Figure 3. PP2A is involved in the de-phosphorylation of STAT5 serine residues in JAK2V617F mutated cells.

(A) SET2 cells were pre-treated for 2 hours with the chemical phosphatase inhibitor Calyculin A (CA; 10 nM) before the addition of 5μM BKM120 for 24 hours. CA exposure resulted in increased phosphorylation of STAT5b serine residues and prevented their BKM120-induced de-phosphorylation, as opposite to STAT5a Y694 residue that remained unchanged. (B) Specific siRNAs were used to silence, although only partially, either PP1 or PP2A to dissect their unique role in the BKM120-induced de-phosphorylation of S731 and S193 of STAT5b. Tubulin was used as loading control. One of 5 different experiments is shown. Densitometric analysis was performed using ImageJ software.