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NIAM-deficient mice are predisposed to the development of proliferative lesions including B-cell lymphomas.

Reed SM, Hagen J, Muniz VP, Rosean TR, Borcherding N, Sciegienka S, Goeken JA, Naumann PW, Zhang W, Tompkins VS, Janz S, Meyerholz DK, Quelle DE - PLoS ONE (2014)

Bottom Line: It is a novel activator of the ARF-Mdm2-Tip60-p53 tumor suppressor pathway as well as other undefined pathways important for genome maintenance.Unexpectedly, basal p53 expression and activity was largely unaffected by NIAM loss in isolated splenic B cells.In sum, NIAM down-regulation in vivo results in a significant predisposition to developing benign tumors or early stage cancers.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, University of Iowa, Iowa City, Iowa, United States of America; Medical Scientist Training Program, University of Iowa, Iowa City, Iowa, United States of America.

ABSTRACT
Nuclear Interactor of ARF and Mdm2 (NIAM, gene designation Tbrg1) is a largely unstudied inhibitor of cell proliferation that helps maintain chromosomal stability. It is a novel activator of the ARF-Mdm2-Tip60-p53 tumor suppressor pathway as well as other undefined pathways important for genome maintenance. To examine its predicted role as a tumor suppressor, we generated NIAM mutant (NIAM(m/m)) mice homozygous for a β-galactosidase expressing gene-trap cassette in the endogenous gene. The mutant mice expressed significantly lower levels of NIAM protein in tissues compared to wild-type animals. Fifty percent of aged NIAM deficient mice (14 to 21 months) developed proliferative lesions, including a uterine hemangioma, pulmonary papillary adenoma, and a Harderian gland adenoma. No age-matched wild-type or NIAM(+/m) heterozygous animals developed lesions. In the spleen, NIAM(m/m) mice had prominent white pulp expansion which correlated with enhanced increased reactive lymphoid hyperplasia and evidence of systemic inflammation. Notably, 17% of NIAM mutant mice had splenic white pulp features indicating early B-cell lymphoma. This correlated with selective expansion of marginal zone B cells in the spleens of younger, tumor-free NIAM-deficient mice. Unexpectedly, basal p53 expression and activity was largely unaffected by NIAM loss in isolated splenic B cells. In sum, NIAM down-regulation in vivo results in a significant predisposition to developing benign tumors or early stage cancers. These mice represent an outstanding platform for dissecting NIAM's role in tumorigenesis and various anti-cancer pathways, including p53 signaling.

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NIAM is not required for basal p53 activity in splenic B cells.Splenic B cells from young, tumor-free wild-type NIAM+/+ or NIAMm/m homozygous mutant mice were isolated and expression of endogenous NIAM, p53, Mdm2 and p21 proteins was assessed by western blotting. Relative levels of p53, Mdm2 and p21 (normalized to GAPDH loading and compared to the untreated, wild-type control sample) were determined following quantification of bands using Image J. Representative results from 4 of 5 pairs of mice (both 8 week and 6 months of age) are shown in Set A, while Set B shows data for one pair of 6 month old mice. Set A and B samples were analyzed on separate gels, and lanes within each set were spliced together from the same autoradiogram for image clarity.
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pone-0112126-g007: NIAM is not required for basal p53 activity in splenic B cells.Splenic B cells from young, tumor-free wild-type NIAM+/+ or NIAMm/m homozygous mutant mice were isolated and expression of endogenous NIAM, p53, Mdm2 and p21 proteins was assessed by western blotting. Relative levels of p53, Mdm2 and p21 (normalized to GAPDH loading and compared to the untreated, wild-type control sample) were determined following quantification of bands using Image J. Representative results from 4 of 5 pairs of mice (both 8 week and 6 months of age) are shown in Set A, while Set B shows data for one pair of 6 month old mice. Set A and B samples were analyzed on separate gels, and lanes within each set were spliced together from the same autoradiogram for image clarity.

Mentions: Selective expansion of splenic marginal zone B cells also occurs in mice with conditional inactivation of p53 in B cells and it is associated with their development of B-cell lymphomas [25], [26]. Since NIAM is a positive regulator of p53 expression and transcriptional activation [12], and some NIAM mice developed B-cell lymphoma, we wondered if the B cell phenotype in NIAMm/m mice could be associated with reduced p53 signaling. Therefore, we examined p53 status in LPS-stimulated splenic B cells isolated from five wild-type NIAM+/+ and five mutant NIAMm/m mice. Western analyses showed complete NIAM loss in NIAMm/m cells compared to wild-type B cells (Fig. 7). We expected NIAM loss would reduce p53 levels and activity, but surprisingly it had no effect on basal expression of p53 or its targets, Mdm2 and p21, in the B cells of most NIAMm/m mice (4 of 5) relative to NIAM-positive B cells (Fig. 7, set A). These results were seen in B cells isolated from both 8 week and 6 month old mice, suggesting the marginal zone B cell expansion in 6 month old NIAM mutant mice is likely independent of p53. Notably, one NIAM mutant mouse had decreased B cell expression of p53 although this did not correlate with reduced expression of Mdm2 or p21, at least under these stress-free conditions (Fig. 7, set B). These analyses show that NIAM is not required for basal p53 activity in splenic B cells but may, depending on the context, predispose to p53 down-regulation. Additional studies examining p53 stimulation and checkpoint activation following DNA damage or other genotoxic insults in NIAM-deficient B cells are warranted.


NIAM-deficient mice are predisposed to the development of proliferative lesions including B-cell lymphomas.

Reed SM, Hagen J, Muniz VP, Rosean TR, Borcherding N, Sciegienka S, Goeken JA, Naumann PW, Zhang W, Tompkins VS, Janz S, Meyerholz DK, Quelle DE - PLoS ONE (2014)

NIAM is not required for basal p53 activity in splenic B cells.Splenic B cells from young, tumor-free wild-type NIAM+/+ or NIAMm/m homozygous mutant mice were isolated and expression of endogenous NIAM, p53, Mdm2 and p21 proteins was assessed by western blotting. Relative levels of p53, Mdm2 and p21 (normalized to GAPDH loading and compared to the untreated, wild-type control sample) were determined following quantification of bands using Image J. Representative results from 4 of 5 pairs of mice (both 8 week and 6 months of age) are shown in Set A, while Set B shows data for one pair of 6 month old mice. Set A and B samples were analyzed on separate gels, and lanes within each set were spliced together from the same autoradiogram for image clarity.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4231569&req=5

pone-0112126-g007: NIAM is not required for basal p53 activity in splenic B cells.Splenic B cells from young, tumor-free wild-type NIAM+/+ or NIAMm/m homozygous mutant mice were isolated and expression of endogenous NIAM, p53, Mdm2 and p21 proteins was assessed by western blotting. Relative levels of p53, Mdm2 and p21 (normalized to GAPDH loading and compared to the untreated, wild-type control sample) were determined following quantification of bands using Image J. Representative results from 4 of 5 pairs of mice (both 8 week and 6 months of age) are shown in Set A, while Set B shows data for one pair of 6 month old mice. Set A and B samples were analyzed on separate gels, and lanes within each set were spliced together from the same autoradiogram for image clarity.
Mentions: Selective expansion of splenic marginal zone B cells also occurs in mice with conditional inactivation of p53 in B cells and it is associated with their development of B-cell lymphomas [25], [26]. Since NIAM is a positive regulator of p53 expression and transcriptional activation [12], and some NIAM mice developed B-cell lymphoma, we wondered if the B cell phenotype in NIAMm/m mice could be associated with reduced p53 signaling. Therefore, we examined p53 status in LPS-stimulated splenic B cells isolated from five wild-type NIAM+/+ and five mutant NIAMm/m mice. Western analyses showed complete NIAM loss in NIAMm/m cells compared to wild-type B cells (Fig. 7). We expected NIAM loss would reduce p53 levels and activity, but surprisingly it had no effect on basal expression of p53 or its targets, Mdm2 and p21, in the B cells of most NIAMm/m mice (4 of 5) relative to NIAM-positive B cells (Fig. 7, set A). These results were seen in B cells isolated from both 8 week and 6 month old mice, suggesting the marginal zone B cell expansion in 6 month old NIAM mutant mice is likely independent of p53. Notably, one NIAM mutant mouse had decreased B cell expression of p53 although this did not correlate with reduced expression of Mdm2 or p21, at least under these stress-free conditions (Fig. 7, set B). These analyses show that NIAM is not required for basal p53 activity in splenic B cells but may, depending on the context, predispose to p53 down-regulation. Additional studies examining p53 stimulation and checkpoint activation following DNA damage or other genotoxic insults in NIAM-deficient B cells are warranted.

Bottom Line: It is a novel activator of the ARF-Mdm2-Tip60-p53 tumor suppressor pathway as well as other undefined pathways important for genome maintenance.Unexpectedly, basal p53 expression and activity was largely unaffected by NIAM loss in isolated splenic B cells.In sum, NIAM down-regulation in vivo results in a significant predisposition to developing benign tumors or early stage cancers.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, University of Iowa, Iowa City, Iowa, United States of America; Medical Scientist Training Program, University of Iowa, Iowa City, Iowa, United States of America.

ABSTRACT
Nuclear Interactor of ARF and Mdm2 (NIAM, gene designation Tbrg1) is a largely unstudied inhibitor of cell proliferation that helps maintain chromosomal stability. It is a novel activator of the ARF-Mdm2-Tip60-p53 tumor suppressor pathway as well as other undefined pathways important for genome maintenance. To examine its predicted role as a tumor suppressor, we generated NIAM mutant (NIAM(m/m)) mice homozygous for a β-galactosidase expressing gene-trap cassette in the endogenous gene. The mutant mice expressed significantly lower levels of NIAM protein in tissues compared to wild-type animals. Fifty percent of aged NIAM deficient mice (14 to 21 months) developed proliferative lesions, including a uterine hemangioma, pulmonary papillary adenoma, and a Harderian gland adenoma. No age-matched wild-type or NIAM(+/m) heterozygous animals developed lesions. In the spleen, NIAM(m/m) mice had prominent white pulp expansion which correlated with enhanced increased reactive lymphoid hyperplasia and evidence of systemic inflammation. Notably, 17% of NIAM mutant mice had splenic white pulp features indicating early B-cell lymphoma. This correlated with selective expansion of marginal zone B cells in the spleens of younger, tumor-free NIAM-deficient mice. Unexpectedly, basal p53 expression and activity was largely unaffected by NIAM loss in isolated splenic B cells. In sum, NIAM down-regulation in vivo results in a significant predisposition to developing benign tumors or early stage cancers. These mice represent an outstanding platform for dissecting NIAM's role in tumorigenesis and various anti-cancer pathways, including p53 signaling.

Show MeSH
Related in: MedlinePlus