Cytokine-induced nuclear translocation of signaling proteins and their analysis using the inducible translocation trap system

Signal transduction triggered by iron to induce the nuclear importation of a Myb3 transcription factor in the parasitic protozoan Trichomonas vaginalis

Iron was previously shown to induce rapid nuclear translocation of a Myb3 transcription factor in the protozoan parasite, Trichomonas vaginalis. In the present study, iron was found to induce a transient increase in cellular cAMP, followed by the nuclear influx of Myb3, whereas the latter was also induced by 8-bromo-cyclic AMP. Iron-inducible cAMP production and nuclear influx of Myb3 were inhibited by suramin and SQ22536, respective inhibitors of the Gα subunit of heterotrimeric G proteins and adenylyl cyclases. In contrast, the nuclear influx of Myb3 induced by iron or 8-bromo-cAMP was delayed or inhibited, respectively, by H89, the inhibitor of protein kinase A. Using liquid chromatography-coupled tandem mass spectrometry, Thr(156) and Lys(143) in Myb3 were found to be phosphorylated and ubiquitinated, respectively. These modifications were induced by iron and inhibited by H89, as shown by immunoprecipitation-coupled Western blotting. Iron-inducible ubiquitination and nuclear influx were aborted in T156A and K143R, but T156D was constitutively ubiquitinated and persistently localized to the nucleus. Myb3 was phosphorylated in vitro by the catalytic subunit of a T. vaginalis protein kinase A, TvPKAc. A transient interaction between TvPKAc and Myb3 and the phosphorylation of both proteins were induced in the parasite shortly after iron or 8-bromo-cAMP treatment. Together, these observations suggest that iron may induce production of cAMP and activation of TvPKAc, which then induces the phosphorylation of Myb3 and subsequent ubiquitination for accelerated nuclear influx. It is conceivable that iron probably exerts a much broader impact on the physiology of the parasite than previously thought to encounter environmental changes.

Apurinic/apyrimidinic endonuclease1/redox factor-1 (Ape1/Ref-1) is essential for IL-21-induced signal transduction through ERK1/2 pathway

IL-21 is a pleiotropic cytokine that regulates T-cell and B-cell differentiation, NK-cell activation, and dendritic cell functions. IL-21 activates the JAK-STAT, ERK, and PI3K pathways. We report here that Ape1/Ref-1 has an essential role in IL-21-induced cell growth signal transduction. Overexpression of Ape1/Ref-1 enhances IL-21-induced cell proliferation, but it is suppressed by overexpressing an N-terminal deletion mutant of Ape1/Ref-1 that lacks the redox domain. Furthermore, knockdown of the Ape1/Ref-1 mRNA dramatically compromises IL-21-induced ERK1/2 activation and cell proliferation with increasing cell death. These impaired activities are recovered by the re-expression of Ape1/Ref-1 in the knockdown cells. Our findings are the first demonstration that Ape1/Ref-1 is an indispensable molecule for the IL-21-mediated signal transduction through ERK1/2 activation.

Temporal and spatial profiling of nuclei-associated proteins upon TNF-alpha/NF-kappaB signaling

The tumor necrosis factor (TNF)-alpha/NF-kappaB-signaling pathway plays a pivotal role in various processes including apoptosis, cellular differentiation, host defense, inflammation, autoimmunity and organogenesis. The complexity of the TNF-alpha/NF-kappaB signaling is in part due to the dynamic protein behaviors of key players in this pathway. In this present work, a dynamic and global view of the signaling components in the nucleus at the early stages of TNF-alpha/NF-kappaB signaling was obtained in HEK293 cells, by a combination of subcellular fractionation and stable isotope labeling by amino acids in cell culture (SILAC). The dynamic profile patterns of 547 TNF-alpha-induced nuclei-associated proteins were quantified in our studies. The functional characters of all the profiles were further analyzed using that Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotation. Additionally, many previously unknown effectors of TNF-alpha/NF-kappaB signaling were identified, quantified and clustered into differential activation profiles. Interestingly, levels of Fanconi anemia group D2 protein (FANCD2), one of the Fanconi anemia family proteins, was found to be increased in the nucleus by SILAC quantitation upon TNF-alpha stimulation, which was further verified by western blotting and immunofluorescence analysis. This indicates that FANCD2 might be involved in TNF-alpha/NF-kappaB signaling through its accumulation in the nucleus. In summary, the combination of subcellular proteomics with quantitative analysis not only allowed for a dissection of the nuclear TNF-alpha/NF-kappaB-signaling pathway, but also provided a systematic strategy for monitoring temporal and spatial changes in cell signaling.