To determine the mechanisms by which dimedone decreases prosurvival and cell cycle progression signals, we examined signaling processes that require reversible cysteine sulfenic acid formation.
Global tyrosine, Lyn, Syk (spleen tyrosine kinase), PLCγ2, and ERK 1/2 phosphorylation were determined in the presence of vehicle or dimedone. Immunoblot analysis of global tyrosine phosphorylation revealed an approximately 2.0-fold increase in phosphorylation within 1 min of BCR stimulation (Fig. 6A and F). Dimedone treatment did not decrease the global tyrosine phosphorylation at 1 min. However, after 5 and 15 min of BCR stimulation, dimedone treatment decreased tyrosine phosphorylation compared with that of vehicle-treated samples. Thus, reversible cysteine sulfenic acid formation plays a role in the maintenance of global tyrosine phosphorylation. Because we observed C59 wnt PI3K inhibitor a decrease in global tyrosine phosphorylation, we wanted to determine if specific tyrosine
phosphorylation events following BCR ligation were altered in the presence of dimedone. Immunoblot analysis of Lyn phosphorylation identified similar phosphorylation levels in the vehicle and dimedone-treated samples at all timepoints (Fig. 6B and G). Phospho-Syk analysis by western blot demonstrated an approximately 12-fold increase in phosphorylation after 1 min of BCR stimulation in the absence of dimedone (Fig. 6C and H). By 5 min, the phosphorylation of Syk had increased approximately 39-fold over ex vivo. However, treatment of cells with dimedone significantly decreased
Syk phosphorylation at 5 and 15 min. Similar results were detected with PLCγ2 (Fig. 6D and I) and ERK 1/2 (Fig. 6E and J) ASK1 phosphorylation in the presence of dimedone. Therefore, reversible cysteine sulfenic acid formation is necessary for the maintenance of global tyrosine, Syk, PLCγ2, and ERK 1/2, but not Lyn, phosphorylation during BCR activation. Since the early tyrosine phosphorylation events were inhibited by dimedone pretreatment, we wanted to determine whether sulfenic acid modification of proteins was altered. To address this, purified B cells were pretreated with vehicle or dimedone prior to measuring sulfenic acid formation in the total proteome and individual candidates. Although somewhat elevated cysteine sulfenic acid levels following dimedone pretreatment were observed, no increase in sulfenic acid levels following B-cell activation were observed in the presence of dimedone (Supporting Information Fig. 2A). Furthermore, when individual proteins were analyzed, dimedone pretreatment decreased (SHP-1 and PTEN) or blocked (SHP-2) sulfenic acid formation following B-cell activation when compared with vehicle (Supporting Information Fig. 2B–D).