Impellizzeri, S. | Search bioRxiv

bioRxiv2024

Control of GSK3beta nuclear localization by amino acid signaling requires GATOR1 but is mTORC1 independent

The availability of certain amino acids regulates cell survival, proliferation, growth, differentiation, and other cellular functions. Sensing of amino acids that converges on the GATOR1 and GATOR2 complexes supports activation of mTORC1 during amino acid replete conditions. Whether amino acid-derived cues regulate additional pathways remains poorly understood. We uncover that amino acid sensing involving GATOR1 and GATOR2 regulates the cellular localization of glycogen synthase kinase 3{beta} (GSK3{beta}). GATOR1 is required to recruit a subset of GSK3{beta} to the lysosome selectively in the presence of amino acids. In addition, while under nutrient replete conditions GSK3{beta} is largely cytosolic, amino acid starvation drives a portion of GSK3{beta} into the nucleus. Acute replenishment of specific amino acids in starved cells triggered nuclear exit of GSK3{beta}. This amino acid-stimulated GSK{beta} nuclear exit required GATOR1 and GATOR2 but was independent of mTORC1 and its activating RagA/B GTPases. This suggests that GATOR1 has a function that diverges from control of mTORC1 to regulate the nucleocytoplasmic shuttling of GSK3{beta}. Furthermore, experimental restriction of GSK3{beta} to the cytoplasm decreased cell survival in amino acid deficient conditions. This suggests that control of GSK3{beta} nuclear localization by GATOR-dependent signals represents a cellular adaptation to metabolic stress that supports cell survival.

cell biology↗

bioRxiv2022

Improved imaging and preservation of lysosome dynamics using silver nanoparticle-enhanced fluorescence

The dynamics of living cells can be studied by live-cell fluorescence microscopy. However, this requires the use of excessive light energy to obtain good signal-to-noise ratio, which can then photobleach fluorochromes, and more worrisomely, lead to photo-toxicity. Upon light excitation, noble metal nanoparticles such as silver nanoparticles (AgNP) generate plasmons, which can then amplify excitation in direct proximity of the nanoparticles surface and couple to the oscillating dipole of nearby radiating fluorophores, modifying their rate of emission and thus, enhancing their fluorescence. Here, we show that AgNP fed to cells to accumulate within lysosomes enhanced the fluorescence of lysosome-targeted Alexa488-conjugated dextran, BODIPY-cholesterol, and DQ-BSA. Moreover, AgNP increased the fluorescence of GFP fused to the cytosolic tail of LAMP1, showing that metal enhanced fluorescence can occur across the lysosomal membrane. The inclusion of AgNPs in lysosomes did not disturb lysosomal properties such as lysosomal pH, degradative capacity, autophagy and autophagic flux, and membrane integrity, though AgNP seemed to increase basal lysosome tubulation. Importantly, by using AgNP, we could track lysosome motility with reduced laser power without damaging and altering lysosome dynamics. Overall, AgNP-enhanced fluorescence may be a useful tool to study the dynamics of the endo-lysosomal pathway while minimizing photo-toxicity. eTOCSilver nanoparticles enhance fluorescence via surface plasmons. Here, we show that loading lysosomes with silver nanoparticles enhances the fluorescence of fluorochrome- and GFP-based molecular probes for lysosomes. This affords reduced excitation and exposure, diminishing photobleaching and phototoxicity, and preserving lysosome dynamics.

cell biology↗