An African-specific polymorphism in the TP53 gene impairs p53 tumor suppressor function in a mouse model.

A nonsynonymous single-nucleotide polymorphism at codon 47 in TP53 exists in African-descent populations (P47S, rs1800371; referred to here as S47). Here we report that, in human cell lines and a mouse model, the S47 variant exhibits a modest decrease in apoptosis in response to most genotoxic stresses compared with wild-type p53 but exhibits a significant defect in cell death induced by cisplatin. We show that, compared with wild-type p53, S47 has nearly indistinguishable transcriptional function but shows impaired ability to transactivate a subset of p53 target genes, including two involved in metabolism:Gls2(glutaminase 2) and Sco2 We also show that human and mouse cells expressing the S47 variant are markedly resistant to cell death by agents that induce ferroptosis (iron-mediated nonapoptotic cell death). We show that mice expressing S47 in homozygous or heterozygous form are susceptible to spontaneous cancers of diverse histological types. Our data suggest that the S47 variant may contribute to increased cancer risk in individuals of African descent, and our findings highlight the need to assess the contribution of this variant to cancer risk in these populations. These data also confirm the potential relevance of metabolism and ferroptosis to tumor suppression by p53.

The role of JNK in the development of hepatocellular carcinoma.

The cJun NH(2)-terminal kinase (JNK) signal transduction pathway has been implicated in the growth of carcinogen-induced hepatocellular carcinoma. However, the mechanism that accounts for JNK-regulated tumor growth is unclear. Here we demonstrate that compound deficiency of the two ubiquitously expressed JNK isoforms (JNK1 and JNK2) in hepatocytes does not prevent hepatocellular carcinoma development. Indeed, JNK deficiency in hepatocytes increased the tumor burden. In contrast, compound JNK deficiency in hepatocytes and nonparenchymal cells reduced both hepatic inflammation and tumorigenesis. These data indicate that JNK plays a dual role in the development of hepatocellular carcinoma. JNK promotes an inflammatory hepatic environment that supports tumor development, but also functions in hepatocytes to reduce tumor development.

Transgenic Expression of the Mitochondrial Chaperone TNFR-associated Protein 1 (TRAP1) Accelerates Prostate Cancer Development.

Protein homeostasis, or proteostasis, is required for mitochondrial function, but its role in cancer is controversial. Here we show that transgenic mice expressing the mitochondrial chaperone TNFR-associated protein 1 (TRAP1) in the prostate develop epithelial hyperplasia and cellular atypia. When examined on a Pten+/- background, a common alteration in human prostate cancer, TRAP1 transgenic mice showed accelerated incidence of invasive prostatic adenocarcinoma, characterized by increased cell proliferation and reduced apoptosis, in situ Conversely, homozygous deletion of TRAP1 delays prostatic tumorigenesis in Pten+/- mice without affecting hyperplasia or prostatic intraepithelial neoplasia. Global profiling of Pten+/--TRAP1 transgenic mice by RNA sequencing and reverse phase protein array reveals modulation of oncogenic networks of cell proliferation, apoptosis, cell motility, and DNA damage. Mechanistically, reconstitution of Pten+/- prostatic epithelial cells with TRAP1 increases cell proliferation, reduces apoptosis, and promotes cell invasion without changes in mitochondrial bioenergetics. Therefore, TRAP1 is a driver of prostate cancer in vivo and an "actionable" therapeutic target.

The degree of CD4+ T cell autoreactivity determines cellular pathways underlying inflammatory arthritis.

Although therapies targeting distinct cellular pathways (e.g., anticytokine versus anti-B cell therapy) have been found to be an effective strategy for at least some patients with inflammatory arthritis, the mechanisms that determine which pathways promote arthritis development are poorly understood. We have used a transgenic mouse model to examine how variations in the CD4(+) T cell response to a surrogate self-peptide can affect the cellular pathways that are required for arthritis development. CD4(+) T cells that are highly reactive with the self-peptide induce inflammatory arthritis that affects male and female mice equally. Arthritis develops by a B cell-independent mechanism, although it can be suppressed by an anti-TNF treatment, which prevented the accumulation of effector CD4(+) Th17 cells in the joints of treated mice. By contrast, arthritis develops with a significant female bias in the context of a more weakly autoreactive CD4(+) T cell response, and B cells play a prominent role in disease pathogenesis. In this setting of lower CD4(+) T cell autoreactivity, B cells promote the formation of autoreactive CD4(+) effector T cells (including Th17 cells), and IL-17 is required for arthritis development. These studies show that the degree of CD4(+) T cell reactivity for a self-peptide can play a prominent role in determining whether distinct cellular pathways can be targeted to prevent the development of inflammatory arthritis.

Viral antigen induces differentiation of Foxp3+ natural regulatory T cells in influenza virus-infected mice.

We examined the formation, participation, and functional specialization of virus-reactive Foxp3(+) regulatory T cells (Tregs) in a mouse model of influenza virus infection. "Natural" Tregs generated intrathymically, based on interactions with a self-peptide, proliferated in response to a homologous viral Ag in the lungs and, to a lesser extent, in the lung-draining mediastinal lymph nodes (medLNs) of virus-infected mice. In contrast, conventional CD4(+) T cells with identical TCR specificity underwent little or no conversion to become "adaptive" Tregs. The virus-reactive Tregs in the medLNs and the lungs of infected mice upregulated a variety of molecules associated with Treg activation, as well as acquired expression of molecules (T-bet, Blimp-1, and IL-10) that confer functional specialization to Tregs. Notably, however, the phenotypes of the T-bet(+) Tregs obtained from these sites were distinct, because Tregs isolated from the lungs expressed significantly higher levels of T-bet, Blimp-1, and IL-10 than did Tregs from the medLNs. Adoptive transfer of Ag-reactive Tregs led to decreased proliferation of antiviral CD4(+) and CD8(+) effector T cells in the lungs of infected hosts, whereas depletion of Tregs had a reciprocal effect. These studies demonstrate that thymically generated Tregs can become activated by a pathogen-derived peptide and acquire discrete T-bet(+) Treg phenotypes while participating in and modulating an antiviral immune response.

Performance, safety, and biocompatibility of a novel PFO closure device in a long-term porcine model.

BACKGROUND: As the catheter-based device closure of the patent foramen ovale (PFO) is expanding, novel devices aim to address the limitations of first-generation occluders (e.g. bulk, erosion, dislodgment). The second-generation device from Encore Medical (Eagan, MN, USA) features an articulating frame structure which allows the device to better conform to atrial anatomies, has lower disc thickness and metal mass/surface area, and is fully retrievable at any point in the procedure. The aim of the study was to evaluate the feasibility and safety of a novel low-profile, fully retrievable, Encore PFO closure device in the animal model. METHODS: Six swine underwent implantation of the novel PFO occluder under fluoroscopic and intra-cardiac echocardiography guidance and survived for 140 days. Interim transthoracic echocardiography (TTE) was conducted on Day 29. Following terminal angiography and TTE at 140 days, the hearts were subjected to gross and histopathologic analysis. RESULTS: All animals were successfully implanted and survived for 140 days. Interim TTE revealed proper device retention with no blood flow across the septum or thrombus in any of the animals. X-ray and pathology results showed preserved implant integrity with no fractures, and complete integration of the devices into the septum with complete re-endothelialization and nearly complete coverage by a mature, relatively thin neoendocardium. No surface fibrin deposition or thrombosis was reported. CONCLUSIONS: In the standard porcine model, device retention and biocompatibility remained favorable following structural and functional device modifications exemplified by the second-generation PFO occluder from Encore Medical, including marked reduction of metal mass.

ß1 integrins mediate resistance to ionizing radiation in vivo by inhibiting c-Jun amino terminal kinase 1.

This study was carried out to dissect the mechanism by which ß1 integrins promote resistance to radiation. For this purpose, we conditionally ablated ß1 integrins in the prostatic epithelium of transgenic adenocarcinoma of mouse prostate (TRAMP) mice. The ability of ß1 to promote resistance to radiation was also analyzed by using an inhibitory antibody to ß1 , AIIB2, in a xenograft model. The role of ß1 integrins and of a ß1 downstream target, c-Jun amino-terminal kinase 1 (JNK1), in regulating radiation-induced apoptosis in vivo and in vitro was studied. We show that ß1 integrins promote prostate cancer (PrCa) progression and resistance to radiation in vivo. Mechanistically, ß1 integrins are shown here to suppress activation of JNK1 and, consequently apoptosis, in response to irradiation. Downregulation of JNK1 is necessary to preserve the effect of ß1 on resistance to radiation in vitro and in vivo. Finally, given the established crosstalk between ß1 integrins and type1 insulin-like growth factor receptor (IGF-IR), we analyzed the ability of IGF-IR to modulate ß1 integrin levels. We report that IGF-IR regulates the expression of ß1 integrins, which in turn confer resistance to radiation in PrCa cells. In conclusion, this study demonstrates that ß1 integrins mediate resistance to ionizing radiation through inhibition of JNK1 activation.

Mitochondrial fission factor is a novel Myc-dependent regulator of mitochondrial permeability in cancer.

BACKGROUND: Mitochondrial functions are exploited in cancer and provide a validated therapeutic target. However, how this process is regulated has remained mostly elusive and the identification of new pathways that control mitochondrial integrity in cancer is an urgent priority. METHODS: We studied clinically-annotated patient series of primary and metastatic prostate cancer, representative cases of multiple myeloma (MM) and publicly available genetic databases. Gene regulation studies involved chromatin immunoprecipitation, PCR amplification and Western blotting of conditional Myc-expressing cell lines. Transient or stable gene silencing was used to quantify mitochondrial functions in bioenergetics, outer membrane permeability, Ca2+ homeostasis, redox balance and cell death. Tumorigenicity was assessed by cell proliferation, colony formation and xenograft tumour growth. FINDINGS: We identified Mitochondrial Fission Factor (MFF) as a novel transcriptional target of oncogenic Myc overexpressed in primary and metastatic cancer, compared to normal tissues. Biochemically, MFF isoforms, MFF1 and MFF2 associate with the Voltage-Dependent Anion Channel-1 (VDAC1) at the mitochondrial outer membrane, in vivo. Disruption of this complex by MFF silencing induces general collapse of mitochondrial functions with increased outer membrane permeability, loss of inner membrane potential, Ca2+ unbalance, bioenergetics defects and activation of cell death pathways. In turn, this inhibits tumour cell proliferation, suppresses colony formation and reduces xenograft tumour growth in mice. INTERPRETATION: An MFF-VDAC1 complex is a novel regulator of mitochondrial integrity and actionable therapeutic target in cancer.

A mutation in the mouse Chd2 chromatin remodeling enzyme results in a complex renal phenotype.

BACKGROUND AND AIMS: Glomerular diseases are the third leading cause of kidney failure worldwide, behind only diabetes and hypertension. The molecular mechanisms underlying the cause of glomerular diseases are still largely unknown. The identification and characterization of new molecules associated with glomerular function should provide new insights into understanding the diverse group of glomerular diseases. The Chd2 protein belongs to a family of enzymes involved in ATP-dependent chromatin remodeling, suggesting that it likely functions as an epigenetic regulator of gene expression via the modification of chromatin structure. METHODS: In this study, we present a detailed histomorphologic characterization of mice containing a mutation in the chromodomain helicase DNA-binding protein 2 (Chd2). RESULTS: We show that Chd2-mutant mice present with glomerulopathy, proteinuria, and significantly impaired kidney function. Additionally, serum analysis revealed decreased hemoglobin and hematocrit levels in Chd2-mutant mice, suggesting that the glomerulopathy observed in these mice is associated with anemia. CONCLUSION: Collectively, the data suggest a role for the Chd2 protein in the maintenance of kidney function.

The cJUN NH2-terminal kinase (JNK) signaling pathway promotes genome stability and prevents tumor initiation.

Breast cancer is the most commonly diagnosed malignancy in women. Analysis of breast cancer genomic DNA indicates frequent loss-of-function mutations in components of the cJUN NH2-terminal kinase (JNK) signaling pathway. Since JNK signaling can promote cell proliferation by activating the AP1 transcription factor, this apparent association of reduced JNK signaling with tumor development was unexpected. We examined the effect of JNK deficiency in the murine breast epithelium. Loss of JNK signaling caused genomic instability and the development of breast cancer. Moreover, JNK deficiency caused widespread early neoplasia and rapid tumor formation in a murine model of breast cancer. This tumor suppressive function was not mediated by a role of JNK in the growth of established tumors, but by a requirement of JNK to prevent tumor initiation. Together, these data identify JNK pathway defects as 'driver' mutations that promote genome instability and tumor initiation.

Evaluation of bone regeneration at critical-sized calvarial defect by DBM/AM composite.

This study investigated the bone-regenerative potential of a demineralized bone and acellular matrix (DBM/AM) composite (AlloCraft DBM) in comparison with autologous bone using an in vivo model. Critical-sized calvarial defects (5 mm) were created in athymic rats. The defects were grafted with either the DBM/AM composite or the acellular human dermal matrix (AM), and compared with the defects filled with autologous bone (positive control) and the empty defect (negative control). Histological and radiographic assessments were carried out at 4 and 8 weeks after surgery to determine the biological healing, the amount and type of new bone formation and the percentage of new bone filled in the critical defects. At 4 weeks, DBM/AM composite group had the highest percentage of the defect filled with new bone (84%), which was significantly greater than autologous bone (62%), AM (41%), and untreated control (32%) groups. At 8 weeks, the DBM/AM continued to have the highest percentage of the defect filled with new bone (91%). The autologous bone group increased the percentage of bone fill to 83%. The defects either filled with AM or left untreated still had less of the defect filled with new bone, 57% and 33%, respectively. The total healing of defects grafted with DBM/AM was comparable with autologous bone group at 8 weeks. The results demonstrated that the DBM/AM composite promoted new bone formation more rapidly than autologous bone at calvarial defect in athymic rats. The study supports that DBM/AM is a potential substitute of autologous bone for bone repair.

A survivin gene signature predicts aggressive tumor behavior.

Gene signatures that predict aggressive tumor behavior at the earliest stages of disease, ideally before overt tissue abnormalities, are urgently needed. To search for such genes, we generated a transgenic model of survivin, an essential regulator of cell division and apoptosis overexpressed in cancer. Transgenic expression of survivin in the urinary bladder did not cause histologic abnormalities of the urothelium. However, microarray analysis revealed that survivin-expressing bladders exhibited profound changes in gene expression profile affecting extracellular matrix and inflammatory genes. Following exposure to a bladder carcinogen, N-butyl-N-(4-hydroxybutyl) nitrosamine (OH-BBN), survivin transgenic animals exhibited accelerated tumor progression, preferential incidence of tumors as compared with premalignant lesions, and dramatically abbreviated survival. Conversely, transgenic expression of a survivin Thr34-->Ala dominant-negative mutant did not cause changes in gene expression or accelerated tumor progression after OH-BBN treatment. Therefore, survivin expression induces global transcriptional changes in the tissue microenvironment that may promote tumorigenesis. Detection of survivin or its associated gene signature may provide an early biomarker of aggressive tumor behavior before the appearance of tissue abnormalities.

Amyloidosis in a Captive Zebra Finch (Taeniopygia guttata) Research Colony.

Five birds in a captive zebra finch research colony were diagnosed with systemic amyloidosis within a 7-mo period by means of postmortem Congo red staining and green birefringence under polarized light. The liver was the most frequently and usually the most seriously affected organ, followed by the spleen and then the kidney. All 5 birds had been clinically affected with various inflammatory, infectious, and neoplastic conditions associated with amyloid A (AA) amyloidosis in humans and animals. Immunohistochemistry using antisera against duck AA protein revealed that tissues from 2 of the 5 birds were positive for the presence of AA protein and systemic inflammation-associated amyloidosis. Although the development of AA amyloidosis has been associated with chronic inflammation, trauma, and various infectious and neoplastic diseases as well as possible genetic predispositions and stresses linked to overcrowding, the root causes for individual cases of AA amyloidosis are incompletely understood. As far as we know, this report is the first description of AA amyloidosis in captive, research zebra finches.

Evaluating adhesion reduction efficacy of type I/III collagen membrane and collagen-GAG resorbable matrix in primary flexor tendon repair in a chicken model.

BACKGROUND: Reduction of peritendinous adhesions after injury and repair has been the subject of extensive prior investigation. The application of a circumferential barrier at the repair site may limit the quantity of peritendinous adhesions while preserving the tendon's innate ability to heal. The authors compare the effectiveness of a type I/III collagen membrane and a collagen-glycosaminoglycan (GAG) resorbable matrix in reducing tendon adhesions in an experimental chicken model of a "zone II" tendon laceration and repair. METHODS: In Leghorn chickens, flexor tendons were sharply divided using a scalpel and underwent repair in a standard fashion (54 total repairs). The sites were treated with a type I/III collagen membrane, collagen-GAG resorbable matrix, or saline in a randomized fashion. After 3 weeks, qualitative and semiquantitative histological analysis was performed to evaluate the "extent of peritendinous adhesions" and "nature of tendon healing." The data was evaluated with chi-square analysis and unpaired Student's t test. RESULTS: For both collagen materials, there was a statistically significant improvement in the degree of both extent of peritendinous adhesions and nature of tendon healing relative to the control group. There was no significant difference seen between the two materials. There was one tendon rupture observed in each treatment group. Surgical handling characteristics were subjectively favored for type I/III collagen membrane over the collagen-GAG resorbable matrix. CONCLUSION: The ideal method of reducing clinically significant tendon adhesions after injury remains elusive. Both materials in this study demonstrate promise in reducing tendon adhesions after flexor tendon repair without impeding tendon healing in this model.

Regulation of lung cancer metastasis by Klf4-Numb-like signaling.

Metastatic traits seem to be acquired by transformed cells with progenitor-like cancer-initiating properties, but there remains little mechanistic insight into this linkage. In this report, we show that the polarity protein Numbl, which is expressed normally in neuronal progenitors, becomes overexpressed and mislocalized in cancer cells from a variety of human tumors. Numbl overexpression relies on loss of the tumor suppressor miRNA-296-5p (miR-296), which actively represses translation of Numbl in normal cells. In turn, deregulated expression of Numbl mediates random tumor cell migration and invasion, blocking anoikis and promoting metastatic dissemination. In clinical specimens of non-small cell lung cancer, we found that Numbl overexpression correlated with a reduction in overall patient survival. Mechanistically, Numbl-mediated tumorigenesis involved suppression of a "stemness" transcriptional program driven by the stem cell programming transcription factor Klf4, thereby preserving a pool of progenitor-like cells in lung cancer. Our results reveal that Numbl-Klf4 signaling is critical to maintain multiple nodes of metastatic progression, including persistence of cancer-initiating cells, rationalizing its therapeutic exploitation to improve the treatment of advanced lung cancer.

A therapeutic dose of ketoprofen causes acute gastrointestinal bleeding, erosions, and ulcers in rats.

Perioperative treatment of several rats in our facility with ketoprofen (5 mg/kg SC) resulted in blood loss, peritonitis, and death within a day to a little more than a week after surgery that was not related to the gastrointestinal tract. Published reports have established the 5-mg/kg dose as safe and effective for rats. Because ketoprofen is a nonselective nonsteroidal antiinflammatory drug that can damage the gastrointestinal tract, the putative diagnosis for these morbidities and mortalities was gastrointestinal toxicity caused by ketoprofen (5 mg/kg). We conducted a prospective study evaluating the effect of this therapeutic dose of ketoprofen on the rat gastrointestinal tract within 24 h. Ketoprofen (5 mg/kg SC) was administered to one group of rats that then received gas anesthesia for 30 min and to another group without subsequent anesthesia. A third group was injected with saline followed by 30 min of gas anesthesia. Our primary hypothesis was that noteworthy gastrointestinal bleeding and lesions would occur in both groups treated with ketoprofen but not in rats that received saline and anesthesia. Our results showed marked gastrointestinal bleeding, erosions, and small intestinal ulcers in the ketoprofen-treated rats and minimal damages in the saline-treated group. The combination of ketoprofen and anesthesia resulted in worse clinical signs than did ketoprofen alone. We conclude that a single 5-mg/kg dose of ketoprofen causes acute mucosal damage to the rat small intestine.

Role of JNK in mammary gland development and breast cancer.

cJun NH(2)-terminal kinase (JNK) signaling has been implicated in the developmental morphogenesis of epithelial organs. In this study, we employed a compound deletion of the murine Jnk1 and Jnk2 genes in the mammary gland to evaluate the requirement for these ubiquitously expressed genes in breast development and tumorigenesis. JNK1/2 was not required for breast epithelial cell proliferation or motility. However, JNK1/2 deficiency caused increased branching morphogenesis and defects in the clearance of lumenal epithelial cells. In the setting of breast cancer development, JNK1/2 deficiency significantly increased tumor formation. Together, these findings established that JNK signaling is required for normal mammary gland development and that it has a suppressive role in mammary tumorigenesis.

α(V)ß(6) integrin expression is induced in the POET and Pten(pc-/-) mouse models of prostatic inflammation and prostatic adenocarcinoma.

Chronic inflammation is proposed to prime the development of prostate cancer. However, the mechanisms of prostate cancer initiation and development are not completely understood. The α(v)ß(6) integrin has been shown to play a role in epithelial development, wound healing and some epithelial cancers [1, 2]. Here, we investigate the expression of α(v)ß(6) in mouse models of prostatic inflammation and prostate cancer to establish a possible relationship between inflammation of the prostate, α(v)ß(6) expression and the progression of prostate cancer. Using immunohistochemical techniques, we show expression of α(v)ß(6) in two in vivo mouse models; the Pten(pc)-/- model containing a prostate- specific Pten tumor suppressor deletion that causes cancer, and the prostate ovalbumin-expressing transgenic (POET) inflammation mouse model. We show that the α(v)ß(6) integrin is induced in prostate cancer and inflammation in vivo in these two mouse models. α(v)ß(6) is expressed in all the mice with cancer in the Pten(pc-/-) model but not in age-matched wild-type mice. In the POET inflammation model, α(v)ß(6) is expressed in mice injected with activated T-cells, but in none of the control mice. In the POET model, we also used real time PCR to assess the expression of Transforming Growth Factor Beta 1 (TGFß1), a factor in inflammation that is activated by α(v)ß(6). In conclusion, through in vivo evidence, we conclude that α(v)ß(6) integrin may be a crucial link between prostatic inflammation and prostatic adenocarcinoma.

Application of a new hydrogel dural sealant that reduces epidural adhesion formation: evaluation in a large animal laminectomy model.

OBJECT: The aim of this study was to evaluate the application and effects of a novel, nonswelling, polyethylene glycol-based hydrogel adhesion barrier and sealant in a canine laminectomy model of CSF leakage and adhesion formation. METHODS: After full-width L-2 and L-5 laminectomies, 1-cm midline durotomies were created and sutured closed, except for the last 1-2 mm on the cranial end to create spontaneous CSF leakage. All 5 control animals received no further treatment. Experimental animals received hydrogel at both durotomy sites via either the Dual Liquid applicator (5 animals) or MicroMyst gas-assisted sprayer (5 animals). Sealing of the CSF leak was confirmed by Valsalva maneuver. At 2 months, 2 animals from each group were killed to evaluate dural healing and epidural adhesion formation. The remaining animals were similarly evaluated 4 months after surgery. One animal died at 66 days due to a cause unrelated to hydrogel treatment. RESULTS: In hydrogel-treated animals, all leaking durotomies were sealed intraoperatively. All animals recovered uneventfully. There were no treatment-related health effects. MicroMyst hydrogel application was more controlled, slower, and significantly less thick (p = 0.0094) than Dual Liquid application. All 5 control animals developed subcutaneous CSF accumulations under the incision within days of surgery, compared with only 1 of 10 hydrogel-treated animals (p = 0.002). At 2 and 4 months, control laminectomy sites showed extensive, dense epidural adhesions blending with neodura, compared with hydrogel-treated sites (p < 0.0001 and p = 0.0234, respectively). At 2 months in hydrogel-treated animals, gel filled the epidural space and no epidural adhesions were noted (p < 0.0001 relative to controls). At 4 months, the hydrogel was absorbed. The hydrogel space was filled with scant, loosely organized connective tissue. CONCLUSIONS: Hydrogel prevented CSF leakage and mitigated epidural scarring without affecting healing of the dura or laminectomy site. The safety profile of the hydrogel appears favorable due to its synthetic composition, polyethylene glycol chemistry, minimal local tissue response, and lack of neurological deficits. Controlled application of such hydrogel materials may reduce the incidence of postoperative leaks, prevent adhesion formation and thus improve recovery from spinal surgery, and improve identification of tissue planes for reoperations.

Role of JNK in a Trp53-dependent mouse model of breast cancer.

The cJun NH2-terminal kinase (JNK) signal transduction pathway has been implicated in mammary carcinogenesis. To test the role of JNK, we examined the effect of ablation of the Jnk1 and Jnk2 genes in a Trp53-dependent model of breast cancer using BALB/c mice. We detected no defects in mammary gland development in virgin mice or during lactation and involution in control studies of Jnk1(-/-) and Jnk2(-/-) mice. In a Trp53(-/+) genetic background, mammary carcinomas were detected in 43% of control mice, 70% of Jnk1(-/-) mice, and 53% of Jnk2(-/-) mice. These data indicate that JNK1 and JNK2 are not essential for mammary carcinoma development in the Trp53(-/+) BALB/c model of breast cancer. In contrast, this analysis suggests that JNK may partially contribute to tumor suppression. This conclusion is consistent with the finding that tumor-free survival of JNK-deficient Trp53(-/+) mice was significantly reduced compared with control Trp53(-/+) mice. We conclude that JNK1 and JNK2 can act as suppressors of mammary tumor development.