STAT3 analysis in NB4 cells. NB4 cells were induced with ATRA (5 μM) for 0, 24, 48, and 72 hours. At each time interval, a representative sample was treated with G-CSF (100 ng/mL) for 15 minutes. Total cell lysates (5 × 10³ cells/μL2 × GSB) from cells induced with ATRA alone (lanes 1-4) or treated with ATRA with subsequent treatment with G-CSF (lanes 5-8) were harvested and subjected to Western blot analysis. The blot was sequentially probed for STAT3, phospho-STAT3 (Tyr 705), and human G-CSFR as outlined in “Materials and methods.” As a positive control, lysates from EML cells overexpressing human G-CSFR were run in parallel (lane 9).