Bcr-Abl kinase activity directly down-regulates the CDK inhibitor p27 in murine Ba/F3 cells.

(A) Ba/F3 cells expressing the temperature sensitive Bcr-Abl were cultivated for 14 hours at the nonpermissive temperature (39°C) in the absence of IL-3 (t = 0). Then cells were either restimulated for 5 hours with fresh medium with or without 1 ng/mL IL-3 at 39°C or shifted to the permissive temperature (33°C) in the absence of IL-3 with or without 1 μmol/L CGP 57148B. Lysates were prepared and subjected to Western blot analysis using anti-p27, and anti-GAP-DH antibody (1:10 000). (B) Ba/F3 cells expressing p185 Bcr-Abl were cultivated at 37 °C in the presence (t = 0) or absence (med) of 1 μmol/L CGP 57148B for 14 hours. Subsequently, cells were washed with PBS and further cultivated without CGP 57148B for the indicated periods. p27 and GAP-DH protein expression were determined by means of Western blot analysis.