Crystal structure of HIV-1 primary receptor CD4 in complex with a potent antiviral antibody

Ibalizumab is a humanized, anti-CD4 monoclonal antibody. It potently blocks HIV-1 infection and targets an epitope in the second domain of CD4 without interfering with immune functions mediated by interaction of CD4 with major histocompatibility complex (MHC) class II molecules. We report here the crystal structure of ibalizumab Fab fragment in complex with the first two domains (D1-D2) of CD4 at 2.2 Å resolution. Ibalizumab grips CD4 primarily by the BC-loop (residues 121-125) of D2, sitting on the opposite side of gp120 and MHC-II binding sites. No major conformational change in CD4 accompanies binding to ibalizumab. Both monovalent and bivalent forms of ibalizumab effectively block viral infection, suggesting that it does not need to crosslink CD4 to exert antiviral activity. While gp120-induced structural rearrangements in CD4 are probably minimal, CD4 structural rigidity is dispensable for ibalizumab inhibition. These results could guide CD4-based immunogen design and lead to a better understanding of HIV-1 entry.

Abstract P2-07-06: Role of CaMKK2-AMPK Signaling in Breast Cancer Metabolic and Hypoxic Stress Responses

Background: Adenosine monophosphate-activated protein kinase (AMPK) is a major regulator of energy homeostasis at both the cellular and whole-body levels. AMPK is activated by elevated intracellular AMP level and by phosphorylation on threonine 172 (T172) in the activation loop of the α catalytic subunit by upstream kinases, LKB1 and Ca2+/calmodulin-dependent protein kinase kinase 2 (CaMKK2). Once activated, AMPK switches on ATP-producing pathways while switching off ATP-consuming processes. Recent studies suggest that AMPK also controls processes relevant to tumor development, including protein synthesis, cell cycle progression, cell growth, survival and stress-induced autophagy. The purpose of our study is to determine the role of CaMKK2 as an AMPK upstream kinase in breast cancer cells, as well as its function in regulating cell proliferation, migration and survival. We chose the prototypical ERα + MCF-7 breast cancer cell line as our research model since this cell line does not express CaMKK1, which has similar functions to CaMKK2 but cannot activate AMPK.

Materials and Methods: Illumina cDNA expression array was preformed on MCF-7, T-47D and MDA-MB-231 breast cancer cell lines, and normalized by rank-invariant method. MCF-7 cells with suppressed CaMKK2 or LKB1 expression were established using lentiviral gene specific shRNA interference. Stable knockdown cells (shNon-Target, shCaMKK2, shLKB1) were subject to acute and chronic stress conditions (i.e. ionomycin, 2-deoxy-D-glucose, hypoxia) and signaling events were evaluated using immunoblot analysis. Proliferation, anchorage-independent growth and motility of the knockdown cells were determined by MTT, soft agar formation and in vitro migration assay. Xenograft tumor studies were performed by inoculating estradiol-supplemented athymic nude mice with shNon-Target, shCaMKK2 and shLKB1 MCF-7 cells into the mammary fat pad. Tumor growth was determined by external caliper measurements twice a week. Forty-five days post-injection, mice were euthanized, tumors removed, weighed and prepared for histological, protein and RNA analyses.

Results: CaMKK2 and LKB1 mRNAs are expressed at a similar level in the ERα + and ERα — breast cancer cell lines tested in the Illumina cDNA expression array. CaMKK2 activated AMPK phosphorylation (T172) under increased intracellular Ca2+ level induced by ionomycin. Under acute stress conditions, CaMKK2 functioned as the predominant AMPK upstream kinase. However, when cells are subject to long-term metabolic and hypoxic stress, CaMKK2 and LKB1 were both required for AMPK activation. Loss of CaMKK2 in MCF-7 cells promoted a moderate growth advantage under metabolic stress, increased soft agar colony formation and elevated cell migration capacity. CaMKK2 knockdown xenografts demonstrated less ductal structure formation, decreased E-Cadherin expression and reduced angiogenesis, as well as reduced VEGF and Glut1 mRNA levels in vivo.

Conclusions: We have demonstrated that Ca2+-CaMKK2 signaling plays an important role in regulating breast cancer cell proliferation, migration and survival pathways. These findings suggest that Ca2+ activation through CaMKK2 promotes AMPK signaling, survival and angiogenesis in response to stress conditions in breast cancer cells.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P2-07-06.

Salivary Streptococcus mutans level: value in caries prediction for 11-12-year-old children

OBJECTIVES

To analyze the associations of salivary Streptococcus mutans (SM) level with caries experience and incidence in children.

METHODS

Five hundred 11-12-year-old children participated in this study, one year later at follow-up 485 children remained. Scores of decayed, missing or filled (DMF) indices were recorded according to WHO criteria at baseline and at follow-up. Baseline salivary SM concentrations were determined with species-specific monoclonal antibodies.

RESULTS

Pearson's correlation coefficient for SM concentration and DMFS at baseline was 0.14 (P = 0.002), for SM concentration and DMFS increment was 0.22 (P < 0.001), for baseline DMFS and caries increment was 0.39. Salivary SM concentration was divided into three categories (scoring 1-3 respectively): 0.01-3, 3.01-25, and > 25 x 10(4)/ml. Compared with children who were classified as category 1, children in category 2 were approximately twice as likely to develop new carious lesions (relative risk = 1.83), whereas those in category 3 were about three times as likely (relative risk = 2.67). However, caries prediction based on salivary SM levels provided negative predictive values (0.770-0.839) much higher than positive predictive values (0.341-0.436).

CONCLUSIONS

Salivary SM level associates positively with caries experience, caries incidence and increment. Caries prediction solely relied on salivary SM levels is not recommended. However, such test may help to identify those at risk children who have not been affected by caries yet.

Deposition of high-quality HfO2 on graphene and the effect of remote oxide phonon scattering

We demonstrate atomic layer deposition of high-quality dielectric HfO2 films on graphene and determine the magnitude of remote oxide surface phonon scattering in dual-oxide structures. The carrier mobility in these HfO2-covered graphene samples reaches 20,000  cm2/V s at low temperature. Distinct contributions to the resistivity from surface optical phonons in the SiO2 substrate and the HfO2 overlayer are isolated. At 300 K, surface phonon modes of the HfO2 film centered at 54 meV limit the mobility to approximately 20,000  cm2/V s.

AZGP1 is a tumor suppressor in pancreatic cancer inducing mesenchymal-to-epithelial transdifferentiation by inhibiting TGF-β-mediated ERK signaling

Epithelial-to-mesenchymal transdifferentiation (EMT) mediated by transforming growth factor-β (TGF-β) signaling leads to aggressive cancer progression. In this study, we identified zinc-α2-glycoprotein (AZGP1, ZAG) as a tumor suppressor in pancreatic ductal adenocarcinoma whose expression is lost due to histone deacetylation. In vitro, ZAG silencing strikingly increased invasiveness of pancreatic cancer cells accompanied by the induction of a mesenchymal phenotype. Expression analysis of a set of EMT markers showed an increase in the expression of mesenchymal markers (vimentin (VIM) and integrin-α5) and a concomitant reduction in the expression of epithelial markers (cadherin 1 (CDH1), desmoplakin and keratin-19). Blockade of endogenous TGF-β signaling inhibited these morphological changes and the downregulation of CDH1, as elicited by ZAG silencing. In a ZAG-negative cell line, human recombinant ZAG (rZAG) specifically inhibited exogenous TGF-β-mediated tumor cell invasion and VIM expression. Furthermore, rZAG blocked TGF-β-mediated ERK2 phosphorylation. PCR array analysis revealed that ZAG-induced epithelial transdifferentiation was accompanied by a series of concerted cellular events including a shift in the energy metabolism and prosurvival signals. Thus, epigenetically regulated ZAG is a novel tumor suppressor essential for maintaining an epithelial phenotype.

Overexpression or Lack of beta 2-Adrenergic Receptor Correlate with Progression of Breast Cancer

Background: Recent studies showed that stress can modulate biological behavior of ovarian carcinoma through adrenergic receptors. Since both nonselective beta-adrenergic receptor antagonist propranolol and selective beta 2-adrenergic receptor (b2AR) antagonist ICI 118,551 instead of b1AR antagonist atenolol could eliminate most of the effects, b2AR is accordingly regarded as the key molecule. In this study, we investigated the role of b2AR in breast cancer. Material and Methods: Gene expression of b2AR was analyzed by RT-PCR in human breast cancer cell lines MDA-MB-231, MDA-MB-435, MDA-MB-468, MCF-7, T47D, BT-549, HCC1937, BCaP-37 and normal mammary epithelial-like cell line HBL-100. b2AR cDNA was transfected into MDA-MB-435 cells. Protein level of b2AR was analyzed by immunohistochemistry in clinical samples, including 25 normal human breast or benign disease breast tissues and 202 breast cancer tissues. Results: b2AR was detected in majority of breast cancer cell lines, except for MDA-MB-435, MCF-7 and T47D, and all of normal or benign disease breast tissues. Both nonselective beta-adrenergic receptor agonist norepinephrine (NE) and selective b2AR agonist terbutaline promoted proliferation and invasion of spontaneous b2AR-positive MDA-MB-231 cells and transfectant MDA-MB-435-b2AR cells, these effects were completely inhibited by selective b2AR antagonist ICI 118,551. In the breast cancer patients, 125 samples (61.9%) expressed b2AR weakly or moderately just as normal breast or benign diseases tissue, and 43 (21.3%) presented significantly stronger b2AR expression, while no b2AR staining was found in other 34 samples (16.8%). Higher expression or lack of b2AR were associated with axillary lymph nodes metastasis and poor disease free survival (DFS). Discussion: Based on our preliminary results, the breast cancer patients could be classified into three subgroups: b2AR “normal”, high expression and negative groups. Overexpression or lack of b2AR associated with metastasis and clinical prognosis in breast cancer. Obviously, abnormal expression of b2AR may influence the outcome of breast cancer.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 4165.

Expression of the Cancer Stem Cell Marker ALDH1A1 in Primary Breast Cancer: A Mechanism for Chemotherapy Resistance

Background: Aldehyde dehydrogenase 1 (ALDH1) has been identified as a marker of breast cancer stem cells, and ALDH1 expression in primary breast tumors has been associated with resistance to chemotherapy and poor prognosis. ALDH1 is an enzyme that can detoxify reactive aldehyde compounds; however the mechanism of ALDH1 chemotherapy resistance and its promotion of the breast cancer stem cell phenotype is unclear. Materials and Methods: Illumina cDNA array was performed on primary breast tumors that were snap-frozen, and RNA was isolated from dense, viable tumor regions. Samples were normalized by rank-invariant method and gene expression was analyzed. Immunohistochemistry was performed for ALDH1A1 on initial and post-neoadjuvant tumor samples from patients who have undergone six cycles of chemotherapy. Clinical data including age, tumor pathology, lymph node status, and response to neoadjuvant therapy were available for analysis. Human breast cancer cell lines (MCF-7 and MDA-MB-468) were treated with increasing doses of retinoic acid (RA) with and without the retinoic acid receptor alpha antagonist, Ro 41-5253. Effects on cell proliferation and signal transduction pathways were assessed. Results: The expression of ALDH1A1 and/or ALDH1A3 isoform mRNA was found to be present in primary human breast tumors. The majority of these cases were noted as triple negative or Her-2 positive tumors. Evaluation of RA receptor expression revealed repressed RAR beta levels in all tumors, whereas RAR alpha expression was retained. Observations of patient tumor samples (pre and post neoadjuvant chemotherapy treatment) demonstrated high ALDH1A1 expression in tumor and stromal cell compartments. The expression was predominant in partial and non-responders to the neoadjuvant therapy. Interestingly, the tumor from a partial responder was converted to extremely high expresser of ALDH1A1 post-neoadjuvant therapy indicating a positive survival selection. Since ALDH1A1 can convert retinaldehyde to retinoic acid, breast cancer cell lines were treated with all-trans RA and responded with a significant decrease in cell proliferation. This effect was partially attenuated by pre-treatment with the RAR alpha antagonist, Ro 41-5253. Importantly, RA treatment of MCF-7 cells repressed MAPK signaling, which was also attenuated by pre-treatment with Ro 41-5253. Discussion: The observations from this study suggest that the expression of the breast cancer stem cell marker, ALDH1A1 on tumor cells or in tumor-associated stromal cells can provide a mechanism for survival of cancer during chemotherapy treatment. The conversion of therapeutic oxidant compounds to retinoic acid by ALDH1 may lead to increased RAR alpha signaling and suppression of proliferation. The suppression of proliferation correlates well with chemotherapy resistance in these neoadjuvant cases. This data demonstrates a possible mechanism for ALDH1 promotion of tumor cell survival under chemotherapy and suggests that treatment with RAR alpha antagonists may promote tumor cell susceptibility to current treatment modalities and improve the therapeutic window for primary, metastatic and chemo-refractory breast cancer.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 1135.

Distribution of ABO blood group allele and identification of three novel alleles in the Chinese Han population

BACKGROUND

The ABO blood group system is clinically important in blood transfusion. The molecular characterization of ABO blood group has clinical and anthropological importance. Here, we determined the ABO alleles distribution and identified three novel alleles in the Chinese Han population.

STUDY DESIGN AND METHODS

Four hundred and seventeen Chinese Han individuals were determined by standard serologic techniques for the ABO blood group phenotypes. The ABO genotypes and alleles were analysed by polymerase chain reaction sequence-based typing (PCR-SBT) for sequencing exon 6 to 7 of the ABO gene. The polymorphisms of intron 5 and 6 of the ABO gene were also analysed by PCR-SBT. The two haplotypes including new alleles were separated by a Dynabeads M-270 Streptavidin protocol.

RESULTS

All ABO genotypes of the samples were consistent with the phenotypes. Fourteen alleles were identified based on the nucleotide sequences of exon 6 and 7, with five common alleles (A101, A102, B101, O01 and O02), six known rare alleles (A205, B110, O04, O05, O07 and O50) and three novel alleles (B112, CisAB06 and 061). The three new alleles appeared with the frequencies of 0.12%, 0.12% and 0.36%, respectively.

CONCLUSION

The detailed frequencies distribution of ABO alleles was studied in the Chinese Han population. We identified 14 alleles, including 3 novel alleles.

High quality x-ray absorption spectroscopy measurements with long energy range at high pressure using diamond anvil cell

We describe an approach for acquiring high quality x-ray absorption fine structure (XAFS) spectroscopy spectra with wide energy range at high pressure using diamond anvil cell (DAC). Overcoming the serious interference of diamond Bragg peaks is essential for combining XAFS and DAC techniques in high pressure research, yet an effective method to obtain accurate XAFS spectrum free from DAC induced glitches has been lacking. It was found that these glitches, whose energy positions are very sensitive to the relative orientation between DAC and incident x-ray beam, can be effectively eliminated using an iterative algorithm based on repeated measurements over a small angular range of DAC orientation, e.g., within +/-3 degrees relative to the x-ray beam direction. Demonstration XAFS spectra are reported for rutile-type GeO2 recorded by traditional ambient pressure and high pressure DAC methods, showing similar quality at 440 eV above the absorption edge. Accurate XAFS spectra of GeO2 glass were obtained at high pressure up to 53 GPa, providing important insight into the structural polymorphism of GeO2 glass at high pressure. This method is expected be applicable for in situ XAFS measurements using a diamond anvil cell up to ultrahigh pressures.

High-mobility few-layer graphene field effect transistors fabricated on epitaxial ferroelectric gate oxides

The carrier mobility mu of few-layer graphene (FLG) field-effect transistors increases tenfold when the SiO2 substrate is replaced by single-crystal epitaxial Pb(Zr0.2Ti0.8)O3 (PZT). In the electron-only regime of the FLG, mu reaches 7x10(4) cm(2)/V s at 300 K for n=2.4x10(12)/cm(2), 70% of the intrinsic limit set by longitudinal acoustic (LA) phonons; it increases to 1.4x10(5) cm(2)/V s at low temperature. The temperature-dependent resistivity rho(T) reveals a clear signature of LA phonon scattering, yielding a deformation potential D=7.8+/-0.5 eV.

Genetic and environmental contributions to allergen sensitization in a Chinese twin study

BACKGROUND

Allergic disease is on the rise worldwide. Effective prevention of allergic disease requires comprehensive understanding of the factors that contribute to its intermediate phenotypes, such as sensitization to common allergens.

OBJECTIVE

To estimate the degree of genetic and environmental contributions to sensitization to food and aeroallergens.

METHODS

Sensitization was defined as a positive skin prick test to an allergen. We calculated the zygosity-specific concordance rates and odds ratios (ORs) for sensitization to food and aeroallergens in 826 Chinese twin pairs [472 monozygotic (MZ) and 354 dizygotic (DZ)] aged 12-28 years. We also applied structural equation modelling procedures to estimate genetic and environmental influences on sensitization.

RESULTS

The concordance rates and risk of sensitization in one twin given the presence vs. the absence of sensitization in the other twin were higher in MZ twins than those in DZ twins. However, a large number of MZ twins were discordant in sensitization to common allergens. These observations suggest both genetic and environmental factors influence sensitization. Consistently, the estimated heritability and individual environmental components of the liability to sensitization ranged from 0.51 to 0.68 and 0.32 to 0.49, respectively, based on the best-fitted structural equation model. We also observed high phenotypic correlations between sensitization to two aeroallergens (cockroach and dust mite: 0.83) and two food allergens (peanut and shellfish: 0.58), but only moderate correlations for the pairs between sensitization to a food and an aeroallergen (0.31-0.46). The shared genetic and environmental factors between paired sensitizations contribute to the observed correlations.

CONCLUSION

We demonstrated that sensitization to common food and aeroallergens were influenced by both genetic and environmental factors. Moreover, we found that paired allergen sensitizations might share some common sets of genes and environmental factors. This study underscores the need to further delineate unique and/or pleiotropic genetic and environmental factors for allergen sensitization.

Combining solution wide-angle X-ray scattering and crystallography: determination of molecular envelope and heavy-atom sites

Solving the phase problem remains central to crystallographic structure determination. A six-dimensional search method of molecular replacement (FSEARCH) can be used to locate a low-resolution molecular envelope determined from small-angle X-ray scattering (SAXS) within the crystallographic unit cell. This method has now been applied using the higher-resolution envelope provided by combining SAXS and WAXS (wide-angle X-ray scattering) data. The method was tested on horse hemoglobin, using the most probable model selected from a set of a dozen bead models constructed from SAXS/WAXS data using the program GASBOR at 5 A resolution (q(max) = 1.25 A(-1)) to phase a set of single-crystal diffraction data. It was found that inclusion of WAXS data is essential for correctly locating the molecular envelope in the crystal unit cell, as well as for locating heavy-atom sites. An anomalous difference map was calculated using phases out to 8 A resolution from the correctly positioned envelope; four distinct peaks at the 3.2sigma level were identified, which agree well with the four iron sites of the known structure (Protein Data Bank code 1ns9). In contrast, no peaks could be found close to the iron sites if the molecular envelope was constructed using the data from SAXS alone (q(max) = 0.25 A(-1)). The initial phases can be used as a starting point for a variety of phase-extension techniques, successful application of which will result in complete phasing of a crystallographic data set and determination of the internal structure of a macromolecule to atomic resolution. It is anticipated that the combination of FSEARCH and WAXS techniques will facilitate the initial structure determination of proteins and provide a good foundation for further structure refinement.