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Biomedical subjects

S Frenkel

Publications and source records attributed to S Frenkel.

At least 19 recordsLinked to original sources
PubMed1999

Suppression of microphthalmia transcriptional activity by its association with protein kinase C-interacting protein 1 in mast cells.

Microphthalmia (mi) is a transcription factor that plays a major role in the regulation of growth and function in mast cells and melanocytes. Association of mi with other proteins is a critical step in the regulation of mi-mediated transcriptional activation. We found protein kinase C-interacting protein 1 (PKCI) specifically associated with mi in yeast two-hybrid screening. Immunoprecipitation of mi from quiescent rat basophilic leukemic cells or mouse melanocytes resulted in the specific co-immunoprecipitation of PKCI. This association was significantly reduced on engagement of the surface FcepsilonRI of mast cells or engagement of the Kit receptor on melanocytes. Hence, cell activation caused disengagement of mi from PKCI. Microphthalmia was previously shown to activate the mouse mast cell protease 6 (mMCP-6) promoter. Cotransfection of mi with PKCI in NIH 3T3 fibroblasts containing an mMCP-6 promoter-luciferase reporter demonstrated an up to 94% inhibition of mi-mediated transcriptional activation. PKCI by itself, although localized in the cytosol and nucleus of the cells, has no known physiological function and did not demonstrate transcriptional activity. Its ability to suppres mi transcriptional activity in the transient transfected fibroblast system suggests that it can function in vivo as a negative regulator of mi-induced transcriptional activation.

3T3 Cells↗
PubMed1998

Nuclear translocation of upstream stimulating factor 2 (USF2) in activated mast cells: a possible role in their survival.

Multiple transcription factors are activated in the cytoplasm and translocated to the nucleus where they exert positive or negative control over cellular genes. Such subcellular traffic of transcription factors usually requires the presence of a positively charged nuclear localization sequence (NLS). Upstream stimulating factor 2 (USF2) is one of the few transcription factors that contain two potential domains for nuclear localization. In addition to the conventional basic NLS, USF2 contains a highly conserved USF-specific region that is involved in its nuclear translocation. In the present work, the induction of translocation of USF2 into the mast cell nucleus was observed and found to be dependent on activation of the cells either by IL-3 or IgE-Ag. It was also observed that the prevention of the translocation of USF2 to the nucleus, using a peptide derived from the specific USF-NLS region, significantly inhibited their IL-3-mediated survival. Thus, our findings show a direct connection between mast cell surface receptor-mediated USF2 nuclear translocation and cell viability.

Amino Acid Sequence↗
PubMed1997

Outside-in signaling in the chondrocyte. Nitric oxide disrupts fibronectin-induced assembly of a subplasmalemmal actin/rho A/focal adhesion kinase signaling complex.

Elevated levels of fibronectin (Fn) in articular cartilage have been linked to the progression of both rheumatoid and osteoarthritis. In this study, we examined intracellular events which follow ligation of Fn to its receptor, the integrin alpha5beta1. In addition, we examined the regulatory influence of nitric oxide on these events, since this free radical has been implicated in cartilage degradation. Exposure of chondrocytes to Fn-coated beads resulted in the circumferential clustering of the alpha5beta1 integrin receptor, which was accompanied by the subplasmalemmal assembly of a focal activation complex comprised of F-actin, the tyrosine kinase, focal adhesion kinase (FAK), the ras related G protein rho A, as well as tyrosine-phosphorylated proteins. Treatment with exogenous nitric oxide (NO) or catabolic cytokines which induce nitric oxide synthase blocked the assembly of F-actin, FAK, rho A and tyrosine-phosphorylated proteins while not affecting the total number of beads bound per cell nor the clustering of alpha5beta1 integrin. Use of a cGMP antagonist (Rp-8-Br cGMPS) or cGMP agonist (Sp-cGMPS) either abolished or mimicked the NO effect, respectively. Adherence of chondrocytes to fibronectin enhanced proteoglycan synthesis by twofold (vs. albumin). In addition, basic fibroblast growth factor (FGF) and insulin growth factor (IGF-1) induced proteoglycan synthesis in chondrocytes adherent to Fn but not albumin suggesting a costimulatory signal transduced by alpha5betal and the FGF receptor. Both constitutive and FGF stimulated proteoglycan synthesis were completely inhibited by nitric oxide. These data indicate that the ligation of alpha5beta1 in the chondrocyte induced the intracellular assembly of an activation complex comprised of the cytoplasmic tail of alpha5beta1 integrin, actin, and the signaling molecules rho A and FAK. We show that NO inhibits the assembly of the intracellular activation complex and the synthesis of proteoglycans, but has no effect on the extracellular aggregation of alpha5beta1 integrin. These observations provide a basis by which nitric oxide can interfere with chondrocyte functions by affecting chondrocyte-matrix interactions.

Actins↗
PubMed1993

Diffusion of fibroblast growth factor from a plaster of Paris carrier.

Fibroblast growth factor (FGF) is a polypeptide that has been shown to have a stimulatory effect on osseous tissues in vitro. This study characterized the release of FGF from plaster of Paris (PLP) and measured the dissolution of PLP in various solutions with the aim of developing a reliable carrier system for the release of FGF in vivo. The study consisted of five experiments: (I) FGF diffusion from PLP pellets, (II) FGF diffusion from PLP discs, (III) PLP dissolution in saline, (IV) PLP dissolution in serum, and (V) FGF adsorption by commercially pure titanium. FGF was observed to be released at a rate directly proportional to the rate of dissolution of the PLP carrier, suggesting that either the FGF binds to the PLP; or, alternatively, the FGF may be entrapped by the PLP. Dissolution rate, and thus release rate, could be varied by varying the mass of the carrier. Greater diffusion of FGF was observed in larger, more slowly dissolving PLP carriers. Dissolution of PLP was observed to be slower in serum than in saline, apparently due to stabilization by factors in the serum but not due to a concentration gradient effect. Titanium coupons did not adsorb significant amounts of FGF. These results indicate that PLP, which has been shown in the past neither to aggravate inflammatory response nor to interfere with bone ingrowth, may serve as delivery vehicle for FGF to osseous tissues in vivo.

Adsorption↗
PubMed1984

Isolated soluble fractions from the murine B16 melanoma induce primary in vitro syngeneic antitumor responses.

This paper extends our previous studies, which documented our ability to isolate immunogenic entities from nonimmunogenic or weakly immunogenic tumors. B16 melanoma cells failed, in our in vitro experimental system, to induce anti-B16 cytotoxic responses in spleen cells derived from normal syngeneic C57BL/6 mice. The B16 melanoma cellular homogenate was fractionated on an Ultrogel AcA 34 column, and the various fractions were tested for their ability to induce anti-B16 cytotoxic responses under the same conditions as those used for intact B16, the nonimmungenic tumor cells. Certain fractions, some of them with relatively low protein concentrations, induced anti-B16 cytotoxic responses in spleen cells of normal C57BL/6 mice, whereas others, some of them with relatively high protein concentrations, failed to induce such responses. One fraction (Fr.), designated Fr. 5/6, was examined in detail. It was found that in normal syngeneic spleen cells this fraction induced effector cells that efficiently killed (at various E : T ratios) the relevant B16 target cells and RBL5 syngeneic tumor cells, but not the YAC allogeneic tumor cells or C57BL/6 lymphoblasts. Furthermore, an excess of unlabeled B16 cells most efficiently blocked the ability of these anti-B16 effector cells to kill radiolabeled B16 target cells. RBL5 tumor cells, YAC tumor cells, or C57BL/6 lymphoblasts failed to block these effector cells efficiently. A significant fraction of the effector cells induced with Fr. 5/6 was characterized as thymus-derived cells (Thy-1+, Ly-2+3+ cells). It was suggested that another fraction of the cellular population was natural killer cells, which cytolyzed the RBL5 target cells. Various theoretical and practical aspects of these findings are discussed.

Animals↗
PubMed1975

Subcellular distribution of phosphatases, proteinases, and ribonucleases in normal human stratum corneum and psoriatic scales.

The subcellular distribution of phosphatases, proteinases, and ribonucleases of normal human stratum corneum and psoriatic scales was determined after differential centrifugation. All psoriatic enzymes showed much increased activities as compared to the normal stratum corneum enzymes. The highest activities of alkaline phosphatase from psoriatic scales could be detected in the nuclear fraction. The main activities of all other tested phosphatases and proteinases were present in the cytoplasmatic fraction. The subcellular distribution of the ribonucleases varied according to the pH value.

Alkaline Phosphatase↗