Although several mechanisms of apoptotic defects have been implicated in B- chronic lymphocytic leukemia (CLL) cells, the exact signaling pathways underlying these defects remain unresolved. Lyn kinase and protein kinase C (PKC)-epsilon play a critical role in B-cell antigen receptor signaling. They are also known to be negative regulators of apoptosis, and are linked to chemo-resistance. Because activation of PKCs results in their translocation from the cytosol to distinct subcellular locations in which they perform their specific functions, we examined the role of Lyn kinase in the cellular localization of PKC-epsilon in B-CLL cells and its link to the apoptotic defects. Untouched peripheral blood B-CLL cells or nonmalignant B cells were isolated from PBMCs of B-CLL patients or normal blood donors. Cytoplasmic and nuclear fractions of B-CLL cells and nonmalignant cells were prepared and examined for PKC-epsilon localization by Western blot analysis. Unlike the cytoplasmic localization in nonmalignant cells, a large fraction of PKC-epsilon in B-CLL cells was located in the nuclear fraction. Nuclear localization of PKC-epsilon in B-CLL cells was linked to the transcriptional activation of the antiapoptotic genes such as Mcl-1, XIAP, and Bcl-2, as well as NF-kappaB activation and VEGF production., both strongly implicated in the apoptotic resistance of B-CLL cells. Treatment of B-CLL cells for 16-20 hours with 10 micromolar Lyn-specific inhibitor peptide targeting a unique interaction site within Lyn (
Disclosures: No relevant conflicts of interest to declare.