Most, if not all, cytokines activate phosphatidylinositol 3-kinase (PI-3K). Although many cytokine receptors have direct binding sites for the p85 subunit of PI-3K, others, such as the interleukin-3 (IL-3) receptor beta common chain (␤c) and the IL-2 receptor beta chain (IL-2R␤), lack such sites, leaving the mechanism by which they activate PI-3K unclear. Here, we show that the protooncoprotein Shc, which promotes Ras activation by recruiting the Grb2-Sos complex in response to stimulation of cytokine stimulation, also signals to the PI-3K/Akt pathway. Analysis of Y3F and "add-back" mutants of ␤c shows that Y577, the Shc binding site, is the major site required for Gab2 phosphorylation in response to cytokine stimulation. When fused directly to a mutant form of IL-2R␤ that lacks other cytoplasmic tyrosines, Shc can promote Gab2 tyrosyl phosphorylation. Mutation of the three tyrosyl phosphorylation sites of Shc, which bind Grb2, blocks the ability of the Shc chimera to evoke Gab2 tyrosyl phosphorylation. Overexpression of mutants of Grb2 with inactive SH2 or SH3 domains also blocks cytokine-stimulated Gab2 phosphorylation. The majority of cytokine-stimulated PI-3K activity associates with Gab2, and inducible expression of a Gab2 mutant unable to bind PI-3K markedly impairs IL-3-induced Akt activation and cell growth. Experiments with the chimeric receptors indicate that Shc also signals to the PI-3K/Akt pathway in response to IL-2. Our results suggest that cytokine receptors lacking direct PI-3K binding sites activate Akt via a Shc/Grb2/Gab2/PI-3K pathway, thereby regulating cell survival and/or proliferation.The proliferation, differentiation, and survival of hematopoietic cells are controlled by multiple cytokines. Cytokines bind to cell surface receptors and activate receptor-associated Janus family tyrosine kinases (Jaks) (25). Activated Jaks are required for the phosphorylation of multiple sites on receptor cytoplasmic domains. These tyrosyl phosphorylation sites recruit signal relay molecules containing src homology-2 (SH2) and/or phosphotyrosine binding (PTB) domains (26). Signal relay molecules convert receptor-proximal events into the activation of downstream signaling pathways, including the Ras/Raf/mitogen-activated protein kinase (MAPK) and the phosphatidylinositol 3-kinase (PI-3K)/Akt cascades. These pathways culminate in the phosphorylation of key transcription factors and other important cellular regulators (e.g., members of the cell survival/death machinery). Cytokine receptors also bind SH2 domain-containing transcription factors termed STATs, which, upon tyrosyl phosphorylation, activate transcription directly (11). Elucidating the molecular details of these signaling pathways is critical to understanding cytokine action.Much is known about how cytokines activate the MAPK and PI-3K pathways. Most cytokine receptors have direct binding sites for the PTB domain of the adapter protein Shc (7, 26). Shc is recruited to activated receptors, where it becomes tyrosyl phosphorylated on as many as three s...

Pigment stoichiometries in the D,/D&ytochrome 6-559 reaction center complex from spinach have been studied by spectrophotometry and normalphase silica HPLC of the solvent extracts. Based on the well-accepted molar ratio Pheo a/P680=2, the results are summarized by Chl a/P680 = 6.01 k 0.37 (n = 24) and b-carotene/P680 = 1.84 f 0.11 (n = 4). These stoichiometries are significantly different from those of bacterial reaction center complexes.

Phosphatidylinositol 3′-kinase (PI3K) is a key component of multiple signaling pathways, where it typically promotes survival, proliferation, and/or adhesion. Here, we show that in TCR signaling, the scaffolding adapter Gab2 delivers an inhibitory signal via PI3K. Overexpression of Gab2 in T cell lines inhibits TCR-evoked activation of the IL-2 promoter, blocking NF-AT- and NF-κB-directed transcription. Inhibition is abrogated by mutating the Gab2 p85-binding sites, by treatment with PI3K inhibitors or by cotransfection of phosphatase homolog of tensin. Our findings provide the first evidence of a negative function for a scaffolding adapter in T cells and identify Gab2/PI3K-containing complexes as novel regulators of TCR signaling.

A simple and sensitive method was developed to measure total hydroperoxides. After the reduction of hydroperoxides with triphenylphosphine (TP) in cyclohexane at 30°C, the amount of triphenylphosphine oxide (TPO) produced is determined by reverse-phase or normal-phase high-performance liquid chromatography (HPLC) in combination with an ultraviolet (UV)-detector by measuring absorption at 220 or 260 nm. TPO was shown to be gener-ated stoichiometrically by reduction of known amounts of either cumene hydroperoxide or methyl 13-hydroper-oxyoctadecadienoate. For various lipids at low levels of oxidation, the peroxide values determined by this method were in good agreement with those obtained by conventional iodometry. The detection limit of TPO in HPLC using absorption at 220 nm was less than 10 pmol. Consequently, total hydroperoxides in lipids at levels corresponding to less than a peroxide value of 1 can be estimated by the TP method on a 10-mg sample.

A lipophilic derivative of neocarzinostatin (NCS), an antitumor antibiotic, was prepared by reaction with a synthetic water‐soluble polymer, [(styrene)1˜3‐(maleic acid4˜7/anhydride1)]. The reaction was carried out at pH 8.6 for 3 h and aimed at modifying the two nonessential aming (of Ala‐1, ε‐amino of Lys‐20). The NCS‐polystyrene (SMANCS was a column of Sephadex G‐100 in 0.05 M ammonium bic and the main product was obtained as a single peak. The elemental and showed an increased C and a decreased N content. U.v. and i.r. absorption ectra for SMANCS showed the presence of styrene. SDS‐acrylamide gel electrophoresis at pH 8.5 and the decreased N content suggested a molecular high of about 25 000, Indicating the numbers of polymers conjugated to be six units, two of which were found attached to the two amino groups. SMANCS was solution in organic solvents, in contrast to NCS, and in water. SMANCS increased chemical and biological stability and appeared molicular in vitro biological activity.

The glucose adsorption onto the -Al sites is probable considering the result obtained by the adsorption measurement described in section 3.1. It has been pointed out in section 3.1 that the adsorption capacity obtained by applying a Langmuir adsorption isotherm to the experimental result is equivalent to the amount of glucose necessary to cover the surface area of the adsorbent alumina. This clearly means that major components (O, Al) constituting the adsorbent surface provide glucose molecules with adsorption sites.

The electrical and structural properties of NdNiC 2 and PrNiC 2 are examined in single-crystalline samples in order to investigate the interplay of charge-density wave (CDW) and magnetic order in ternary rare-earth nickel carbides, RNiC 2 , where R is a rare-earth element. PrNiC 2 (no magnetic order down to 1.5 K) and NdNiC 2 [antiferromagnetic (AF) transition at 17.2 K] show resistance anomalies at 89 and 121 K, respectively, which are revealed to be CDW transitions by observing X-ray satellite reflections. NdNiC 2 also shows a gradual decrease in both resistivity and CDW amplitude below the Néel temperature. In the AF phase, the magnetoresistance sharply decreases where a ferromagnetic (FM) order occurs, which is realized above the spin-flop magnetic field. These results clearly suggest that the relationships between CDW and magnetic order in RNiC 2 depend on whether the magnetic order is AF or FM.Charge-density wave (CDW) transition is one of the representative phenomena in low-dimensional materials, and is actively investigated in the field of high-T C superconductors. The nesting of low-dimensional Fermi surfaces leads to electronic instability, i.e., Peierls instability, which induces CDW, that is, a periodic charge density modulation coupled to an underlying lattice by the electron-lattice interaction. 1) Since the discovery of CDW transitions in real materials, such as the quasi-1D organic conductor, TTF-TCNQ, 2) and inorganic compounds, K 0:3 MoO 33) and NbSe 3 , 4) peculiar phenomena, such as the dynamics of CDW sliding and low-dimensional fluctuation above the transition temperature, have been intensively studied.The recent target of the study of CDW has changed from the physical property itself to understanding competing phenomena between a CDW and other electronic phases, such as superconductivity 5) and magnetism. In the latter topic, there have been few reports of a clear coupling between a CDW and a magnetic order, although some intermetallic rare-earth compounds in which a CDW and an antiferromagnetic (AF) order coexist, such as Er 5 Ir 4 Si 10 , have been reported. 6,7) Recently, a strong interplay of a CDW and a ferromagnetic (FM) order was reported in one of the ternary rareearth nickel carbides, SmNiC 2 . 8,9) This compound has a CDW transition at 148 K and the CDW is suppressed at 17.7 K, where an FM order occurs. SmNiC 2 belongs to the RNiC 2 (R: rare-earth element) family that crystallizes in the CeNiC 2 -type orthorhombic structure (space group: Amm2). 10) In this system, nickel atoms are not magnetic and rare-earth elements mainly contribute to the magnetic properties showing the character of interacting local magnetic moments through the RKKY interaction. 11) In the early 1990s, magnetic structures in RNiC 2 had been intensively investigated and various magnetic orders had been reported, such as an incommensurate-commensurate AF transition in DyNiC 2 , 12) an FM order in SmNiC 2 , and AF orders in CeNiC 2 and NdNiC 2 . 13) In the 2000s, Murase et al. reported that some RNiC 2 compounds ...

We previously reported a xanthan gum (Xan) hydrogel showing excellent mechanical properties. Mineralization of hydroxyapatite (Hap) upon the Xan hydrogel would provide a unique biomaterial applicable for bone tissue engineering. Here, we show the mineralization of Hap upon the Xan hydrogel by means of an alternate soaking process. Hap was gradually grown upon the Xan-matrix surface with increasing number of soaking cycles due to the ionic interactions between calcium cations and carboxyl groups. Interestingly, the mineralization induced a microstructure change in the gel-matrix from a layered structure to a porous structure. The mechanical properties of the resulting Hap-Xan composite hydrogels were further investigated by a tensile test, where the Hap-Xan composite hydrogel with an appropriate amount of Hap (Xan/Hap=2.7) was capable of approximately 370% elongation.