Figure 2
Figure 2. Anti-IgM antibodies induce tyrosine phosphorylation of JAK2 and STAT3 in CLL cells. (A) Ruxolitinib inhibited IgM-induced tyrosine phosphorylation of STAT3. CLL cells were pretreated with dasatinib, U0126, or ruxolitinib for 30 minutes. The cells were then harvested and incubated for 18 hours with or without 10 μg/mL anti-IgM antibodies (Abs.). Cell lysates were analyzed using western immunoblotting with total STAT3, anti-serine and anti-tyrosine pSTAT3, and anti-phosphorylated Lyn (pLyn) antibodies. HeLa cells served as positive controls. Samples from patients 13, 14, 15, and 16 (supplemental Table 1) were used. (B) Ruxolitinib inhibits tyrosine pSTAT3 in a dose-dependent manner. CLL cells were incubated without or with 10 μg/mL anti-IgM antibodies. Ruxolitinib was added for 30 minutes at concentrations ranging from 0.04 to 1.00 μM, and the cells were harvested and analyzed using western immunoblotting. Set-2 cells were used as positive controls. As shown in the upper panel, ruxolitinib inhibited tyrosine pSTAT3 in IgM-stimulated but not unstimulated CLL cells in a dose-dependent manner. This experiment was repeated twice using samples from patients 1 and 6 (supplemental Table 1). As shown in the left lower panel, densitometry analysis of western immunoblots from 4 different patients confirmed that ruxolitinib inhibited tyrosine pSTAT3 in IgM-stimulated but not in unstimulated CLL cells. Samples from patients 13, 14, 15, and 16 (supplemental Table 1) were used. As shown in the right lower panel, ruxolitinib inhibited tyrosine pSTAT3 in a dose-dependent manner. Densitometry analysis of western immunoblots of 6 different experiments was conducted. Depicted are the means ± standard deviation of the relative optical density of tyrosine pSTAT3, quantified and normalized to total levels of STAT3. This experiment was conducted 6 times using samples from patients 1, 2, 6, 7, 10, and 11 (supplemental Table 1). (C) Anti-JAK2 antibody coimmunoprecipitation of pJAK2 and tyrosine pSTAT3 in IgM-stimulated CLL cells. CLL cells from 4 patients were incubated for 2 hours with or without 10 μg/mL anti-IgM antibodies. Cell lysates were prepared, and JAK2 was immunoprecipitated (I.P.) with anti-JAK2 antibodies using protein A-agarose beads. Cells incubated with beads only (B) were used as negative controls. The immune complex was separated using sodium dodecyl sulfate–polyacrylamide gel electrophoresis and analyzed using western immunoblotting with anti-tyrosine pSTAT3, anti-tyrosine JAK2, and anti-JAK2 antibodies. K562 cells were used as positive controls. As shown, JAK2 was immunoprecipitated from lysates of IgM-treated or untreated CLL cells. However, phosphotyrosine STAT3 and pJAK2 were coimmunoprecipitated from IgM-treated but not untreated cells. These experiments were conducted using samples from patients 8, 9, 12, and 13. Representative results are depicted. Data obtained using cells from patients 12 and 13 are not shown (supplemental Table 1). (D) Ruxolitinib induces PARP cleavage in CLL cells. Cells were incubated for 18 hours with or without 10 μg/mL anti-IgM antibodies, and 0.04, 0.20, or 1.00 μM ruxolitinib was added for 30 minutes. The cells were then harvested and analyzed using western immunoblotting with anti-PARP antibodies. This experiment was repeated 6 times using samples from patients 1, 2, 6, 7, 10, and 11 (supplemental Table 1). (E) Ruxolitinib induces apoptosis of CLL cells. As shown in the upper panel, CLL cells were incubated for 18 hours with 10 μg/mL anti-IgM antibodies, and ruxolitinib was added to culture at increasing concentrations for 30 minutes. Apoptosis was assessed using flow cytometry with annexin V/PI staining. As shown, ruxolitinib induced apoptosis of CLL cells in a dose-dependent manner. Cells from patient 11 (supplemental Table 1) were used. As shown in the lower panel, ruxolitinib (but not dasatinib or U0126) induced apoptosis of IgM-stimulated CLL cells in a time-dependent manner. CLL cells were incubated without or with anti-IgM antibodies; ruxolitinib (1.0 μM), dasatinib (1.0 μM), or U0126 (50 μM) was added for 2 hours (right panel) or for different time intervals (1, 2, 3, 6, and 24 hours); and apoptosis was assessed after washout using the annexin V/PI assay, assessed by flow cytometry. As shown, ruxolitinib induced apoptosis of IgM-stimulated cells in a time-dependent manner, whereas dasatinib or U0126 did not affect the apoptosis rate of CLL cells. This experiment was repeated twice using cells from patients 1 and 7 (supplemental Table 1). (F) CLL cells from 3 patients (patients 20, 21, and 22) were incubated for 6 to 72 hours with or without ruxolitinib in the presence or absence of anti-IgM antibodies. Apoptosis rates of ruxolitinib-treated relative to untreated cells are depicted. As shown, ruxolitinib induced apoptosis of IgM-treated but not IgM-untreated CLL cells. *P < .05; **P < .001.

Anti-IgM antibodies induce tyrosine phosphorylation of JAK2 and STAT3 in CLL cells. (A) Ruxolitinib inhibited IgM-induced tyrosine phosphorylation of STAT3. CLL cells were pretreated with dasatinib, U0126, or ruxolitinib for 30 minutes. The cells were then harvested and incubated for 18 hours with or without 10 μg/mL anti-IgM antibodies (Abs.). Cell lysates were analyzed using western immunoblotting with total STAT3, anti-serine and anti-tyrosine pSTAT3, and anti-phosphorylated Lyn (pLyn) antibodies. HeLa cells served as positive controls. Samples from patients 13, 14, 15, and 16 (supplemental Table 1) were used. (B) Ruxolitinib inhibits tyrosine pSTAT3 in a dose-dependent manner. CLL cells were incubated without or with 10 μg/mL anti-IgM antibodies. Ruxolitinib was added for 30 minutes at concentrations ranging from 0.04 to 1.00 μM, and the cells were harvested and analyzed using western immunoblotting. Set-2 cells were used as positive controls. As shown in the upper panel, ruxolitinib inhibited tyrosine pSTAT3 in IgM-stimulated but not unstimulated CLL cells in a dose-dependent manner. This experiment was repeated twice using samples from patients 1 and 6 (supplemental Table 1). As shown in the left lower panel, densitometry analysis of western immunoblots from 4 different patients confirmed that ruxolitinib inhibited tyrosine pSTAT3 in IgM-stimulated but not in unstimulated CLL cells. Samples from patients 13, 14, 15, and 16 (supplemental Table 1) were used. As shown in the right lower panel, ruxolitinib inhibited tyrosine pSTAT3 in a dose-dependent manner. Densitometry analysis of western immunoblots of 6 different experiments was conducted. Depicted are the means ± standard deviation of the relative optical density of tyrosine pSTAT3, quantified and normalized to total levels of STAT3. This experiment was conducted 6 times using samples from patients 1, 2, 6, 7, 10, and 11 (supplemental Table 1). (C) Anti-JAK2 antibody coimmunoprecipitation of pJAK2 and tyrosine pSTAT3 in IgM-stimulated CLL cells. CLL cells from 4 patients were incubated for 2 hours with or without 10 μg/mL anti-IgM antibodies. Cell lysates were prepared, and JAK2 was immunoprecipitated (I.P.) with anti-JAK2 antibodies using protein A-agarose beads. Cells incubated with beads only (B) were used as negative controls. The immune complex was separated using sodium dodecyl sulfate–polyacrylamide gel electrophoresis and analyzed using western immunoblotting with anti-tyrosine pSTAT3, anti-tyrosine JAK2, and anti-JAK2 antibodies. K562 cells were used as positive controls. As shown, JAK2 was immunoprecipitated from lysates of IgM-treated or untreated CLL cells. However, phosphotyrosine STAT3 and pJAK2 were coimmunoprecipitated from IgM-treated but not untreated cells. These experiments were conducted using samples from patients 8, 9, 12, and 13. Representative results are depicted. Data obtained using cells from patients 12 and 13 are not shown (supplemental Table 1). (D) Ruxolitinib induces PARP cleavage in CLL cells. Cells were incubated for 18 hours with or without 10 μg/mL anti-IgM antibodies, and 0.04, 0.20, or 1.00 μM ruxolitinib was added for 30 minutes. The cells were then harvested and analyzed using western immunoblotting with anti-PARP antibodies. This experiment was repeated 6 times using samples from patients 1, 2, 6, 7, 10, and 11 (supplemental Table 1). (E) Ruxolitinib induces apoptosis of CLL cells. As shown in the upper panel, CLL cells were incubated for 18 hours with 10 μg/mL anti-IgM antibodies, and ruxolitinib was added to culture at increasing concentrations for 30 minutes. Apoptosis was assessed using flow cytometry with annexin V/PI staining. As shown, ruxolitinib induced apoptosis of CLL cells in a dose-dependent manner. Cells from patient 11 (supplemental Table 1) were used. As shown in the lower panel, ruxolitinib (but not dasatinib or U0126) induced apoptosis of IgM-stimulated CLL cells in a time-dependent manner. CLL cells were incubated without or with anti-IgM antibodies; ruxolitinib (1.0 μM), dasatinib (1.0 μM), or U0126 (50 μM) was added for 2 hours (right panel) or for different time intervals (1, 2, 3, 6, and 24 hours); and apoptosis was assessed after washout using the annexin V/PI assay, assessed by flow cytometry. As shown, ruxolitinib induced apoptosis of IgM-stimulated cells in a time-dependent manner, whereas dasatinib or U0126 did not affect the apoptosis rate of CLL cells. This experiment was repeated twice using cells from patients 1 and 7 (supplemental Table 1). (F) CLL cells from 3 patients (patients 20, 21, and 22) were incubated for 6 to 72 hours with or without ruxolitinib in the presence or absence of anti-IgM antibodies. Apoptosis rates of ruxolitinib-treated relative to untreated cells are depicted. As shown, ruxolitinib induced apoptosis of IgM-treated but not IgM-untreated CLL cells. *P < .05; **P < .001.

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