PIK3R3 and gastrointestinal stromal tumor: Results showed that expression of p55PIK and KIT protein as well as NF-κB p65 phosphorylation (pp65(Ser536)) were decreased in tumors receiving Lenti-shRNAp55PIK, indicating that down-regulation of p55PIK not only led to the re-sensitization of IMA-resistance-GIST cells to Imatinib but also inhibited the NF-κB signaling and KIT expression (Figure 4E).