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Biomedical subjects

A Scheschonka

Publications and source records attributed to A Scheschonka.

9 recordsLinked to original sources
PubMed2003

Pre- and posttreatment MR imaging in AIDS-related Kaposi sarcoma of the conjunctiva and lacrimal gland.

AIDS-related Kaposi sarcoma can affect the eye: the (bulbar) conjunctiva and lacrimal gland being rare sites of occurrence. We present a case of AIDS-related Kaposi sarcoma of the conjunctiva in which MR imaging was effective in suggesting the diagnosis and aiding therapeutic strategy. We also discuss advances in imaging of ocular and orbital malignancies presented in the recent literature.

AIDS-Related Opportunistic Infections↗
PubMed2002

Development of obsessive-compulsive behaviour following cortisone treatment.

In this report, we will describe the first case of obsessive-compulsive behaviour following oral corticosteroid treatment in a 75-year old adult male patient with pulmonary disease, but without previous psychiatric symptoms or organic brain disorder. We will also discuss the clinical and pathophysiological considerations.

Adult↗
PubMed2000

Regulator of G protein signaling 1 (RGS1) markedly impairs Gi alpha signaling responses of B lymphocytes.

Regulator of G protein signaling (RGS) proteins modulate signaling through pathways that use heterotrimeric G proteins as transducing elements. RGS1 is expressed at high levels in certain B cell lines and can be induced in normal B cells by treatment with TNF-alpha. To determine the signaling pathways that RGS1 may regulate, we examined the specificity of RGS1 for various G alpha subunits and assessed its effect on chemokine signaling. G protein binding and GTPase assays revealed that RGS1 is a Gi alpha and Gq alpha GTPase-activating protein and a potential G12 alpha effector antagonist. Functional studies demonstrated that RGS1 impairs platelet activating factor-mediated increases in intracellular Ca+2, stromal-derived factor-1-induced cell migration, and the induction of downstream signaling by a constitutively active form of G12 alpha. Furthermore, germinal center B lymphocytes, which are refractory to stromal-derived factor-1-triggered migration, express high levels of RGS1. These results indicate that RGS proteins can profoundly effect the directed migration of lymphoid cells.

Animals↗
PubMed2000

RGS3 is a GTPase-activating protein for g(ialpha) and g(qalpha) and a potent inhibitor of signaling by GTPase-deficient forms of g(qalpha) and g(11alpha).

Many Regulators of G protein Signaling (RGS) proteins accelerate the intrinsic GTPase activity of G(ialpha) and G(qalpha)-subunits [i.e., behave as GTPase-activating proteins (GAPs)] and several act as G(qalpha)-effector antagonists. RGS3, a structurally distinct RGS member with a unique N-terminal domain and a C-terminal RGS domain, and an N-terminally truncated version of RGS3 (RGS3CT) both stimulated the GTPase activity of G(ialpha) (except G(zalpha)) and G(qalpha) but not that of G(salpha) or G(12alpha). RGS3 and RGS3CT had G(qalpha) GAP activity similar to that of RGS4. RGS3 impaired signaling through G(q)-linked receptors, although RGS3CT invariably inhibited better than did full-length RGS3. RGS3 potently inhibited G(qalpha)Q209L- and G(11alpha)Q209L-mediated activation of a cAMP-response element-binding protein reporter gene and G(qalpha)Q209L induced inositol phosphate production, suggesting that RGS3 efficiently blocks G(qalpha) from activating its downstream effector phospholipase C-beta. Whereas RGS2 and to a lesser extent RGS10 also inhibited signaling by these GTPase-deficient G proteins, other RGS proteins including RGS4 did not. Mutation of residues in RGS3 similar to those required for RGS4 G(ialpha) GAP activity, as well as several residues N terminal to its RGS domain impaired RGS3 function. A greater percentage of RGS3CT localized at the cell membrane than the full-length version, potentially explaining why RGS3CT blocked signaling better than did full-length RGS3. Thus, RGS3 can impair Gi- (but not Gz-) and Gq-mediated signaling in hematopoietic and other cell types by acting as a GAP for G(ialpha) and G(qalpha) subfamily members and as a potent G(qalpha) subfamily effector antagonist.

Cells, Cultured↗
PubMed1998

Regulation of chemotactic and proadhesive responses to chemoattractant receptors by RGS (regulator of G-protein signaling) family members.

Serpentine Galphai-linked receptors support rapid adhesion and directed migration of leukocytes and other cell types. The intracellular mechanisms mediating and regulating chemoattractant-directed adhesion and locomotion are only now beginning to be explored. RGS (for regulator of G-protein signaling) proteins are a recently described family that regulate Galphai-stimulated pathways by acting as GTPase-activating proteins. Little is known about the GTPase activity of the Galphai proteins involved in adhesion and chemotaxis, or the significance of their regulation to these responses. Using transiently transfected lymphoid cells as a model system, we show that expression of RGS1, RGS3, and RGS4 inhibits chemoattractant-induced migration. In contrast, RGS2, a regulator of Galphaq activity, had no effect on cell migration to any chemoattractant. RGS1, RGS3, and RGS4 also reduced rapid chemoattractant-triggered adhesion, although the proadhesive response appears quantitatively less sensitive to RGS action than chemotaxis. The results suggest that the duration of the Galphai signal may be a particularly important parameter in the chemotactic responses of leukocytes, and demonstrate the potential for RGS family members to regulate cellular adhesive and migratory behaviors.

Cell Adhesion↗
PubMed1998

Expression of GTPase-deficient Gialpha2 results in translocation of cytoplasmic RGS4 to the plasma membrane.

The members of a recently identified protein family termed regulators of G-protein signaling (RGS) act as GTPase-activating proteins for certain Galpha subunits in vitro, but their physiological effects in cells are uncertain in the face of similar biochemical activity and overlapping patterns of tissue expression. Consistent with its activity in in vitro GTPase-activating protein assays, RGS4 interacts efficiently with endogenous proteins of the Gi and Gq subclasses of Galpha subunits but not with G12alpha or Gsalpha. Unlike other RGS proteins such as RGS9, RGS-GAIP, and Sst2p, which have been reported to be largely membrane-associated, a majority of cellular RGS4 is found as a soluble protein in the cytoplasm. However, the expression of a GTPase-deficient Gialpha subunit (Gialpha2-Q204L) resulted in the translocation of both wild type RGS4 and a non-Gialpha-binding mutant (L159F) to the plasma membrane. These data suggest that RGS4 may be recruited to the plasma membrane indirectly by G-protein activation and that multiple RGS proteins within a given cell might be differentially localized to determine a physiologic response to a G-protein-linked stimulus.

Animals↗
PubMed1997

Potential role for a regulator of G protein signaling (RGS3) in gonadotropin-releasing hormone (GnRH) stimulated desensitization.

The cellular and molecular mechanisms of gonadotrope desensitization are unknown but transduction of the GnRH signal is known to involve sequentially the GnRH receptor, Gq alpha protein, phospholipase C beta-1, inositol-1,4,5-trisphosphate (IP3), and intracellular Ca+2 release. Here, we report the results of studies of a new family of proteins known as regulators of G protein signaling (RGS) that recently have been implicated in desensitization of several ligand induced processes. Using DNA-mediated transfection, we co-expressed the GnRH receptor and RGS1,2,3, or 4 in COS-1 cells. Control cells and those expressing RGS1,2, and 4 produced five fold increases in IP3 levels during the 30 sec after treatment with GnRH. In contrast, RGS3 expression suppressed by 75% the GnRH-induced IP3 responses. RGS3 was shown to bind Gq alpha protein in a model in vitro system: recombinant RGS3-glutathione-S-transferase (GST) fusion protein bound five-fold more 35S-met labeled Gq alpha protein than did with GST alone, suggesting that the mechanism of RGS3 action is attenuation of Gq alpha protein activation of phospholipase C. RGS3 mRNA and protein were observed to be expressed endogenously in the gonadotropic alpha T3-1 cell line. These results suggest a potential role for RGS3 in modulating the LH secretory responsiveness of the pituitary gonadotrope to GnRH.

Animals↗
PubMed1990

Temporal relationships between the loss of vitamin E, protein sulfhydryls and lipid peroxidation in microsomes challenged with different prooxidants.

Microsomal membranes exposed to various prooxidants displayed distinct patterns in the temporal relationships between the loss of antioxidants and the onset of lipid peroxidation. Prooxidants included ADP-chelated iron with reductants (NADPH and ascorbate), or compounds that generate peroxyl radicals (tert-butyl hydroperoxide and 2,2'-azobis(2-amidinopropane)), or free metal ions (Fe2+ and Cu2+). Lipid peroxidation initiated by Fe2+ began simultaneously with the loss of alpha-tocopherol, while about 15% of alpha-tocopherol was lost during the lag phase preceding lipid peroxidation in systems containing chelated iron. A substantial depletion of alpha-tocopherol (49-69%) preceded peroxidation when initiated by peroxyl radicals, while 97% of the antioxidant disappeared preceding peroxidation initiated by copper. The loss of protein sulfhydryl groups also varied between the prooxidants (ranging from 0 to 82% loss prior to the onset of peroxidation) to a degree that roughly paralleled the loss of vitamin E. Therefore, important determinants of peroxidation are prooxidant-dependent, and not only include alpha-tocopherol and sulfhydryl groups, but also membrane integrity, propagation reactions and the availability of catalytic transition metals.

Chemical Phenomena↗