Biomedical subjects

B H Koller

Publications and source records attributed to B H Koller.

At least 37 records · Page 2Linked to original sources

PubMed2000

Disruption of the A(3) adenosine receptor gene in mice and its effect on stimulated inflammatory cells.

The A(3) adenosine receptor (A3AR) is one of four receptor subtypes for adenosine and is expressed in a broad spectrum of tissues. In order to study the function of A3AR, a mouse line carrying a mutant A(3) allele was generated. Mice homozygous for targeted disruption of the A3AR gene, A3AR(-/-), are fertile and visually and histologically indistinguishable from wild type mice. The lack of a functional receptor in the A3AR(-/-) mice was confirmed by molecular and pharmacological analyses. The absence of A3AR protein expression in the A3AR(-/-) mice was demonstrated by lack of N(6)-(4-amino-3-[(125)I]iodobenzyl)adenosine binding to bone marrow-derived mast cell membranes that were found to express high levels of A3AR in wild type mice. In A3AR(-/-) mice, the density of A(1) and A(2A) adenosine receptor subtypes was the same as in A3AR(+/+) mice as determined by radioligand binding to brain membranes. Additionally, A(2B) receptor transcript expression was not affected by ablation of the A3AR gene. A3AR(-/-) mice have basal heart rates and arterial blood pressures indistinguishable from A3AR(+/+) mice. Functionally, in contrast to wild type mice, adenosine and the A3AR-specific agonist, 2-chloro-N(6)-(3-iodobenzyl)-adenosine-5'-N-methyl-carboxamide (2-Cl-IB-MECA), elicit no potentiation of antigen-dependent degranulation of bone marrow-derived mast cells from A3AR(-/-) mice as measured by hexosaminidase release. Also, the ability of 2Cl-IB-MECA to inhibit lipopolysaccharide-induced tumor necrosis factor-alpha production in vivo was decreased in A3AR(-/-) mice in comparison to A3AR(+/+) mice. The A(2A) adenosine receptor agonist, 2-p-(2-carboxyethyl)phenylamino)-5'-N-ethylcarboxamidoadenosine, produced inhibition of lipopolysaccharide-stimulated tumor necrosis factor-alpha production in both A3AR(-/-) and A3AR(+/+) mice. These results show that the inhibition in vivo can be mediated by multiple subtypes, specifically the A(3) and A(2A) adenosine receptors, and A3AR activation plays an important role in both pro- and anti-inflammatory responses.

Adenosine↗

PubMed2000

Intestinal ion transport in NKCC1-deficient mice.

The Na(+)-K(+)-2Cl(-) cotransporter (NKCC1) located on the basolateral membrane of intestinal epithelia has been postulated to be the major basolateral Cl(-) entry pathway. With targeted mutagenesis, mice deficient in the NKCC1 protein were generated. The basal short-circuit current did not differ between normal and NKCC1 -/- jejuna. In the -/- jejuna, the forskolin response (22 microA/cm(2); bumetanide insensitive) was significantly attenuated compared with the bumetanide-sensitive response (52 microA/cm(2)) in normal tissue. Ion-replacement studies demonstrated that the forskolin response in the NKCC1 -/- jejuna was HCO(3)(-) dependent, whereas in the normal jejuna it was independent of the HCO(3)(-) concentration in the buffer. NKCC1 -/- ceca exhibited a forskolin response that did not differ significantly from that of normal ceca, but unlike that of normal ceca, was bumetanide insensitive. Ion-substitution studies suggested that basolateral HCO(3)(-) as well as Cl(-) entry (via non-NKCC1) paths played a role in the NKCC1 -/- secretory response. In contrast to cystic fibrosis mice, which lack both basal and stimulated Cl(-) secretion and exhibit severe intestinal pathology, the absence of intestinal pathology in NKCC1 -/- mice likely reflects the ability of the intestine to secrete HCO(3)(-) and Cl(-) by basolateral entry mechanisms independent of NKCC1.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed2000

Adenosine and inosine increase cutaneous vasopermeability by activating A(3) receptors on mast cells.

Adenosine has potent effects on both the cardiovascular and immune systems. Exposure of tissues to adenosine results in increased vascular permeability and extravasation of serum proteins. The mechanism by which adenosine brings about these physiological changes is poorly defined. Using mice deficient in the A(3) adenosine receptor (A(3)AR), we show that increases in cutaneous vascular permeability observed after treatment with adenosine or its principal metabolite inosine are mediated through the A(3)AR. Adenosine fails to increase vascular permeability in mast cell-deficient mice, suggesting that this tissue response to adenosine is mast cell-dependent. Furthermore, this response is independent of activation of the high-affinity IgE receptor (FcepsilonR1) by antigen, as adenosine is equally effective in mediating these changes in FcepsilonR1 beta-chain-deficient mice. Together these results support a model in which adenosine and inosine induce changes in vascular permeability indirectly by activating mast cells, which in turn release vasoactive substances. The demonstration in vivo that adenosine, acting through a specific receptor, can provoke degranulation of this important tissue-based effector cell, independent of antigen activation of the high-affinity IgE receptor, supports an important role for this nucleoside in modifying the inflammatory response.

Adenosine↗

PubMed2000

Failure of spermatogenesis in mouse lines deficient in the Na(+)-K(+)-2Cl(-) cotransporter.

The Na(+)-K(+)-2Cl(-) cotransporter (NKCC1) carries 1 molecule of Na(+) and K(+) along with 2 molecules of Cl(-) across the cell membrane. It is expressed in a broad spectrum of tissues and has been implicated in cell volume regulation and in ion transport by secretory epithelial tissue. However, the specific contribution of NKCC1 to the physiology of the various organ systems is largely undefined. We have generated mouse lines carrying either of 2 mutant alleles of the Slc12a2 gene, which encodes this cotransporter: a null allele and a mutation that results in deletion of 72 amino acids of the cytoplasmic domain. Both NKCC1-deficient mouse lines show behavioral abnormalities characteristic of mice with inner ear defects. Male NKCC1-deficient mice are infertile because of defective spermatogenesis, as shown by the absence of spermatozoa in histological sections of their epididymides and the small number of spermatids in their testes. Consistent with this observation, we show that Slc12a2 is expressed in Sertoli cells, pachytene spermatocytes, and round spermatids isolated from wild-type animals. Our results indicate a critical role for NKCC1-mediated ion transport in spermatogenesis and suggest that the cytoplasmic domain of NKCC1 is essential in the normal functioning of this protein.

Animals↗

PubMed1999

BRCA1 deficient embryonic stem cells display a decreased homologous recombination frequency and an increased frequency of non-homologous recombination that is corrected by expression of a brca1 transgene.

BRCA1 is a nuclear phosphoprotein that has been classified as a tumor suppressor based on the fact that women carrying a mutated copy of the BRCA1 gene are at increased risk of developing breast and ovarian cancer. The association of BRCA1 with RAD51 has led to the hypothesis that BRCA1 is involved in DNA repair. We describe here the generation and analysis of murine embryonic stem (ES) cell lines in which both copies of the murine homologue of the human BRCA1 gene have been disrupted by gene targeting. We show that exogenous DNA introduced into these BRCA1 deficient cells by electroporation is randomly integrated into the genome at a significantly higher rate than in wild type ES cells. In contrast, integration of exogenous DNA by homologous recombination occurs in BRCA1 deficient cells at a significantly lower rate than in wild type controls. When BRCA1 expression is re-established at 5-10% of normal levels by introduction of a Brca1 transgene into BRCA1 deficient ES cells, the frequency of random integration is reduced to wild type levels, although the frequency of homologous recombination is not significantly improved. These results suggest that BRCA1 plays a role in determining the response of cells to double stranded DNA breaks.

Animals↗

PubMed1999

Determination of the contribution of cysteinyl leukotrienes and leukotriene B4 in acute inflammatory responses using 5-lipoxygenase- and leukotriene A4 hydrolase-deficient mice.

Arachidonic acid metabolism by 5-lipoxygenase leads to production of the potent inflammatory mediators, leukotriene (LT) B4 and the cysteinyl LT. Relative synthesis of these subclasses of LT, each with different proinflammatory properties, depends on the expression and subsequent activity of LTA4 hydrolase and LTC4 synthase, respectively. LTA4 hydrolase differs from other proteins required for LT synthesis because it is expressed ubiquitously. Also, in vitro studies indicate that it possesses an aminopeptidase activity. Introduction of cysteinyl LT and LTB4 into animals has shown LTB4 is a potent chemoattractant, while the cysteinyl LT alter vascular permeability and smooth muscle tone. It has been impossible to determine the relative contributions of these two classes of LT to inflammatory responses in vivo or to define possible synergy resulting from the synthesis of both classes of mediators. To address this question, we have generated LTA4 hydrolase-deficient mice. These mice develop normally and are healthy. Using these animals, we show that LTA4 hydrolase is required for the production of LTB4 in an in vivo inflammatory response. We show that LTB4 is responsible for the characteristic influx of neutrophils accompanying topical arachidonic acid and that it contributes to the vascular changes seen in this model. In contrast, LTB4 influences only the cellular component of zymosan A-induced peritonitis. Furthermore, LTA4 hydrolase-deficient mice are resistant to platelet-activating factor, identifying LTB4 as one mediator of the physiological changes seen in systemic shock. We do not identify an in vivo role for the aminopeptidase activity of LTA4 hydrolase.

Acute Disease↗

PubMed1999

Nucleotide-regulated calcium signaling in lung fibroblasts and epithelial cells from normal and P2Y(2) receptor (-/-) mice.

To test for the role of the P2Y(2) receptor (P2Y(2)-R) in the regulation of nucleotide-promoted Ca(2+) signaling in the lung, we generated P2Y(2)-R-deficient (P2Y(2)-R(-/-)) mice and measured intracellular Ca(2+)(i) responses (DeltaCa(2+)(i)) to nucleotides in cultured lung fibroblasts and nasal and tracheal epithelial cells from wild type and P2Y(2)-R(-/-) mice. In the wild type fibroblasts, the rank order of potencies for nucleotide-induced DeltaCa(2+)(i) was as follows: UTP >/= ATP >> ADP > UDP. The responses induced by these agonists were completely absent in the P2Y(2)-R(-/-) fibroblasts. Inositol phosphate responses paralleled those of DeltaCa(2+)(i) in both groups. ATP and UTP also induced Ca(2+)(i) responses in wild type airway epithelial cells. In the P2Y(2)-R(-/-) airway epithelial cells, UTP was ineffective. A small fraction (25%) of the ATP response persisted. Adenosine and alpha,beta-methylene ATP were ineffective, and ATP responses were not affected by adenosine deaminase or by removal of extracellular Ca(2+), indicating that neither P1 nor P2X receptors mediated this residual ATP response. In contrast, 2-methylthio-ADP promoted a substantial Ca(2+)(i) response in P2Y(2)-R(-/-) cells, which was inhibited by the P2Y(1) receptor antagonist adenosine 3'-5'-diphosphate. These studies demonstrate that P2Y(2)-R is the dominant purinoceptor in airway epithelial cells, which also express a P2Y(1) receptor, and that the P2Y(2)-R is the sole purinergic receptor subtype mediating nucleotide-induced inositol lipid hydrolysis and Ca(2+) mobilization in mouse lung fibroblasts.

Animals↗

PubMed1999

Effect of loss of P2Y(2) receptor gene expression on nucleotide regulation of murine epithelial Cl(-) transport.

Extracellular nucleotides are believed to be important regulators of ion transport in epithelial tissues as a result of their ability to activate cell surface receptors. Although numerous receptors that bind nucleotides have been identified, the complexity of this receptor family, combined with the lack of pharmacological agents specific for these receptors, has made the assignment of particular receptors and ligands to physiological responses difficult. Because ATP and UTP appear equipotent and equieffective in regulating ion transport in many epithelia, we tested the hypothesis that the P2Y(2) receptor (P2Y(2)-R) subtype mediates these responses in mouse epithelia, with gene targeting techniques. Mice with the P2Y(2)-R locus targeted and inactivated (P2Y(2)-R(-/-)) were generated, airways (trachea), gallbladder, and intestines (jejunum) excised, and Cl(-) secretory responses to luminal nucleotide additions measured in Ussing chambers. Comparison of P2Y(2)-R(+/+) with P2Y(2)-R(-/-) mice revealed that P2Y(2)-R mediated most (>85-95%) nucleotide-stimulated Cl(-) secretion in trachea, about 50% of nucleotide responses in the gallbladder, and none of the responses in the jejunum. Dose-effect relationships for nucleotides in tissues from P2Y(2)-R(-/-) mice suggest that the P2Y(6)-R regulates ion transport in gallbladder and to a lesser extent trachea, whereas P2Y(4) and/or unidentified receptor(s) regulate ion transport in jejunum. We conclude that the P2Y(2) receptor is the dominant P2Y purinoceptor that regulates airway epithelial ion transport, whereas other P2Y receptor subtypes are relatively more important in other nonrespiratory epithelia.

Adenosine Triphosphate↗

PubMed1999

Reduced IL-4-, lipopolysaccharide-, and IFN-gamma-induced MHC class II expression in mice lacking class II transactivator due to targeted deletion of the GTP-binding domain.

Class II transactivator (CIITA) is an unusual transcriptional coactivator in that it contains a functionally important, GTP-binding consensus domain. To assess the functional role of the GTP-binding domain of CIITA in vivo, we have generated knockout mice that bear a mutation in the CIITA gene spanning the GTP-binding domain. Upon analysis, these mice show no detectable CIITA mRNA; hence, they represent mice with deleted CIITA rather than mice with defects in the GTP-binding domain only. In these knockout mice, MHC class II expression is nearly eliminated, although a faint RT-PCR signal is visible in spleen, lymph node, and thymus, suggestive of the presence of CIITA-independent regulation of MHC class II expression. Invariant chain expression is also greatly reduced, but to a lesser extent than MHC class II. Serum IgM is not decreased, but the serum IgG level is greatly reduced, further confirming the absence of MHC class II Ag-dependent Ig class switching. Induction of MHC class II expression by IL-4 or LPS was absent on B cells, and Mac-1+ cells showed no detectable induction of MHC class II by either IL-4, LPS, or IFN-gamma. These findings demonstrate a requirement for CIITA in IFN-gamma-, IL-4-, and endotoxin-induced MHC class II expression as well as the possibility of rare CIITA-independent MHC class II expression.

Animals↗

PubMed1999

Mice with reduced NMDA receptor expression display behaviors related to schizophrenia.

N-methyl-D-aspartate receptors (NMDARs) represent a subclass of glutamate receptors that play a critical role in neuronal development and physiology. We report here the generation of mice expressing only 5% of normal levels of the essential NMDAR1 (NR1) subunit. Unlike NR1 null mice, these mice survive to adulthood and display behavioral abnormalities, including increased motor activity and stereotypy and deficits in social and sexual interactions. These behavioral alterations are similar to those observed in pharmacologically induced animal models of schizophrenia and can be ameliorated by treatment with haloperidol or clozapine, antipsychotic drugs that antagonize dopaminergic and serotonergic receptors. These findings support a model in which reduced NMDA receptor activity results in schizophrenic-like behavior and reveals how pharmacological manipulation of monoaminergic pathways can affect this phenotype.

Animals↗

PubMed1999

Deficiency of 5-lipoxygenase abolishes sex-related survival differences in MRL-lpr/lpr mice.

Leukotrienes, the 5-lipoxygenase (5LO) products of arachidonic acid metabolism, have many proinflammatory actions that have been implicated in the pathogenesis of a variety of inflammatory diseases. To investigate the role of LTs in autoimmune disease, we generated an MRL-lpr/lpr mouse line with a targeted disruption of the 5lo gene. MRL-lpr/lpr mice spontaneously develop autoimmune disease that has many features resembling human systemic lupus erythematosus, including sex-related survival differences; female MRL-lpr/lpr mice experience significant early mortality compared with males. Unexpectedly, we found that mortality was accelerated in male 5LO-deficient MRL-lpr/lpr mice compared with male wild-type MRL-lpr/lpr animals. In contrast, the 5lo mutation had no effect on survival in females. Mortality was also accelerated in male MRL-lpr/lpr mice that were treated chronically with a pharmacological inhibitor of LT synthesis. Furthermore, LT-dependent inflammatory responses are enhanced in male MRL-lpr/lpr mice compared with females, and the 5lo mutation has greater impact on these responses in males. Because immune complex-mediated glomerulonephritis is the major cause of death in MRL-lpr/lpr mice and has been related to arachidonic acid metabolites, we also assessed kidney function and histopathology. In male MRL-lpr/lpr mice, renal plasma flow was significantly reduced in the 5lo-/- compared with the 5lo+/+ group, although there were no differences in the severity of renal histopathology, lymphoid hyperplasia, or arthritis between the groups. These findings suggest that the presence of a functional 5lo gene confers a survival advantage on male MRL-lpr/lpr mice and that, when 5LO function is inhibited, either genetically or pharmacologically, this advantage is abolished.

Acute Disease↗

PubMed1999

A novel receptor tyrosine kinase, Mer, inhibits TNF-alpha production and lipopolysaccharide-induced endotoxic shock.

The regulation of monocyte function and the inhibition of TNF-alpha production during bacterial sepsis are critical in attenuating adverse host responses to endotoxemia. To study the function of a novel receptor tyrosine kinase, mer, that is expressed in monocytes, we generated mice (merkd) that lack the signaling tyrosine kinase domain. Upon LPS challenge, merkd animals died of endotoxic shock (15/17, 88.2%), whereas control wild-type mice survived (1/15, 6.7% died). Susceptible merkd mice exhibited edema, leukocyte infiltration, and signs of endotoxic shock that correlated with higher levels of TNF-alpha found in the serum of merkd mice as compared with wild-type control animals. Death due to LPS-induced endotoxic shock in merkd mice was blocked by administration of anti-TNF-alpha Ab, suggesting that overproduction of this cytokine was principally responsible for the heightened suseptibility. The increase in TNF-alpha production appeared to be the result of a substantial increase in the LPS-dependent activation of NF-kappa B nuclear translocation resulting in greater TNF-alpha production by macrophages from merkd mice. Thus, Mer receptor tyrosine kinase signaling participates in a novel inhibitory pathway in macrophages important for regulating TNF-alpha secretion and attenuating endotoxic shock.

Animals↗

PubMed1999

Brca1 controls homology-directed DNA repair.

Germline mutations in BRCA1 confer a high risk of breast and ovarian tumors. The role of BRCA1 in tumor suppression is not yet understood, but both transcription and repair functions have been ascribed. Evidence that BRCA1 is involved in DNA repair stems from its association with RAD51, a homolog of the yeast protein involved in the repair of DNA double-strand breaks (DSBs) by homologous recombination. We report here that Brca1-deficient mouse embryonic stem cells have impaired repair of chromosomal DSBs by homologous recombination. The relative frequencies of homologous and nonhomologous DNA integration and DSB repair were also altered. The results demonstrate a caretaker role for BRCA1 in preserving genomic integrity by promoting homologous recombination and limiting mutagenic nonhomologous repair processes.

Animals↗

PubMed1999

Decreased platelet aggregation, increased bleeding time and resistance to thromboembolism in P2Y1-deficient mice.

Platelet activation is characterized by shape change, induction of fibrinogen receptor expression and release of granular contents, leading to aggregation and plug formation. While this response is essential for hemostasis, it is also important in the pathogenesis of a broad spectrum of diseases, including myocardial infarction, stroke and unstable angina. Adenosine 5'-diphosphate (ADP) induces platelet aggregation, but the mechanism for this has not been established, and the relative contribution of ADP in hemostasis and the development of arterial thrombosis is poorly understood. We show here that the purinoceptor P2Y1 is required for platelet shape change in response to ADP and is also a principal receptor mediating ADP-induced platelet aggregation. Activation of P2Y1 resulted in increased intracellular calcium but no alteration in cyclic adenosine monophosphate (cAMP) levels. P2Y1-deficient platelets partially aggregated at higher ADP concentrations, and the lack of P2Y1 did not alter the ability of ADP to inhibit cAMP, indicating that platelets express at least one additional ADP receptor. In vivo, the lack of P2Y1 expression increased bleeding time and protected from collagen- and ADP-induced thromboembolism. These findings support the hypothesis that the ATP receptor P2Y1 is a principal receptor mediating both physiologic and pathological ADP-induced processes in platelets.

Adenosine Diphosphate↗

PubMed1999

Growth retardation, DNA repair defects, and lack of spermatogenesis in BRCA1-deficient mice.

BRCA1 is a nuclear phosphoprotein expressed in a broad spectrum of tissues during cell division. The inheritance of a mutant BRCA1 allele dramatically increases a woman's lifetime risk for developing both breast and ovarian cancers. A number of mouse lines carrying mutations in the Brca1 gene have been generated, and mice homozygous for these mutations generally die before day 10 of embryonic development. We report here the survival of a small number of mice homozygous for mutations in both the p53 and Brca1 genes. The survival of these mice is likely due to additional unknown mutations or epigenetic effects. Analysis of the Brca1(-/-) p53(-/-) animals indicates that BRCA1 is not required for the development of most organ systems. However, these mice are growth retarded, males are infertile due to meiotic failure, and the mammary gland of the female mouse is underdeveloped. Growth deficiency due to loss of BRCA1 was more thoroughly examined in an analysis of primary fibroblast lines obtained from these animals. Like p53(-/-) fibroblasts, Brca1(-/-) p53(-/-) cells proliferate more rapidly than wild-type cells; however, a high level of cellular death in these cultures results in reduced overall growth rates in comparison to p53(-/-) fibroblasts. Brca1(-/-) p53(-/-) fibroblasts are also defective in transcription-coupled repair and display increased sensitivity to DNA-damaging agents. We show, however, that after continued culture, and perhaps accelerated by the loss of BRCA1 repair functions, populations of Brca1(-/-) p53(-/-) fibroblasts with increased growth rates can be isolated. The increased survival of BRCA1-deficient fibroblasts in the absence of p53, and with the subsequent accumulation of additional growth-promoting changes, may mimic the events that occur during malignant transformation of BRCA1-deficient epithelia.

Animals↗

PubMed1999

Identification of specific EP receptors responsible for the hemodynamic effects of PGE2.

To identify the E-prostanoid (EP) receptors that mediate the hemodynamic actions of PGE2, we studied acute vascular responses to infusions of PGE2 using lines of mice in which each of four EP receptors (EP1 through EP4) have been disrupted by gene targeting. In mixed groups of males and females, vasodepressor responses after infusions of PGE2 were significantly diminished in the EP2 -/- and EP4 -/- lines but not in the EP1 -/- or EP3 -/- lines. Because the actions of other hormonal systems that regulate blood pressure differ between sexes, we compared the roles of individual EP receptors in males and females. We found that the relative contribution of each EP-receptor subclass was strikingly different in males from that in females. In females, the EP2 and EP4 receptors, which signal by stimulating adenylate cyclase, mediate the major portion of the vasodepressor response to PGE2. In males, the EP2 receptor has a modest effect, but most of the vasodepressor effect is mediated by the phospholipase C-coupled EP1 receptor. Finally, in male mice, the EP3 receptor actively opposes the vasodepressor actions of PGE2. Thus the hemodynamic actions of PGE2 are mediated through complex interactions of several EP-receptor subtypes, and the role of individual EP receptors differs dramatically in males from that in females. These differences may contribute to sexual dimorphism of blood pressure regulation.

Animals↗

PubMed1999

Reproductive failure and reduced blood pressure in mice lacking the EP2 prostaglandin E2 receptor.

Prostaglandins (PGs) are bioactive lipids that modulate a broad spectrum of biologic processes including reproduction and circulatory homeostasis. Although reproductive functions of mammals are influenced by PGs at numerous levels, including ovulation, fertilization, implantation, and decidualization, it is not clear which PGs are involved and whether a single mechanism affects all reproductive functions. Using mice deficient in 1 of 4 prostaglandin E2 (PGE2) receptors -- specifically, the EP2 receptor -- we show that Ep2(-/-) females are infertile secondary to failure of the released ovum to become fertilized in vivo. Ep2(-/-) ova could be fertilized in vitro, suggesting that in addition to previously defined roles, PGs may contribute to the microenvironment in which fertilization takes place. In addition to its effects on reproduction, PGE2 regulates regional blood flow in various vascular beds. However, its role in systemic blood pressure homeostasis is not clear. Mice deficient in the EP2 PGE2 receptor displayed resting systolic blood pressure that was significantly lower than in wild-type controls. Blood pressure increased in these animals when they were placed on a high-salt diet, suggesting that the EP2 receptor may be involved in sodium handling by the kidney. These studies demonstrate that PGE2, acting through the EP2 receptor, exerts potent regulatory effects on two major physiologic processes: blood pressure homeostasis and in vivo fertilization of the ovum.

Animals↗

PubMed1999

Mammary tumor formation in p53- and BRCA1-deficient mice.

The inheritance of a mutant copy of the BRCA1 gene greatly increases a woman's lifetime risk for ovarian and breast cancer. While a homologous gene has been identified in mouse, mice carrying mutations in this gene do not display a detectable increase in tumor formation. To determine whether mutations in p53 might increase the incidence of tumors associated with the loss of BRCA1 function in mice, we have generated mice carrying mutations at both of these loci. We report here that the presence of a mutant Brca1 allele does not alter survival of either p53-/- or p53+/- mice. Although the tumor spectrum was not dramatically altered, an increased incidence of mammary tumors was observed in the Brca1+/-p53-/- mice. Four mammary tumors were seen in the Brca1+/-p53-/- group whereas only one such tumor was seen among the p53-/- control group. In addition, although the presence of a mutant Brca1 allele did not alter the survival rate or the incidence of most tumor types in the p53+/- mice, 5 of the 23 tumors isolated from the Brca1+/-p53+/- mice treated with ionizing radiation were of mammary epithelial origin, and 3 of these had lost expression of the wild-type Brca1 gene. In contrast, no such tumors were observed in the irradiated p53+/- controls. Although the number of mammary tumors observed in these animals is small, these results are suggestive of a role for BRCA1 in mammary tumor formation after exposure to specific DNA damaging agents.

Animals↗