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Non-canonical NF-κB activation and abnormal B cell accumulation in mice expressing ubiquitin protein ligase-inactive c-IAP2.

Conze DB, Zhao Y, Ashwell JD - PLoS Biol. (2010)

Bottom Line: The resulting fusion proteins lack the c-IAP2 RING domain, the region responsible for its ubiquitin protein ligase (E3) activity.Canonical but not non-canonical activation depended on MALT1 paracaspase activity, and expression of E3-inactive c-IAP2 activated non-canonical NF-κB.Mice in which endogenous c-IAP2 was replaced with an E3-inactive mutant accumulated abnormal B cells with elevated non-canonical NF-κB and had increased numbers of B cells with a marginal zone phenotype, gut-associated lymphoid hyperplasia, and other features of MALT lymphoma.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Immune Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA.

ABSTRACT
Chromosomal translocations between loci encoding MALT1 and c-IAP2 are common in MALT lymphomas. The resulting fusion proteins lack the c-IAP2 RING domain, the region responsible for its ubiquitin protein ligase (E3) activity. Ectopic expression of the fusion protein activates the canonical NF-κB signaling cascade, but how it does so is controversial and how it promotes MALT lymphoma is unknown. Considering recent reports implicating c-IAP1 and c-IAP2 E3 activity in repression of non-canonical NF-κB signaling, we asked if the c-IAP2/MALT fusion protein can initiate non-canonical NF-κB activation. Here we show that in addition to canonical activation, the fusion protein stabilizes NIK and activates non-canonical NF-κB. Canonical but not non-canonical activation depended on MALT1 paracaspase activity, and expression of E3-inactive c-IAP2 activated non-canonical NF-κB. Mice in which endogenous c-IAP2 was replaced with an E3-inactive mutant accumulated abnormal B cells with elevated non-canonical NF-κB and had increased numbers of B cells with a marginal zone phenotype, gut-associated lymphoid hyperplasia, and other features of MALT lymphoma. Thus, the c-IAP2/MALT1 fusion protein activates NF-κB by two distinct mechanisms, and loss of c-IAP2 E3 activity in vivo is sufficient to induce abnormalities common to MALT lymphoma.

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Serum immunoglobulin levels in c-IAP2H570/H570A mice.Wild type (+/+) and c-IAP2H570A/H570A (mut/mut) mice were 8–10-wk-old, each dot represents the titer for an individual mouse, and the horizontal lines indicate the mean titer for each genotype.
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pbio-1000518-g004: Serum immunoglobulin levels in c-IAP2H570/H570A mice.Wild type (+/+) and c-IAP2H570A/H570A (mut/mut) mice were 8–10-wk-old, each dot represents the titer for an individual mouse, and the horizontal lines indicate the mean titer for each genotype.

Mentions: Homozygous c-IAP2 knockin mice were viable, fertile, and displayed no obvious phenotypic abnormalities. Analysis of peripheral lymphoid organs in 6–7-month-old c-IAP2H570A/H570A mice, however, revealed a number of abnormalities. Unlike the spleen, cell numbers of pooled peripheral lymph nodes (axial, brachial, superficial cervical, and inguinal) as well as mesenteric lymph nodes were markedly increased (Figure 3G, A, and D). There was a reduction in the percentage of T cells with a corresponding increase in the percentage of B (B220+) cells (Figure 3B, E, and H). The result was approximately a 5-fold and 4-fold increase in the absolute number of pooled and mesenteric lymph node B cells, respectively, and a smaller (2-fold) increase in T cell number (Figure 3C and F). The CD4+∶CD8+ T cell ratio in c-IAP2H570A/H570A mice was normal (unpublished data). c-IAP2H570A/H570A lymphocytes had an unactivated phenotype, with normal levels of B7.1 and I-Ab (B cells) and CD25 and CD69 (T cells) (unpublished data). Two- to three-month-old c-IAP2H570A/H570A mice also had increases in lymph node B cells, although to a lesser extent than older animals (Figure S4). Analysis of B and T cell precursors in bone marrow and thymus, respectively, revealed no abnormalities. Among splenic B cells there was reproducibly an approximately 3-fold increase in the percentage of cells with a marginal zone phenotype (CD21hiCD23−), with a compensatory decrease in the percentage of follicular (CD21intCD23hi) and immature (CD21−CD23−) B cells (Figure 3J). Although lymph nodes normally have few B cells with a marginal zone phenotype [52], there was a small increase in these cells in c-IAP2H570A/H570A lymph nodes. Circulating IgA was increased approximately 3-fold in c-IAP2H570A/H570A mice, and there were highly statistically significant increases in IgM and IgG3, and a reduction in IgG1 as well (Figure 4). No statistically significant changes were found in IgG2b and IgE levels.


Non-canonical NF-κB activation and abnormal B cell accumulation in mice expressing ubiquitin protein ligase-inactive c-IAP2.

Conze DB, Zhao Y, Ashwell JD - PLoS Biol. (2010)

Serum immunoglobulin levels in c-IAP2H570/H570A mice.Wild type (+/+) and c-IAP2H570A/H570A (mut/mut) mice were 8–10-wk-old, each dot represents the titer for an individual mouse, and the horizontal lines indicate the mean titer for each genotype.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2964333&req=5

pbio-1000518-g004: Serum immunoglobulin levels in c-IAP2H570/H570A mice.Wild type (+/+) and c-IAP2H570A/H570A (mut/mut) mice were 8–10-wk-old, each dot represents the titer for an individual mouse, and the horizontal lines indicate the mean titer for each genotype.
Mentions: Homozygous c-IAP2 knockin mice were viable, fertile, and displayed no obvious phenotypic abnormalities. Analysis of peripheral lymphoid organs in 6–7-month-old c-IAP2H570A/H570A mice, however, revealed a number of abnormalities. Unlike the spleen, cell numbers of pooled peripheral lymph nodes (axial, brachial, superficial cervical, and inguinal) as well as mesenteric lymph nodes were markedly increased (Figure 3G, A, and D). There was a reduction in the percentage of T cells with a corresponding increase in the percentage of B (B220+) cells (Figure 3B, E, and H). The result was approximately a 5-fold and 4-fold increase in the absolute number of pooled and mesenteric lymph node B cells, respectively, and a smaller (2-fold) increase in T cell number (Figure 3C and F). The CD4+∶CD8+ T cell ratio in c-IAP2H570A/H570A mice was normal (unpublished data). c-IAP2H570A/H570A lymphocytes had an unactivated phenotype, with normal levels of B7.1 and I-Ab (B cells) and CD25 and CD69 (T cells) (unpublished data). Two- to three-month-old c-IAP2H570A/H570A mice also had increases in lymph node B cells, although to a lesser extent than older animals (Figure S4). Analysis of B and T cell precursors in bone marrow and thymus, respectively, revealed no abnormalities. Among splenic B cells there was reproducibly an approximately 3-fold increase in the percentage of cells with a marginal zone phenotype (CD21hiCD23−), with a compensatory decrease in the percentage of follicular (CD21intCD23hi) and immature (CD21−CD23−) B cells (Figure 3J). Although lymph nodes normally have few B cells with a marginal zone phenotype [52], there was a small increase in these cells in c-IAP2H570A/H570A lymph nodes. Circulating IgA was increased approximately 3-fold in c-IAP2H570A/H570A mice, and there were highly statistically significant increases in IgM and IgG3, and a reduction in IgG1 as well (Figure 4). No statistically significant changes were found in IgG2b and IgE levels.

Bottom Line: The resulting fusion proteins lack the c-IAP2 RING domain, the region responsible for its ubiquitin protein ligase (E3) activity.Canonical but not non-canonical activation depended on MALT1 paracaspase activity, and expression of E3-inactive c-IAP2 activated non-canonical NF-κB.Mice in which endogenous c-IAP2 was replaced with an E3-inactive mutant accumulated abnormal B cells with elevated non-canonical NF-κB and had increased numbers of B cells with a marginal zone phenotype, gut-associated lymphoid hyperplasia, and other features of MALT lymphoma.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Immune Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA.

ABSTRACT
Chromosomal translocations between loci encoding MALT1 and c-IAP2 are common in MALT lymphomas. The resulting fusion proteins lack the c-IAP2 RING domain, the region responsible for its ubiquitin protein ligase (E3) activity. Ectopic expression of the fusion protein activates the canonical NF-κB signaling cascade, but how it does so is controversial and how it promotes MALT lymphoma is unknown. Considering recent reports implicating c-IAP1 and c-IAP2 E3 activity in repression of non-canonical NF-κB signaling, we asked if the c-IAP2/MALT fusion protein can initiate non-canonical NF-κB activation. Here we show that in addition to canonical activation, the fusion protein stabilizes NIK and activates non-canonical NF-κB. Canonical but not non-canonical activation depended on MALT1 paracaspase activity, and expression of E3-inactive c-IAP2 activated non-canonical NF-κB. Mice in which endogenous c-IAP2 was replaced with an E3-inactive mutant accumulated abnormal B cells with elevated non-canonical NF-κB and had increased numbers of B cells with a marginal zone phenotype, gut-associated lymphoid hyperplasia, and other features of MALT lymphoma. Thus, the c-IAP2/MALT1 fusion protein activates NF-κB by two distinct mechanisms, and loss of c-IAP2 E3 activity in vivo is sufficient to induce abnormalities common to MALT lymphoma.

Show MeSH
Related in: MedlinePlus