Proceedings of the National Academy of Sciences, 2016
The adaptor protein TNF receptor-associated factor 3 (TRAF3) regulates signaling through B-lympho... more The adaptor protein TNF receptor-associated factor 3 (TRAF3) regulates signaling through B-lymphocyte receptors, including CD40, BAFF receptor, and Toll-like receptors, and also plays a critical role inhibiting B-cell homoeostatic survival. Consistent with these findings, loss-of-function human TRAF3 mutations are common in B-cell cancers, particularly multiple myeloma and B-cell lymphoma. B cells of B-cell-specific TRAF3(-/-) mice (B-Traf3(-/-)) display remarkably enhanced survival compared with littermate control (WT) B cells. The mechanism for this abnormal homeostatic survival is poorly understood, a key knowledge gap in selecting optimal treatments for human B-cell cancers with TRAF3 deficiency. We show here for the first time to our knowledge that TRAF3 is a resident nuclear protein that associates with the transcriptional regulator cAMP response element binding protein (CREB) in both mouse and human B cells. The TRAF-C domain of TRAF3 was necessary and sufficient to localize TRAF3 to the nucleus via a functional nuclear localization signal. CREB protein was elevated in TRAF3(-/-) B cells, without change in mRNA, but with a decrease in CREB ubiquitination. CREB-mediated transcriptional activity was increased in TRAF3-deficient B cells. Consistent with these findings, Mcl-1, an antiapoptotic target of CREB-mediated transcription, was increased in the absence of TRAF3 and enhanced Mcl-1 was suppressed with CREB inhibition. TRAF3-deficient B cells were also preferentially sensitive to survival inhibition with pharmacologic CREB inhibitor. Our results identify a new mechanism by which nuclear TRAF3 regulates B-cell survival via inhibition of CREB stability, information highly relevant to the role of TRAF3 in B-cell malignancies.
The number of Foxp3+ regulatory T cells (Treg cells) must be tightly controlled for efficient sup... more The number of Foxp3+ regulatory T cells (Treg cells) must be tightly controlled for efficient suppression of autoimmunity with no impairment of normal immune responses. Here we found that the adaptor TRAF3 was intrinsically required for restraining the lineage determination of thymic Treg cells. T cell-specific deficiency in TRAF3 resulted in a two- to threefold greater frequency of Treg cells, due to the more efficient transition of precursors of Treg cells into Foxp3+ Treg cells. TRAF3 dampened interleukin 2 (IL-2) signaling by facilitating recruitment of the tyrosine phosphatase TCPTP to the IL-2 receptor complex, which resulted in dephosphorylation of the signaling molecules Jak1 and Jak3 and negative regulation of signaling via Jak and the transcription factor STAT5. Our results identify a role for TRAF3 as an important negative regulator of signaling via the IL-2 receptor that affects the development of Treg cells.
Our laboratory reported previously that TNF receptor associated factor 3 (TRAF3) is a positive re... more Our laboratory reported previously that TNF receptor associated factor 3 (TRAF3) is a positive regulator of TCR signaling and T cell function. In the current study, we present new findings that reveal differential roles for TRAF3 in the regulation of CD4+ and CD8(+) T cells. In response to TCR stimulation in vitro, TRAF3 has greater impact in CD4(+) T cells than in CD8+ T cells. However, T cell-specific TRAF3 deficient mice (CD4Cre TRAF3(fl°x)/(fl°x); T-TRAF3(-/-)) have a greater number of CD4(+)CD44(hi) effector/memory T cells than littermate control (LMC) mice, possibly due to an inefficient suppressive effect of TRAF3 deficient Foxp3+ regulatory T cells. In contrast, CD8(+)CD44(hi)CD62L(hi) central memory (Tcm) cells are markedly reduced in T-TRAF3(-/-) mice in comparison to LMC mice, although CD8(+)CD44(hi)CD62L(l°w) effector memory T (Tem) cells and naïve T cells (CD8(+)CD44(l°w)CD62L(hi)) do not show significant differences in number. Importantly, TRAF3-deficient Tcm cells exh...
TRAF3 is an adapter protein that serves and regulates the functions of several types of receptors... more TRAF3 is an adapter protein that serves and regulates the functions of several types of receptors, located both inside the cell and at the plasma membrane. These include members of the TNF receptor superfamily (TNFR-SF), toll-like receptors (TLR), and cytokine receptors. It has become increasingly evident that the roles and functions of TRAF3 are highly context-dependent. TRAF3 can serve distinct roles for different receptors in the same cell, and also has highly cell-type-dependent functions. This review focuses upon the current state of knowledge regarding how TRAF3 regulates the biology and effector functions of B and T lymphocytes, two major cell types of the adaptive immune response in which TRAF3 has markedly distinct roles.
Tumor necrosis factor receptor-associated factor 3 (TRAF3) is an adaptor protein that inhibits si... more Tumor necrosis factor receptor-associated factor 3 (TRAF3) is an adaptor protein that inhibits signaling by CD40 and by the receptor for B cell-activating factor (BAFF) and negatively regulates homeostatic B cell survival. Loss-of-function mutations in TRAF3 are associated with human B cell malignancies, in particular multiple myeloma. The cytokine interleukin-6 (IL-6) supports the differentiation and survival of normal and neoplastic plasma cells. We found that mice with a deficiency in TRAF3 specifically in B cells (B-Traf3(-/-) mice) had about twice as many plasma cells as did their littermate controls. TRAF3-deficient B cells had enhanced responsiveness to IL-6, and genetic loss of IL-6 in B-Traf3(-/-) mice restored their plasma cell numbers to normal. TRAF3 inhibited IL-6 receptor (IL-6R)-mediated signaling by facilitating the association of PTPN22 (a nonreceptor protein tyrosine phosphatase) with the kinase Janus-activated kinase 1 (Jak1), which in turn blocked phosphorylation...
In the classic 'two-signal' model for B cell activation, signal 1 through the antigen rec... more In the classic 'two-signal' model for B cell activation, signal 1 through the antigen receptor plus signal 2 through lymphokine receptors and CD40 leads to proliferation, but signal 1 alone leads to tolerance or anergy. In a protocol designed to deliver signal 1 in vitro with anti-delta without signal 2, purified small dense B cells from untreated mice exposed to any of three monoclonal anti-delta antibodies or to polyclonal anti-delta in vitro showed modest S phase entry at 50 microg/ml. In contrast, at low doses (0.1-0.5 microg/ml) of anti-delta, there was no cell cycle entry at 64 h, but apoptosis was accelerated at 16 h. Polyclonal anti-mu and three monoclonal anti-mus did not show this early apoptosis induction. Anti-CD40 and IL-4 inhibited apoptosis in B cells treated with 0.5 microg/ml anti-delta and increased S phase entry at 10 microg/ml anti-delta. Low-dose anti-delta (but not anti-mu) induced increased B7-2 and class II MHC expression on a subset of B cells, many ...
Journal of immunology (Baltimore, Md. : 1950), 1990
By cross-linking surface Ig to the Fc gamma R, whole (IgG)-rabbit anti-Ig antibodies have been sh... more By cross-linking surface Ig to the Fc gamma R, whole (IgG)-rabbit anti-Ig antibodies have been shown to substantially inhibit proliferation induced by LPS and F(ab')2 anti-Ig, and polyphosphoinositide hydrolysis induced by F(ab')2 anti-Ig. Surprisingly, however, whole anti-Ig was unable to inhibit induction of transferrin receptor (TfR) expression by LPS or F(ab')2 anti-Ig. Indeed, whole anti-Ig on its own induced TfR as early as 4 h. TfR induction by F(ab')2 anti-Ig and by LPS was accompanied by an early increase in TfR mRNA, and was prevented by inhibitors of protein and RNA synthesis and therefore can be ascribed to a transcriptional mechanism. In contrast, whole anti-Ig induced TfR even in the presence of protein and RNA synthesis inhibitors. Little or no TfR mRNA was detectable after 4 or 16 h of exposure to whole anti-Ig, whereas increased TfR mRNA was evident after 4 h of F(ab')2 anti-Ig or LPS. Antibody to the Fc gamma R (2.4G2) restores the ability of wh...
Tumor necrosis factor receptor-associated factor 3 (TRAF3) is an adaptor protein that directly bi... more Tumor necrosis factor receptor-associated factor 3 (TRAF3) is an adaptor protein that directly binds to a number of receptors of the tumor necrosis factor receptor (TNF-R) superfamily. Despite in vitro evidence that TRAF3 plays diverse roles in different cell types, little is known about the in vivo functions of TRAF3. To address this gap in knowledge and to circumvent the early lethal effect of TRAF3 null mutations, we generated conditional TRAF3-deficient mice. B-cell-specific Traf3(-/-) mice displayed severe peripheral B cell hyperplasia, which culminated in hyperimmunoglobulinemia and increased T-independent antibody responses, splenomegaly and lymphadenopathy. Resting splenic B cells from these mice exhibited remarkably prolonged survival ex vivo independent of B cell activating factor and showed increased amounts of active nuclear factor-kappaB2 but decreased amounts of nuclear protein kinase Cdelta. Furthermore, these mice developed autoimmune manifestations as they aged. The...
Journal of immunology (Baltimore, Md. : 1950), Jan 15, 1993
Small dense splenic B lymphocytes from adult specific pathogen-free mice were shown to undergo ap... more Small dense splenic B lymphocytes from adult specific pathogen-free mice were shown to undergo apoptosis in vitro as indicated by internucleosomal DNA fragmentation, hypodiploid DNA content of isolated nuclei, and morphologic features by electron microscopy. Unstimulated cultures showed spontaneous apoptosis increasing gradually and monotonically from < 2 to 32% of B cells by 16 h. The rate of accumulation of apoptotic cells was reduced by the addition of IL-4 or PMA, but not by the inactive phorbol ester, 4 alpha PDD. In contrast, inhibitors of protein kinase C (H7 and staurosporine) increased the percentage of cells undergoing apoptosis to > 70% by 12 h; HA 1004, genistein, and herbimycin A all had no effect on apoptosis. Thus, protein kinase C activity regulates apoptosis, but there is no evidence that protein kinases A and G and tyrosine kinases are involved. Cycloheximide increased apoptosis, indicating that apoptosis may be restrained in B cells by the presence of one or...
Advances in Experimental Medicine and Biology, 2007
The tumor necrosis factor receptor (TNFR) superfamily molecule CD40 is expressed by a wide variet... more The tumor necrosis factor receptor (TNFR) superfamily molecule CD40 is expressed by a wide variety of cell types following activation signals, and constitutively on B lymphocytes, macrophages, and dendritic cells. CD40 signals to cells stimulate kinase activation, gene expression, production of a antibody and a variety of cytokines, expression or upregulation of surface molecules, and protection or promotion of apoptosis. Initial steps in CD40-mediated signal cascades involve the interactions of CD40 with various members of the TNFR-associated factor (TRAF) family of cytoplasmic proteins. This review summarizes current understanding of the nature of these interactions, and how they induce and regulate CD40 functions.
We found that the mouse B cell lymphoma 38C13 underwent apoptosis in vitro when deprived of iron ... more We found that the mouse B cell lymphoma 38C13 underwent apoptosis in vitro when deprived of iron by three independent methods: (1) exposure to a synergistic pair of rat IgG monoclonal antibodies against the mouse transferrin receptor; (2) exposure to the iron chelator deferoxamine (DFO), and (3) exposure to a defined culture medium without any added iron (iron-poor medium). When each antibody was present at a concentration of 5 micrograms/ml, the number of living cells declined to approximately 25% after a 24-hour incubation. After 48 h, there were no surviving cells. When DFO was present at a concentration of 10 microM, the effects were similar, but delayed by 24 h. when iron-poor medium was used, the effects and kinetics were similar to those seen with antibody treatment. For each method of iron deprivation, the reduction in cell viability correlated with the development of apoptosis, as assessed by DNA fragmentation analysis and propidium iodide staining. Electron microscopy studies provided additional confirmation of apoptotic cell death. The addition of 500 microM ferric citrate completely prevented apoptosis for each of the three methods of iron deprivation. These studies provide new and compelling evidence to support the view that iron deprivation can specifically induce apoptosis and serve to strengthen the rationale for further studies of iron deprivation as a form of cancer treatment.
The proliferative response of primary B cells to CpG oligonucleotides (ODN) involves induction of... more The proliferative response of primary B cells to CpG oligonucleotides (ODN) involves induction of nuclear activation promoting-1 (AP-1) transcription factor. AP-1 subunits c-Fos, Fos-B, Jun-B, and Jun-D, but not Fra-1 or Fra-2, were all induced by CpG ODNs in B cells within 30 minutes of stimulation, followed by c-Jun at 1-2 hours. c-Jun reached maximum at 6 hours. By 40 hours, Jun-B and Jun-D became dominant. Synthetic ODNs containing a single guanosine triplet/tetrad appropriately distanced from the 5&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; pyrimidine-rich unit, which inhibit CpG-driven cell cycle entry and apoptosis protection, blocked AP-1 induction by stimulatory ODNs when they were added simultaneously. After 30 minutes of stimulation, adding inhibitor no longer affected AP-1 at 6 hours. No AP-1 subunits escaped ODN inhibition. In a cell line transfected with an AP-1-beta-galactosidase reporter construct, CpG ODN-induced AP-1 transcriptional activity was prevented by inhibitory ODN, but lipopolysaccharide (LPS)-induced AP-1 activity was not. These data suggest that inhibitory ODNs block the CpG ODN-driven signaling pathway at a site proximal to AP-1 induction.
Epstein-Barr virus (EBV) is associated with aggressive B cell lymphomas (BCLs). Latent membrane p... more Epstein-Barr virus (EBV) is associated with aggressive B cell lymphomas (BCLs). Latent membrane protein 1 (LMP1) of EBV is an oncogenic protein required for EBV B cell transformation. However, LMP1 is a weak oncogene in mice. Mice expressing Myc inserted 5&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; of the Eμ enhancer (iMyc(Eμ)), mimicking the t(8;14) translocation of endemic Burkitt lymphoma, develop delayed onset BCLs. To investigate potential cooperation between LMP1 and oncogenic MYC, we produced mice expressing the LMP1 signaling domain via a hybrid CD40-LMP1 transgene (mCD40-LMP1), and the dysregulated MYC protein of aggressive EBV+ BCLs. mCD40-LMP1/iMyc(Eμ) mice trended toward earlier BCL onset. BCLs from mCD40-LMP1/iMyc(Eμ) mice expressed LMP1 and were transplantable into immunocompetent recipients. iMyc(Eμ) and mCD40-LMP1/iMyc(Eμ) mice developed BCLs with similar immunophenotypes. LMP1 signaling was intact in BCLs as shown by inducible interleukin-6. Additionally, LMP1 signaling to tumor cells induced the two isoforms of Pim1, a constitutively active prosurvival kinase implicated in lymphomagenesis.
Proceedings of the National Academy of Sciences, 2016
The adaptor protein TNF receptor-associated factor 3 (TRAF3) regulates signaling through B-lympho... more The adaptor protein TNF receptor-associated factor 3 (TRAF3) regulates signaling through B-lymphocyte receptors, including CD40, BAFF receptor, and Toll-like receptors, and also plays a critical role inhibiting B-cell homoeostatic survival. Consistent with these findings, loss-of-function human TRAF3 mutations are common in B-cell cancers, particularly multiple myeloma and B-cell lymphoma. B cells of B-cell-specific TRAF3(-/-) mice (B-Traf3(-/-)) display remarkably enhanced survival compared with littermate control (WT) B cells. The mechanism for this abnormal homeostatic survival is poorly understood, a key knowledge gap in selecting optimal treatments for human B-cell cancers with TRAF3 deficiency. We show here for the first time to our knowledge that TRAF3 is a resident nuclear protein that associates with the transcriptional regulator cAMP response element binding protein (CREB) in both mouse and human B cells. The TRAF-C domain of TRAF3 was necessary and sufficient to localize TRAF3 to the nucleus via a functional nuclear localization signal. CREB protein was elevated in TRAF3(-/-) B cells, without change in mRNA, but with a decrease in CREB ubiquitination. CREB-mediated transcriptional activity was increased in TRAF3-deficient B cells. Consistent with these findings, Mcl-1, an antiapoptotic target of CREB-mediated transcription, was increased in the absence of TRAF3 and enhanced Mcl-1 was suppressed with CREB inhibition. TRAF3-deficient B cells were also preferentially sensitive to survival inhibition with pharmacologic CREB inhibitor. Our results identify a new mechanism by which nuclear TRAF3 regulates B-cell survival via inhibition of CREB stability, information highly relevant to the role of TRAF3 in B-cell malignancies.
The number of Foxp3+ regulatory T cells (Treg cells) must be tightly controlled for efficient sup... more The number of Foxp3+ regulatory T cells (Treg cells) must be tightly controlled for efficient suppression of autoimmunity with no impairment of normal immune responses. Here we found that the adaptor TRAF3 was intrinsically required for restraining the lineage determination of thymic Treg cells. T cell-specific deficiency in TRAF3 resulted in a two- to threefold greater frequency of Treg cells, due to the more efficient transition of precursors of Treg cells into Foxp3+ Treg cells. TRAF3 dampened interleukin 2 (IL-2) signaling by facilitating recruitment of the tyrosine phosphatase TCPTP to the IL-2 receptor complex, which resulted in dephosphorylation of the signaling molecules Jak1 and Jak3 and negative regulation of signaling via Jak and the transcription factor STAT5. Our results identify a role for TRAF3 as an important negative regulator of signaling via the IL-2 receptor that affects the development of Treg cells.
Our laboratory reported previously that TNF receptor associated factor 3 (TRAF3) is a positive re... more Our laboratory reported previously that TNF receptor associated factor 3 (TRAF3) is a positive regulator of TCR signaling and T cell function. In the current study, we present new findings that reveal differential roles for TRAF3 in the regulation of CD4+ and CD8(+) T cells. In response to TCR stimulation in vitro, TRAF3 has greater impact in CD4(+) T cells than in CD8+ T cells. However, T cell-specific TRAF3 deficient mice (CD4Cre TRAF3(fl°x)/(fl°x); T-TRAF3(-/-)) have a greater number of CD4(+)CD44(hi) effector/memory T cells than littermate control (LMC) mice, possibly due to an inefficient suppressive effect of TRAF3 deficient Foxp3+ regulatory T cells. In contrast, CD8(+)CD44(hi)CD62L(hi) central memory (Tcm) cells are markedly reduced in T-TRAF3(-/-) mice in comparison to LMC mice, although CD8(+)CD44(hi)CD62L(l°w) effector memory T (Tem) cells and naïve T cells (CD8(+)CD44(l°w)CD62L(hi)) do not show significant differences in number. Importantly, TRAF3-deficient Tcm cells exh...
TRAF3 is an adapter protein that serves and regulates the functions of several types of receptors... more TRAF3 is an adapter protein that serves and regulates the functions of several types of receptors, located both inside the cell and at the plasma membrane. These include members of the TNF receptor superfamily (TNFR-SF), toll-like receptors (TLR), and cytokine receptors. It has become increasingly evident that the roles and functions of TRAF3 are highly context-dependent. TRAF3 can serve distinct roles for different receptors in the same cell, and also has highly cell-type-dependent functions. This review focuses upon the current state of knowledge regarding how TRAF3 regulates the biology and effector functions of B and T lymphocytes, two major cell types of the adaptive immune response in which TRAF3 has markedly distinct roles.
Tumor necrosis factor receptor-associated factor 3 (TRAF3) is an adaptor protein that inhibits si... more Tumor necrosis factor receptor-associated factor 3 (TRAF3) is an adaptor protein that inhibits signaling by CD40 and by the receptor for B cell-activating factor (BAFF) and negatively regulates homeostatic B cell survival. Loss-of-function mutations in TRAF3 are associated with human B cell malignancies, in particular multiple myeloma. The cytokine interleukin-6 (IL-6) supports the differentiation and survival of normal and neoplastic plasma cells. We found that mice with a deficiency in TRAF3 specifically in B cells (B-Traf3(-/-) mice) had about twice as many plasma cells as did their littermate controls. TRAF3-deficient B cells had enhanced responsiveness to IL-6, and genetic loss of IL-6 in B-Traf3(-/-) mice restored their plasma cell numbers to normal. TRAF3 inhibited IL-6 receptor (IL-6R)-mediated signaling by facilitating the association of PTPN22 (a nonreceptor protein tyrosine phosphatase) with the kinase Janus-activated kinase 1 (Jak1), which in turn blocked phosphorylation...
In the classic 'two-signal' model for B cell activation, signal 1 through the antigen rec... more In the classic 'two-signal' model for B cell activation, signal 1 through the antigen receptor plus signal 2 through lymphokine receptors and CD40 leads to proliferation, but signal 1 alone leads to tolerance or anergy. In a protocol designed to deliver signal 1 in vitro with anti-delta without signal 2, purified small dense B cells from untreated mice exposed to any of three monoclonal anti-delta antibodies or to polyclonal anti-delta in vitro showed modest S phase entry at 50 microg/ml. In contrast, at low doses (0.1-0.5 microg/ml) of anti-delta, there was no cell cycle entry at 64 h, but apoptosis was accelerated at 16 h. Polyclonal anti-mu and three monoclonal anti-mus did not show this early apoptosis induction. Anti-CD40 and IL-4 inhibited apoptosis in B cells treated with 0.5 microg/ml anti-delta and increased S phase entry at 10 microg/ml anti-delta. Low-dose anti-delta (but not anti-mu) induced increased B7-2 and class II MHC expression on a subset of B cells, many ...
Journal of immunology (Baltimore, Md. : 1950), 1990
By cross-linking surface Ig to the Fc gamma R, whole (IgG)-rabbit anti-Ig antibodies have been sh... more By cross-linking surface Ig to the Fc gamma R, whole (IgG)-rabbit anti-Ig antibodies have been shown to substantially inhibit proliferation induced by LPS and F(ab')2 anti-Ig, and polyphosphoinositide hydrolysis induced by F(ab')2 anti-Ig. Surprisingly, however, whole anti-Ig was unable to inhibit induction of transferrin receptor (TfR) expression by LPS or F(ab')2 anti-Ig. Indeed, whole anti-Ig on its own induced TfR as early as 4 h. TfR induction by F(ab')2 anti-Ig and by LPS was accompanied by an early increase in TfR mRNA, and was prevented by inhibitors of protein and RNA synthesis and therefore can be ascribed to a transcriptional mechanism. In contrast, whole anti-Ig induced TfR even in the presence of protein and RNA synthesis inhibitors. Little or no TfR mRNA was detectable after 4 or 16 h of exposure to whole anti-Ig, whereas increased TfR mRNA was evident after 4 h of F(ab')2 anti-Ig or LPS. Antibody to the Fc gamma R (2.4G2) restores the ability of wh...
Tumor necrosis factor receptor-associated factor 3 (TRAF3) is an adaptor protein that directly bi... more Tumor necrosis factor receptor-associated factor 3 (TRAF3) is an adaptor protein that directly binds to a number of receptors of the tumor necrosis factor receptor (TNF-R) superfamily. Despite in vitro evidence that TRAF3 plays diverse roles in different cell types, little is known about the in vivo functions of TRAF3. To address this gap in knowledge and to circumvent the early lethal effect of TRAF3 null mutations, we generated conditional TRAF3-deficient mice. B-cell-specific Traf3(-/-) mice displayed severe peripheral B cell hyperplasia, which culminated in hyperimmunoglobulinemia and increased T-independent antibody responses, splenomegaly and lymphadenopathy. Resting splenic B cells from these mice exhibited remarkably prolonged survival ex vivo independent of B cell activating factor and showed increased amounts of active nuclear factor-kappaB2 but decreased amounts of nuclear protein kinase Cdelta. Furthermore, these mice developed autoimmune manifestations as they aged. The...
Journal of immunology (Baltimore, Md. : 1950), Jan 15, 1993
Small dense splenic B lymphocytes from adult specific pathogen-free mice were shown to undergo ap... more Small dense splenic B lymphocytes from adult specific pathogen-free mice were shown to undergo apoptosis in vitro as indicated by internucleosomal DNA fragmentation, hypodiploid DNA content of isolated nuclei, and morphologic features by electron microscopy. Unstimulated cultures showed spontaneous apoptosis increasing gradually and monotonically from < 2 to 32% of B cells by 16 h. The rate of accumulation of apoptotic cells was reduced by the addition of IL-4 or PMA, but not by the inactive phorbol ester, 4 alpha PDD. In contrast, inhibitors of protein kinase C (H7 and staurosporine) increased the percentage of cells undergoing apoptosis to > 70% by 12 h; HA 1004, genistein, and herbimycin A all had no effect on apoptosis. Thus, protein kinase C activity regulates apoptosis, but there is no evidence that protein kinases A and G and tyrosine kinases are involved. Cycloheximide increased apoptosis, indicating that apoptosis may be restrained in B cells by the presence of one or...
Advances in Experimental Medicine and Biology, 2007
The tumor necrosis factor receptor (TNFR) superfamily molecule CD40 is expressed by a wide variet... more The tumor necrosis factor receptor (TNFR) superfamily molecule CD40 is expressed by a wide variety of cell types following activation signals, and constitutively on B lymphocytes, macrophages, and dendritic cells. CD40 signals to cells stimulate kinase activation, gene expression, production of a antibody and a variety of cytokines, expression or upregulation of surface molecules, and protection or promotion of apoptosis. Initial steps in CD40-mediated signal cascades involve the interactions of CD40 with various members of the TNFR-associated factor (TRAF) family of cytoplasmic proteins. This review summarizes current understanding of the nature of these interactions, and how they induce and regulate CD40 functions.
We found that the mouse B cell lymphoma 38C13 underwent apoptosis in vitro when deprived of iron ... more We found that the mouse B cell lymphoma 38C13 underwent apoptosis in vitro when deprived of iron by three independent methods: (1) exposure to a synergistic pair of rat IgG monoclonal antibodies against the mouse transferrin receptor; (2) exposure to the iron chelator deferoxamine (DFO), and (3) exposure to a defined culture medium without any added iron (iron-poor medium). When each antibody was present at a concentration of 5 micrograms/ml, the number of living cells declined to approximately 25% after a 24-hour incubation. After 48 h, there were no surviving cells. When DFO was present at a concentration of 10 microM, the effects were similar, but delayed by 24 h. when iron-poor medium was used, the effects and kinetics were similar to those seen with antibody treatment. For each method of iron deprivation, the reduction in cell viability correlated with the development of apoptosis, as assessed by DNA fragmentation analysis and propidium iodide staining. Electron microscopy studies provided additional confirmation of apoptotic cell death. The addition of 500 microM ferric citrate completely prevented apoptosis for each of the three methods of iron deprivation. These studies provide new and compelling evidence to support the view that iron deprivation can specifically induce apoptosis and serve to strengthen the rationale for further studies of iron deprivation as a form of cancer treatment.
The proliferative response of primary B cells to CpG oligonucleotides (ODN) involves induction of... more The proliferative response of primary B cells to CpG oligonucleotides (ODN) involves induction of nuclear activation promoting-1 (AP-1) transcription factor. AP-1 subunits c-Fos, Fos-B, Jun-B, and Jun-D, but not Fra-1 or Fra-2, were all induced by CpG ODNs in B cells within 30 minutes of stimulation, followed by c-Jun at 1-2 hours. c-Jun reached maximum at 6 hours. By 40 hours, Jun-B and Jun-D became dominant. Synthetic ODNs containing a single guanosine triplet/tetrad appropriately distanced from the 5&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; pyrimidine-rich unit, which inhibit CpG-driven cell cycle entry and apoptosis protection, blocked AP-1 induction by stimulatory ODNs when they were added simultaneously. After 30 minutes of stimulation, adding inhibitor no longer affected AP-1 at 6 hours. No AP-1 subunits escaped ODN inhibition. In a cell line transfected with an AP-1-beta-galactosidase reporter construct, CpG ODN-induced AP-1 transcriptional activity was prevented by inhibitory ODN, but lipopolysaccharide (LPS)-induced AP-1 activity was not. These data suggest that inhibitory ODNs block the CpG ODN-driven signaling pathway at a site proximal to AP-1 induction.
Epstein-Barr virus (EBV) is associated with aggressive B cell lymphomas (BCLs). Latent membrane p... more Epstein-Barr virus (EBV) is associated with aggressive B cell lymphomas (BCLs). Latent membrane protein 1 (LMP1) of EBV is an oncogenic protein required for EBV B cell transformation. However, LMP1 is a weak oncogene in mice. Mice expressing Myc inserted 5&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; of the Eμ enhancer (iMyc(Eμ)), mimicking the t(8;14) translocation of endemic Burkitt lymphoma, develop delayed onset BCLs. To investigate potential cooperation between LMP1 and oncogenic MYC, we produced mice expressing the LMP1 signaling domain via a hybrid CD40-LMP1 transgene (mCD40-LMP1), and the dysregulated MYC protein of aggressive EBV+ BCLs. mCD40-LMP1/iMyc(Eμ) mice trended toward earlier BCL onset. BCLs from mCD40-LMP1/iMyc(Eμ) mice expressed LMP1 and were transplantable into immunocompetent recipients. iMyc(Eμ) and mCD40-LMP1/iMyc(Eμ) mice developed BCLs with similar immunophenotypes. LMP1 signaling was intact in BCLs as shown by inducible interleukin-6. Additionally, LMP1 signaling to tumor cells induced the two isoforms of Pim1, a constitutively active prosurvival kinase implicated in lymphomagenesis.
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