Genetic tuning of the novel avian influenza A(H7N9) virus during interspecies transmission, China, 2013

A novel avian influenza A(H7N9) virus causing human infection emerged in February 2013 in China. To elucidate the mechanism of interspecies transmission, we compared the signature amino acids of avian influenza A(H7N9) viruses from human and non-human hosts and analysed the reassortants of 146 influenza A(H7N9) viruses with full genome sequences. We propose a genetic tuning procedure with continuous amino acid substitutions and reassorting that mediates host adaptation and interspecies transmission. When the early influenza A(H7N9) virus, containing ancestor haemagglutinin (HA) and neuraminidase (NA) genes similar to A/Shanghai/05 virus, circulated in waterfowl and transmitted to terrestrial poultry, it acquired an NA stalk deletion at amino acid positions 69 to 73. Then, receptor binding preference was tuned to increase the affinity to human-like receptors through HA G186V and Q226L mutations in terrestrial poultry. Additional mammalian adaptations such as PB2 E627K were selected in humans. The continual reassortation between H7N9 and H9N2 viruses resulted in multiple genotypes for further host adaptation. When we analysed a potential association of mutations and reassortants with clinical outcome, only the PB2 E627K mutation slightly increased the case fatality rate. Genetic tuning may create opportunities for further adaptation of influenza A(H7N9) and its potential to cause a pandemic.

Abstract P5-03-03: Effect of rapamycin on the function and transformation of aged murine mammary stem cells

Age is the number one risk fact for breast cancer with only 5% of all breast cancers occurring in women under 40 years old and age specific incidence of invasive breast cancer increases from less than 1.5% at age 40, to about 3% at age 50 and over 4% by age 70 in American women. Recent research implicated that adult mammary stem cells (MaSCs) might be responsible for the initiation and progression of certain types of breast cancer. Our preliminary study showed that aging is associated with a significant increase of MaSC frequency, but with a functional decline of self-renewal and differentiation as well as increased neoplastic transformation potential. These findings indicate that aged MaSCs might be the precursors of preneoplastic lesions and serve as the cell of origin for malignant transformation in breast tissue. Therefore, intervention of MaSC aging process could be an effective method for cancer prevention. The drug of rapamycin has been shown to extend life span and ameliorate age-related pathologies (e.g., cancer) in murine models, and a recent study suggested that rapamycin's anti-aging effect may partially act through enhancing the function of tissue-specific stem cells. It is unknown whether rapamycin treatment will also enhance the function of aged MaSCs and decrease their transformation potential. In this study, we fed C57BL/6 mice with microencapsulated rapamycin-containing food (14 mg/kg, food designed to deliver ∼2.24 mg of rapamycin per kg body weight/day to achieve about 4 ng/ml of rapamycin per kg body weight/day) or control diet with empty capsules for 2 year (starting at 2-month old) or 5-10 days (starting at 25.5-month old) and then isolated primary mammary cells at 26-month old for MaSC quantification using an in vitro mammosphere formation and 3D-ECM sphere differentiation assay as well as by the in vivo cleared mammary fat pad transplantation assay. Our findings indicate that short-term (5-10 days) or long-term (> 2 year) rapamycin treatment reversed phenotypic changes associated with aged MaSC, which was mainly characterized by decreased luminal-to-basal cell ratio and increased MaSC frequency. Histological analysis of regenerated glands of aged MaSCs derived from control and rapamycin-treated mice showed a significant decrease of early neoplastic transformation potential in rapamycin-treated group. Subsequent in vivo serial transplantation and mating experiments revealed that rapamycin treatment reverted aged MaSCs more resemble to young MaSCs in self-renewal/differentiation function during regeneration and improved lobulo-alveolar differentiation function for lactation. In conclusion, our findings suggest that rapamycin can rejuvenate the function of aged MaSCs as well as reduce their incidence of preneoplastic transformation.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-03-03.

Isoflurane facilitates synaptic NMDA receptor endocytosis in mice primary neurons

Inhalation anesthetic isoflurane has been reported to induce caspase activation and accumulation of β-amyloid (Aβ), however, the down-stream consequences of these effects are largely unknown. Isoflurane has also been shown to impair learning and memory, however, the up-stream mechanisms of these effects remain largely to be determined. Facilitation of synaptic NMDA receptor endocytosis can reduce synaptic function, leading to learning and memory impairment. We therefore set out to determine the effects of isoflurane on synaptic NMDA receptor endocytosis. Primary neurons from wild-type and Alzheimer's disease transgenic mice were treated with 2% isoflurane for six hours. Synaptic surface levels of NMDA receptor 2B (NR2B) and NR2B internalization were determined by surface and cleavable biotinylation assay, western blot analysis and immunofluorescence. Here we show that isoflurane can induce caspase-3 activation, increase levels of β-site amyloid precursor protein-cleaving enzyme and cause accumulation of Aβ in the primary neurons. Isoflurane facilitates synaptic NR2B endocytosis as evidenced by reducing surface NR2B levels, increasing NR2B internalization, and decreasing the ratio of synaptic surface NR2B to synapsin in mice primary neurons. Moreover, caspase activation inhibitor Z-VAD and γ-secretase inhibitor L-685,458 attenuated the isoflurane-facilitated NR2B endocytosis. These results suggest that isoflurane induces caspase activation and Aβ accumulation, leading to facilitation of synaptic NMDA receptor endocytosis, which potentially serve as the upstream mechanism of the isoflurane-induced impairment of learning and memory. These findings will encourage further studies to determine the underlying mechanism by which isoflurane and other anesthetics promote Alzheimer's disease neuropathogenesis and induce cognitive dysfunction.

Surgical incision induces phosphorylation of AMPA receptor GluR1 subunits at Serine-831 sites and GluR1 trafficking in spinal cord dorsal horn via a protein kinase Cγ-dependent mechanism

Spinal α-amino-3-hydroxy-5-methy-4-isoxazole propionate (AMPA) receptor plays an important role in acute pain induced by surgical tissue injuries. Our previous study has shown that the enhanced phosphorylation of AMPA receptor GluR1 subunits at Serine-831 sites by protein kinase C (PKC) in the spinal cord dorsal horn is involved in post-surgical pain hypersensitivity. However, which isoforms of PKC are responsible for the phosphorylation of AMPA receptor GluR1 subunits at Serine-831 sites remains to be established. In the present study, using an animal model of postoperative pain, we found that surgical tissue injuries enhanced the membrane translocation level of PKCγ, but not PKCα, βI, and βII, and induced the trafficking of GluR1, but not GluR2 into neuronal plasma membrane. Intrathecal (i.t.) pretreatment of small interfering RNA targeting PKCγ to reduce the PKCγ expression in the spinal cord significantly attenuated the pain hypersensitivity and inhibited the phosphorylation of AMPA receptor GluR1 subunits at Serine-831 sites as well as GluR1 membrane trafficking. Our study indicates that the surgical incision-induced phosphorylation of AMPA receptor GluR1 subunits at Serine-831 sites and GluR1 trafficking are regulated by a PKCγ-dependent mechanism.

Abstract P5-03-06: Bisphenol A and mammary stem cells: implications in breast cancer susceptibility

It has been speculated that the increasing incidence of breast cancer might be linked to the increased exposure to environmental synthetic estrogens, such as bisphenol A (BPA), which is a most pervasive chemical in modern life as a component of polycarbonate plastics and epoxy resins used widely for food and beverage containers and dental sealants. Perinatal exposure to low, environmentally relevant doses of BPA in rodents resulted in the induction of pre-neoplastic ductal hyperplasia, carcinoma in situ, and increased susceptibility to tumorigenesis. However, the underlying mechanism for these observations is unclear. The murine mammary stem cells (MaSCs) are present in fetal mammary rudiments and could be the putative targets for BPA-induced tumorigenesis. More recently, MaSCs of different lineages have been matched with different subtypes of breast cancer by their specific gene-expression signatures. We thus hypothesize that mammary gland exposed to BPA at a susceptible window may lead to its susceptibility to tumorigenesis through a MaSC and/or stem cell niche mediated mechanism. To test this hypothesis, we exposed 21-day old Balb/C mice to BPA by gavage at 25 µg/kg/day during puberty for 3 weeks, and then isolated primary mammary cells at different time points (6-week, 2 and 4-month) for MaSC quantification using an in vitro mammosphere formation and 3D-ECM sphere differentiation assay as well as the in vivo cleared mammary fat pad regeneration assay. Our findings indicate that low dose BPA exposure at puberty can accelerate puberty onset, increase lateral branches and hyperplasia in adult mammary glands. Further, a single oral dose of DMBA at 30 mg/kg administrated at 2-month old resulted in a 2.4-fold increase in hyperplasia of mammary glands harvested at 4-month old when compared with BPA treated group without DMBA. Most significantly, puberty BPA exposure increased luminal MaSCs during gland development and this resulted in an increase of luminal cells in adult glands. In addition, puberty BPA exposure also altered basal MaSCs in such a way that regenerated glands from these basal MaSCs yielded higher preneoplastic lesion than control basal MaSCs, indicating puberty BPA exposure render basal MaSCs more susceptible to transformation. We also found significant increase of gene expression in steroid hormonal receptors (e.g. ERs and PR) in the stromal compartment (or stem cell niche), which suggest that the changes we observed above for the luminal and basal MaSCs may be caused indirectly through altered stromal environment upon BPA exposure during early life stage. Future studies are necessary to differentiate the effect of BPA exposure on MaSCs or the MaSC niche. In conclusion, our study showed that BPA-induced morphogenesis changes in mammary gland had a stem cell origin. More importantly, our findings suggest that BPA-induced susceptibility of mammary glands to tumorigenesis may also have a stem cell origin.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-03-06.

Abstract P5-03-04: Effect of aging on the function and transformation of murine mammary stem cells

Epidemiological studies have shown that the risk of getting breast cancer progressively increases with age. A woman is 100 times more susceptible to develop breast cancer in her 60s than in her 20s. A better understanding of altered cellular and molecular mechanisms leading to the development of sporadic breast cancers as a result of aging are urgently needed for its prevention and treatment in growing population of older women. Recent research implicated that adult mammary stem cells (MaSCs) might be responsible for the initiation and progression of certain types of breast cancer. But no studies have been reported on how lifelong exposure of MaSCs to endogenous and environmental stresses during aging compromises their self-renewal and differentiation function and predispose them to neoplastic transformation either spontaneously or after carcinogen exposure. In our study, we have investigated the effect of progressive aging and carcinogen exposure on MaSC number and function in a murine model. The FACS isolated MaSC enriched basal cells, characterized by their immunophenotype (Lin−CD49fhighCD24med) were utilized to evaluate MaSC frequency and function during aging by in vitro mammosphere formation and 3D-ECM sphere differentiation assay as well as by in vivo cleared mammary fat pad transplantation (IVT). The results of our study showed that the percentage of MaSCs analyzed by both FACS profile and in vitro assays, increased steadily with increasing age observed at 2, 7, 17 and 25 month-old C57BL/6 mice. Subsequent IVT using mammosphers or 3D structures formed by young (4 months) and old MaSCs (28 months) derived from C57BL/6 mice showed similar in vivo functional mammary gland regenerative capacity indicating similar self-renewal/differentiation ability between young and old MaSCs. However, we found that the regenerated glands from old MaSCs had significantly higher number of spontaneous pre-neoplastic lesions (52.0%) than those from young MaSCs (18.3%). Significantly, MaSC frequency was also increased by the in vivo exposure of a carcinogen, N-Methyl-N-Nitrosourea (MNU, 25 mg/kg body weight, once a week for three consecutive weeks), in old mice with no effect on total mammary cell number. Furthermore, the old MaSCs expanded by MNU treatment were still capable of in vivo regeneration with similar success rate as that of normal old MaSCs. But, we observed increased frequency of hyperplasia and dysplasia in the regenerated glands initiated by MNU treated old MaSC. Our results indicate that MaSCs might be the precursors of preneoplastic lesions and old MaSCs appear to be predisposed to premalignant transformation, which is enhanced by the exposure to a DNA damaging agent.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-03-04.

Oligonucleotides complementary to c-myb messenger RNA inhibit growth and induce apoptosis in human Burkitt lymphoma cells

A 24-mer (antisense) phosphorothioate oligonucleotide (ODN) corresponding to the codons 2-9 of the c-myb gene was evaluated for its effects on the growth of a human Burkitt lymphoma cell line (Raji) in vitro. Raji cells incubated with different concentrations of c-myb antisense ODN (5-15 mu g/ml) for 24-72 h showed a significant dose-dependent decrease in growth. The same concentrations of control (sense) or scrambled c-myb phosphorothioate ODNs did not inhibit Raji cell growth. The c-myb antisense ODN, but not the control ODNs, significantly decreased c-myb mRNA levels in treated cells as determined by RT-PCR. Additionally, the c-myb antisense ODN induced apoptosis of Raji cells as demonstrated by i) flow cytometry to enumerate the A(o) (apoptotic cell population) population of propidium iodide stained cells; ii) electron microscopy to evaluate the cell morphology; and iii) DNA fragmentation pattern. Thus, an antisense c-myb ODN causes significant growth inhibition of Burkitt lymphoma cells, and one mechanism of growth inhibition is the induction of apoptosis of the lymphoma cells. In addition, antisense c-myb ODN did not reduce CFU-GM or BFU-e colony-forming ability of normal hematopoietic stem/progenitor cells. Because the inhibition is sequence-specific and Burkitt lymphoma cell selective, evaluation of the therapeutic effects of c-myb antisense ODN against Burkitt lymphoma is warranted.

O030 Evasion of the OAS-RNase L pathway by murine coronavirus ns2 protein is required for viral replication and hepatitis

Introduction

The 2′,5′-oligoadenylate synthetase-ribonuclease L (OAS-RNase L) system is a potent IFN induced antiviral pathway. Following infection, IFNs induce a group of OAS genes whose products are activated by viral double-stranded RNA. OAS uses ATP to generate 2′,5′-linked oligoadenylates (2-5A). 2-5A binds to and activates the ubiquitous cellular endoribonuclease RNase L causing cleavages of single stranded regions of both viral and cellular RNA thus inhibiting viral replication. In addition, detection of the newly generated short RNAs by cellular pattern recognition receptors, MDA5 and RIG-I, further enhances IFN production and the ensuing antiviral activities. The intracellular concentration of 2-5A is believed to be the primary factor controlling RNase L activation. The liver contains abundant innate immune cells, which provide the first line of defense against pathogens. However, the factors that determine whether a virus can bypass this defense to access and infect the liver parenchyma are not well understood. The murine coronavirus, mouse hepatitis virus (MHV), strain A59, infection of mice provides a model for virus induced hepatitis. The MHV accessory protein, ns2, antagonizes the type I IFN response in macrophages and promotes the induction of hepatitis. Here we will describe how the ns2 protein facilitates the development of viral hepatitis by blocking OAS-RNase L pathway.

Methods

Bone marrow macrophages (BMM) from wild type (wt) and RNase L−/− mice were infected with A59 and ns2 mutant MHV. Viral titers were determined by plaque assays. RNase L activity was monitored by rRNA integrity in RNA chips. Intracellular levels of 2-5A were measured using RNase L activation assays. Effects of ns2 on 2-5A levels in cells were determined by transfecting ns2 or mutant ns2 cDNAs into HEK-293T cells. Recombinant ns2 and mutant ns2H126R proteins were purified and incubated with 2-5A in vitro and the 2-5A breakdown products were measured by HPLC. Hepatitis was determined by histology following inoculation A59 or ns2 mutant MHV into wt and RNase L−/− mice.

Results

We found evidence for a new molecular mechanism of subversion of the RNase L pathway in macrophages that regulates acute hepatitis during MHV infection. Coronavirus ns2 belongs to the LigT-like protein family, within the 2H phosphoesterase superfamily, some of which possess cyclophosphodiesterase activity (CPD). We have found that ns2 is not a CPD, but instead is a 2′,5′-phosphodiesterase (PDE) that cleaves, and thus eliminates 2-5A, the activator of RNase L. We observed that ns2 blocks the IFN inducible OAS-RNase L pathway to facilitate hepatitis development. Ns2 prevents activation of RNase L and consequently limits viral RNA degradation. An ns2 mutant virus was unable to replicate in the liver or induce hepatitis in wt mice, but was highly pathogenic in RNase L−/− mice. Thus, RNase L is a critical cellular factor for protection against viral infection of the liver and the resulting hepatitis.

Conclusion

MHV accessory protein ns2 is a 2′,5′-PDE which degrades 2-5A and limits RNase L activation thus facilitating virus-induced hepatitis in mice.

Early changes in cerebral oxidative stress and apoptotic neuronal injury after various flows for selective cerebral perfusion in piglets

BACKGROUND

The impact of various flows for selective cerebral perfusion (SCP) on cerebral oxidative stress in the immature brain is unknown. We examined early changes in cerebral markers of oxidative damage, apoptotic protein activation and histological outcome after different flows for SCP in a piglet model of deep hypothermic circulatory arrest (DHCA).

METHODS

Twenty piglets, randomly divided into four groups (each n = 5), were placed on cardiopulmonary bypass (CPB) at 20°C, then underwent DHCA for 60 minutes. SCP was conducted at flow rates of 0, 25, 50 and 80 ml·kg(-1)·min(-1) through the innominate artery in the DHCA, SCP 25, SCP 50, and SCP 80 groups, respectively. The animals were killed at 2 hours off CPB. Brain tissues were examined for the activity of SOD, MDA and caspase-3, and histological damage was quantitatively assayed by light microscopic examinations.

RESULTS

There were no significant differences in the activities of SOD, MDA and the SOD/MDA index between the groups. Caspase-3 activity significantly decreased in the SCP 25, SCP 50 and SCP 80 groups compared with the DHCA group. However, the caspase-3 level was higher in the SCP 80 group than in the SCP 25 and SCP 50 group. There were no significant correlations between MDA, SOD, SOD/MDA index and caspase-3.

CONCLUSIONS

In this acute model, under different flows for SCP, cerebral MDA and SOD activities show no change, whereas activated caspase-3 has a marked change. There was no relationship between oxidative stress, indicated by MDA and SOD, and apoptotic protein activation in the early phase after DHCA.