Constitutively activated phosphatidylinositol-3 kinase (PI-3K) is involved in the defect of apoptosis in B-CLL: association with protein kinase Cdelta.
In the present study we analyzed the role of phophatidylinositol-3 kinase (PI-3K) in B chronic lymphocytic leukemia (B-CLL) cells. PI-3K is activated by many stimuli and is linked to several different signaling pathways. We demonstrated that inhibition of PI-3K by a specific inhibitor, LY294002, induced apoptosis in B-CLL cells in vitro. This effect was specific for the inhibition of PI-3K because inhibition of other signaling pathways such as extracellular signaling-regulated kinase (ERK), p38, or p70S6 kinase did not affect spontaneous apoptosis. Furthermore, PI-3K was constitutively activated in freshly isolated B-CLL cells. Corresponding to enhanced apoptosis, LY294002 down-regulated expression of the antiapoptotic proteins X-linked inhibitor of apoptosis protein (XIAP) and Mcl-1. Next, we investigated which factors downstream of PI-3K were activated in B-CLL cells. We demonstrated that protein kinase B/Akt is expressed in all tested CLL samples but no activation of Akt was detected. In contrast, we observed a constitutive activation of protein kinase Cdelta (PKCdelta) in freshly isolated B-CLL cells. PKCdelta is linked to PI-3K and is phosphorylated at Thr505 in response to PI-3K activation. We further demonstrated that tyrosine phosphorylation and activity of PKCdelta were dependent on PI-3K activity in B-CLL cells. Inhibition of PKCdelta by the specific inhibitor Rottlerin strikingly enhanced apoptosis. In contrast, peripheral blood B cells of healthy donors were resistant to inhibition of PI-3K or PKCdelta. We conclude that activated PI-3K might be important in the pathogenesis of B-CLL, and survival signals might be mediated via PKCdelta. Therefore, inhibition of PI-3K or PKCdelta may be an innovative approach to treat B-CLL.
Ringshausen
Ingo
I
Third Department of Medicine, Technical University of Munich, Germany. i.ringshausen@lrz.tum.de
Schneller
Folker
F
Bogner
Christian
C
Hipp
Susanne
S
Duyster
Justus
J
Peschel
Christian
C
Decker
Thomas
T
D017209:Apoptosis / Q000187:drug effects; D016022:Case-Control Studies; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000201:enzymology* / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism / Q000502:physiology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology; D051745:Protein Kinase C-delta; D015398:Signal Transduction
D004791:Enzyme Inhibitors; D007527:Isoenzymes; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C; D051745:Protein Kinase C-delta; C497258:PRKCD protein, human