PICOT, protein kinase C θ-interacting protein, is a novel regulator of FcεRI-mediated mast cell activation

PICOT (PKC-interacting cousin of thioredoxin) consists of one thioredoxin homology domain in the N-terminal and two tandem PICOT homology domains in the C-terminal. PICOT specifically interacts with protein kinase C θ (PKC-θ) via its thioredoxin homology domain and acts as an important modulator of T cell receptor (TCR)-signaling. Using PICOT overexpressing rat basophilic leukemia cells (RBL-2H3), we evaluated the effect of PICOT overexpression on the FcεRI-mediated signaling. In comparison to the control cells, introduction of PICOT to RBL-2H3 cells induced increased degranulation and the activation of NFAT and in the expression of IL-4 and TNF-α transcripts by FcεRI-crosslinking, whereas no significant change was observed with the elevation of ERK1/2 and p38 MAP kinase phosphorylation and NF-κB activation by FcεRI aggregation. More interesting was the exogenous PICOT overexpression in RBL-2H3 cells causing a large decrease in the elevation of JNK phosphorylation. PICOT-regulated FcεRI-mediated signals in RBL-2H3 cells and acted as a positive regulator on IL-4 and TNF-α expression, NFAT and degranulation signal pathways and a negative regulator on a JNK signal pathway. Considering that PICOT has no enzymatic activity, the regulation of PICOT on FcεRI-signaling may depend on PICOT-associated molecule(s).