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S Ratnofsky

Publications and source records attributed to S Ratnofsky.

11 recordsLinked to original sources
PubMed1996

Proteolytic activation of protein kinase C delta by an ICE/CED 3-like protease induces characteristics of apoptosis.

Recent studies have shown that protein kinase C (PKC) delta is proteolytically activated at the onset of apoptosis induced by DNA-damaging agents, tumor necrosis factor, and anti-Fas antibody. However, the relationship of PKC delta cleavage to induction of apoptosis is unknown. The present studies demonstrate that full-length PKC delta is cleaved at DMQD330N to a catalytically active fragment by the cysteine protease CPP32. The results also demonstrate that overexpression of the catalytic kinase fragment in cells is associated with chromatin condensation, nuclear fragmentation, induction of sub-G1 phase DNA and lethality. By contrast, overexpression of full-length PKC delta or a kinase inactive PKC delta fragment had no detectable effect. The findings suggest that proteolytic activation of PKC delta by a CPP32-like protease contributes to phenotypic changes associated with apoptosis.

Amino Acid Sequence↗
PubMed1994

LPAP, a novel 32-kDa phosphoprotein that interacts with CD45 in human lymphocytes.

CD45, a leukocyte-specific protein tyrosine phosphatase involved in signal transduction, has previously been shown to associate with a 32-kDa phosphoprotein in human T-lymphocytes and T-lymphoma cell lines. The 32-kDa protein was purified and its coding cDNA cloned. Since expression of the protein was found to be restricted to B- and T-lymphocytes it was termed LPAP (lymphocyte phosphatase-associated phosphoprotein). LPAP exists in two differentially phosphorylated forms in resting human T-lymphocytes c, both of which undergo alterations during T-lymphocyte activation. Analysis of LPAP protein and mRNA expression in CD45-deficient mutant T-cell lines suggests that LPAP protein is subjected to degradation in the absence of its binding partner, CD45. Stable expression of LPAP protein seems to require particular portions of CD45 distinct from the phosphatase domains. In pervanadate-treated human T-lymphocytes LPAP undergoes phosphorylation on tyrosine residues in vivo. Since tyrosine phosphorylation of LPAP is undetectable in T-lymphocytes expressing enzymatically active CD45, these data suggest that LPAP likely represents a novel substrate for CD45.

Amino Acid Sequence↗
PubMed1994

Identification of a novel dimeric phosphoprotein (PP29/30) associated with signaling receptors in human T lymphocytes and natural killer cells.

Two-dimensional gel electrophoresis of in vitro phosphorylated proteins coprecipitated by CD2 monoclonal antibody (mAb) from Brij58 lysates of resting human T lymphocytes and natural killer (NK) cells resulted in the identification of a novel 29/30-kD disulfide-linked dimer (pp29/30). Comparative two-dimensional analysis of CD2, CD3, CD4, CD5, and CD8 immunoprecipitates revealed that pp29/30 associates with these signaling receptor complexes but not with CD18, CD27, and CD29 in human T lymphocytes. Analysis of CD2 immunoprecipitates prepared from T cell antigen receptor/CD3-modulated T lymphocytes indicated that pp29/30 preferentially associates and comodulates with the human T cell antigen receptor (TCR). Since tyrosine phosphorylated pp29/30 selectively interacts with the Src homology type 2 domains (SHZ) of the protein tyrosine kinases p56lck and p59fyn but not ZAP70 the present data suggest that pp29/30 represents a novel signaling receptor associated phosphoprotein likely involved in the activation of human T lymphocytes and NK cells.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1993

SH2 domains recognize specific phosphopeptide sequences.

A phosphopeptide library was used to determine the sequence specificity of the peptide-binding sites of SH2 domains. One group of SH2 domains (Src, Fyn, Lck, Fgr, Abl, Crk, and Nck) preferred sequences with the general motif pTyr-hydrophilic-hydrophilic-Ile/Pro while another group (SH2 domains of p85, phospholipase C-gamma, and SHPTP2) selected the general motif pTyr-hydrophobic-X-hydrophobic. Individual members of these groups selected unique sequences, except the Src subfamily (Src, Fyn, Lck, and Fgr), which all selected the sequence pTyr-Glu-Glu-Ile. The variability in SH2 domain sequences at likely sites of contact provides a structural basis for the phosphopeptide selectivity of these families. Possible in vivo binding sites of the SH2 domains are discussed.

Amino Acid Sequence↗
PubMed1990

The cytoplasmic domain of CD4 is required for stable association with the lymphocyte-specific tyrosine protein kinase p56lck.

The CD4 T cell surface molecule binds MHC class II determinants expressed on antigen-presenting cells. CD4 is thought to enhance T cell activation by serving as an adhesion molecule as well as possibly by transducing an independent intracellular signal during the process of antigen stimulation. The recent observation that CD4 is physically associated with the Src-related tyrosine protein kinase p56lck suggests that tyrosine phosphorylation might be involved in these CD4 "signaling" events. The results presented in this report demonstrate that deletion of the cytoplasmic domain of CD4 significantly diminishes its ability to stably associate with p56lck. This observation provides a biochemical basis for the decreased ability of this mutant CD4 molecule to enhance T cell activation during suboptimal antigen stimulation.

Amino Acid Sequence↗
PubMed1989

Direct evidence for binding of CD8 to HLA class I antigens.

Adhesion of T lymphocytes is an essential step for antigen recognition and lymphocyte activation. mAbs to T cell surface proteins have been used to define the receptor-ligand proteins that appear to be involved in adhesion. Since most assays measure the effects of mAbs on T lymphocyte function, it is not known whether mAb-mediated blocking is due to a disruption of receptor-ligand interactions or results in inhibition of some aspect of receptor-mediated triggering. It has been suggested that the CD8 molecule augments T cell avidity for the target cells by binding to determinants on target cell MHC class I molecules. In the present report, we demonstrated that purified CD8 molecules incorporated into large lipid vesicles (artificial target cells) mediate the adhesion of these vesicles to cells expressing HLA proteins, while vesicles expressing purified HLA class I antigens bind to CD8+ T cells. Furthermore, vesicles bearing CD8 will form conjugates with vesicles expressing HLA class I proteins. These conjugates were found to be specifically inhibited by mAbs to CD8 or HLA class I molecules. We also demonstrate that CD2-reconstituted vesicles can form conjugates with vesicles bearing LFA-3. These experiments provide direct evidence for an interaction of the CD8 molecule with class I MHC proteins as well as between CD2 proteins and LFA-3 proteins, thus supporting the hypothesis that these molecules can mediate cell-cell adhesion.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1985

Excretory urography in current practice: evidence against overutilization.

Excretory urography could be performed less frequently if some combinations of genitourinary signs and symptoms were found to be predictive of either a specific disease or normality. To explore this possibility, the authors conducted a prospective study involving more than 3,000 patients at three institutions (a teaching hospital, a community hospital, and a health maintenance organization). Predictive algorithms were obtained by application of a polychotomous logistic regression model but did poorly at differentiating normal from abnormal patients or arriving at a specific diagnosis. Selection of patients on the basis of the logistic model would have required testing 90% of all patients in order to detect 95% of those with abnormal urograms. These results suggest that current clinical selection criteria for excretory urography are effective, and that present frequency of utilization is appropriate.

Diagnosis, Differential↗
PubMed1984

Selection criteria for upper gastrointestinal examinations: attempts at improvement.

An attempt was made to improve upon selection criteria for the performance of upper gastrointestinal (UGI) series in three settings: a teaching hospital, a community hospital, and a health maintenance organization. Two statistical techniques, the polychotomous logistic model (to develop predictive algorithms for the identification of specific diseases) and the maximum attainable discrimination technique, were used to show the relationship between the percentage of patients with any disease detected and the percentage of UGI examinations performed. Results showed that neither technique improved significantly upon selection criteria for identifying patients with abnormal UGI series.

Decision Theory↗
PubMed1982

In vitro generation of helper T cells and suppressor T cells that regulate the cytolytic T lymphocyte response to trinitrophenyl-modified syngeneic cells.

Helper T cells and suppressor T cells have been generated in vitro that regulate the cytolytic T lymphocyte (CTL) response to trinitrophenyl (TNP)-modified syngeneic cells. B6D2F1 helper cells generated to TNP-modified parental (P1) cells augment the CTL response to those P1-TNP-modified antigens but not to P2-TNP-modified antigens. The generation of these helper T cells requires the presence of splenic adherent cells and these helper T cells are radioresistant. A soluble factor can be obtained from the helper T cell cultures that can also augment the CTL response. The suppressor T cells generated in culture do not demonstrate the specificity observed with the helper T cells; however, they are antigen-dependent in their induction. Whether helper or suppressor activity is obtained depends upon the length of time cells are cultured in vitro.

Animals↗
PubMed1982

Antigen-specific suppression of cytotoxic T cell responses: an idiotype-bearing factor regulates the cytotoxic T cell response to azobenzenearsonate-coupled cells.

When A/J mice are injected subcutaneously with azobenzenearsonate- (ABA) coupled spleen cells, their splenocytes contain primed ABA-specific cytotoxic T lymphocyte (CTL) precursors. Animals that are not primed in vivo do not develop vigorous CTL activity when assessed after in vitro culture with ABA-coupled stimulators. Suppressor molecules derived from ligand-induced first-order ABA-specific suppressor T cells were evaluated for their ability to limit cytolytic T cell development. We have shown that an idiotype-bearing, hapten-specific suppressor factor suppresses priming for CTL in an H-2-unrestricted but allotype-restricted manner. The implication of these studies to regulatory networks is discussed.

Animals↗