A metalloprotease-disintegrin, MDC9/meltrin-gamma/ADAM9 and PKCdelta are involved in TPA-induced ectodomain shedding of membrane-anchored heparin-binding EGF-like growth factor.

The ectodomains of many proteins located at the cell surface are shed upon cell stimulation. One such protein is the heparin-binding EGF-like growth factor (HB-EGF) that exists in a membrane-anchored form which is converted to a soluble form upon cell stimulation with TPA, an activator of protein kinase C (PKC). We show that PKCdelta binds in vivo and in vitro to the cytoplasmic domain of MDC9/meltrin-gamma/ADAM9, a member of the metalloprotease-disintegrin family. Furthermore, the presence of constitutively active PKCdelta or MDC9 results in the shedding of the ectodomain of proHB-EGF, whereas MDC9 mutants lacking the metalloprotease domain, as well as kinase-negative PKCdelta, suppress the TPA-induced shedding of the ectodomain. These results suggest that MDC9 and PKCdelta are involved in the stimulus-coupled shedding of the proHB-EGF ectodomain.     

ALDH2 polymorphism for the risk of cervical carcinogenesis

To investigate the clinical significance of ALDH2 genetic polymorphisms in cervical carcinogenesis. ALDH2 polymorphisms together with human papillomavirus (HPV) types were examined in a total of 195 cervical smear in exfoliated cervical cell samples using Real-Time polymerase chain reaction (PCR) System. The frequency for the AG+AA genotype was seven in the normal group (70.0 %), 16 in the LSIL group (57.1 %), and 27 in the HSIL group (90.0 %). A significant difference was found between the LSIL and HSIL groups (P = 0.0064). Patients with HSIL lesions frequently had high-risk HPV infections and concurrently belonged to the AG+AA group. ALDH2 genotype in cervical cell samples may be associated with more severe precancerous lesions of the cervix in a Japanese population.     

Site-specific labeling of cytoplasmic peptide:N-glycanase by N,N'-diacetylchitobiose-related compounds

Peptide:N-glycanase (PNGase) is the deglycosylating enzyme, which releases N-linked glycan chains from N-linked glycopeptides and glycoproteins. Recent studies have revealed that the cytoplasmic PNGase is involved in the degradation of misfolded/unassembled glycoproteins. This enzyme has a Cys, His, and Asp catalytic triad, which is required for its enzymatic activity and can be inhibited by "free" N-linked glycans. These observations prompted us to investigate the possible use of haloacetamidyl derivatives of N-glycans as potent inhibitors and labeling reagents of this enzyme. Using a cytoplasmic PNGase from budding yeast (Png1), Man9GlcNAc2-iodoacetoamide was shown to be a strong inhibitor of this enzyme. The inhibition was found to be through covalent binding of the carbohydrate to a single Cys residue on Png1, and the binding was highly selective. The mutant enzyme in which Cys191 of the catalytic triad was changed to Ala did not bind to the carbohydrate probe, suggesting that the catalytic Cys is the binding site for this compound. Precise determination of the carbohydrate attachment site by mass spectrometry clearly identified Cys191 as the site of covalent attachment. Molecular modeling of N,N'-diacetylchitobiose (chitobiose) binding to the protein suggests that the carbohydrate binding site is distinct from but adjacent to that of Z-VAD-fmk, a peptide-based inhibitor of this enzyme. These results suggest that cytoplasmic PNGase has a separate binding site for chitobiose and other carbohydrates, and haloacetamide derivatives can irreversibly inhibit that catalytic Cys in a highly specific manner.     

Efflux of sphingomyelin, cholesterol, and phosphatidylcholine by ABCG1

Cholesterol and phospholipids are essential to the body, but an excess of cholesterol or lipids is toxic and a risk factor for arteriosclerosis. ABCG1, one of the half-type ABC proteins, is thought to be involved in cholesterol homeostasis. To explore the role of ABCG1 in cholesterol homeostasis, we examined its subcellular localization and function. ABCG1 and ABCG1-K120M, a WalkerA lysine mutant, were localized to the plasma membrane in HEK293 cells stably expressing ABCG1 and formed a homodimer. A stable transformant expressing ABCG1 exhibited efflux of cholesterol and choline phospholipids in the presence of BSA, and the cholesterol efflux was enhanced by the presence of HDL, whereas cells expressing ABCG1-K120M did not, suggesting that ATP binding and/or hydrolysis is required for the efflux. Mass and TLC analyses revealed that ABCG1 and ABCA1 secrete several species of sphingomyelin (SM) and phosphatidylcholine (PC), and SMs were preferentially secreted by ABCG1, whereas PCs were preferentially secreted by ABCA1. These results suggest that ABCA1 and ABCG1 mediate the lipid efflux in different mechanisms, in which different species of phospholipids are secreted, and function coordinately in the removal of cholesterol and phospholipids from peripheral cells.     

马铃薯Y病毒普通系外壳蛋白基因在大肠杆菌中的表达

将马铃薯Y病毒普通系(PVY0)的外壳蛋白基因克隆到表达质粒pMAL-c2中,构建这一基因在大肠杆菌中的表达载体pMAL-c2-PVY0CP.SDS-PAGE及Western blotting检测结果表明,这一表达栽体在E.coli DH5α中经IPTG诱导可表达分子量为71.8kDa的特异性融合蛋白.以amylose resin亲合柱层析纯化这一融合蛋白为抗原,免疫家兔制备了效价为1:1024的特异性抗血清.用该抗血清可通过对流免疫电泳、免疫双扩散及Western blotting对PVY进行检测.     

Cyclic AMP-dependent memory mutants are defective in the food choice behavior of <Emphasis Type="Italic">Drosophila</Emphasis>

Acute choice behavior in ingesting two different concentrations of sucrose in Drosophila is presumed to include learning and memory. Effects on this behavior were examined for four mutations that block associative learning (dunce, rutabaga, amnesiac, and radish). Three of these mutations cause cyclic AMP signaling defects and significantly reduced taste discrimination. The exception was radish, which affects neither. Electrophysiological recordings confirmed that the sensitivity of taste receptors is almost indistinguishable in all flies, whether wild type or mutant. These results suggest that food choice behavior in Drosophila involves central nervous learning and memory operating via cyclic AMP signaling pathways.     

Tumor cells enhance their own CD44 cleavage and motility by generating hyaluronan fragments

Hyaluronan (HA) is an extracellular matrix glycosaminoglycan that interacts with cell-surface receptors, including CD44. Although HA usually exists as a high molecular mass polymer, HA of a much lower molecular mass that shows a variety of biological activities can be detected under certain pathological conditions, particularly in tumors. We previously reported that low molecular weight HAs (LMW-HAs) of a certain size range induce the proteolytic cleavage of CD44 from the surface of tumor cells and promote tumor cell migration in a CD44-dependent manner. Here, we show that MIA PaCa-2, a human pancreatic carcinoma cell line, secreted hyaluronidases abundantly and generated readily detectable levels of LMW-HAs ranging from approximately 10- to 40-mers. This occurred in the absence of any exogenous stimulation. The tumor-derived HA oligosaccharides were able to enhance CD44 cleavage and tumor cell motility. Inhibition of the CD44-HA interaction resulted in the complete abrogation of these cellular events. These results are consistent with the concept that tumor cells generate HA oligosaccha-rides that bind to tumor cell CD44 through the expression of their own constitutive hyaluronidases. This enhances their own CD44 cleavage and cell motility, which would subsequently promote tumor progression. Such an autocrine/paracrine-like process may represent a novel activation mechanism that would facilitate and promote the malignant potential of tumor cells.     

The role of tumor necrosis factor-α for interleukin-10 production by murine dendritic cells

In the present study, we examined the role of tumor necrosis factor (TNF) in interleukin (IL)-10 production by dendritic cells (DCs) using bone-marrow derived DCs from wild type (WT) and TNF-α knockout (TNF-α^−/−) mice. Toll-like receptor (TLR) stimulation induced substantial level of IL-10 production by WT DCs, but significantly low level of IL-10 production by TNF-α^−/− DCs. In contrast, no significant difference was detected in IL-12 p40 production between WT and TNF-α^−/− DCs. Addition of TNF-α during TLR stimulation recovered the impaired ability of TNF-α^−/− DCs for IL-10 production. This recovery appeared to be associated with an activation of extracellular signal-regulated kinase, p38 mitogen-activated protein kinase, and phosphatidylinositol 3-kinase/Akt following the TNF-α addition. Blocking these kinases significantly inhibited IL-10 production by TNF-α^−/− DCs stimulated with TLR ligands plus TNF-α. Thus, TNF-α may be a key molecule to regulate the balance between anti-inflammatory versus inflammatory cytokine production in DCs.     

Activation by calmodulin of inositol-1,4,5-trisphosphate 3-kinase in guinea pig peritoneal macrophages

The activity of inositol-1,4,5-trisphosphate 3-kinase in the cytosol fraction of guinea pig macrophages was assayed with special reference to the dependence on the free Ca2+ concentration. The enzyme activity, as assessed by the production of inositol 1,3,4,5-tetrakisphosphate was reversibly activated by free Ca2+ concentrations ranging from 10(-7) to 10(-6)M. The calmodulin antagonists, W-7 and chlorpromazine, inhibited the Ca2+-activated enzyme activity in a dose-dependent fashion, thereby indicating that calmodulin may be involved in the activation by Ca2+. The content of calmodulin in the cytosol fraction (about 2.8 micrograms/mg of cytosol protein) was markedly reduced to less than 0.03 microgram/mg of proteins by subfractionation by ammonium sulfate, followed by an anion-exchange chromatography. The subfraction obtained by the chromatography showed no Ca2+ dependence in the enzyme activity, while an exogenous addition of calmodulin with 10(-6)M Ca2+ increased the enzyme activity. The enzyme activity was retained on a calmodulin-affinity column in the presence of Ca2+, and was eluted from the column by lowering the free Ca2+ concentration by adding ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid. These results clearly indicate that calmodulin activates the inositol-1,4,5-trisphosphate 3-kinase activity.     

The extracellular domain of p185(c-neu) induces density-dependent inhibition of cell growth in malignant mesothelioma cells and reduces growth of mesothelioma in vivo

EGFR is involved in the density-dependent inhibition of cell growth, while coexpression of EGFR with erbB2 can render normal cells transformed. In this study, we have examined the effect of a species of p185 that contains the transmembrane domain and the extracellular domain of p185(c-neu), on growth properties of a human malignant mesothelioma cell line that coexpresses EGFR and erbB2. The ectodomain form of p185(c-neu) enhanced density-dependent inhibition of cell growth and we found that p21 induction appeared to be responsible for this inhibitory effect. Previously, the extracellular domain species was shown to suppress the transforming abilities of EGFR and p185(c-neu/erbB2) in a dominant-negative manner. The ability of this subdomain to affect tumor growth is significant, as it reduced in vivo tumor growth. Unexpectedly, we found that the domain did not abrogate all of EGFR functions. We noted that EGFR-induced density-dependent inhibition of cell growth was retained. Tyrosine kinase inhibitors of EGFR did not cause density-dependent inhibition of cell growth of malignant mesothelioma cells. Therefore, simultaneously inhibiting the malignant phenotype and inducing density-dependent inhibition of cell growth in malignant mesothelioma cells by the extracellular domain of p185(c-neu) may represent an important therapeutic advance.