IGFBP3 and neoplasm: Conversely, suppressor of cytokine signaling 2 (SOCS2), a negative regulator of the IGF1 signaling pathway [22], was also reduced in the PRR15-shRNA cells (1.4-fold, p = 0.009), which counteracts the changes observed in IGF1R and IGFBP3. Furthermore, phosphatase and tensin homolog (PTEN), a well-described tumor suppressor, was significantly down-regulated in the PRR15-deficient cells.