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The activation of IgM- or isotype-switched IgG- and IgE-BCR exhibits distinct mechanical force sensitivity and threshold.

Wan Z, Chen X, Chen H, Ji Q, Chen Y, Wang J, Cao Y, Wang F, Lou J, Tang Z, Liu W - Elife (2015)

Bottom Line: We observed that IgM-BCR activation is dependent on mechanical forces and exhibits a multi-threshold effect.Mechanistically, we found that the cytoplasmic tail of the IgG-BCR heavy chain is both required and sufficient to account for the low mechanical force threshold.These results defined the mechanical force sensitivity and threshold that are required to activate different isotyped BCRs.

View Article: PubMed Central - PubMed

Affiliation: MOE Key Laboratory of Protein Sciences, Tsinghua University, Beijing, China.

ABSTRACT
B lymphocytes use B cell receptors (BCRs) to sense the physical features of the antigens. However, the sensitivity and threshold for the activation of BCRs resulting from the stimulation by mechanical forces are unknown. Here, we addressed this question using a double-stranded DNA-based tension gauge tether system serving as a predefined mechanical force gauge ranging from 12 to 56 pN. We observed that IgM-BCR activation is dependent on mechanical forces and exhibits a multi-threshold effect. In contrast, the activation of isotype-switched IgG- or IgE-BCR only requires a low threshold of less than 12 pN, providing an explanation for their rapid activation in response to antigen stimulation. Mechanistically, we found that the cytoplasmic tail of the IgG-BCR heavy chain is both required and sufficient to account for the low mechanical force threshold. These results defined the mechanical force sensitivity and threshold that are required to activate different isotyped BCRs.

No MeSH data available.


Related in: MedlinePlus

The lower mechanical force threshold of IgG-BCR activation is dependent on its cytoplasmic tail.(A) Schematic illustration of the strategy of swapping the cytoplasmic tail of B1-8-IgG- or B1-8-IgM-BCRs. (B–G) Quantification of the synaptic accumulation of BCRs in J558L cells expressing memory B1-8-IgG-BCR (B), J558L cells expressing memory B1-8-IgG-BCR equipped with a mIgM cytoplasmic tail, termed GGM (C), J558L cells expressing naive B1-8-IgM-BCR (E) and J558L cells expressing naive B1-8-IgM-BCR equipped with a mIgG cytoplasmic tail, termed MMG (F). Also given are the synaptic accumulations of pSyk in GGM (D) and MMG cells (G). In all of these plots, bars represent mean ±SEM. Two-tailed t tests were performed for the statistical comparisons. Data were from at least 30 cells in each group of three independent experiments.DOI:http://dx.doi.org/10.7554/eLife.06925.017
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fig7: The lower mechanical force threshold of IgG-BCR activation is dependent on its cytoplasmic tail.(A) Schematic illustration of the strategy of swapping the cytoplasmic tail of B1-8-IgG- or B1-8-IgM-BCRs. (B–G) Quantification of the synaptic accumulation of BCRs in J558L cells expressing memory B1-8-IgG-BCR (B), J558L cells expressing memory B1-8-IgG-BCR equipped with a mIgM cytoplasmic tail, termed GGM (C), J558L cells expressing naive B1-8-IgM-BCR (E) and J558L cells expressing naive B1-8-IgM-BCR equipped with a mIgG cytoplasmic tail, termed MMG (F). Also given are the synaptic accumulations of pSyk in GGM (D) and MMG cells (G). In all of these plots, bars represent mean ±SEM. Two-tailed t tests were performed for the statistical comparisons. Data were from at least 30 cells in each group of three independent experiments.DOI:http://dx.doi.org/10.7554/eLife.06925.017

Mentions: The unexpected extremely low mechanical force threshold (might be less than 12 pN or even lower) for the memory IgG-BCR but not the naive IgM-BCR activation drove us to ask the next question: why does the memory IgG-BCR behave differently from the naive IgM-BCR? This question is especially intriguing as both memory IgG-BCR and naive IgM-BCR use the exact same BCR component, the Igα and Igβ heterodimer, to initiate BCR signaling. In contrast, the mIgG and the mIgM are the BCR components to recognize the antigens (Schamel and Reth, 2000; Tolar et al., 2005). In addition to the constant region of the Ig, mIgG and mIgM also differ greatly in their cytoplasmic domain. In fact, mIgM has only three-amino acids in its cytoplasmic tail (KVK), while all mIgG subtypes have 28-amino acid cytoplasmic tails, which are extremely conserved across species (Reth, 1989; Tarlinton, 1997; Liu et al., 2010a, 2012b). Early mice model studies utilizing biochemical assays and live cell imaging demonstrated that the cytoplasmic tail of mIgG is both necessary and sufficient to confer an enhanced activation of IgG-BCR expressing memory B cells compared to the case of IgM-BCR expressing naive B cells (Kaisho et al., 1997; Martin and Goodnow, 2002; Wakabayashi et al., 2002; Horikawa et al., 2007; Waisman et al., 2007; Engels et al., 2009; Liu et al., 2010b, 2012b; Engels et al., 2014). To examine the contribution of the cytoplasmic tail of mIgG in the low mechanical force threshold for the activation of the memory IgG-BCR, we took advantage of the four types of J558L cells expressing naive B1-8-IgM-BCR and memory B1-8-IgG-BCR with cytoplasmic tail swapped forms as reported in our previous study (Liu et al., 2010b): (1) memory B1-8-IgG-BCR; (2) mIgG swapped with a mIgM cytoplasmic tail (memory B1-8-IgG-BCR equipped with a mIgM cytoplasmic tail, termed GGM thereafter); (3) naive B1-8-IgM-BCR; (4) mIgM swapped with a mIgG cytoplasmic tail (naive B1-8-IgM-BCR equipped with a mIgG cytoplasmic tail, termed MMG thereafter) (Figure 7A). We found that the J558L cells expressing GGM showed the force dependent activation by accumulating more BCRs and pSyk into the IS with the higher mean rupture force NP-TGT molecules, similar to the case of J558L cells expressing naive B1-8-IgM-BCR (Figure 7B–D). In contrast, it was apparent that the J558L cells expressing MMG behaved similarly to the case of J558L cells expressing memory B1-8-IgG-BCR in a force-independent manner (Figure 7E–G). All of these results suggested that the lower mechanical force threshold of memory IgG-BCR activation depends on its cytoplasmic tail.10.7554/eLife.06925.017Figure 7.The lower mechanical force threshold of IgG-BCR activation is dependent on its cytoplasmic tail.


The activation of IgM- or isotype-switched IgG- and IgE-BCR exhibits distinct mechanical force sensitivity and threshold.

Wan Z, Chen X, Chen H, Ji Q, Chen Y, Wang J, Cao Y, Wang F, Lou J, Tang Z, Liu W - Elife (2015)

The lower mechanical force threshold of IgG-BCR activation is dependent on its cytoplasmic tail.(A) Schematic illustration of the strategy of swapping the cytoplasmic tail of B1-8-IgG- or B1-8-IgM-BCRs. (B–G) Quantification of the synaptic accumulation of BCRs in J558L cells expressing memory B1-8-IgG-BCR (B), J558L cells expressing memory B1-8-IgG-BCR equipped with a mIgM cytoplasmic tail, termed GGM (C), J558L cells expressing naive B1-8-IgM-BCR (E) and J558L cells expressing naive B1-8-IgM-BCR equipped with a mIgG cytoplasmic tail, termed MMG (F). Also given are the synaptic accumulations of pSyk in GGM (D) and MMG cells (G). In all of these plots, bars represent mean ±SEM. Two-tailed t tests were performed for the statistical comparisons. Data were from at least 30 cells in each group of three independent experiments.DOI:http://dx.doi.org/10.7554/eLife.06925.017
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Related In: Results  -  Collection

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fig7: The lower mechanical force threshold of IgG-BCR activation is dependent on its cytoplasmic tail.(A) Schematic illustration of the strategy of swapping the cytoplasmic tail of B1-8-IgG- or B1-8-IgM-BCRs. (B–G) Quantification of the synaptic accumulation of BCRs in J558L cells expressing memory B1-8-IgG-BCR (B), J558L cells expressing memory B1-8-IgG-BCR equipped with a mIgM cytoplasmic tail, termed GGM (C), J558L cells expressing naive B1-8-IgM-BCR (E) and J558L cells expressing naive B1-8-IgM-BCR equipped with a mIgG cytoplasmic tail, termed MMG (F). Also given are the synaptic accumulations of pSyk in GGM (D) and MMG cells (G). In all of these plots, bars represent mean ±SEM. Two-tailed t tests were performed for the statistical comparisons. Data were from at least 30 cells in each group of three independent experiments.DOI:http://dx.doi.org/10.7554/eLife.06925.017
Mentions: The unexpected extremely low mechanical force threshold (might be less than 12 pN or even lower) for the memory IgG-BCR but not the naive IgM-BCR activation drove us to ask the next question: why does the memory IgG-BCR behave differently from the naive IgM-BCR? This question is especially intriguing as both memory IgG-BCR and naive IgM-BCR use the exact same BCR component, the Igα and Igβ heterodimer, to initiate BCR signaling. In contrast, the mIgG and the mIgM are the BCR components to recognize the antigens (Schamel and Reth, 2000; Tolar et al., 2005). In addition to the constant region of the Ig, mIgG and mIgM also differ greatly in their cytoplasmic domain. In fact, mIgM has only three-amino acids in its cytoplasmic tail (KVK), while all mIgG subtypes have 28-amino acid cytoplasmic tails, which are extremely conserved across species (Reth, 1989; Tarlinton, 1997; Liu et al., 2010a, 2012b). Early mice model studies utilizing biochemical assays and live cell imaging demonstrated that the cytoplasmic tail of mIgG is both necessary and sufficient to confer an enhanced activation of IgG-BCR expressing memory B cells compared to the case of IgM-BCR expressing naive B cells (Kaisho et al., 1997; Martin and Goodnow, 2002; Wakabayashi et al., 2002; Horikawa et al., 2007; Waisman et al., 2007; Engels et al., 2009; Liu et al., 2010b, 2012b; Engels et al., 2014). To examine the contribution of the cytoplasmic tail of mIgG in the low mechanical force threshold for the activation of the memory IgG-BCR, we took advantage of the four types of J558L cells expressing naive B1-8-IgM-BCR and memory B1-8-IgG-BCR with cytoplasmic tail swapped forms as reported in our previous study (Liu et al., 2010b): (1) memory B1-8-IgG-BCR; (2) mIgG swapped with a mIgM cytoplasmic tail (memory B1-8-IgG-BCR equipped with a mIgM cytoplasmic tail, termed GGM thereafter); (3) naive B1-8-IgM-BCR; (4) mIgM swapped with a mIgG cytoplasmic tail (naive B1-8-IgM-BCR equipped with a mIgG cytoplasmic tail, termed MMG thereafter) (Figure 7A). We found that the J558L cells expressing GGM showed the force dependent activation by accumulating more BCRs and pSyk into the IS with the higher mean rupture force NP-TGT molecules, similar to the case of J558L cells expressing naive B1-8-IgM-BCR (Figure 7B–D). In contrast, it was apparent that the J558L cells expressing MMG behaved similarly to the case of J558L cells expressing memory B1-8-IgG-BCR in a force-independent manner (Figure 7E–G). All of these results suggested that the lower mechanical force threshold of memory IgG-BCR activation depends on its cytoplasmic tail.10.7554/eLife.06925.017Figure 7.The lower mechanical force threshold of IgG-BCR activation is dependent on its cytoplasmic tail.

Bottom Line: We observed that IgM-BCR activation is dependent on mechanical forces and exhibits a multi-threshold effect.Mechanistically, we found that the cytoplasmic tail of the IgG-BCR heavy chain is both required and sufficient to account for the low mechanical force threshold.These results defined the mechanical force sensitivity and threshold that are required to activate different isotyped BCRs.

View Article: PubMed Central - PubMed

Affiliation: MOE Key Laboratory of Protein Sciences, Tsinghua University, Beijing, China.

ABSTRACT
B lymphocytes use B cell receptors (BCRs) to sense the physical features of the antigens. However, the sensitivity and threshold for the activation of BCRs resulting from the stimulation by mechanical forces are unknown. Here, we addressed this question using a double-stranded DNA-based tension gauge tether system serving as a predefined mechanical force gauge ranging from 12 to 56 pN. We observed that IgM-BCR activation is dependent on mechanical forces and exhibits a multi-threshold effect. In contrast, the activation of isotype-switched IgG- or IgE-BCR only requires a low threshold of less than 12 pN, providing an explanation for their rapid activation in response to antigen stimulation. Mechanistically, we found that the cytoplasmic tail of the IgG-BCR heavy chain is both required and sufficient to account for the low mechanical force threshold. These results defined the mechanical force sensitivity and threshold that are required to activate different isotyped BCRs.

No MeSH data available.


Related in: MedlinePlus