The non-receptor tyrosine kinase c-Src, hereafter referred to as Src, is overexpressed or activated in multiple human malignancies. There has been much speculation about the functional role of Src in colorectal cancer (CRC), with Src amplification and potential activating mutations in up to 20%of the human tumours, although this has never been addressed due to multiple redundant family members. Here, we have used the adult Drosophila and mouse intestinal epithelium as paradigms to define a role for Src during tissue homeostasis, damage-induced regeneration and hyperplasia. Through genetic gain and loss of function experiments, we demonstrate that Src is necessary and sufficient to drive intestinal stem cell (ISC) proliferation during tissue self-renewal, regeneration and tumourigenesis. Surprisingly, Src plays a non-redundant role in the mouse intestine, which cannot be substituted by the other family kinases Fyn and Yes. Mechanistically, we show that Src drives ISC proliferation through upregulation of EGFR and activation of Ras/MAPK and Stat3 signalling. Therefore, we demonstrate a novel essential role for Src in intestinal stem/progenitor cell proliferation and tumourigenesis initiation in vivo.
Apc; intestinal stem cells; regeneration; Src; tumourigenesis
To estimate the association of age of viral suppression and central nervous system penetration effectiveness (CPE) score with neurocognitive functioning among school-age children with perinatally-acquired HIV infection (PHIV+).
We analyzed data from two U.S.-based multisite prospective cohort studies.
Multivariable general linear regression models were used to evaluate associations of age at viral suppression and CPE scores [of initial ART regimen and weighted average] with WISC-III or WISC-IV neurocognitive assessments [full scale IQ (FSIQ); performance IQ/ perceptual reasoning index (PIQ/PRI); and verbal IQ/ verbal comprehension index (VIQ/VCI)], adjusted for demographic and clinical covariates. Sensitivity analyses were stratified by birth cohort (before vs after 1996).
396 PHIV+ children were included. Estimated differences in mean FSIQ (comparing virally suppressed vs. unsuppressed children) by each age cutoff were 3.7, 2.2, 3.2, 4.4, and 3.9 points at ages 1, 2, 3, 4, and 5, respectively. For PIQ/PRI, estimated mean differences were 3.7, 2.4, 2.2, 4.6, and 4.5 at ages 1 through 5 respectively. In both cases, these differences were significant only at the age 4 and 5 thresholds. After stratifying by birth cohort the association between age at suppression and cognitive function persisted only among those born after 1996. Age at viral suppression was not associated with VIQ/VCI; CPE score was not associated with FSIQ, verbal comprehension or perceptual reasoning indices.
Virologic suppression during infancy or early childhood is associated with improved neurocognitive outcomes in school-aged PHIV+ children. In contrast, CPE scores showed no association with neurocognitive outcomes.
Paediatrics; HIV; cognition; antiretroviral therapy; viral load; central nervous system
The PI3K/Akt survival pathway is often dysregulated in cancer. Our previous studies have demonstrated that coexpression of activated Akt1 with activated ErbB2 or polyoma virus middle T antigen uncoupled from the PI3K pathway (PyVmT Y315/322F) accelerates mammary tumor development but cannot rescue the metastatic phenotype associated with these models. Here we report the generation of transgenic mice expressing activated Akt2 in the mammary epithelium. Like the MMTV-Akt1 strain, mammary-specific expression of Akt2 delayed mammary gland involution. However, in contrast to Akt1, coexpression of Akt2 with activated ErbB2 or PyVmT Y315/322F in the mammary glands of transgenic mice did not impact the latency of tumor development. Strikingly Akt2 coexpresssion markedly increased the incidence of pulmonary metastases in both tumor models demonstrating a unique role in tumor progression. Together these observations argue that these highly conserved kinases have distinct biological and biochemical outputs that play opposing roles in mammary tumor induction and metastasis.
Akt; ErbB2; PyVmT; mammary tumorigenesis; metastasis
Newborns are more susceptible to severe disease from infection than adults, with maturation of immune responses implicated as a major factor. The type I interferon response delays mortality and limits viral replication in adult mice in a model of herpes simplex virus (HSV) encephalitis. We found that intact type I interferon signaling did not control HSV disease in the neonatal brain. However, the multifunctional HSV protein γ34.5 involved in countering type I interferon responses was important for virulence in the brain in both age groups. To investigate this observation further, we studied a specific function of γ34.5 which contributes to HSV pathogenesis in the adult brain, inhibition of the cellular process of autophagy. Surprisingly, we found that the beclin binding domain of γ34.5 responsible for inhibiting autophagy was dispensable for HSV disease in the neonatal brain, as infection of newborns with the deletion mutant decreased time to mortality compared to the rescue virus. Additionally, a functional beclin binding domain in HSV γ34.5 did not effectively inhibit autophagy in the neonate, unlike in the adult. Type I IFN responses promote autophagy in adult, a finding we confirmed in the adult brain after HSV infection; however, in the newborn brain we observed that autophagy was activated through a type I IFN-independent mechanism. Furthermore, autophagy in the wild-type neonatal mouse was associated with increased apoptosis in infected regions of the brain. Observations in the mouse model were consistent with those in a human case of neonatal HSV encephalitis. Our findings reveal age-dependent differences in autophagy for protection from HSV encephalitis, indicating developmental differences in induction and regulation of this innate defense mechanism after HSV infection in the neonatal brain.
Disease after infection with a pathogen results from an intersection between the infectious agent and the host. Newborns are particularly susceptible to infectious illness compared to adults, and HSV infection commonly results in devastating encephalitis. We studied the interaction of HSV with the type I interferon pathway and found that a specific activity of the viral protein γ34.5, which counters host autophagy to promote encephalitis in adults, was not required to cause disease in newborns. Furthermore, autophagy was not inhibited by HSV in the neonate and was not activated by type I interferon signaling, unlike in the adult. Activated autophagy was associated with increased apoptosis, which may contribute to the increased pathology in newborns. Our findings reveal development-specific differences in the pathogenesis of HSV encephalitis, including a distinct role for autophagy in the neonatal brain.
14-3-3ζ is overexpressed in over 40% of breast cancers but its pathophysiological relevance to tumorigenesis has not been established. Here we show that 14-3-3ζ overexpression is sufficient to induce tumorigenesis in a transgenic mouse model of breast cancer. MMTV-LTR promoter driven HA-14-3-3ζ transgenic mice (MMTV-HA-14-3-3ζ) developed mammary tumors whereas control mice did not. Whey acidic protein promoter driven HA-14-3-3ζ transgenic mice (WAP-HA-14-3-3ζ) developed hyperplastic lesions and showed increased susceptibility to carcinogen-induced tumorigenesis. When crossed with MMTV-neu transgenic mice, 14-3-3ζ.neu transgenic mice exhibited accelerated mammary tumorigenesis and metastasis compared to MMTV-neu mice. Mechanistically, 14-3-3ζ overexpression enhanced MAPK/c-Jun signaling leading to increased miR-221 transcription, which inhibited p27 CDKI translation, and consequently, promoted cell proliferation. Importantly, this 14-3-3ζ/miR-221/p27/proliferation axis is also functioning in patients' breast tumors and associates with high grade cancers. Taken together, our findings show that 14-3-3ζ overexpression has a causal role in mammary tumorigenesis and progression, acting through miR-221 in cooperation with known oncogenic events to drive neoplastic cell proliferation.
Breast cancer; 14-3-3ζ; microRNA; transgenic mice
Accelerated glucose metabolism is a common feature of cancer cells. Hexokinases catalyze the first committed step of glucose metabolism. Hexokinase 2 (HK2) is expressed at high level in cancer cells, but only in a limited number of normal adult tissues. Using Hk2 conditional knockout mice, we showed that HK2 is required for tumor initiation and maintenance in mouse models of KRas-driven lung cancer, and ErbB2-driven breast cancer, despite continued HK1 expression. Similarly HK2 ablation inhibits the neoplastic phenotype of human lung and breast cancer cells in vitro and in vivo. Systemic Hk2 deletion is therapeutic in mice bearing lung tumors without adverse physiological consequences. Hk2 deletion in lung cancer cells suppressed glucose-derived ribonucleotides and impaired glutamine-derived carbon utilization in anaplerosis.
Tetraspanins are transmembrane proteins that serve as scaffolds for multiprotein complexes containing, for example, integrins, growth factor receptors and matrix metalloproteases, and modify their functions in cell adhesion, migration and transmembrane signaling. CD151 is part of the tetraspanin family and it forms tight complexes with β1 and β4 integrins, both of which have been shown to be required for tumorigenesis and/or metastasis in transgenic mouse models of breast cancer. High levels of the tetraspanin CD151 have been linked to poor patient outcome in several human cancers including breast cancer. In addition, CD151 has been implicated as a promoter of tumor angiogenesis and metastasis in various model systems.
Here we investigated the effect of Cd151 deletion on mammary tumorigenesis by crossing Cd151-deficient mice with a spontaneously metastasising transgenic model of breast cancer induced by the polyoma middle T antigen (PyMT) driven by the murine mammary tumor virus promoter (MMTV).
Cd151 deletion did not affect the normal development and differentiation of the mammary gland. While there was a trend towards delayed tumor onset in Cd151−/− PyMT mice compared to Cd151+/+ PyMT littermate controls, this result was only approaching significance (Log-rank test P-value =0.0536). Interestingly, Cd151 deletion resulted in significantly reduced numbers and size of primary tumors but did not appear to affect the number or size of metastases in the MMTV/PyMT mice. Intriguingly, no differences in the expression of markers of cell proliferation, apoptosis and blood vessel density was observed in the primary tumors.
The findings from this study provide additional evidence that CD151 acts to enhance tumor formation initiated by a range of oncogenes and strongly support its relevance as a potential therapeutic target to delay breast cancer progression.
Tetraspanin; CD151; Breast; Cancer; Metastasis
Breast cancer is attributable to modifiable risk factors including the intake of dietary n-3 polyunsaturated fatty acids (PUFA). A key piece of evidence, yet to be addressed, that would demonstrate a causal relationship between n-3 PUFA and breast cancer, is a dose-dependent effect of n-3 PUFA on tumour outcomes. Thus, the objective of the present study was to determine whether n-3 PUFA reduces mammary gland tumor outcomes in a dose-dependent manner in female MMTV-neu(ndl)-YD5 transgenic mice, an aggressive model of human breast cancer.
Harems were provided one of three experimental diets comprised of 0, 3 or 9% (w/w) menhaden fish oil containing n-3 PUFA. Female offspring were weaned onto the same parental diet and maintained on their respective diet for 20 weeks. Tumour onset, size and multiplicity were measured throughout the study. Fatty acid composition of mammary gland and tumours were determined by gas–liquid chromatography.
Tumour size was significantly (p < 0.05) reduced in a dose-dependent manner. n-3 PUFA were also incorporated in a dose-dependent manner; differential incorporation was observed for eicosapentaenoic and docosapentaenoic acids into mammary gland tissue, while docosahexaenoic acid was preferentially incorporated into tumours.
Overall, the present study provides fundamental knowledge about the dose-dependent effect of n-3 PUFA on tumour outcomes in a pre-clinical model and also sheds light on the differential role of individual n-3 PUFA on tumour outcomes.
n-3 PUFA; Eicosapentaenoic acid; Docosahexaenoic acid; Mammary gland; MMTV-neu mice; Breast cancer; Tumour; Tumour multiplicity; Tumour volume; Phospholipids
RUNX2, a master regulator of osteogenesis, is oncogenic in the lymphoid lineage; however, little is known about its role in epithelial cancers. Upregulation of RUNX2 in cell lines correlates with increased invasiveness and the capacity to form osteolytic disease in models of breast and prostate cancer. However, most studies have analysed the effects of this gene in a limited number of cell lines and its role in primary breast cancer has not been resolved. Using a human tumour tissue microarray, we show that high RUNX2 expression is significantly associated with oestrogen receptor (ER)/progesterone receptor (PR)/HER2-negative breast cancers and that patients with high RUNX2 expression have a poorer survival rate than those with negative or low expression. We confirm RUNX2 as a gene that has a potentially important functional role in triple-negative breast cancer. To investigate the role of this gene in breast cancer, we made a transgenic model in which Runx2 is specifically expressed in murine mammary epithelium under the control of the mouse mammary tumour virus (MMTV) promoter. We show that ectopic Runx2 perturbs normal development in pubertal and lactating animals, delaying ductal elongation and inhibiting lobular alveolar differentiation. We also show that the Runx2 transgene elicits age-related, pre-neoplastic changes in the mammary epithelium of older transgenic animals, suggesting that elevated RUNX2 expression renders such tissue more susceptible to oncogenic changes and providing further evidence that this gene might have an important, context-dependent role in breast cancer.
RUNX2; Breast cancer; Transgenic model; Mammary development
Herpes simplex virus (HSV) pathogenesis in mice differs based on availability of the principal entry receptors herpesvirus entry mediator (HVEM) and nectin-1 in a manner dependent upon route of inoculation. After intravaginal or intracranial inoculation of adult mice, nectin-1 is a major mediator of neurologic disease, while the absence of either receptor attenuates disease after ocular infection. We tested the importance of receptor availability and route of infection on disease in mouse models of neonatal HSV. We infected 7-day-old mice lacking neither or one principal HSV receptor or both principal HSV receptors with HSV-2 via a peripheral route (intranasal), via a systemic route (intraperitoneal), or by inoculation directly into the central nervous system (intracranial). Mortality, neurologic disease, and visceral dissemination of virus were significantly attenuated in nectin-1 knockout mice compared with HVEM knockout or wild-type mice after intranasal inoculation. Mice lacking both entry receptors (double-knockout mice) showed no evidence of disease after inoculation by any route. Nectin-1 knockout mice had delayed mortality after intraperitoneal inoculation relative to wild-type and HVEM knockout mice, but virus was able to spread to the brain and viscera in all genotypes except double-knockout mice. Unlike in adult mice, HVEM was sufficient to mediate disease in neonatal mice after direct intracranial inoculation, and the absence of HVEM delayed time to mortality relative to that of wild-type mice. Additionally, in wild-type neonatal mice inoculated intracranially, HSV antigen did not primarily colocalize with NeuN-positive neurons. Our results suggest that differences in receptor expression between adults and newborns may partially explain differences in susceptibility to HSV-2.
Background. Herpes simplex virus resistance to acyclovir is well described in immune-compromised patients. Management of prolonged infection and recurrences in such patients may be problematic.
Methods. A patient with neuroblastoma developed likely primary herpes gingivostomatitis shortly after starting a course of chemotherapy, with spread to the eye during treatment with acyclovir. Viral isolates were serially obtained from separate sites after treatment was begun and tested for susceptibility to acyclovir and foscarnet by plaque reduction and plating efficiency assays. The thymidine kinase and DNA polymerase genes from each isolate were sequenced.
Results. Initial isolates from a throat swab, an oral lesion, and conjunctiva were resistant to acyclovir within 13 days of treatment. Subsequent isolates while on foscarnet were initially acyclovir-susceptible, but reactivation of an acyclovir-resistant isolate was subsequently documented while on acyclovir suppression. Genotypic analysis identified a previously unreported UL23 mutation in some resistant isolates. None of the amino acid changes identified in UL30 were associated with resistance.
Conclusions. Phenotypic and genotypic antiviral resistance of herpes simplex isolates may vary from different compartments and over time in individual immune-compromised hosts, highlighting the importance of obtaining cultures from all sites. Phenotypic resistance testing should be considered for isolates obtained from at-risk patients not responding to first-line therapy. Empiric combination treatment with multiple antivirals could be considered in some situations.
Using transgenic mouse models of breast cancer that ablate Src homology and collagen A (ShcA) expression or oncogene-coupled ShcA signaling, we previously showed that this adaptor is critical for mammary tumor onset and progression. We now provide the first evidence that ShcA regulates mammary tumorigenesis, in part, through its ability to regulate the adaptive immune response. Inactivation of ShcA signaling within tumor cells results in extensive CD4+ T-cell infiltration and induction of a humoral immune response in mammary tumors. This is associated with a robust CTL response in preneoplastic lesions that are deficient in ShcA signaling. Moreover, mammary tumor progression of ShcA-deficient hyperplasias is accelerated in a T cell–deficient background. We also uncover a clinically relevant correlation between high ShcA expression and low CTL infiltration in human breast cancers. Finally, we define a novel ShcA-regulated immune signature that functions as an independent prognostic marker of survival in human epidermal growth factor receptor 2+ and basal breast cancers. We reveal a novel role for tumor cell–derived ShcA in the establishment and maintenance of an immunosuppressive state.
Effective in vivo models of breast cancer are crucial for studying the development and progression of the disease in humans. We sought to engineer a novel mouse model of polyomavirus middle T antigen (PyV mT)-mediated mammary tumourigenesis in which inducible expression of this well-characterized viral oncoprotein is coupled to Cre recombinase (TetO-PyV mT-IRES-Cre recombinase or MIC).
MIC mice were crossed to the mouse mammary tumour virus (MMTV)-reverse tetracycline transactivator (rtTA) strain to generate cohorts of virgin females carrying one or both transgenes. Experimental (rtTA/MIC) and control (rtTA or MIC) animals were administered 2 mg/mL doxycycline beginning as early as eight weeks of age and monitored for mammary tumour formation, in parallel with un-induced controls of the same genotypes.
Of the rtTA/MIC virgin females studied, 90% developed mammary tumour with complete penetrance to all glands in response to doxycycline and a T50 of seven days post-induction, while induced or un-induced controls remained tumour-free after one year of induction. Histological analyses of rtTA/MIC mammary glands and tumour revealed that lesions followed the canonical stepwise progression of PyV mT tumourigenesis, from hyperplasia to mammary intraepithelial neoplasia/adenoma, carcinoma, and invasive carcinoma that metastasizes to the lung; at each of these stages expression of PyV mT and Cre recombinase transgenes was confirmed. Withdrawal of doxycycline from rtTA/MIC mice with end-stage mammary tumours led to rapid regression, yet animals eventually developed PyV mT-expressing and -non-expressing recurrent masses with varied tumour histopathologies.
We have successfully created a temporally regulated mouse model of PyV mT-mediated mammary tumourigenesis that can be used to study Cre recombinase-mediated genetic changes simultaneously. While maintaining all of the hallmark features of the well-established constitutive MMTV-PyV mT model, the utility of this strain derives from the linking of PyV mT and Cre recombinase transgenes; mammary epithelial cells are thereby forced to couple PyV mT expression with conditional ablation of a given gene. This transgenic mouse model will be an important research tool for identifying synthetic viable genetic events that enable PyV mT tumours to evolve in the absence of a key signaling pathway.
Infection of susceptible cells by herpes simplex virus (HSV) requires the interaction of the HSV gD glycoprotein with one of two principal entry receptors, herpes virus entry mediator (HVEM) or nectins. HVEM naturally functions in immune signaling, and the gD-HVEM interaction alters innate signaling early after mucosal infection. We investigated whether the gD-HVEM interaction during priming changes lymphocyte recall responses in the murine intravaginal model. Mice were primed with attenuated HSV-2 expressing wild-type gD or mutant gD unable to engage HVEM and challenged 32 days later with virulent HSV-2 expressing wild-type gD. HSV-specific CD8+ T cells were decreased at the genital mucosa during the recall response after priming with virus unable to engage HVEM but did not differ in draining lymph nodes. CD4+ T cells, which are critical for entry of HSV-specific CD8+ T cells into mucosa in acute infection, did not differ between the two groups in either tissue. An inverse association between Foxp3+ CD4+ regulatory T cells and CD8+ infiltration into the mucosa was not statistically significant. CXCR3 surface expression was not significantly different among different lymphocyte subsets. We conclude that engagement of HVEM during the acute phase of HSV infection influences the antiviral CD8+ recall response by an unexplained mechanism.
Trastuzumab is an iconic rationally designed targeted therapy for HER2-positive breast cancers. However, the low response rate and development of resistance call for novel approaches for the treatment of patients. Here, we report that concurrent targeting of tumor cells and activation of T cells in the tumor microenvironment results in a synergistic inhibitory effect on tumor growth and overcomes resistance in two distinct PTEN loss–mediated trastuzumab-resistant mammary tumor mouse models. In vivo combination treatment with HER2/Neu antibody and Akt inhibitor triciribine effectively inhibited tumor growth in both models via inhibiting PI3K/AKT and mitogen-activated protein kinase signaling accompanied by increased T-cell infiltration in the tumor microenvironment. We showed that both CD8+ and CD4+ T cells were essential to the optimal antitumor effect of this combination treatment in an IFN- γ–dependent manner. Importantly, the antitumor activities of HER2/Neu antibody and triciribine combination treatment were further improved when coinhibitory receptor cytotoxic T-lymphocyte–associated antigen 4 was blocked to enhance the T-cell response. Our data indicate that multitargeted combinatorial therapies targeting tumor cells and concomitantly enhancing T-cell response in the tumor microenvironment could cooperate to exert maximal therapeutic activity, suggesting a promising clinical strategy for treating trastuzumab-resistant breast cancers and other advanced malignancies.
Metazoans respond to various forms of environmental stress by inducing the phosphorylation of the α subunit of the translation initiation factor eIF2 at serine 51 (eIF2αP), a modification that leads to a global inhibition of mRNA translation. Herein, we demonstrate that eIF2αP is induced by pharmacological inhibition of the phosphoinositide-3-kinase (PI3K)-Akt pathway as well as by genetic or small interfering (si)RNA-mediated ablation of Akt. Increased eIF2αP is an evolutionary conserved process that involves the endoplasmic reticulum (ER)-resident protein kinase PERK, which is negatively regulated by Akt-dependent phosphorylation at threonine 799. PERK activity and eIF2αP are downregulated by activated Akt in mouse mammary gland tumors as well as in cells exposed to ER stress or oxidative stress leading to the induction of cell survival or death respectively. In unstressed cells, the PERK-eIF2αP pathway guards survival and facilitates adaptation to the deleterious effects of PI3K or Akt inactivation. As such, inactivation of the PERK-eIF2αP arm increases the susceptibility of tumor cells to death by pharmacological inhibitors of PI3K or Akt. Thus, in addition to mTOR the PERK-eIF2αP pathway provides a link between Akt signaling and translational control with implications in tumor formation and treatment.
translational control; PERK; eIF2α phosphorylation; Akt/PKB; endoplasmic reticulum stress; oxidative stress; chemotherapeutic drugs
Germline and somatic mutations in STK11, the gene encoding the serine/threonine kinase LKB1, are strongly associated with tumorigenesis. While loss of LKB1 expression has been linked to breast cancer, the mechanistic role of LKB1 in regulating breast cancer development, metastasis, and tumor metabolism has remained unclear.
We have generated and analyzed transgenic mice expressing ErbB2 in the mammary epithelium of LKB1 wild-type or LKB1-deficient mice. We have also utilized ErbB2-expressing breast cancer cells in which LKB1 levels have been reduced using shRNA approaches. These transgenic and xenograft models were characterized for the effects of LKB1 loss on tumor initiation, growth, metastasis and tumor cell metabolism.
We demonstrate that loss of LKB1 promotes tumor initiation and induces a characteristic shift to aerobic glycolysis (‘Warburg effect’) in a model of ErbB2-mediated breast cancer. LKB1-deficient breast cancer cells display enhanced early tumor growth coupled with increased cell migratory and invasive properties in vitro. We show that ErbB2-positive tumors deficient for LKB1 display a pro-growth molecular and phenotypic signature characterized by elevated Akt/mTOR signaling, increased glycolytic metabolism, as well as increased bioenergetic markers both in vitro and in vivo. We also demonstrate that mTOR contributes to the metabolic reprogramming of LKB1-deficient breast cancer, and is required to drive glycolytic metabolism in these tumors; however, LKB1-deficient breast cancer cells display reduced metabolic flexibility and increased apoptosis in response to metabolic perturbations.
Together, our data suggest that LKB1 functions as a tumor suppressor in breast cancer. Loss of LKB1 collaborates with activated ErbB2 signaling to drive breast tumorigenesis and pro-growth metabolism in the resulting tumors.
Breast cancer; ErbB2; LKB1; Metabolism
Increasing evidence suggests that HER2-amplified breast cancer cells use HER3/ErbB3 to drive therapeutic resistance to HER2 inhibitors. However, the role of ErbB3 in the earliest events of breast epithelial transformation remains unknown. Using mouse mammary specific models of Cre-mediated ErbB3 ablation, we show that ErbB3 loss prevents the progressive transformation of HER2-overexpressing mammary epithelium. Decreased proliferation and increased apoptosis were seen in MMTV-HER2 and MMTV-Neu mammary glands lacking ErbB3, thus inhibiting premalignant HER2-induced hyperplasia. Using a transgenic model in which HER2 and Cre are expressed from a single polycistronic transcript, we showed that palpable tumor penetrance decreased from 93.3% to 6.7% upon ErbB3 ablation. Penetrance of ductal carcinomas in situ was also decreased. In addition, loss of ErbB3 impaired Akt and p44/42 phosphorylation in preneoplastic HER2-overexpressing mammary glands and in tumors, decreased growth of preexisting HER2-overexpressing tumors, and improved tumor response to the HER2 tyrosine kinase inhibitor lapatinib. These events were rescued by reexpression of ErbB3, but were only partially rescued by ErbB36F, an ErbB3 mutant harboring six tyrosine-to-phenylalanine mutations that block its interaction with phosphatidyl inositol 3-kinase. Taken together, our findings suggest that ErbB3 promotes HER2-induced changes in the breast epithelium before, during, and after tumor formation. These results may have important translational implications for the treatment and prevention of HER2-amplified breast tumors through ErbB3 inhibition.
Selenium is an essential micronutrient in the diet of humans and other mammals. Based largely on animal studies and epidemiological evidence, selenium is purported to be a promising cancer chemopreventive agent. However, the biological mechanisms by which chemopreventive activity takes place are poorly understood. It remains unclear whether selenium acts in its elemental form, through incorporation into organic compounds, through selenoproteins or any combination of these. The purpose of this study was to determine whether selenoproteins mitigate the risk of developing chemically induced mammary cancer. Selenoprotein expression was ablated in mouse mammary epithelial cells through genetic deletion of the selenocysteine (Sec) tRNA gene (Trsp), whose product, designated selenocysteine tRNA, is required for selenoprotein translation. Trsp floxed and mouse mammary tumor virus (MMTV)-cre mice were crossed to achieve tissue-specific excision of Trsp in targeted mammary glands. Eight- to twelve-week-old second generation Trspfl/+;wt, Trspfl/+;MMTV-cre, Trsp
fl/fl;wt and Trspfl/fl;MMTV-cre female mice were administered standard doses of the carcinogen, 7,12-dimethylbenzylbenz[a]antracene. Our results revealed that heterozygous, Trspfl/+;MMTV-cre mice showed no difference in tumor incidence, tumor rate and survival compared with the Trspfl/+;wt mice. However, 54.8% of homozygous Trspfl/f
l;MMTV-cre mice developed mammary tumors and exhibited significantly shorter survival than the corresponding Trspfl/fl;wt mice, where only 36.4% developed tumors. Loss of the homozygous Trsp alleles was associated with the reduction of selenoprotein expression. The results suggest that mice with reduced selenoprotein expression have increased susceptibility to developing carcinogen-induced mammary tumors and that a major protective mechanism against carcinogen-induced mammary cancer requires the expression of these selenoproteins.
The phosphatidylinositol 3' kinase/Akt pathway is frequently dysregulated in cancer which can have unfavorable consequences in terms of cell proliferation, survival, metabolism and migration. Increasing evidence suggests that Akt1, Akt2 and Akt3 play unique roles in breast cancer initiation and progression. We have recently shown that in contrast to Akt1 which accelerates mammary tumor induction in transgenic mice, Akt2 promotes metastasis of tumor cells without affecting the latency of tumor development. Despite the distinct phenotypic outputs resulting from Akt1 or Akt2 activation, very little is known regarding the mode by which such unique functions originate from these highly related kinases. Here we discuss potential mechanisms contributing to the differing functional specificity of Akt1 and Akt2 with respect to migration, invasion and metastasis.
Akt; breast cancer; metastasis; transgenic mouse; invasion
Herpes simplex viruses types 1 and 2 (HSV-1 and HSV-2) infect a large proportion of the world's population. Infection is life-long and can cause periodic mucocutaneous symptoms, but it only rarely causes life-threatening disease among immunocompetent children and adults. However, when HSV infection occurs during the neonatal period, viral replication is poorly controlled and a large proportion of infants die or develop disability even with optimal antiviral therapy. Increasingly, specific differences are being elucidated between the immune system of newborns and those of older children and adults, which predispose to severe infections and reflect the transition from fetal to postnatal life. Studies in healthy individuals of different ages, individuals with primary or acquired immunodeficiencies, and animal models have contributed to our understanding of the mechanisms that control HSV infection and how these may be impaired during the neonatal period. This paper outlines our current understanding of innate and adaptive immunity to HSV infection, immunologic differences in early infancy that may account for the manifestations of neonatal HSV infection, and the potential of interventions to augment neonatal immune protection against HSV disease.
Cytotoxic T cells are important in controlling herpes simplex virus type 2 (HSV-2) reactivation and peripheral lesion resolution. Humans latently infected with HSV-2 have cytotoxic T cells directed against epitopes present in tegument proteins. Studies in mice of immunity to HSV have commonly focused on immunodominant responses in HSV envelope glycoproteins. These antigens have not proved to be an effective prophylactic vaccine target for most of the human population. The murine immune response against HSV tegument proteins has not been explored. We analysed cellular responses in BALB/c mice directed against the tegument proteins encoded by UL46, UL47 and UL49 and against the envelope glycoprotein gD after DNA vaccination or HSV-2 infection. After DNA vaccination, the splenocyte T-cell response to overlapping peptides from UL46 and UL47 was more than 500 gamma interferon spot-forming units per 106 responder cells. Peptide truncation studies, responder cell fractionation and major histocompatibility complex binding studies identified several CD8+ and CD4+ epitopes. Cellular responses to tegument protein epitopes were also detected after HSV-2 infection. Tegument proteins are rational candidates for further HSV-2 vaccine research.
Breast cancer progression involves multiple genetic events, which can activate dominant-acting oncogenes and disrupt the function of specific tumor suppressor genes. This article describes several key oncogene and tumor suppressor signaling networks that have been implicated in breast cancer progression. Among the tumor suppressors, the article emphasizes BRCA1/2 and p53 tumor suppressors. In addition to these well characterized tumor suppressors, the article highlights the importance of PTEN tumor suppressor in counteracting PI3K signaling from activated oncogenes such as ErbB2. This article discusses the use of mouse models of human breast that recapitulate the key genetic events involved in the initiation and progression of breast cancer. Finally, the therapeutic potential of targeting these key tumor suppressor and oncogene signaling networks is discussed.
Mouse models can recapitulate genetic events that disrupt signaling by ErbB2, p53, and PTEN during breast cancer progression. They also reveal that mutations in Brca1 can produce different tumor subtypes, depending on the context.
Loss of the tumor suppressor phosphatase and tensin homologue deleted on chromosome 10 (PTEN) and amplification or elevated expression of ErbB-2 are both involved in human breast cancer. To directly test the importance of these genetic events in mammary tumorigenesis, we have assessed whether mammary-specific disruption of PTEN could cooperate with activation of ErbB-2. Transgenic mice expressing ErbB-2 under the transcriptional control of its endogenous promoter (ErbB-2KI) were interbred with mice carrying conditional PTEN alleles and an MMTV/Cre transgene. Loss of one or both PTEN alleles resulted in a dramatic acceleration of mammary tumor onset and an increased occurrence of lung metastases in the ErbB-2KI strain. Tumor progression in PTEN-deficient/ErbB-2KI strains was associated with elevated ErbB-2 protein levels, which were not due to ErbB-2 amplification or to a dramatic increase in ErbB-2 transcripts. Moreover, the PTEN-deficient/ErbB-2KI–derived mouse mammary tumors display striking morphologic heterogeneity in comparison with the homogeneous pathology of the ErbB-2KI parental strain. Therefore, inactivation of PTEN would not only have a dramatic effect on ErbB-2–induced mammary tumorigenesis but would also lead to the formation of mammary tumors that, in part, display pathologic and molecular features associated with the basal-like subtype of primary human breast cancer.
Consistent with their essential role in cell adhesion to the extracellular matrix, integrins and their associated signaling pathways have been shown to be involved in cell proliferation, migration, invasion and survival, processes required in both tumorigenesis and metastasis. β1-integrins represent the predominantly expressed integrins in mammary epithelial cells and have been proven crucial for mammary gland development and differentiation. Here we provide an overview of the studies that have used transgenic mouse models of mammary tumorigenesis to establish β1-integrin as a critical mediator of breast cancer progression and thereby as a potential therapeutic target for the development of new anticancer strategies.