Differential effects of Fas cross-linking on phospholipase D activation and related lipid metabolism in Fas-resistant A20 cells

A20 murine lymphoma cells undergoing Fas-mediated apoptosis showed increase in the activity of phospholipase D (PLD), which is involved in proliferative or mitogenic cellular responses. Using A20 cell lines that were resistant to Fas-induced apoptosis, we investigated the differential effects of Fas cross-linking on PLD activity and sphingolipid metabolism. The basal PLD activities in all of the selected three Fas-resistant clones (#5, #8, and #11) were about 2~4 folds higher than that of wild type A20 cells. Among the PLD isoforms, PLD2 expression was increased in all of the selected Fas-resistant clones. The Fas downstream signaling events triggered by Fas cross-linking, including the activations of PLD, phosphatidylcholine-specific phospholipase C (PC-PLC), sphingomyelinase (SMase), the increase in diacylglycerol (DAG) and protein phosphorylation levels, and the translocation of protein kinase C to membrane were not changed in both of Fas-resistant clone #5 and #8. In contrast, Fas cross-linking stimulated the activity of PLD, PC-PLC, and SMase, translocation of PKC, and protein phosphorylation in Fas-resistant clone #11, similar to that of wild type cells. We also found that clone #11 had a different Fas sequence encoding Fas B which has been known to inhibit Fas-induced apoptosis. These findings suggest that increased PLD2 expression resulting in increased basal PLD activity and the blockade of Fas downstream signaling cascades may be involved to limit apoptosis induced by Fas cross-linking.     

A functional comparison between the HER2(high)/HER3 and the HER2(low)/HER3 dimers on heregulin-β1-induced MMP-1 and MMP-9 expression in breast cancer cells

Overexpression of HER2 correlates with more aggressive tumors and increased resistance to cancer chemotherapy. However, a functional comparison between the HER2(high)/HER3 and the HER2(low)/HER3 dimers on tumor metastasis has not been conducted. Herein we examined the regulation mechanism of heregulin- β1 (HRG)-induced MMP-1 and -9 expression in breast cancer cell lines. Our results showed that the basal levels of MMP-1 and -9 mRNA and protein expression were increased by HRG treatment. In addition, HRG-induced MMP-1 and -9 expression was significantly decreased by MEK1/2 inhibitor, U0126 but not by phosphatidylinositol 3-kinase (PI-3K) inhibitor, LY294002. To confirm the role of MEK/ERK pathway on HRG-induced MMP-1 and -9 expression, MCF7 cells were transfected with constitutively active adenoviral- MEK (CA-MEK). The level of MMP-1 and -9 expressions was increased by CA-MEK. MMP-1 and -9 mRNA and protein expressions in response to HRG were higher in HER2 overexpressed cells than in vector alone. The phosphorylation of HER2, HER3, ERK, Akt, and JNK were also significantly increased in HER2 overexpressed MCF7 cells compared with vector alone. HRG-induced MMP-1 and -9 expressions were significantly decreased by lapatinib, which inhibits HER1 and HER2 activity, in both vector alone and HER2 overexpressed MCF7 cells. Finally, HRG-induced MMP-1 and MMP-9 expression was decreased by HER3 siRNA overexpression. Taken together, we suggested that HRG-induced MMP-1 and MMP-9 expression is mediated through HER3 dependent pathway and highly expressed HER2 may be associated with more aggressive metastasis than the low expressed HER2 in breast cancer cells.     

On approximation of dominating tree in wireless sensor networks

We study the following problem: Given a weighted graph G = (V, E, w) with \({w: E \rightarrow \mathbb{Z}^+}\) , the dominating tree (DT) problem asks us to find a minimum total edge weight tree T such that for every \({v \in V}\) , v is either in T or adjacent to a vertex in T. To the best of our knowledge, this problem has not been addressed in the literature. Solving the DT problem can yield a routing backbone for broadcast protocols since (1) each node does not have to construct their own broadcast tree, (2) utilize the virtual backbone to reduce the message overhead, and (3) the weight of backbone representing the energy consumption is minimized. We prove the hardness of this problem, including the inapproximability result and present an approximation algorithm together with an efficient heuristic. Finally, we verify the effectiveness of our proposal through simulation.     

INHIBITION OF 80 kDa PROTEIN PHOSPHORYLATION BY SHORT-WAVELENGTH UV LIGHT IN NIH 3T3 CELLS

The exposure of NIH 3T3 fibroblast cells to 254 nm UV radiation resulted in a temporary depression of DNA synthesis and inhibition of 80 kDa protein phosphorylation. This inhibition of protein phosphorylation was correlated with decreased protein kinase C activity in the membrane fractions of UV-damaged cells. The inositol tnphosphate contents measured, by the competitive binding assay using bovine adrenal binding protein, showed 80% reduction in the fibroblasts treated with 15 J/m² of UV light. The intracellular diacylglycerol concentration was also markedly reduced in UV-damaged cells. The results suggest that UV light causes acute reductions of inositol triphosphate and diacylglycerol contents in cells along with decreases in membrane protein kinase C activity, which leads to the inhibition of phosphorylation of an acidic protein of 80 kDa.