CD74 Is a Novel Survival Receptor in Chronic Lymphocytic Leukemia.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 2812-2812
Author(s):  
Inbal Binsky ◽  
Michal Haran ◽  
Diana Starlets ◽  
Nurit Harpaz ◽  
Lev Shvidel ◽  
...  
Keyword(s):  
B Cells ◽  
Cell Surface ◽  
Cell Survival ◽  
Early Stage ◽  
Annexin V ◽  
Lymphocytic Leukemia ◽  
Signaling Cascade ◽  
Advanced Stage ◽  
C Cells ◽  
Actin Mrna

Abstract Scientific Background: Previous studies have shown that chronic lymphocytic leukemia (CLL) lymphocytes express relatively large amounts of CD74 mRNA compared to normal B cells. We have recently demonstrated in a murine model that CD74 stimulation with anti-CD74 antibody leads to an induction of a signaling cascade resulting in NF-κ B activation, entry of the stimulated cells into the S phase, elevation of DNA synthesis, cell division, and augmented expression of BCL-XL. These findings therefore demonstrated that surface CD74 functions as a survival receptor. In the current study we aimed to determine whether activation of cell surface CD74 in B-CLL cells leads to induction of a signaling cascade resulting in cell survival. Meterials and methods: B cells were purified from the peripheral blood of CLL patients of different stages. CD74 stimulation was achieved using anti-CD74 or MIF (a natural occurring ligand of CD74). IL-8 expression and function was determined by RT-PCR, western blot, ELISA and Annexin V staining. Results: In all CLL patients there was a significantly increased expression of cell surface CD74. Activation of cell surface CD74 initiates a signaling cascade that results in secretion of Interleukin 8 (see Fig1), which in turn regulates cell survival(see Fig 1,2). Conclussion: Our data show that over-expression of CD74 in CLL is an important survival mechanism, operational from the very early stages of the disease, and inherent in all further stages. This survival mechanism thus appears to be an early and significant event in the pathogenesis of the disease. Our findings open prospects for novel therapeutic strategies aimed at this survival pathway. Legends: Fig 1: CD74 induces IL-8 and Bcl-2 expression in CLL B cells. (A,C) Cells were incubated in the presence or absence of anti-CD74 antibody, Id2, a control antibody or MIF for 18 h. (A,C) RNA was purified and levels of IL-8, Bcl-2 and actin mRNA were analyzed. The results presented are representative of 7 early-stage and 5 advanced-stage B-CLL patients. (B) ) Cells’ conditioned medium was collected and their IL-8 levels were analyzed by ELISA. The results presented are representative of 3 independent experiments. Fig 1:. CD74 induces IL-8 and Bcl-2 expression in CLL B cells. (A,C) Cells were incubated in the presence or absence of anti-CD74 antibody, Id2, a control antibody or MIF for 18 h. (A,C) RNA was purified and levels of IL-8, Bcl-2 and actin mRNA were analyzed. The results presented are representative of 7 early-stage and 5 advanced-stage B-CLL patients. (B) ) Cells’ conditioned medium was collected and their IL-8 levels were analyzed by ELISA. The results presented are representative of 3 independent experiments. Fig 2: IL-8 secreted following CD74 stimulation regulates B-CLL cell survival.
 (A, B) B-CLL cells were incubated in the presence or absence of anti-CD74 (B), anti-IL-8 (A, B) or a control antibody (c-jun; A) for 48 h. Cells were stained with annexin V and analyzed by FACS. The results presented are representative of 3 early-stage and 4 advanced-stage B-CLL patients. (C) B-CLL cells were incubated in the presence or absence of a control antibody (c-jun), anti-CD74, anti-IL-8 or IL-8 for 48 h. Cell death was analyzed by ELISA. The graph shows the average of one experiment, representative of 4. Fig 2:. IL-8 secreted following CD74 stimulation regulates B-CLL cell survival.
 (A, B) B-CLL cells were incubated in the presence or absence of anti-CD74 (B), anti-IL-8 (A, B) or a control antibody (c-jun; A) for 48 h. Cells were stained with annexin V and analyzed by FACS. The results presented are representative of 3 early-stage and 4 advanced-stage B-CLL patients. (C) B-CLL cells were incubated in the presence or absence of a control antibody (c-jun), anti-CD74, anti-IL-8 or IL-8 for 48 h. Cell death was analyzed by ELISA. The graph shows the average of one experiment, representative of 4.

Raf-1 Is Over Expressed in Chronic Lymphocytic Leukemia and Promotes Cell Survival by Phosphorylation of ERK and BAD

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 3120-3120 ◽  
Author(s):  
Miao Wang ◽  
P.M. Kluin ◽  
Stefano Rosati ◽  
Marjan Luinge ◽  
Simon M. G. J. Daenen ◽  
...  
Keyword(s):  
Cell Cycle ◽  
B Cells ◽  
Western Blot ◽  
Cell Survival ◽  
Cell Lines ◽  
Annexin V ◽  
Lymphocytic Leukemia ◽  
Cyclin D3 ◽  
Qrt Pcr ◽  
Mrna Ratio

Abstract Introduction: The serine threonine kinase Raf-1 plays a protective role in many cell types, but its expression and function in CLL cells has not been studied in detail. In the present study, we analyzed Raf-1 expression and tested the hypothesis that Raf-1 is critical for CLL cell survival. Materials and Methods: By using qRT-PCR and western blot, we compared the expression of Raf-1 of mRNA and protein levels in purified B cells from 45 CLL cases and CD38 negative B cells from 5 reactive tonsils. By western blot, we analyzed the activity of phospho-Raf-1 (ser338) and its downstream targets (phospho-ERK1/2, phospho-BAD) in 23 CLL cases and 4 CLL cell lines (JVM-3, MEC-1, MEC-2 and MO1043) before and after IgM stimulation. By immunoprecipitation, we analyzed if Raf-1 co-localizes with Bcl-2. We correlated the change in phosphorylation status (Raf-1, ERK and BAD) in response to IgM stimulation with the ZAP-70/SYK mRNA ratio, which was detected by qRT-PCR in purified B cells from CLL cases. After using specific inhibitors, including the Raf-1 inhibitor GW5074, the Raf-1 destabilizer Geldanamycin and Bcl-2 inhibitor YC137, we investigated apoptosis by Annexin V flowcytometry in CLL cases and CLL cell lines as well as cell cycle changes in the 4 cell lines by flowcytometry. Results: In comparison to normal resting (CD38 negative) B cells, there was a strongoverexpression of Raf-1 in CLL cells, both at at the mRNA and protein level. Using qRT-PCR there was an almost linear correlation between Raf-1 and Bcl-2 expression. Moreover, the phosphorylation status of Raf-1 and ERK in response to IgM stimulation strongly correlated with the ZAP-70/SYK mRNA ratio. Using immunoprecipitation and confocal miscroscopy we found colocalization of Raf-1 with Bcl-2, which might account for the observed constitutive activation of BAD in CLL cells. The Raf-1 inhibitor GW5074, Raf-1 destabilizer Geldanamycin and Bcl-2 inhibitor YC137 all led to p-Raf-1 inhibition as well as downregulation of p-ERK and p-BAD. Additionally, all three inhibitors downregulated cyclin D3 and cyclin E, which are important for G0/G1 transition. We also found that GW5074 induced apoptosis in CLL cell lines and primary cells of CLL cases. Conclusion/Discussion: In conclusion, our study identifies Raf-1 as a critical anti-apoptotic and cell cycle regulating kinase in CLL cells.

scholarly journals Targeting Inhibition of N6-Methyladenosine Demethylase Fto Displays Potent Anti-Tumor Activities in Chronic Lymphocytic Leukemia

Blood ◽  
2020 ◽  
Vol 136 (Supplement 1) ◽  
pp. 35-36
Author(s):  
Ya Zhang ◽  
Xinting Hu ◽  
Yang Han ◽  
Xiangxiang Zhou ◽  
Huimin Zhang ◽  
...  
Keyword(s):  
B Cells ◽  
Cell Survival ◽  
Western Blotting ◽  
De Novo ◽  
Annexin V ◽  
Lymphocytic Leukemia ◽  
Rna Seq ◽  
Healthy Donors ◽  
Western Blotting Assay

Introduction Accumulating evidence indicates that Fat mass and obesity-associated protein (FTO), a N6-methyladenosine (m6A) RNA demethylase exerts crucial roles in oncogenesis. FB23-2, a novel inhibitor selectively targeting FTO m6A demethylase activity displayed promising potency in acute myeloid leukemia. Yet, no literature has been reported regarding the effects of FTO and FB23-2 in the tumorigenesis and development of chronic lymphocytic leukemia (CLL). Hence, the aim of this study was to investigate the clinical significance and mechanisms of FTO regulation in CLL. Methods Peripheral blood samples from 55 de novo CLL patients (36 males and 19 females; age range 32-82 years, median 62 years) were collected with informed consents in Shandong Provincial Hospital. CD19+ B cells were isolated with informed consents from healthy donors. Expression levels of FTO mRNA and protein in CLL cells were determined by quantitative RT-PCR and western blotting. Methylated RNA immunoprecipitation sequencing (MeRIP-Seq) and RNA sequencing (RNA-seq) were conduct to profile RNA m6A methylation and expression of CLL cells. Lentiviral vectors were constructed to stably silence and overexpress FTO in CLL cells. Besides, cell viability, apoptosis and cell cycle were assessed by cell counting kit-8, annexin V-PE/7AAD and PI/ RNase staining, respectively. Results Aberrantly increased expression of FTO was observed in CLL patients and CLL cell lines at mRNA and protein level compared with normal B cells from healthy donors (Figure 1A-B). Clinical correlation analyses suggested FTO high expression was significantly associated with 11q23 deletion (p=0.012; Figure 1C). Furthermore, Keplan-Meier plot indicated that elevated FTO expression predicted adverse outcome in CLL patients (HR=1.758, p=0.019; Figure 1D). ROC curve confirmed the prognostic value of FTO in survival of CLL patients (AUC=0.600, p=0.018; Figure 1E). To explore the potential role of FTO in CLL tumorigenesis, CLL cells were transfected with lentiviral vectors to stably silence and overexpress FTO. CLL primary cells and MEC1 cells with silence of FTO exhibited attenuated cell proliferation, increased fast-onset apoptosis (Figure 2A-D). Western blotting assay suggested significant down-regulated Bcl-2, enhanced cleaved-PARP and BAX expression in FTO-deficient CLL cells. Whereas, gain-of-function assay showed promoted cell survival in FTO-overexpressed CLL cells (Figure 2F-G). Additionally, serial dilution of FTO inhibitor FB23-2 decreased viability of MEC1 and primary CLL cells in time-dependent manner, and displayed rare cytotoxicity in normal B cells (Figure 3A-B). Besides, annexin V-PE/7AAD and western blotting assay indicated obvious apoptosis was induced with treatment of FB23-2 in CLL primary cells from 9 de novo CLL patients (Figure 3C-D). Importantly, obvious G2/M phase arrest and enhanced sensitivity to Venetoclax were also detected in FTO-reduced CLL cells. Furthermore, interactive MERIP-seq and RNA-seq of CLL cells with control and deleted FTO expression were performed to investigate the m6A Methylation-Mediated mechanism of FTO regulation of CLL pathogenesis. A total of 573 significantly changed peaks, of which 301 were significantly up-regulated and 272 peaks were significantly down-regulated (Figure 4A). Differentiated peaks were located in 3'UTR (42.58%) and 5'UTR (24.43%). Annotations of bioinformatics analyses indicated that FTO was functionally enriched in cell apoptosis in CLL progression (Figure 4B). Western blotting assay suggested significant down-regulated p-CHK2, c-myc, p-p53, cyclinD1 and enhanced p-H2AX expression in FTO-deficient CLL cells, indicating FTO accelerated CLL cell survival via DNA damage pathway (Figure 4C). Conclusion Taken together, our investigations identified for the first time the oncogenic role of FTO in CLL tumorigenesis and regulatory mechanism of FTO inhibitor FB23-2 in CLL cells by MERIP sequencing and ex vivo evaluation. Expression of FTO was upregulated and associated with inferior prognosis of CLL patients. FB23-2 exerted potent therapeutic potential in abrogating cell survival and inducing cell cycle arrest via m6A methylation. This study provides a rationale on evaluation of FTO-targeted intervention formulating a novel treatment paradigm in progressed CLL that warrants clinical investigation. Disclosures No relevant conflicts of interest to declare.

scholarly journals A monoclonal antibody identifying a cell surface antigen shared by common acute lymphoblastic leukemias and B lineage cells

Blood ◽  
1980 ◽  
Vol 56 (6) ◽  
pp. 1141-1144 ◽  
Author(s):  
MF Greaves ◽  
W Verbi ◽  
J Kemshead ◽  
R Kennett
Keyword(s):  
Monoclonal Antibody ◽  
B Cells ◽  
Cell Surface ◽  
Lymphoblastic Leukemia ◽  
Blast Crisis ◽  
Fetal Brain ◽  
Lymphocytic Leukemia ◽  
Cell Surface Antigens ◽  
A Cell ◽  
B Lineage

Abstract A monoclonal antibody designated PI153/3, which reacts with neuroblastoma and fetal brain, is shown to identify also a cell surface determinant shared by pre-B and mature B cells and their corresponding leukemias including chronic lymphocytic leukemia, non-Hodgkin's lymphoma, B acute lymphoblastic leukemia, and hairy cell leukemia, but not plasmacytoma. Almost all non-T, non-B acute “lymphoid” leukemias bind PI153/3. The latter includes 71 of 74 common ALL tested, most but not all “unclassified” or “null” ALL and cases of both acute undifferentiated leukemia and Ph1 positive chronic myeloid leukemia in blast crisis with common ALL phenotypes. The antigen is absent or present at very low density on normal and leukemic T lymphocyte, myeloid and erythroid cells. The determinant appears to co-redistribute with cell surface immunoglobulin in B lymphocytes and segregates independently of other cell surface antigens associated with B cells and/or cALL including HLA-DR (Ia-like antigens) and the cALL (gp 100) antigen.

scholarly journals Prognostic impact of prevalent chronic lymphocytic leukemia stereotyped subsets: analysis within prospective clinical trials of the German CLL Study Group (GCLLSG)

Haematologica ◽  
2019 ◽  
Vol 105 (11) ◽  
pp. 2598-2607 ◽  
Author(s):  
Sonia Jaramillo ◽  
Andreas Agathangelidis ◽  
Christof Schneider ◽  
Jasmin Bahlo ◽  
Sandra Robrecht ◽  
...  
Keyword(s):  
Clinical Trials ◽  
Chronic Lymphocytic Leukemia ◽  
Early Stage ◽  
International Prognostic Index ◽  
Prognostic Index ◽  
Lymphocytic Leukemia ◽  
Phase Iii ◽  
Prognostic Impact ◽  
Advanced Stage ◽  
Multicenter Clinical Trials

Almost one-third of all patients with chronic lymphocytic leukemia (CLL) express stereotyped B cell receptor immunoglobulins (BcR IG) and can be assigned to distinct subsets, each with a particular BcR IG. The largest stereotyped subsets are #1, #2, #4 and #8, associated with specific clinicobiological characteristics and outcomes in retrospective studies. We assessed the associations and prognostic value of these BcR IG in prospective multicenter clinical trials reflective of two different clinical situations: i) early-stage patients (watch-and-wait arm of the CLL1 trial) (n=592); ii) patients in need of treatment, enrolled in 3 phase III trials (CLL8, CLL10, CLL11), treated with different chemo-immunotherapies (n=1861). Subset #1 was associated with del(11q), higher CLL international prognostic index (CLL-IPI) scores and similar clinical course to CLL with unmutated immunoglobulin heavy variable (IGHV) genes (U-CLL) in both early and advanced stage groups. IGHV-mutated (M-CLL) subset #2 cases had shorter time-to-first-treatment (TTFT) versus other M-CLL cases in the early-stage cohort (HR: 4.2, CI: 2-8.6, p<0.001), and shorter time-to-next-treatment (TTNT) in the advanced-stage cohort (HR: 2, CI: 1.2-3.3, p=0.005). M-CLL subset #4 was associated with lower CLL-IPI scores and younger age at diagnosis; in both cohorts, these patients showed a trend towards better outcomes versus other M-CLL. U-CLL subset #8 was associated with trisomy 12. Overall, this study shows that major stereotyped subsets have distinctive characteristics. For the first time in prospective multicenter clinical trials, subset # 2 appeared as an independent prognostic factor for earlier TTFT and TTNT and should be proposed for risk stratification of patients.

scholarly journals Role for low-affinity receptor for IgE (CD23) in normal and leukemic B- cell proliferation

Blood ◽  
1994 ◽  
Vol 84 (6) ◽  
pp. 1881-1886 ◽  
Author(s):  
S Fournier ◽  
M Rubio ◽  
G Delespesse ◽  
M Sarfati
Keyword(s):  
Cell Proliferation ◽  
B Cells ◽  
B Cell ◽  
Cell Activation ◽  
Early Stage ◽  
Lymphocytic Leukemia ◽  
Interleukin 4 ◽  
B Cell Activation ◽  
Type B ◽  
Cd23 Expression

Abstract CD23 gene is overexpressed and abnormally regulated in the most frequent adult leukemic disorder, B chronic lymphocytic leukemia (B- CLL). Switch on and off in the upregulation of surface CD23 expression consistently occurs in the early stage of normal B-cell activation, suggesting a key role for CD23 in this process. We show here that, after ligation of mlg in the presence of interleukin-4, the increase of CD23 protein precedes B-cell DNA synthesis and mainly results from the strong induction of CD23 type-B isoform. Exposure of normal B cells to conventional or phosphorothioate-derivatized CD23 antisense oligonucleotides (predominantly type B) significantly augments B-cell proliferation induced by antigen receptor stimulation or direct contact with activated T cells. Unexpectedly, CD23 antisense, but not sense, oligonucleotides specifically enhance rather than suppress CD23 expression on B cells. Finally, a selective increase in CD23 type-B expression provokes the entry of resting (Go) CLL B cells into G1 and S phase of the cell cycle in the absence of any other stimulus, whereas it synergizes with tumor necrosis factor-alpha to increase the number of activated B cells. These results provide compelling evidence that CD23 represents an important molecule directly involved in the process of normal or leukemic B-cell activation and growth.

Interleukin-21 receptor (IL-21R) is up-regulated by CD40 triggering and mediates proapoptotic signals in chronic lymphocytic leukemia B cells

Blood ◽  
2006 ◽  
Vol 107 (9) ◽  
pp. 3708-3715 ◽  
Author(s):  
Daniela de Totero ◽  
Raffaella Meazza ◽  
Simona Zupo ◽  
Giovanna Cutrona ◽  
Serena Matis ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
B Cells ◽  
Chronic Lymphocytic Leukemia ◽  
Caspase 3 ◽  
Active Form ◽  
Growth Arrest ◽  
Lymphocytic Leukemia ◽  
Signaling Cascade ◽  
Caspase 8 ◽  
Interleukin 21

Interleukin-21 (IL-21) is a member of the IL-2 cytokine family, which mediates proliferation or growth arrest and apoptosis of normal B cells, depending on their activation state. Here we demonstrate that surface IL-21 receptor (R) is expressed at variable levels by chronic lymphocytic leukemia (CLL) B cells freshly isolated from 33 different patients. IL-21R expression was up-regulated following cell stimulation via surface CD40. Therefore, IL-21 effects were more evident in CD40-activated CLL B cells. IL-21 induced an early signaling cascade in CLL B cells, which included JAK-1 and JAK-3 autophosphorylation and tyrosine phosphorylation of STAT-1, STAT-3, and STAT-5. IL-21 signaling failed to stimulate CLL B-cell proliferation, but induced their apoptosis. In addition, IL-21 counteracted the proliferative and antiapoptotic signals delivered by IL-15 to CLL B cells. IL-21-mediated apoptosis involved activation of caspase-8 and caspase-3, cleavage of Bid to its active form t-Bid, and cleavage of PARP and of p27Kip-1. Recent data indicate that CLL B cells require interaction with the microenvironment for their survival and expansion. The present findings thus provide a set of new mechanisms involved in the balance between cell-survival and apoptotic signals in CLL B cells.

Human Antagonistic Anti-CD40 Antibody, CHIR-12.12, Inhibits CD40-Mediated Survival of Chronic Lymphocytic Leukemia B Cells Leading to Cellular Apoptosis.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 2965-2965 ◽  
Author(s):  
Anu Cherukuri ◽  
Edward Kadel ◽  
Sang H. Lee ◽  
Cheryl Goldbeck ◽  
Carla Heise ◽  
...  
Keyword(s):  
B Cells ◽  
Chronic Lymphocytic Leukemia ◽  
Cell Survival ◽  
Signaling Pathways ◽  
P38 Mapk ◽  
Hodgkin’S Lymphoma ◽  
Caspase 3 ◽  
Lymphocytic Leukemia ◽  
Hodgkin's Lymphoma ◽  
Non Hodgkin's Lymphoma

Abstract CD40 and CD40 ligand (CD40L) interaction is a key regulator of B-chronic lymphocytic leukemia (CLL) survival. CD40 activation leads to binding with tumor necrosis factor receptor-associated factors (TRAFs) and the subsequent activation of multiple downstream signaling pathways involved in cellular proliferation and survival. We have generated a novel fully human IgG1 anti-CD40 antagonistic monoclonal antibody, CHIR-12.12, using XenoMouse® mice (Abgenix, Inc). CHIR-12.12 blocks CD40L binding to CD40 and inhibits CD40L-induced proliferation/survival of normal human B cells, primary CLL cells, and primary non-Hodgkin’s lymphoma (NHL) cells. We have also demonstrated that it has highly potent antibody-dependent cellular cytotoxicity (ADCC) against primary CLL and non-Hodgkin’s lymphoma cells. We have now investigated its effects on primary CLL cell survival. Soluble human CD40L prolongs primary CLL cell survival in culture, and treatment with CHIR-12.12 inhibits this survival when measured 48–72 hours after addition of CHIR-12.12. CD40L-mediated survival is associated with activation and phosphorylation of Akt, p38 MAPK, ERK, and IkB kinases a and b. Additionally, the anti-apoptotic proteins Mcl-1, Bcl-xl, and XIAP are induced, and markers of apoptosis (cleaved PARP and Caspase-3) are reduced. In contrast, CHIR-12.12 treatment of CD40L-stimulated primary CLL cells ex vivo inhibited downstream phosphorylation of Akt, p38 MAPK, ERK, and IkB kinases (IKK) a and b. Additionally, CHIR-12.12 treatment resulted in induction of cleaved caspase-3 and PARP, and reduction of XIAP, Mcl-1, and Bcl-xl expression, ultimately leading to CLL cell apoptosis. These results demonstrate that CHIR-12.12 inhibits CD40L-mediated signaling pathways and cell survival and could be a potential therapeutic treatment for CLL. CHIR-12.12 is currently in a Phase I clinical study for CLL.

Introduction of Constitutivelly Active Akt in Primary CLL B-Cells Results in Upregulation of Mcl-1, Bcl-XL and Cyclin D3 and Promotes Leukemic Cell Survival.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 2805-2805
Author(s):  
Pablo Longo ◽  
Stefania Gobessi ◽  
Luca Laurenti ◽  
Simona Sica ◽  
Giuseppe Leone ◽  
...  
Keyword(s):  
B Cells ◽  
Cell Survival ◽  
Leukemic Cell ◽  
Lymphocytic Leukemia ◽  
Cyclin D3 ◽  
Leukemic Cells ◽  
Interleukin 4 ◽  
Antiapoptotic Proteins ◽  
Sustained Activation ◽  
Constitutively Active

Abstract The PI3K/Akt and Raf/MEK/ERK pathways are key regulators of various cellular responses, including proliferation, survival, differentiation, migration and malignant transformation. These pathways are activated in chronic lymphocytic leukemia B-cells by a number of survival or growth stimulatory signals, such as immobilized anti-IgM antibodies, interleukin-4, phorbol-ester, CXCL12, or stimulatory CpG oligonucleotides. Moreover, enhanced activation of Akt has been implicated in the pathogenesis of the CLL-like disorder that develops in mice transgenic for the TCL1 oncogene. To further delineate the relative contribution of the PI3K/Akt and Raf/MEK/ERK pathways in regulating leukemic cell growth and survival, we introduced constitutively active Akt or constitutively active MEK2 in primary CLL B-cells by nucleofection. Expression of constitutively active Akt consistently promoted survival, as evidenced by a higher percentage of Annexin V/PI negative cells after 48 hours in culture (median 52%) compared to samples transfected with control vector (median 31%). Immunoblot analysis of several important antiapoptotic proteins revealed that enforced activation of Akt upregulates Mcl-1 and Bcl-xL, whereas no changes were observed in the levels of Bcl-2. Expression of constitutively active Akt also induced an increase in size and granularity of the leukemic cells, indicating increased metabolic activity. These changes were associated with significant induction of cyclin D3, indicating that activation of Akt is required for both leukemic cell survival and cell cycle progression. In contrast, introduction of constitutively active MEK2 induced sustained activation of ERK, but showed only a modest increase in the percentage of viable CLL B-cells (median 36%) and no significant changes in the levels of any of the investigated antiapoptotic proteins. These experiments provide direct evidence that sustained activation of Akt promotes leukemic cell survival and upregulates Mcl-1, an antiapoptotic protein that has been associated with resistance to chemotherapy in patients with CLL.

The Akt/Mcl-1 Pathway Plays a Prominent Role in Mediating Pro-Survival Signals Derived from the B-Cell Receptor in Chronic Lymphocytic Leukemia B-Cells.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 341-341
Author(s):  
Pablo G. Longo ◽  
Luca Laurenti ◽  
Stefania Gobessi ◽  
Simona Sica ◽  
Giuseppe Leone ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Cell Survival ◽  
Cell Receptor ◽  
B Cell Receptor ◽  
Lymphocytic Leukemia ◽  
Igm Antibodies ◽  
B Cell Survival ◽  
Sustained Activation ◽  
Constitutively Active

Abstract Studies of the immunoglobulin variable region gene repertoire have provided compelling evidence that antigen-stimulation through the B-cell receptor (BCR) plays a crucial role in the pathogenesis and progression of chronic lymphocytic leukemia (CLL). In addition, previous studies from our lab have shown that CLL B-cells become more resistant to spontaneous and chemotherapy-induced apoptosis following sustained engagement of the BCR with immobilized anti-IgM antibodies, which mimic stimulation with membrane-bound antigens. Investigation of downstream signaling pathways revealed that sustained BCR engagement induces prolonged activation of the PI3K/Akt and MEK/ERK pathways, which are key regulators of survival and proliferation in various cell types. To further define the role of sustained activation of the Akt and ERK kinases in regulating CLL growth and survival, we transfected constitutively active mutants of Akt (myr.Akt) and MEK2 in primary leukemic cells and evaluated changes in the expression of relevant apoptosis- and cell-cycle regulatory proteins. Introduction of constitutively active MEK2 resulted in activation of ERK, but did not induce significant changes in the levels of most investigated proteins (Bcl-2, Bcl-xL, Bim, Bax or Mcl-1). The only exception was the inhibitor of apoptosis protein XIAP, which showed increased expression in most but not all experiments. In contrast, transfection of myr.Akt showed a consistent increase in the levels of the antiapoptotic protein Mcl-1, which ranged from 1.5 to more than 4-fold higher levels with respect to cells transfected with control vectors. Increased expression of Mcl-1 was observed in all experiments and paralleled the rise in Mcl-1 that occurred following stimulation of CLL B-cells with immobilized anti-IgM antibodies. The increase in Mcl-1 protein levels was entirely due to post-transcriptional mechanisms, since quantification by real-time PCR did not show an increase in Mcl-1 mRNA levels. Constitutively active Akt also upregulated Bcl-xL and XIAP, although this increase was lower than the increase in Mcl-1. In addition, CLL cells transfected with myr.Akt showed induction of cyclin D3 and an increase in cell size and viability, indicating that sustained activation of Akt is required for both leukemic cell survival and cell cycle progression. To determine the relative importance of Mcl-1, Bcl-xL and XIAP in CLL B-cell survival, we downregulated expression of these proteins in primary CLL B-cells by RNA interference. Surprisingly, downregulation of Bcl-xL and XIAP had no effect on CLL B-cell survival. In contrast, silencing of Mcl-1 induced rapid and potent apoptosis in all investigated cases and abrogated the prosurvival effect of stimulation with immobilized anti-IgM antibodies. Together, these data provide direct evidence that pro-survival BCR signaling in CLL B-cells is mediated, at least in part, through the Akt/Mcl-1 pathway. In addition, they suggest that Mcl-1 could be an attractive candidate for targeting, either with small molecule inhibitors or with pharmacological agents that interfere with BCR signals propagated by the Akt kinase.

Chronic Lymphocytic Leukemia (CLL) Cells Require Microenvironmental Stimuli to Resist Apoptosis through Activation of STAT3 Mediated by VEGF.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 1069-1069
Author(s):  
Iris Gehrke ◽  
Julian Paesler ◽  
Rajesh Kumar Gandhirajan ◽  
Regina Razavi ◽  
Alexandra Filipovich ◽  
...  
Keyword(s):  
Bone Marrow ◽  
B Cells ◽  
Chronic Lymphocytic Leukemia ◽  
Cell Survival ◽  
Lymphocytic Leukemia ◽  
Vegf Receptor ◽  
Mrna Levels ◽  
Activated State ◽  
Survival Effect

Abstract B-cell chronic lymphocytic leukemia (CLL) is characterized by an accumulation of mature, but incompetent B-cells due to a decrease of apoptosis rather than an increase in proliferation. Vascular endothelial growth factor (VEGF) has been suggested to play an important role in this so called apoptotic block. However, so far little is understood whether VEGF is acting mainly as a microenvironmental stimulus and/or whether CLL cells themselves contribute to the enhanced apoptotic resistance by maintaining an autocrine VEGF loop. Moreover, it is unknown by which mechanisms VEGF prevents apoptosis and whether this can be circumvented by inhibition of VEGF signaling. By quantitative real time PCR we found no significant difference in mRNA VEGF levels in B-cells from CLL patients and healthy donors after isolation from blood. In contrast, ELISA revealed clearly increased levels of secreted VEGF in plasma of CLL patients and in the supernatant under culture conditions compared to healthy individuals. In addition, we found the VEGF receptor 2 (VEGFR2), which is existent in CLL and healthy B-cells, in a phosphorylated, hence activated state, to a significantly higher extent in CLL cells as assessed by intracellular phospho flow cytometry. In conclusion, despite its expression in healthy B-cells VEGF does not seem to be secreted and therefore, no VEGF receptor phosphorylation takes place. Whereas CLL cells exhibit a long life span in vivo, they die rapidly in vitro, suggesting major survival factors being existent in the CLL cells microenvironment. We found levels of secreted VEGF in supernatant decreasing with time in culture, going along with decreasing levels of phosphorylated VEGFR2 and increasing cell death as assessed by Annexin V-FITC/PI staining. This further supports the role of VEGF in CLL cell survival. Coculturing primary CLL cells with the bone marrow stromal derived cell line HS5 dramatically increased VEGF transcription and secretion and improved cell survival. Hence, VEGF expression in CLL cells is not only mediated by autocrine, but also paracrine stimuli involving bone marrow stromal. Knocking down VEGF in HS5 cells and subsequent coculture with CLL cells might prove the major role of VEGF in this survival supporting coculture setting. Besides coculturing also supplement of culture medium with recombinant human VEGF (rhVEGF) increased survival, but to a lesser extent than coculture, indicating a direct cell-cell interaction as advantageous. Furthermore, we found a downregulation of anti apoptotic proteins, such as X-linked inhibitor of apoptosis protein (XIAP), myeloid cell leukemia 1 (MCL1) and BclXL upon VEGF stimulation. Also cyclinD1 was upregulated as seen by immunoblotting. We further tried to discover the underlying mechanism of how VEGF mediates its pro survival effect and found STAT3 to become phosphorylated on tyrosine 705 upon VEGF stimulation. In CLL STAT3 is known to be constitutively phosphorylated on serine 727. This phosphorylation is not sufficient to induce target gene expression though. We could show that Y705 phosphorylation of STAT3 is responsible for upregulation of anti apoptotic BCLXL and cyclinD1. A PCR array detecting mRNA levels of 84 transcription factors in untreated and VEGF stimulated CLL cells shall provide more information about mechanistical details how VEGF mediates it pro survival effect. Since VEGF seems to be a major player in CLL cell survival it might be a suitable target to overcome the apoptotic block. In first experiments we found an induction of apoptosis after neutralization of VEGF or inhibition of the VEGF receptor. This additionally highlights the severe importance of VEGF in the apoptotic block in CLL cells. Therefore, VEGF might serve as an excellent therapeutic target in CLL.

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