HETEROCHROMATIN PROTEIN 1α DISTRIBUTION AND NANOG-BINDING DYNAMICS TO THE CHROMATIN ARE AFFECTED BY AKT1 IN A SUMOYLATION DEPENDENT MANNER

FRANCIA, MARCOS GABRIEL; OSES, CAMILA; ROBERTI, SABRINA LORENA; GARCÍA, MORA RENEÉ; COZZA, LUCAS HELIO; DIAZ, MARIA CANDELARIA; ROVNER, FEDERICO; ORSINGHER, VICTOR ; GRECCO, HERNAN EDGARDO ; LEVI, VALERIA; GUBERMAN, ALEJANDRA SONIA

Congreso; From Concept to Clinic: Advances in Stem Cell Research ISSCR 2023; 2023

AKT is a serine-threonine kinase that regulates diverse processes in various cell types. In mouse embryonic stem cells (mESCs), it plays a key role in maintaining pluripotency, specially promoting the expression of the pluripotency transcription factor (TF) Nanog. AKT activation depends on its recruitment to the plasma membrane and subsequent phosphorylation, as well as other post-translational modifications (PTMs), including conjugation to the small ubiquitin-related modifier (SUMO), which altogether fine-tune its activity and target specificity.In this work, we explored the effects of SUMOylation on AKT1 distribution and function in mESCs. To this purpose, we generated mCherry-fused AKT1 variants with different SUMOylation capability and analyzed their distribution by confocal microscopy in mESCs. We found that this PTM impacts on the distribution and heterogeneity of AKT1 in the nucleus and cytoplasm. Specifically, both SUMOylation and the E17K mutation promoted AKT1 nuclear localization. These findings led us to hypothesize that this effect on AKT1 distribution could affect its interaction and affinity for its targets, ultimately impacting in its function. To explore this hypothesis, we studied the effect of AKT SUMOylatability on the distribution of Heterochromatin protein 1α by quantitative confocal microscopy analysis, and on the dynamic interactions of NANOG with the chromatin, by Fluorescence Correlation Spectroscopy.We found that both SUMOylation and the E17K mutation impact on the overall chromatin landscape of mESCs and affect the chromatin-binding dynamics of NANOG. Remarkably, the oncogenic E17K AKT1 mutant produced the most prominent changes in these parameters, particularly increasing the binding of NANOG to its targets in a SUMOylation-dependent manner. These findings demonstrate that SUMOylation modulates AKT1 subcellular distribution, the chromatin landscape, and the TF dynamics, adding an extra layer of regulation to its function in mESCs.