Targeted deletion of CD44v7 exon leads to decreased endothelial cell injury but not tumor cell killing mediated by interleukin-2-activated cytolytic lymphocytes

In the current study, we investigated the nature and role of CD44 variant isoforms involved in endothelial cell (EC) injury and tumor cell cytotoxicity mediated by IL-2-activated killer (LAK) cells. Treatment of CD44 wild-type lymphocytes with IL-2 led to increased gene expression of CD44 v6 and v7 variant isoforms and to significant induction of vascular leak syndrome (VLS). CD44v6-v7 knockout (KO) and CD44v7 KO mice showed markedly reduced levels of IL-2-induced VLS. The decreased VLS in CD44v6-v7 KO and CD44v7 KO mice did not result from differential activation and expansion of CD8+ T cells, NK, and NK-T cells or from altered degree of perivascular lymphocytic infiltration in the lungs. LAK cells from CD44v7 KO mice showed a significant decrease in their ability to adhere to and mediate lysis of EC but not lysis of P815 tumor cells in vitro. CD44v7-mediated lysis of EC by LAK cells was dependent on the activity of phosphatidylinositol 3-kinase and tyrosine kinases. Interestingly, IL-2-activated LAK cells expressing CD44hi but not CD44lo were responsible for EC lysis. Furthermore, lysis of EC targets could be blocked by addition of soluble or enzymatic cleavage of CD44v6-v7-binding glycosaminoglycans. Finally, anti-CD44v7 mAbs caused a significant reduction in the adherence to and killing of EC and led to suppression of IL-2-induced VLS. Together, this study suggests that the expression of CD44v7 on LAK cells plays a specific role in EC injury and that it may be possible to reduce EC injury but not tumor cell killing by specifically targeting CD44v7.     

Identification of a novel system L amino acid transporter structurally distinct from heterodimeric amino acid transporters

A cDNA that encodes a novel Na+-independent neutral amino acid transporter was isolated from FLC4 human hepatocarcinoma cells by expression cloning. When expressed in Xenopus oocytes, the encoded protein designated LAT3 (L-type amino acid transporter 3) transported neutral amino acids such as l-leucine, l-isoleucine, l-valine, and l-phenylalanine. The LAT3-mediated transport was Na+-independent and inhibited by 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid, consistent with the properties of system L. Distinct from already known system L transporters LAT1 and LAT2, which form heterodimeric complex with 4F2 heavy chain, LAT3 was functional by itself in Xenopus oocytes. The deduced amino acid sequence of LAT3 was identical to the gene product of POV1 reported as a prostate cancer-up-regulated gene whose function was not determined, whereas it did not exhibit significant similarity to already identified transporters. The Eadie-Hofstee plots of LAT3-mediated transport were curvilinear, whereas the low affinity component is predominant at physiological plasma amino acid concentration. In addition to amino acid substrates, LAT3 recognized amino acid alcohols. The transport of l-leucine was electroneutral and mediated by a facilitated diffusion. In contrast, l-leucinol, l-valinol, and l-phenylalaninol, which have a net positive charge induced inward currents under voltage clamp, suggesting these compounds are transported by LAT3. LAT3-mediated transport was inhibited by the pretreatment with N-ethylmaleimide, consistent with the property of system L2 originally characterized in hepatocyte primary culture. Based on the substrate selectivity, affinity, and N-ethylmaleimide sensitivity, LAT3 is proposed to be a transporter subserving system L2. LAT3 should denote a new family of organic solute transporters.     

QSulf1 remodels the 6-O sulfation states of cell surface heparan sulfate proteoglycans to promote Wnt signaling

The 6-O sulfation states of cell surface heparan sulfate proteoglycans (HSPGs) are dynamically regulated to control the growth and specification of embryonic progenitor lineages. However, mechanisms for regulation of HSPG sulfation have been unknown. Here, we report on the biochemical and Wnt signaling activities of QSulf1, a novel cell surface sulfatase. Biochemical studies establish that QSulf1 is a heparan sulfate (HS) 6-O endosulfatase with preference, in particular, toward trisulfated IdoA2S-GlcNS6S disaccharide units within HS chains. In cells, QSulf1 can function cell autonomously to remodel the sulfation of cell surface HS and promote Wnt signaling when localized either on the cell surface or in the Golgi apparatus. QSulf1 6-O desulfation reduces XWnt binding to heparin and HS chains of Glypican1, whereas heparin binds with high affinity to XWnt8 and inhibits Wnt signaling. CHO cells mutant for HS biosynthesis are defective in Wnt-dependent Frizzled receptor activation, establishing that HS is required for Frizzled receptor function. Together, these findings suggest a two-state "catch or present" model for QSulf1 regulation of Wnt signaling in which QSulf1 removes 6-O sulfates from HS chains to promote the formation of low affinity HS-Wnt complexes that can functionally interact with Frizzled receptors to initiate Wnt signal transduction.     

Optimizing antibody immobilization strategies for the construction of protein microarrays

Antibody microarrays have the potential to revolutionize protein expression profiling. The intensity of specific signal produced on a feature of such an array is related to the amount of analyte that is captured from the biological mixture by the immobilized antibody (the "capture agent"). This in turn is a function of the surface density and fractional activity of the capture agents. Here we investigate how these two factors are affected by the orientation of the capture agents on the surface. We compare randomly versus specifically oriented capture agents based on both full-sized antibodies and Fab' fragments. Each comparison was performed using three different antibodies and two types of streptavidin-coated monolayer surfaces. The specific orientation of capture agents consistently increases the analyte-binding capacity of the surfaces, with up to 10-fold improvements over surfaces with randomly oriented capture agents. Surface plasmon resonance revealed a dense monolayer of Fab' fragments that are on average 90% active when specifically oriented. Randomly attached Fab's could not be packed at such a high density and generally also had a lower specific activity. These results emphasize the importance of attaching proteins to surfaces such that their binding sites are oriented toward the solution phase.     

Characterization of an extracellular medium-chain-length poly(3-hydroxyalkanoate) depolymerase from Streptomyces sp. KJ-72

A bacterial strain capable of degrading medium-chain-length polyhydroxyalkanoates (MCL-PHAs) was isolated from a soil sample. This organism, which was identified as Streptomyces sp. KJ-72, secreted MCL-PHA depolymerase into the culture fluid only when it was cultivated on MCL-PHAs. The extracellular MCL-PHA depolymerase of the organism was purified to electrophoretic homogeneity by ion exchange column chromatography and gel filtration. The enzyme consisted of a monomeric subunit having a molecular mass of 27.1 kDa and isoelectric point of 4.7. The maximum activity was observed at pH 8.7 and 50 °C. The enzyme was sensitive to N-bromosuccinimide and acetic anhydride, indicating the presence of tryptophan and lysine residues in the catalytic domain. The enzyme was able to hydrolyze various chain-length p-nitrophenyl esters of fatty acids and polycaprolactone as well as various types of MCL-PHAs. However, lipase activity of the enzyme was not detected. The main hydrolysis product of poly(3-hydroxyheptanoate) was identified to be the dimer of 3-hydroxyheptanoate. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phosphorylation-dependent cleavage of p130cas in apoptotic rat-1 cells

We previously demonstrated caspase-mediated cleavage of p130cas during apoptosis and identified two caspase-3 cleavage sites [1]. In this study, we investigated the phosphorylation-dependent cleavage of p130cas in apoptotic Rat-1 fibroblast cells. Lysophosphatidic acid and fibronectin induced p130cas phosphorylation, which in turn resulted in resistance to caspase-mediated cleavage. Alternatively, dephosphorylation by calf intestinal alkaline phosphatase, PP1, and LAR stimulated cleavage of p130cas by caspase-3, generating a 31-kDa fragment. During apoptosis, p130cas dephosphorylation seems to precede its cleavage. The phosphorylation of tyrosine and serine residues immediately adjacent to the two cleavage sites (DVPD(416) and DSPD(748)) strongly affected p130cas cleavage by caspase-3, both in vitro and in vivo. Furthermore, the generation of the 31-kDa cleavage fragment was strongly regulated by phosphorylation of a tyrosine residue at position 751 (DSPD(748) and GQY(751)). Our results collectively suggest that degradation of p130cas during apoptosis is modulated in a phosphorylation-dependent manner.     

Increased Ca2+ storage capacity in the sarcoplasmic reticulum by overexpression of HRC (histidine-rich Ca2+ binding protein)

The histidine-rich Ca(2+) binding protein (HRC) is a high capacity Ca(2+) binding protein in the sarcoplasmic reticulum (SR). Because HRC appears to interact directly with triadin, HRC may play a role in the regulation of Ca(2+) release during excitation-contraction coupling. In this study, we examined the physiological effects of HRC overexpression in rat neonatal cardiomyocytes. Both caffeine-induced and depolarization-induced Ca(2+) release from the SR were increased significantly in the HRC overexpressing cardiomyocytes. Consistently, the Ca(2+) content, normally depleted from the SR in the presence of cyclopiazonic acid (CPA), remained elevated in these cells. In contrast, the density and the ryanodine-binding kinetics of the ryanodine receptor (RyR)/Ca(2+) release channel were slightly reduced or not significantly altered in the HRC overexpressing cardiomyocytes. We suggest that HRC is involved in the regulation of releasable Ca(2+) content into the SR.     

Diagnosis of natural killer cell lymphoma by cytology and flow cytometric immunophenotyping. A case report

BACKGROUND: Natural killer (NK) cell lymphoma is a rare type of non-Hodgkin's lymphoma. It classically presents in the nasal region in Asian patients. There are few reports of its cytologic features. We describe a case that we diagnosed by fine needle aspiration (FNA) biopsy using flow cytometry immunophenotyping and cytomorphology. CASE: A 55-year-old, Chinese man presented with symptoms consistent with nasal obstruction. At examination, a polypoid lesion extending from the nose to the back of the throat was found. An intraoral FNA biopsy was performed. Representative smears were obtained and the remainder of the material sent for flow cytometry. A diagnosis of NK cell lymphoma was made. The patient was given chemotherapy and radiotherapy, with complete resolution of the lesion. Recurrence was noted on follow up seven months later. Pieces of tissue were taken for histology and flow cytometry and showed recurrent NK cell lymphoma. The lesion was again successfully treated by chemotherapy followed by radiotherapy. CONCLUSION: In the correct setting, a definitive diagnosis of non-Hodgkin's lymphoma can be made by FNA biopsy. This case of NK cell lymphoma was diagnosed by FNA biopsy using cytomorphology, flow cytometry immunophenotyping and clinical correlation.     

The Hexapeptide inhibitor of Galbeta 1,3GalNAc-specific alpha 2,3-sialyltransferase as a generic inhibitor of sialyltransferases

The mammalian Galbeta1,3GalNAc-specific alpha2,3-sialyltransferase (ST3Gal I) was expressed as a secreted glycoprotein in High Five (Trichoplusia ni) cells. Using this recombinant ST3Gal I, we screened the synthetic hexapeptide combinatorial library to explore a sialyltransferase inhibitor. We found that the hexapeptide, NH(2)-GNWWWW, exhibited the most strong inhibition of ST3Gal I among five different hexapeptides that were finally selected. The kinetic analysis of ST3Gal I inhibition demonstrated that this hexapeptide could act as a competitive inhibitor (K(i) = 1.1 microm) on CMP-NeuAc binding to the enzyme. Moreover, the hexapeptide was shown to strongly inhibit both N-glycan-specific alpha2,3- and alpha2,6-sialyltranferase in vitro, suggesting that this peptide may inhibit the broad range of sialyltransferases regardless of their linkage specificity. The inhibitory activity in vivo was investigated by RCA-I lectin blot analyses and by metabolic d-[6-(3)H]GlcNH(2) radiolabeling analyses of N- and O-linked oligosaccharides in Chines hamster ovary cells. Our results demonstrate that the hexapeptide can act as a generic inhibitor of the N- and O-glycan-specific sialyltransferases in mammalian cells, which results in the significantly reduced NeuAc expression on cellular glycoproteins in vivo.