SLPI is involved in signal transduction pathways. (A) NB4 cells were transduced with SLPI-specific or control-RFP–tagged shRNA. RFP⁺ cells were sorted and treated with ATRA for 2 days. Representative western blot images showing total NF-κB p65 and IκBα proteins. Ponceau was used as a loading control. (B) BM CD34⁺ cells were transduced with SLPI-specific or control-RFP–tagged shRNA, RFP⁺ cells were sorted and treated or not with 10 ng/mL of G-CSF for 10 minutes; phospho-ERK1/2, phospho-STAT5, and phospho–LEF-1 proteins were quantified using intracellular staining with appropriate antibody and FACS analysis. Mean fluorescence intensity of phospho-ERK1/2, phospho-STAT5, and phospho–LEF-1 proteins in RFP⁺ cell population is presented. Data are mean ± SD and are derived from 2 independent experiments, each in duplicate (*P < .05). (C) c-Myc, survivin, and cyclin D1 mRNA expression in NB4 cells transduced with shRNA constructs and treated with ATRA as indicated in panel A. c-Myc, survivin, and cyclin D1 mRNA expression, normalized to that of β-actin and presented in arbitrary units (AUs), was measured by qRT-PCR; data represent mean ± SD of triplicates.