Co-IP of endogenous CK2 with JAK1 and JAK2 and phosphorylation of JAK2 by CK2 in vitro. Lysates of γ2A-JAK2 cells were immunoprecipitated (IP) with anti-CK2α and normal goat IgG (G-IgG, negative control) (A, E, H) or with anti-STAT-3, anti-JAK1, or normal rabbit IgG (R-IgG, negative control) (F-G). (B) γ2A-JAK2 cells were untreated or treated with 5 ng/mL of OSM for 15 minutes. Cell lysates were immunoprecipitated with the indicated antibodies. (C) Lysates of γ2A-GHR-JAK2 cells (lane 2) and γ2A-GHR-JAK2_KD cells (lanes 1 and 3) were immunoprecipitated with the indicated antibodies. (D) Left panel: 293T cells were transfected with HA-tagged JAK2 full-length or deletion constructs, immunoprecipitated, and immunoblotted (IB) with the indicated antibodies. Right panel: schematic presentation of the proteins encoded by JAK2 constructs. The deleted amino acids are indicated. (I) 0.5 μg of JAK2 was incubated with 500 U of CK2 (α and β) in the absence or presence of 50μM of TBB and resolved by 6% SDS-PAGE, followed by autoradiography (top panel) and Coomassie blue staining (bottom panel).