Aberrant activation of extracellular signal‑regulated kinase 1/2 (ERK1/2) by phosphorylation modification can trigger tumor cell development in glioma. S‑nitrosylation, which refers to the covalent addition of a nitric oxide (NO) group to a cysteine (Cys) thiol, is an important post‑translational modification that occurs on numerous cancer‑associated proteins. Protein S‑nitrosylation can increase or decrease protein activity and stability, and subsequent signal transduction and cellular processes. However, the association between ERK1/2 S‑nitrosylation and ERK1/2 phosphorylation, and the effects of ERK1 S‑nitrosylation on glioma cell survival are currently unknown. U251 glioma cells were treated with NO donors sodium nitroprusside (SNP) or S‑nitrosoglutathione (GSNO). CCK8 assay was used to assess the cell viability. NO levels in the medium were detected by Griess assay. Western blot analysis and biotin switch assay were employed to detect the ERK1/2 phosphorylation and S-nitrosylation. ERK1 wild-type and mutant plasmids were constructed, and used to transfect the U251 cells. Caspase-3 western blot analysis and flow cytometry were employed to assess cell apoptosis. The present study demonstrated that treatment with the NO donors SNP or GSNO led to an increase in ERK1/2 S‑nitrosylation, and a reduction in ERK1/2 phosphorylation, which was accompanied by growth inhibition of U251 glioma cells. Mutational analysis demonstrated that Cys183 was vital for S‑nitrosylation of ERK1, and that preventing ERK1 S‑nitrosylation by replacing Cys183 with alanine partially reversed GSNO‑induced cell apoptosis, and reductions in cell viability and ERK1/2 phosphorylation. In addition, increased ERK1/2 phosphorylation was associated with decreased ERK1/2 S‑nitrosylation in human glioma tissues. These findings identified the relationship between ERK1/2 S‑nitrosylation and phosphorylation in vitro and in vivo, and revealed a novel mechanism of ERK1/2 underlying tumor cell development and apoptotic resistance of glioma.

Severe burn injury is an acute inflammatory state with massive alterations in gene expression and levels of growth factors, cytokines and free radicals. During the catabolic processes, changes in insulin sensitivity and skeletal muscle wasting (unintended loss of 5-15% of lean body mass) are observed clinically. Here, we reveal a novel molecular mechanism of Akt1/protein kinase Bα (Akt1/PKBα) regulated via cross-talking between dephosphorylation of Thr308 and S-nitrosylation of Cys296 post severe burn injury, which were characterized using nano-LC interfaced with tandem quadrupole time-of-fight mass spectrometry (Q-TOF)micro tandem mass spectrometry in both in vitro and in vivo studies. For the in vitro studies, Akt1/PKBα was S-nitrosylated with S-nitrosoglutathione and derivatized by three methods. The derivatives were isolated by SDS-PAGE, trypsinized and analyzed by the tandem MS. For the in vivo studies, Akt1/PKBα in muscle lysates from burned rats was immunoprecipitated, derivatized with HPDP-Biotin and analyzed as above. The studies demonstrated that the NO free radical reacts with the free thiol of Cys296 to produce a Cys296-SNO intermediate which accelerates interaction with Cys310 to form Cys296-Cys310 in the kinase loop. MS/MS sequence analysis indicated that the dipeptide, linked via Cys296-Cys310, underwent dephosphorylation at Thr308. These effects were not observed in lysates from sham animals. As a result of this dual effect of burn injury, the loose conformation that is slightly stabilized by the Lys297-Thr308 salt bridge may be replaced by a more rigid structure which may block substrate access. Together with the findings of our previous report concerning mild IRS-1 integrity changes post burn, it is reasonable to conclude that the impaired Akt1/PKBα has a major impact on FOXO3 subcellular distribution and activities.