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Brca2 deficiency leads to T cell loss and immune dysfunction.

Jeong JH, Jo A, Park P, Lee H, Lee HO - Mol. Cells (2015)

Bottom Line: In the current study we showed that the number of peripheral T cells, particularly naïve pools, drastically declined with age.This decline was primarily ascribed to improper peripheral maintenance.Our study reveals molecular events occurring in Brca2-deficient T cells and suggests that both heterozygous and homozygous Brca2 mutation may lead to dysfunction in T cell populations.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences and Institute of Molecular Biology and Genetics, Seoul National University, Seoul 151-742, Korea.

ABSTRACT
Germline mutations in the breast cancer type 2 susceptibility gene (BRCA2) are linked to familial breast cancer and the progressive bone marrow failure syndrome Fanconi anaemia. Established Brca2 mouse knockout models show embryonic lethality, but those with a truncating mutation at the C-terminus survive to birth and develop thymic lymphoma at an early age. To overcome early lethality and investigate the function of BRCA2, we used T cell-specific conditional Brca2 knockout mice, which were previously shown to develop thymic lymphoma at a low penetrance. In the current study we showed that the number of peripheral T cells, particularly naïve pools, drastically declined with age. This decline was primarily ascribed to improper peripheral maintenance. Furthermore, heterozygous mice with one wild-type Brca2 allele manifested reduced T cell numbers, suggesting that Brca2 haploinsufficiency might also result in T cell loss. Our study reveals molecular events occurring in Brca2-deficient T cells and suggests that both heterozygous and homozygous Brca2 mutation may lead to dysfunction in T cell populations.

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The p53 pathway is activated in T cells of [Brca2F11/F11; Lck-Cre] mice. Western blot analysis was performed on the thymic (A) and CD4+ splenic T cells as fresh (B) or 48 h after anti-CD3 and anti-CD28 antibody stimulation (C), from the WT and [Brca2F11/F11; Lck-Cre] mice. Actin was used as a loading control. Signals for p53 phosphorylation (mouse pSer18) were detectable only in activated T cells. Western blot data were quantified by densitometry and normalized by Actin signals (bar graphs on the right). On the bar graphs, Y axis is an arbitrary unit and each bar represents average +/− SD from 3 mice. The p values < 0.05 are marked as asterisks.
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f5-molcell-38-3-251: The p53 pathway is activated in T cells of [Brca2F11/F11; Lck-Cre] mice. Western blot analysis was performed on the thymic (A) and CD4+ splenic T cells as fresh (B) or 48 h after anti-CD3 and anti-CD28 antibody stimulation (C), from the WT and [Brca2F11/F11; Lck-Cre] mice. Actin was used as a loading control. Signals for p53 phosphorylation (mouse pSer18) were detectable only in activated T cells. Western blot data were quantified by densitometry and normalized by Actin signals (bar graphs on the right). On the bar graphs, Y axis is an arbitrary unit and each bar represents average +/− SD from 3 mice. The p values < 0.05 are marked as asterisks.

Mentions: Brca2 is an essential regulator of homologous recombination, a vital pathway for error-free repair of DNA double strand breaks (Thorslund and West, 2007). Therefore, in the absence of functional Brca2 proliferating cells accumulate DNA double strand breaks, which activate the p53 checkpoint (Connor et al., 1997; Sharan et al., 1997). The activation of p53 might trigger cell cycle arrest or cell death and could explain the T cell deficit in Brca2-deficient mice. To investigate whether p53 was activated in the Brca2-deficient T cells, we assessed the expression and phosphorylation of p53. In response to DNA damages, p53 is known to undergo extensive post-translational modifications and to become stabilized and activated (Dai and Gu, 2010). Phosphorylation at Ser15 in human p53 has been shown to relieve the inhibition or degradation of p53 by MDM2 (Shieh et al., 1997), whereas the mouse equivalent pSer18 has been implicated in the pro-apoptotic function of p53 (Sluss et al., 2004). As shown in Fig. 5, p53 protein expression was increased to a moderate extent in thymic and splenic T cells of the [Brca2F11/F11; Lck-Cre] mice (Figs. 5A and 5B). Upon T cell activation, up-regulation and phosphorylation (pSer18) of p53 was apparent in the Brca2-deficient T cells (Fig. 5C). We then examined several p53 downstream targets, such as p21 and Puma. The induction of p21 and Puma has been linked to cell cycle arrest and apoptosis respectively (Jung et al., 2010; Yu et al., 2003). Moderate induction of both p21 and Puma was observed in thymic and splenic T cells in the [Brca2F11/F11; Lck-Cre] mice (Figs. 5A and 5B). Upon T cell activation, up-regulation of p21 and Puma was clearly observed in Brca2-deficient T cells (Fig. 5C). Together, these results demonstrate the activation of p53 pathway in Brca2-deficient T cells and suggest that the p53 checkpoint might be responsible for the loss of Brca2-deficient T cells.


Brca2 deficiency leads to T cell loss and immune dysfunction.

Jeong JH, Jo A, Park P, Lee H, Lee HO - Mol. Cells (2015)

The p53 pathway is activated in T cells of [Brca2F11/F11; Lck-Cre] mice. Western blot analysis was performed on the thymic (A) and CD4+ splenic T cells as fresh (B) or 48 h after anti-CD3 and anti-CD28 antibody stimulation (C), from the WT and [Brca2F11/F11; Lck-Cre] mice. Actin was used as a loading control. Signals for p53 phosphorylation (mouse pSer18) were detectable only in activated T cells. Western blot data were quantified by densitometry and normalized by Actin signals (bar graphs on the right). On the bar graphs, Y axis is an arbitrary unit and each bar represents average +/− SD from 3 mice. The p values < 0.05 are marked as asterisks.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4363725&req=5

f5-molcell-38-3-251: The p53 pathway is activated in T cells of [Brca2F11/F11; Lck-Cre] mice. Western blot analysis was performed on the thymic (A) and CD4+ splenic T cells as fresh (B) or 48 h after anti-CD3 and anti-CD28 antibody stimulation (C), from the WT and [Brca2F11/F11; Lck-Cre] mice. Actin was used as a loading control. Signals for p53 phosphorylation (mouse pSer18) were detectable only in activated T cells. Western blot data were quantified by densitometry and normalized by Actin signals (bar graphs on the right). On the bar graphs, Y axis is an arbitrary unit and each bar represents average +/− SD from 3 mice. The p values < 0.05 are marked as asterisks.
Mentions: Brca2 is an essential regulator of homologous recombination, a vital pathway for error-free repair of DNA double strand breaks (Thorslund and West, 2007). Therefore, in the absence of functional Brca2 proliferating cells accumulate DNA double strand breaks, which activate the p53 checkpoint (Connor et al., 1997; Sharan et al., 1997). The activation of p53 might trigger cell cycle arrest or cell death and could explain the T cell deficit in Brca2-deficient mice. To investigate whether p53 was activated in the Brca2-deficient T cells, we assessed the expression and phosphorylation of p53. In response to DNA damages, p53 is known to undergo extensive post-translational modifications and to become stabilized and activated (Dai and Gu, 2010). Phosphorylation at Ser15 in human p53 has been shown to relieve the inhibition or degradation of p53 by MDM2 (Shieh et al., 1997), whereas the mouse equivalent pSer18 has been implicated in the pro-apoptotic function of p53 (Sluss et al., 2004). As shown in Fig. 5, p53 protein expression was increased to a moderate extent in thymic and splenic T cells of the [Brca2F11/F11; Lck-Cre] mice (Figs. 5A and 5B). Upon T cell activation, up-regulation and phosphorylation (pSer18) of p53 was apparent in the Brca2-deficient T cells (Fig. 5C). We then examined several p53 downstream targets, such as p21 and Puma. The induction of p21 and Puma has been linked to cell cycle arrest and apoptosis respectively (Jung et al., 2010; Yu et al., 2003). Moderate induction of both p21 and Puma was observed in thymic and splenic T cells in the [Brca2F11/F11; Lck-Cre] mice (Figs. 5A and 5B). Upon T cell activation, up-regulation of p21 and Puma was clearly observed in Brca2-deficient T cells (Fig. 5C). Together, these results demonstrate the activation of p53 pathway in Brca2-deficient T cells and suggest that the p53 checkpoint might be responsible for the loss of Brca2-deficient T cells.

Bottom Line: In the current study we showed that the number of peripheral T cells, particularly naïve pools, drastically declined with age.This decline was primarily ascribed to improper peripheral maintenance.Our study reveals molecular events occurring in Brca2-deficient T cells and suggests that both heterozygous and homozygous Brca2 mutation may lead to dysfunction in T cell populations.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences and Institute of Molecular Biology and Genetics, Seoul National University, Seoul 151-742, Korea.

ABSTRACT
Germline mutations in the breast cancer type 2 susceptibility gene (BRCA2) are linked to familial breast cancer and the progressive bone marrow failure syndrome Fanconi anaemia. Established Brca2 mouse knockout models show embryonic lethality, but those with a truncating mutation at the C-terminus survive to birth and develop thymic lymphoma at an early age. To overcome early lethality and investigate the function of BRCA2, we used T cell-specific conditional Brca2 knockout mice, which were previously shown to develop thymic lymphoma at a low penetrance. In the current study we showed that the number of peripheral T cells, particularly naïve pools, drastically declined with age. This decline was primarily ascribed to improper peripheral maintenance. Furthermore, heterozygous mice with one wild-type Brca2 allele manifested reduced T cell numbers, suggesting that Brca2 haploinsufficiency might also result in T cell loss. Our study reveals molecular events occurring in Brca2-deficient T cells and suggests that both heterozygous and homozygous Brca2 mutation may lead to dysfunction in T cell populations.

Show MeSH
Related in: MedlinePlus