Structural aspects of the association of FcepsilonRI with detergent-resistant membranes

We recently showed that aggregation of the high affinity IgE receptor on mast cells, FcepsilonRI, causes this immunoreceptor to associate rapidly with specialized regions of the plasma membrane, where it is phosphorylated by the tyrosine kinase Lyn. In this study, we further characterize the detergent sensitivity of this association on rat basophilic leukemia-2H3 mast cells, and we compare the capacity of structural variants of FcepsilonRI and other receptors to undergo this association. We show that this interaction is not mediated by the beta subunit of the receptor or the cytoplasmic tail of the gamma subunit, both of which are involved in signaling. Using chimeric receptor constructs, we found that the extracellular segment of the FcepsilonRI alpha subunit was not sufficient to mediate this association, implicating FcepsilonRI alpha and/or gamma transmembrane segments. To determine the specificity of this interaction, we compared the association of several other receptors. Interleukin-1 type I receptors on Chinese hamster ovary cells and alpha4 integrins on rat basophilic leukemia cells showed little or no association with isolated membrane domains, both before and after aggregation on the cells. In contrast, interleukin-2 receptor alpha (Tac) on Chinese hamster ovary cells exhibited aggregation-dependent membrane domain association similar to FcepsilonRI. These results provide insights into the structural basis and selectivity of lipid-mediated interactions between certain transmembrane receptors and detergent-resistant membranes.     

Docosahexaenoic Acid Incorporation Is Not Affected by Doxorubicin Chemotherapy in either Whole Cell or Lipid Raft Phospholipids of Breast Cancer Cells in vitro and Tumor Phospholipids in vivo

To better understand how docosahexaenoic acid (DHA) improves the effects of doxorubicin (DOX), we examined DHA ± DOX on changes in whole cell and lipid raft phospholipids (PL) of MDA-MB-231 and MCF-7 breast cancer cells. We sought to confirm whether the relative changes in PL DHA content of MDA-MB-231 cells could be extended to PL from MDA-MB-231 tumors grown in mice fed a DHA supplemented diet ±DOX. Treatment with DHA did not change PL composition yet DOX increased the proportion of phosphatidylserine in MCF-7 cell lipid rafts by two-fold (p < 0.001). Regardless of DOX, the relative percent incorporation of DHA was higher in MDA-MB-231 cells compared to MCF-7 cells in phosphatidylserine, phosphatidylethanolamine, and phosphatidylcholine (whole cell and lipid rafts); and higher in phosphatidylethanolamine vs. phosphatidylcholine (4.4-fold in MCF-7 and 6-fold in MDA-MB-231 cells respectively). DHA treatment increased eicosapentaenoic acid and docosapentaenoic acid in MDA-MB-231 cells but not MCF-7 cells. Increased DHA content in MDA-MB-231 cells, MCF-7 cells, and MDA-MB-231 tumors in all PL moieties (except sphingomyelin) corresponded with reduced arachidonic acid (p < 0.05). Feeding mice 2.8% (w/w of fat) DHA ± DOX increased tumor necrotic regions (p < 0.05). This study established differential incorporation of DHA into whole cell and lipid rafts between human breast cancer cell lines. However, within each cell line, this incorporation was not altered by DOX confirming that DOX does not change membrane lipid composition. Furthermore, our findings indicate that membrane changes observed in vitro are translatable to in vivo changes and that DHA + DOX could contribute to the anticancer effects through increased necrosis.     

Lubricant behaviour in loaded rubber contacts

In some work on the lubrication of soft contacts using optical interferometry a number of effects have been brought to light which are complementary to work of Gaman, Higginson and Harman [1]. In the present work the normal approach of a rubber specimen to a flat glass plate is taken to the point where the lubricant completely disappears. A simple theoretical model shows that the disappearance of the fluid is due to absorption of the fluid into the rubber and not a squeezing out through the very thin residual film existing around the trapped bubble.     

High-speed photographic studies of impact on thin layers of emulsion explosive

A photographic study, at microsecond framing rates, has been made of the impact behaviour of thin layer samples of emulsion explosives. The experiments were performed using a drop-weight apparatus with transparent anvils. The effects of incorporating aluminium granules (∼100 μm in size) and glass microspheres (50 μm to 150 μm diameter) in the emulsion matrix were also studied. It was possible to record the flow of the emulsion both with and without additives. Of particular interest were observations of the onset and development of crystallization in the layer. In no case was there evidence for initiation of explosion.