Roles of Lck, Syk and ZAP-70 tyrosine kinases in TCR-mediated phosphorylation of the adapter protein Shc

The adapter protein Shc has been implicated in mitogenic signaling via growth factor receptors, antigen receptors and cytokine receptors. Recent studies have suggested that tyrosine phosphorylation of Shc may play a key role in T lymphocyte proliferation via interaction of phosphorylated Shc with downstream molecules involved in activation of Ras and Myc proteins. However, the sites on Shc that are tyrosine phosphorylated in response to TCR engagement and the ability of different T cell tyrosine kinases to phosphorylate Shc have not been defined. In this report, we show that during TCR signaling, the tyrosines Y239, Y240 and Y317 of Shc are the primary sites of tyrosine phosphorylation. Mutation of all three tyrosines completely abolished tyrosine phosphorylation of Shc following TCR stimulation. Our data also suggest that multiple T cell tyrosine kinases contribute to tyrosine phosphorylation on Shc. In T cells, CD4/Lck-dependent tyrosine phosphorylation on Shc was markedly diminished when Y317 was mutated, suggesting a preference of Lck for the Y317 site. The syk-family kinases (Syk and ZAP-70) were able to phosphorylate the Y239 and Y240 sites, and less efficiently the Y317 site. Moreover, co-expression of Syk or ZAP-70 with Lck resulted in enhanced phosphorylation of Shc on all three sites, suggesting a synergy between the syk-family and scr-family kinases. Of the two potential Grb2 binding sites (Y239 and Y317), Y239 appears to play a greater role in recruiting Sos through Grb2. These studies have implications for Ras activation and mitogenic signaling during T cell activation.     

Geometric criterion for the absence of limit cycles in nonlinear control systems

In most autonomous systems, the generation of periodic modes is considered to be an instability. Considering feedback systems composed of a time-invariant linear operator in cascade with an odd memoryless nonlinearity, a method is derived which provides a geometric interpretation of frequency regions in the Nyquist plane, over which simple oscillations cannot occur. This criterion answers a question of system behaviour when the Popov criterion is violated.     

Self ratings of fear in a fear-invoking situation.

"Airborne trainees were asked to mark on a self rating scale the amount of fear they felt during mock-tower jumping. One group of trainees rated fear in the mock tower just prior to jumping and the second group completed the rating after they had finished mock-tower training. For both groups, performance was related to the self rating of fear. Those who subsequently passed the Airborne course estimated that they were less afraid than those who failed it… . The study appeared to show the reliability and validity of a self rating on fear." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Shc interaction with Src homology 2 domain containing inositol phosphatase (SHIP) in vivo requires the Shc-phosphotyrosine binding domain and two specific phosphotyrosines on SHIP

The adapter protein Shc has been implicated in mitogenic signaling via growth factor receptors, cytokine receptors, and antigen receptors on lymphocytes. Besides the well characterized interaction of Shc with molecules involved in Ras activation, Shc also associates with a 145-kDa tyrosine-phosphorylated protein upon triggering via antigen receptors and many cytokine receptors. This 145-kDa protein has been recently identified as an SH2 domain containing 5'-inositol phosphatase (SHIP) and has been implicated in the regulation of growth and differentiation in hematopoietic cells. In this report, we have addressed the molecular details of the interaction between Shc and SHIP in vivo. During T cell receptor signaling, tyrosine phosphorylation of SHIP and its association with Shc occurred only upon activation. We demonstrate that the phosphotyrosine binding domain of Shc is necessary and sufficient for its association with tyrosine-phosphorylated SHIP. Through site-directed mutagenesis, we have identified two tyrosines on SHIP, Tyr-917, and Tyr-1020, as the principal contact sites for the Shc-phosphotyrosine binding domain. Our data also suggest a role for the tyrosine kinase Lck in phosphorylation of SHIP. We also show that the SH2 domain of SHIP is dispensable for the Shc-SHIP interaction in vivo. These data have implications for the localization of the Shc.SHIP complex and regulation of SHIP function during T cell receptor signaling.     

Relative stability of global errors of nonparametric function estimators

This paper presents relative stability properties of various nonparametric density estimators (histogram, kernel estimates) and of regression estimators (partitioning, kernel, and nearest neighbor estimates). In density estimation, let En denote the L/sub 1/ error of an estimate calculated from n data, whereas in regression estimation, the L/sub 2/ error of the estimate is used. Sufficient conditions for E/sub n//E{E/sub n/}/spl rarr/1 in probability are provided. If this limit holds, the asymptotic behavior of the random error E/sub n/ can be characterized by its expectation E{E/sub n/},, and one may apply, for example, the established rate-of-convergence results for E{En}.     

Evidence for a requirement for both phospholipid and phosphotyrosine binding via the Shc phosphotyrosine-binding domain in vivo

The adapter protein Shc is a critical component of mitogenic signaling pathways initiated by a number of receptors. Shc can directly bind to several tyrosine-phosphorylated receptors through its phosphotyrosine-binding (PTB) domain, and a role for the PTB domain in phosphotyrosine-mediated signaling has been well documented. The structure of the Shc PTB domain demonstrated a striking homology to the structures of pleckstrin homology domains, which suggested acidic phospholipids as a second ligand for the Shc PTB domain. Here we demonstrate that Shc binding via its PTB domain to acidic phospholipids is as critical as binding to phosphotyrosine for leading to Shc phosphorylation. Through structure-based, targeted mutagenesis of the Shc PTB domain, we first identified the residues within the PTB domain critical for phospholipid binding in vitro. In vivo, the PTB domain was essential for localization of Shc to the membrane, as mutant Shc proteins that failed to interact with phospholipids in vitro also failed to localize to the membrane. We also observed that PTB domain-dependent targeting to the membrane preceded the PTB domain's interaction with the tyrosine-phosphorylated receptor and that both events were essential for tyrosine phosphorylation of Shc following receptor activation. Thus, Shc, through its interaction with two different ligands, is able to accomplish both membrane localization and binding to the activated receptor via a single PTB domain.     

High-frequency tool-spindle for multifunctional, replaceable rotor-modules

The increasing demand for micro-parts and -structures requires micro-tools, precision machines and components. For machining the microparts, tool-spindles with very high rotational speeds of the spindle rotor are needed. In this paper a new developed small high-frequency tool-spindle capable for use of multifunctional micro machining and measuring tools is introduced.     

Modification of glassy carbon surfaces with synthetic laminin-derived peptides for nerve cell attachment and neurite growth

Working memory and its contribution to performance on strategic memory tests in schizophrenia were studied. Patients (n = 18) and control participants (n = 15), all men, received tests of immediate memory (forward digit span), working memory (listening, computation, and backward digit span), and long-term strategic (free recall, temporal order, and self-ordered pointing) and nonstrategic (recognition) memory. Schizophrenia patients performed worse on all tests. Education, verbal intelligence, and immediate memory capacity did not account for deficits in working memory in schizophrenia patients. Reduced working memory capacity accounted for group differences in strategic memory but not in recognition memory. Working memory impairment may be central to the profile of impaired cognitive performance in schizophrenia and is consistent with hypothesized frontal lobe dysfunction associated with this disease. Additional medial-temporal dysfunction may account for the recognition memory deficit.     

Block-stochastic matrices and associated finite-state languages

Summary Finite automata are considered whose transition matrix is blockstochastic. The block-stochastic structure defines an equivalence relation among states of the automata. The implications of this relation are investigated, especially with respect to the languages accepted in the states of the automata.

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Zusammenfassung Es werden Endliche Automaten betrachtet, deren Übergangsmatrix block-stochastisch ist. Die block-stochastische Struktur definiert eine Äquivalenzbeziehung zwischen Zuständen des Automaten. Die Bedeutung und Auswirkung dieser Relation wird untersucht, und zwar insbesonders in Hinsicht auf die in den einzelnen Zuständen des Automaten angenommenen Sprachen.