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Biomedical subjects

I Graef

Publications and source records attributed to I Graef.

9 recordsLinked to original sources
PubMed2001

Jun N-terminal kinase 2 modulates thymocyte apoptosis and T cell activation through c-Jun and nuclear factor of activated T cell (NF-AT).

The Jun N-terminal kinases (JNKs) recently have been shown to be required for thymocyte apoptosis and T cell differentiation and/or proliferation. To investigate the molecular targets of JNK signaling in lymphoid cells, we used mice in which the serines phosphorylated by JNK in c-Jun were replaced by homologous recombination with alanines (junAA mice). Lymphocytes from these mice showed no phosphorylation of c-Jun in response to activation stimuli, whereas c-Jun was rapidly phosphorylated in wild-type cells. Despite the fact that c-jun is essential for early development, junAA mice develop normally; however, c-Jun N-terminal phosphorylation was required for efficient T cell receptor-induced and tumor necrosis factor-alpha-induced thymocyte apoptosis. In contrast, c-Jun phosphorylation by JNK is not required for T cell proliferation or differentiation. Because jnk2-/- T cells display a proliferation defect, we concluded that JNK2 must have other substrates required for lymphocyte function. Surprisingly, jnk2-/- T cells showed reduced NF-AT DNA-binding activity after activation. Furthermore, overexpression of JNK2 in Jurkat T cells strongly enhanced NF-AT-dependent transcription. These results demonstrate that JNK signaling differentially uses c-Jun and NF-AT as molecular effectors during thymocyte apoptosis and T cell proliferation.

Animals↗
PubMed2001

c-Jun NH2-terminal kinase (JNK)1 and JNK2 have similar and stage-dependent roles in regulating T cell apoptosis and proliferation.

Apoptotic and mitogenic stimuli activate c-Jun NH2-terminal kinases (JNKs) in T cells. Although T cells express both JNK1 and JNK2 isozymes, the absence of JNK2 alone can result in resistance to anti-CD3-induced thymocyte apoptosis and defective mature T cell proliferation. Similar defects in thymocyte apoptosis and mature T cell proliferation, the latter due to reduced interleukin 2 production, are also caused by JNK1 deficiency. Importantly, T cell function was compromised in Jnk1(+/-)Jnk2(+/-) double heterozygous mice, indicating that JNK1 and JNK2 play similar roles in regulating T cell function. The reduced JNK dose results in defective c-Jun NH2-terminal phosphorylation in thymocytes but not in peripheral T cells, in which nuclear factors of activated T cells (NK-ATs)-DNA binding activity is affected. Thus, JNK1 and JNK2 control similar functions during T cell maturation through differential targeting of distinct substrates.

Animals↗
PubMed1996

The mechanism of action of cyclosporin A and FK506.

The immunosuppressants cyclosporin A (CsA), FK506, and rapamycin suppress the immune response by inhibiting evolutionary conserved signal transduction pathways. CsA, FK506, and rapamycin bind to their intracellular receptors, immunophilins, creating composite surfaces that block the activity of specific targets. For CsA/cyclophilin and FK506/FKBP the target is calcineurin. Because of the large surface area of interaction of the drug-immunophilin complex with calcineurin, FK506 and CsA have a specificity for their biologic targets that is equivalent to growth factor-receptor interactions. To date, all the therapeutic as well as toxic effects of these drugs have been shown to be due to inhibition of calcineurin. Inhibition of the action of calcineurin results in a complete block in the translocation of the cytosolic component of the nuclear factor of activated T cells (NF-AT), resulting in a failure to activate the genes regulated by the NF-AT transcription factor. These genes include those required for B-cell help such as interleukin (IL-4) and CD40 ligand as well as those necessary for T-cell proliferation such as IL-2. The purpose of this article is to illustrate the means by which these drugs produce immunosuppression.

Animals↗
PubMed1995

A general strategy for producing conditional alleles of Src-like tyrosine kinases.

The Src-like tyrosine kinases require membrane localization for transformation and probably for their normal role in signal transduction. We utilized this characteristic to prepare Src-like tyrosine kinases that can be readily activated with the rationally designed chemical inducer of dimerization FK1012. Dimerization of cytoplasmic Src-like tyrosine kinases was not sufficient for signaling, but their recruitment to the plasma membrane led to the rapid activation of transcription factors identical to those regulated by crosslinking the antigen receptor. Moreover, recruitment of activated Src-like kinases to the membrane replaced signaling by the T-lymphocyte antigen receptor complex, leading to the activation of both the Ras/protein kinase C and Ca2+/calcineurin pathways normally activated by antigen receptor signaling. Since these chemical inducers of dimerization are cell permeable, this approach permits the production of conditional alleles of any of the Src-like tyrosine kinases, thereby allowing a delineation of their developmental roles.

Alkaline Phosphatase↗
PubMed1993

Both human and mouse cells expressing H-2Kb and ovalbumin process the same peptide, SIINFEKL.

HeLa cells, derived from a human cervix carcinoma line, were transfected with a mouse MHC class I gene, H-2Kb, and chicken ovalbumin. H-2Kb-restricted cytotoxic mouse T cells specific for ovalbumin recognized the double-transfected human cells with similar efficiency as ovalbumin-transfected EL4 mouse thymoma cells (H-2b). The naturally processed ovalbumin T cell epitope was eluted from H-2Kb molecules from double-transfected HeLa cells and was biochemically compared to a synthetic peptide, SIINFEKL, known to be the natural Kb ligand of ovalbumin-transfected H-2b mouse cells. The results indicate that the ovalbumin-derived Kb-ligand of double-transfected HeLa cells is also SIINFEKL. Thus, both human cervix carcinoma cells and mouse thymoma cells expressing Kb and ovalbumin process the same octapeptide. Together with previous data, derived by comparing Kb ligands of unknown sequences from both human and mouse cells expressing Kb, it can be concluded that both mouse and human cells are capable of processing the same ligands for mouse MHC class I molecules. Hence, the general specificity of the peptide-generating mechanism for class I ligands is apparently conserved between evolutionary distant species.

Amino Acid Sequence↗
PubMed1990

The effect of substance L on glucose-mediated cross-links of collagen in the diabetic db/db mouse.

Genetically diabetic mice (db/db) were given 50 mg/kg body weight/day substance L, a nontoxic basic amino acid and compared to control diabetic mice without treatment. The oral administration of the compound was started at the age of 3 months and the animals were sacrificed at the age of 7 months. No adverse effects were observed in animals given the substance L. Total food consumption, drinking water intake and body weight were comparable between the groups. Nonenzymatic glycosylation of serum proteins and hemoglobin was not significantly different in the groups. Renal pathological lesions in the control diabetic mice showed glomerular mesangial expansion and on electron microscopy thickened glomerular basement membranes with a mean thickness of 3,204 +/- 186 A. Treated animals showed significantly less mesangial crescents and thinner glomerular basement membrane thickness of 2,520 +/- 252 A (p less than 0.01). The experimental animals showed in addition a lower mean kidney weight. Glomerular but not tubular proteinuria was reduced in the treated group. Basement membrane collagen type IV isolated from kidneys of experimental animals was more soluble in acidity and showed a lower degree of cross-linking as evaluated by SDS-polyacrylamide gel electrophoresis. We conclude that substance L is beneficial to diabetic renal changes. We suggest that this positive effect could be due to the inhibition of glucose-mediated abnormal cross-linking of collagenous structures by the interaction of substance L with reactive carbonyl residues of glycosylation adducts of collagen. Other possible mechanisms are discussed.

Administration, Oral↗