Calorimetric and Fourier transform infrared spectroscopic studies on the interaction of glycophorin with phosphatidylserine/dipalmitoylphosphatidylcholine-d62 mixtures

Glycophorin has been isolated in pure form from human erythrocyte membranes and reconstituted into lipid vesicles composed of binary mixtures of bovine brain phosphatidylserine (PS) and acyl-chain perdeuterated dipalmitoylphosphatidylcholine (DPPC-d62). The effect of protein on lipid melting behavior and order has been monitored with differential scanning calorimetry and Fourier transform infrared spectroscopy (FT-IR). The phase diagram for PS/DPPC-d62 is consistent with that previously reported for PS/DPPC (Stewart et al. (1979) Biochim. Biophys. Acta 556, 1-16) and indicates that acyl chain perdeuteration does not greatly alter the lipid mixing characteristics. The use of deuterated lipid allows the examination of lipid order by FT-IR of each lipid component in the binary mixtures as well as in the ternary (lipid/lipid/protein) systems. Addition of glycophorin to a 30:70 PS/DPPC-d62 binary lipid mixture results in a preferential glycophorin/PS interaction leading to bulk lipid enriched in DPPC-d62. This is revealed in two ways: first, through cooperative calorimetric transitions increased in temperature from the binary lipid system and second, through FT-IR melting curves of the DPPC-d62 component which shows transitions increased in both onset and completion temperatures in the presence of protein. In addition, non-cooperative melting events are observed at temperatures below the onset of phase separation. The FT-IR data are used to assign these non-cooperative events to the melting of the PS component. For the 50:50 lipid mixture with protein, two transitions are observed in the DSC experiments. The IR results indicate that both lipid components are involved with the lower temperature event.     

Use of deuterated phospholipids in raman spectroscopic studies of membrane structure. I. Multilayers of dimyristoyl phosphatidylcholine (and its -d54 derivative) with distearoyl phosphatidylcholine

The temperature dependence of the Raman spectrum has been studied for binary phospholipid mixtures of dimyristoyl phosphatidylcholine (and its chain deuterated $\text{-d}{}_{54}$ derivative) with distearoyl phosphatidylcholine. Two distinct melting regions are observed for the 1 : 1 mole ratio mixture. The use of deuterated phospholipid permits the identification of the lower (≈22°C) transition with primarily the melting of the shorter chain component, and the higher (≈47°C) transition primarily with the melting of the longer chains. The C-H stretching vibrations of the distearoyl component respond to the melting of the dimyristoyl component, an apparent consequence of alterations in the lateral interactions of the distearoyl chains. These changes in the C-H spectral region suggest that phase separation does not occur in the gel state for this system. The results are in reasonable accord with recent calorimetric studies (Mabrey, S. and Sturtevant, J.M. (1976) Proc. Natl. Acad. Sci. U.S. 73, 3862–3866). The feasibility of using deuterated phospholipids to monitor the conformation of each component in a binary phospholipid mixture is demonstrated.     

Identification of Tumor Antigens in the HLA Peptidome of Patient-derived Xenograft Tumors in Mouse

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Highlights

• •Sufficient tumor tissues are often unavailable large HLA peptidome discovery.
• •Using patient derived xenograft (PDX) tumors can overcome this limitation.
• •The large PDX HLA peptidomes expand significantly those of the original biopsies.
• •The HLA peptidomes of the PDX tumors included many tumor antigens.

     

Regulation of phosphorylation of the c-erbB-2/HER2 gene product by a monoclonal antibody and serum growth factor(s) in human mammary carcinoma cells.

Monoclonal antibody (MAb) 4D5 was used to analyze the phosphorylation of p185HER2, the gene product of c-erbB-2/HER2, in SK-BR-3 cells. Culture in the continuous presence of 4D5 reduced the in vivo steady-state levels of p185HER2 phosphorylation by 80% in a dose-dependent manner, suggesting that MAb 4D5 may have interfered with the activation of phosphorylation of p185HER2. The observed MAb-mediated reduction of p185HER2 phosphorylation could not be completely accounted for by down-regulation. When cultures were grown under serum-free conditions, the steady-state levels of p185HER2 phosphorylation were reduced by 56%, and addition of 4D5 further inhibited phosphorylation to 20% of steady-state levels. With continuous exposure to increasing concentrations of newborn calf serum in these cultures, there was a linear increase in tyrosine-specific phosphorylation of p185HER2, reaching a 5.4-fold increase with 10% newborn calf serum. Phosphorylation of p185HER2 in the presence of newborn calf serum was not attributable to stimulation of the epidermal growth factor receptor by epidermal growth factor or by transforming growth factor-alpha. Extension of these observations to two other mammary carcinoma cell lines. MDA-MB-453 and BT-474, also demonstrated a significant capacity of serum to induce p185HER2 phosphorylation. The demonstration of antibody-mediated partial inhibition of phosphorylation under serum-free conditions suggests that mammary carcinoma cells may also produce and secrete a factor or factors which may activate p185HER2. Our observation that growth-inhibitory MAb 4D5 is able to reduce the phosphorylation of p185HER2 by newborn calf serum and by a cellular-derived factor(s) suggests the existence of a growth factor(s) which uses phosphorylation of p185HER2 as a signal transduction pathway to regulate cell proliferation.     

Anti-epidermal growth factor receptor antibodies inhibit the autocrine-stimulated growth of MDA-468 human breast cancer cells

The response of malignant and nonmalignant human breast cell lines to the growth inhibitory effects of monoclonal antibodies against the epidermal growth factor (EGF) receptor was studied. A series of human breast cell lines, which express EGF receptor, were used: MDA-468, MDA-231, and Hs578T human breast cancer cells and the transformed human mammary epithelial cell lines 184A1N4 and 184A1N4-T that have been benzo[a]pyrene immortalized and further transformed with SV40T, respectively. Four antibodies of two different classes were tested: 225 immunoglobulin G (IgG), 108.4 IgG, 96 immunoglobulin M (IgM), and 42 IgM. All four antibodies inhibited the anchorage-dependent and -independent, EGF-stimulated growth of 184A1N4 and 184A1N4-T cells, respectively, and this growth inhibition could be reversed by the addition of increasing concentrations of EGF. In contrast, the antibodies inhibited the anchorage-dependent and -independent growth of MDA-468 cells in the absence of exogenous EGF suggesting that the antibodies were acting to block access of an endogenously produced ligand to the EGF receptor. In the presence of antibody and increasing concentrations of EGF, MDA-468 cell growth was first stimulated then inhibited as the EGF concentration increased, thus, uncovering the growth stimulatory potential of low concentrations of EGF in these cells. Data is presented that indicates MDA-468 cells secrete a transforming growth factor with autocrine growth stimulatory capabilities. The growth of MDA-231 and Hs578T cells, which contain activated ras oncogenes, was not inhibited by the antibodies and the growth of these cell lines was not stimulated by EGF. Of the cell lines studied only MDA-468 cells appear to possess an autocrine growth stimulatory capacity.     

Primary culture of axolotl spinal cord ependymal cells

In order to examine the role of ependymal cells in the spinal cord regeneration of urodele amphibians, procedures were established to identify and culture these cells. Cell isolation and culture conditions were determined for ependymal cells from larval and adult axolotls (Ambystoma mexicanum). Dissociated cells prepared from intact spinal cords were cultured on fibronectin- or laminin-coated dishes. Dissociated cells attached more rapidly to fibronectin, but attached and spread on both fibronectin and laminin. Essentially pure populations of ependymal cells were obtained by removing 2 week old ependymal outgrowth from lesion sites of adult spinal cords. These ependymal outgrowths attached and grew only on fibronectin-coated dishes. Growth and trophic factors were tested to formulate a medium that would support ependymal cell proliferation. The necessary peptide hormones were PDGF, EGF, and insulin. TGF-beta(1) affected the organization of cell outgrowth. Initially, longterm culture required the presence of high levels of axolotl serum. Addition of purified bovine hemaglobin in the culture medium reduced the serum requirement. Outgrowth from expiants was subcultured by transferring groups of cells. Intrinsic markers were used to identify ependymal cells in culture. The ependymal cells have characteristic ring-shaped nucleoli in both intact axolotl spinal cords and in culture. Indirect immunofluorescence examination of intermediate filaments showed that ependymal cells were glial fibrillary acidic protein (GFAP) negative and vimentin positive in culture. Identification of dividing cells was made using (3)H-thymidine incorporation and autoradiography, and by the presence of mitotic figures in the cultured cells.     

Infrared reflection-absorption of melittin interaction with phospholipid monolayers at the air/water interface.

The interaction of melittin with monolayers of 1,2-dipalmitoylphosphatidylcholine and 1,2-dipalmitoylphosphatidylserine has been investigated with infrared external reflection-absorption spectroscopy. Improved instrumentation permits determination of acyl chain conformation and peptide secondary structure in situ at the air/water interface. The IR frequency of the 1,2-dipalmitoylphosphatidylcholine antisymmetric acyl chain CH2 stretching vibration decreases by 1.3 cm-1 upon melittin insertion, consistent with acyl chain ordering, whereas the same vibrational mode increases by 0.5 cm-1 upon peptide interaction with the 1,2-dipalmitoylphosphatidylserine monolayer, indicative of chain disordering. Thus the peptide interacts quite differently with zwitterionic compared with negatively charged monolayer surfaces. Melittin in the monolayer adopted a secondary structure with an amide l(l') frequency (1635 cm-1) dramatically different from the alpha-helical motif (amide l frequency 1656 cm-1 in a dry or H2O hydrated environment, amide l' frequency 1645 cm-1 in an H-->D exchanged alpha-helix) assumed in bilayer or multibilayer environments. This work represents the first direct in situ spectroscopic indication that peptide secondary structure in lipid monolayers may differ from that in bilayers.     

External reflection FTIR of peptide monolayer films in situ at the air/water interface: experimental design, spectra-structure correlations, and effects of hydrogen-deuterium exchange.

A Fourier transform infrared spectrometer has been interfaced with a surface balance and a new external reflection infrared sampling accessory, which permits the acquisition of spectra from protein monolayers in situ at the air/water interface. The accessory, a sample shuttle that permits the collection of spectra in alternating fashion from sample and background troughs, reduces interference from water vapor rotation-vibration bands in the amide I and amide II regions of protein spectra (1520-1690 cm-1) by nearly an order of magnitude. Residual interference from water vapor absorbance ranges from 50 to 200 microabsorbance units. The performance of the device is demonstrated through spectra of synthetic peptides designed to adopt alpha-helical, antiparallel beta-sheet, mixed beta-sheet/beta-turn, and unordered conformations at the air/water interface. The extent of exchange on the surface can be monitored from the relative intensities of the amide II and amide I modes. Hydrogen-deuterium exchange may lower the amide I frequency by as much as 11-12 cm-1 for helical secondary structures. This shifts the vibrational mode into a region normally associated with unordered structures and leads to uncertainties in the application of algorithms commonly used for determination of secondary structure from amide I contours of proteins in D2O solution.