Involvement of protein kinase C and phosphatidylinositol 3–kinase pathways in the survival of B-cell chronic lymphocytic leukemia cells

Abstract

B-cell chronic lymphocytic leukemia (B-CLL) is characterized by the accumulation of long-lived CD5+ B lymphocytes. TPA (12-O-tetradecanoylphorbol 13- acetate) and interleukin-4 (IL-4) inhibit apoptosis of B-CLL lymphocytes ex vivo. We used specific inhibitors of protein kinase C (PKC), extracellular-regulated kinase (ERK), and phosphatidylinositol 3–kinase (PI3-kinase) to study their involvement in TPA- and IL-4–induced survival of B-CLL lymphocytes. BisI, a specific inhibitor of PKC, induced apoptosis and inhibited the antiapoptotic activity of TPA and IL-4. B-CLL cells have a basal PKC activity that was increased by TPA but not by IL-4. TPA, but not IL-4, induced ERK activation. However, the inhibition of ERK activation did not affect the viability of B-CLL lymphocytes, demonstrating that this pathway is not involved in their survival. Inhibition of PI3-kinase by LY294002 induced apoptosis of B-CLL cells and inhibited the survival effect of IL-4 and TPA. In addition, Akt, a downstream effector of PI3-kinase activity, was phosphorylated by TPA and IL-4 in B-CLL cells, though PI3-kinase had no effect on PKC-dependent phosphorylation of Akt. Furthermore, the inhibition of PKC or PI3-kinase increased dexamethasone- and fludarabine-induced apoptosis ex vivo in the presence of survival factors. These results demonstrate that PKC and PI3-kinase are involved in the survival of B-CLL cells and suggest that inhibitors of these pathways could be combined with the drugs used in the treatment of B-CLL.

Sorafenib induces cell death in chronic lymphocytic leukemia by translational downregulation of Mcl-1

“…21 Therefore, we analyzed Erk1/2 phosphorylation in sorafenib-treated CLL cells as a surrogate protein for PDGFR signalling. In accordance with other reports, 22 a proportion of quiescent CLL cells contain no constitutively activated Erk1/2. We did not find significant baseline phosphorylation of Erk1/2 in the CLL samples we investigated (Figure 2c).…”

IL-4 protects the B-cell lymphoma cell line CH31 from anti-IgM-induced growth arrest and apoptosis: contribution of the PI-3 kinase/AKT pathway

“…IL-4 is known to induce the activation of several signal transduction pathways in Janus kinase (JAK)-dependent manners [43]; both the IRS/PI-3K and the STAT6 pathways have been linked to suppression of apoptosis in other cell types [11][12][13]. Thus, we first analyzed the ability of IL-4 to induce these pathways in CH31 ( Figure 6A).…”

“…A pathway independent of IRS was also found to contribute to the IL-4-induced protection from apoptosis in this model; however, this pathway was independent of signal transducer and activator of transcription 6 (STAT6). Furthermore, pharmacologic inhibitors of PKC and PI-3K were able to block the IL-4-induced phosphorylation of Akt and the enhanced survival of human B-CLL [12]. On the other hand, activation of the STAT6 pathway was shown to play a role in the IL-4-induced suppression of Fas-induced apoptosis of primary CD40L-activated B cells, while the IRS2/PI-3K pathway appeared dispensable [13].…”

Reduced expression of the tumor suppressor PHLPP1 enhances the antiapoptotic B-cell receptor signal in chronic lymphocytic leukemia B-cells

“…[3][4][5] This kinase is also activated in response to many other microenvironmental stimuli that increase leukemic cell survival or induce proliferation, including CXCL12, CD40 ligand, IL-4, CpG oligonucleotides, lysophosphatidic acid, high-density lipoprotein particles and contact with bone marrow stromal cells. [6][7][8][9][10][11][12][13] In addition, increased basal Akt activity has been reported in some studies, suggesting that constitutive Akt signaling may contribute to the increased survival of the malignant lymphocytes. In line with this possibility, specific inhibition or downregulation of Akt has been shown to induce apoptosis in freshly isolated CLL cells.…”