Abstract
Src is a non‐receptor protein tyrosine kinase that transduces signals regulating cell growth and differentiation. We report here that activation of signaling pathway after blockade of tyrosine phosphorylation by PP2 (4‐amino‐5‐(4‐chloro‐phenyl)‐7‐(t‐butyl)pyrazolo[3,4‐d]pyrimidine), a potent and selective inhibitor of the Src‐family tyrosine kinase, can lead to cell death in murine B cell leukemia, 70Z/3. Death from PP2 occurred by apoptosis as indicated by the induction of caspase activation and annexin V/propidium iodide staining. Interestingly, PP2 was found to be able to enhance the DNA binding activity of nuclear factor κB (NF‐κB) before induction of apoptosis without accompanying by increased phosphorylation of inhibitor of NF‐κB‐α (IκB‐α). Additionally, immunoblotting analysis with PP2‐treated cell extract demonstrated that, compared to other protein kinase C (PKC) isotypes, the translocation of novel PKC isotypes from the cytosol to membrane fraction was sustained for a longer time. These data suggest that the inhibition of Src‐mediated tyrosine phosphorylation by PP2 may tilt the balance between each PKC isotypes, which in turn, activate NF‐κB transcription factor, leading to apoptosis. © 2004 Wiley‐Liss, Inc.