAcylated FOXO3 (FOX-OV) or a Ser-to-Ala mutant (S284A) in PANC-1 cells indicated that S284 O -GlcNAc acts as a critical block of the FOXO tumor suppressor and induces proliferation in PANC-1 cancer cells by stimulating the MDM2-p53-p21 axis. Furthermore, S284A mutant cells lacking S284 O -GlcNAc and FOX-OV cells exhibited opposing MDM2-p53-p21 axis expression patterns at both the mRNA and protein levels. Thus, our study provides evidence to support a role for S284 O -GlcNAc as a critical block of FOXO3 to induce subsequent cancer cell growth via abrogation of the p53 regulatory circuit. Significance: These findings highlight a posttranslational mechanism for indirect abrogation of the p53 pathway, one that may occur with some frequency in human cancer cells. Cancer Res; 78(5); 1214-24. ©2018 AACR .