EGFR Signal Transduction in Cancer Cells

<p>Arrows indicate stimulation, and T-bars, inhibition. EGFR-I, EGFR inhibitor; MEK, MAPK kinase.</p

Effect of Polyethylene Glycol on the Formation of Magnetic Nanoparticles Synthesized by <i>Magnetospirillum magnetotacticum</i> MS-1

<div><p>Magnetotactic bacteria (MTB) synthesize intracellular magnetic nanocrystals called magnetosomes, which are composed of either magnetite (Fe₃O₄) or greigite (Fe₃S₄) and covered with lipid membranes. The production of magnetosomes is achieved by the biomineralization process with strict control over the formation of magnetosome membrane vesicles, uptake and transport of iron ions, and synthesis of mature crystals. These magnetosomes have high potential for both biotechnological and nanotechnological applications, but it is still extremely difficult to grow MTB and produce a large amount of magnetosomes under the conventional cultural conditions. Here, we investigate as a first attempt the effect of polyethylene glycol (PEG) added to the culture medium on the increase in the yield of magnetosomes formed in <i>Magnetospirillum magnetotacticum</i> MS-1. We find that the yield of the formation of magnetosomes can be increased up to approximately 130 % by adding PEG200 to the culture medium. We also measure the magnetization of the magnetosomes and find that the magnetosomes possess soft ferromagnetic characteristics and the saturation mass magnetization is increased by 7 %.</p></div

Effect of PEGs added to the culture medium on the growth of <i>M</i>. <i>magnetotacticum</i> MS-1.

<p>The cell concentration was evaluated, counting directly the number of cells in the culture medium using a Bacteria Counting Chamber. The closed circles, squares and triangles, and open circles and squares, respectively, correspond to the growth curves in the absence of PEG and in the presence of PEG200, PEG6,000, PEG20,000, and PEG500,000. The average values were calculated from three independent experiments. The error bars represent the standard deviations.</p

Effect of PEGs on the growth of <i>M</i>. <i>magnetotacticum</i> MS-1 and the formation of magnetosomes.

<p><b>*</b> The cell concentration was evaluated, counting directly the number of cells in the culture medium using a Bacteria Counting Chamber.</p><p>*<b>*</b> The average values were obtained from two independent experiments.</p><p>*<b>*</b>* Normalized production rate of magnetosomes <i>P</i> was defined by </p><p></p><p></p><p></p><p><mi>P</mi><mo>=</mo></p><p><mi>C</mi><mi>p</mi></p><mo>×</mo><p><mi>N</mi><mi>p</mi></p><p><mrow></mrow><mrow></mrow></p><mo>/</mo><mo stretchy="false">(</mo><p><mi>C</mi><mn>0</mn></p><mo>×</mo><p><mi>N</mi><mn>0</mn></p><mo stretchy="false">)</mo><mo>,</mo><p></p><p></p><p></p><p></p> where <i>C</i>_<i>p</i> and <i>N</i>_<i>p</i> are, respectively, the final cell concentration and the average number of magnetosomes synthesized in each cell in the presence of PEG, whereas <i>C</i>₀ and <i>N</i>₀ are those in the absence of PEG.<p></p><p>Effect of PEGs on the growth of <i>M</i>. <i>magnetotacticum</i> MS-1 and the formation of magnetosomes.</p

TEM images of magnetosomes synthesized in <i>M</i>. <i>magnetotacticum</i> MS-1 incubated in the culture medium containing PEGs.

<p>(A) Magnetosomes synthesized in the absence of PEG; (B), (C), (D), (E) Magnetosomes synthesized in the presence of 0.5% PEG200, 0.5% PEG6,000, 0.5% PEG20,000, and 0.5% PEG500,000. The scale bars represent 0.5 μm.</p

Formation of Core-Shell Nanoparticles Composed of Magnetite and Samarium Oxide in <i>Magnetospirillum magneticum</i> Strain RSS-1

<div><p>Magnetotactic bacteria (MTB) synthesize magnetosomes composed of membrane-enveloped magnetite (Fe₃O₄) or greigite (Fe₃S₄) particles in the cells. Recently, several studies have shown some possibilities of controlling the biomineralization process and altering the magnetic properties of magnetosomes by adding some transition metals to the culture media under various environmental conditions. Here, we successfully grow <i>Magnetospirillum magneticum</i> strain RSS-1, which are isolated from a freshwater environment, and find that synthesis of magnetosomes are encouraged in RSS-1 in the presence of samarium and that each core magnetic crystal composed of magnetite is covered with a thin layer of samarium oxide (Sm₂O₃). The present results show some possibilities of magnetic recovery of transition metals and synthesis of some novel structures composed of magnetic particles and transition metals utilizing MTB.</p></div

TEM images of strain RSS-1, magnetosomes and extracted magnetic nanoparticles.

<p>(a) TEM image of a strain RSS-1 cell grown in the medium containing 250 μM Fe-q:250 μM Sm-q. (b) HRTEM image of magnetic nanoparticles extracted from strain RSS-1 grown in the presence of 250 μM Fe-q:250 μM Sm-q. (c) Magnified image of a magnetic nanoparticle indicated by a red square in image (b). Red arrows indicate a surface layer covering the core magnetic nanoparticle.</p

ZFC and FC magnetization curves.

<p>The curves are normalized by the maximum values of the saturation magnetization. Field-cooling (FC) and zero-field-cooling (ZFC) measurements of the magnetization of magnetite nanoparticles synthesized by strain RSS-1 grown in the presence of 250 μM Fe-q and 250 μM Fe-q:250 μM Sm-q are shown. Arrows show the Verwey transition temperature (<i>T</i>_v).</p

Growth curves of strain RSS-1, the number of magnetic nanoparticles synthesized in each cell and the size distribution of Fe₃O₄ NPs and Fe₃O₄@Sm₂O₃ core-shell NPs.

<p>(a) Growth of strain RSS-1 in the medium containing iron and/or samarium quinate. (b) Distribution of the number of magnetic nanoparticles in each cell. (c) Distribution of the size of Fe₃O₄ NPs and Fe₃O₄@Sm₂O₃ core-shell NPs.</p

HRSTEM image and STEM-EDS elemental maps of magnetite nanoparticles.

<p>STEM-EDS elemental maps corresponding to Fe, O and Sm, and overlay of the three elements are shown.</p