Specific PKC inhibitor (GF109203X) maintains the basal tyrosine phosphorylation state of CBL. Human IFN γ differentiated U937 cells were treated with or without GF 109203X (2.5 μM) on ice for 15 min. and then stimulated with PMA (200 ng/ml) for 1, 5 & 10 min. at 37°C. Cell lysates were prepared and immunoprecipitated (IP) with anti-CBL antibody. Lane 1 represents precipitation with preimmune antisera. Lane 2, no stimulation. Lane 3, 4 & 5 and 9, 10 & 11 represent U937 cells stimulated with PMA (200 ng/ml) or 32.2 F(ab)2 for 1, 5 & 10 min. respectively. Lane 6, 7 & 8, represents cells preincubated with GF 109203X followed by PMA stimulation. This blot was reprobed with anti-CBL and anti-CRKL antibody.