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At least 19 recordsLinked to original sources

PubMed1992

Transport system ASC for neutral amino acids. An electroneutral sodium/amino acid cotransport sensitive to the membrane potential.

The influx of L-threonine through system ASC does not influence the membrane potential in cultured human fibroblasts although comparable fluxes of amino acids through another Na(+)-dependent agency, system A, effectively depolarize the cells. The membrane potential, however, stimulates the influx of amino acids through system ASC with a maximal effect at -50 mV. The sensitivity of amino acid influx through system ASC to the membrane potential is not constant, but rather, is dependent on intracellular and extracellular concentrations of the substrates, Na+ and amino acids, of the system. Conditions which favor the loading of the ASC carrier at the external surface reduce the sensitivity of ASC-mediated amino acid influx to the membrane potential; in contrast, the sensitivity of this amino acid influx increases under conditions which favor loading of the carrier at the internal surface. Trans-stimulation, a well-known characteristic of system ASC, also varies with the concentrations of the substrates of the system and, in fact, this characteristic is not observed when external Na+ is low. These data may be accommodated by a model in which an electrically silent mode of operation of the transporter is dominant. The influence of the membrane potential on the transport system is dependent on the extent to which a charge-translocating step in the cycling of the carrier is rate limiting (relative rate limitance).

Adolescent↗

PubMed1977

Reaginic antibody production to Ascaris suum allergen, ASC-1. I. The function of glutaraldehyde-polymerized antigen in the induction of reaginic (IgE) antibodies in the rat.

Rats immunized with a purified Ascaris suum allergen (Asc-1) or with its dinitrophenylated derivate (DNP-Asc-1) produced high levels of reaginic (IgE) antibodies. A second injection of antigen given 30 days later did not result in an anamnestic IgE antibody response. Immunization of adult-thymectomized, lethally-irradiated and bone-marrow reconstituted (ATxB) rats with soluble Asc-1 or DNP-Asc-1 failed to stimulate reaginic antibody production. The administration of glutaraldehyde-polymerized antigen induced in some but not all ATxB rats, low but detectable levels of IgE antibodies. These levels increased following a second injection of nonpolymerized antigen in A1 (OH)3 gels. Priming of animals with polymerized carrier and Bordetella pertussis did not stimulate a primary anticarrier IgE response but led to an enhanced antihapten IgE response following the administration of soluble DNP-Asc-1 in A1(OH)3. The results are consistent with the notion that a sharply reduced but clearly functional T-derived helper cell population could be triggered by the polymerized but not by the soluble form of the immunogen.

Allergens↗

PubMed1975

Amyloid-related serum component (protein ASC) IN LEPROSY PATIENTS.

The presence of amyloid-related serum component, protein ASC, in serum samples from 63 leprosy patients was investigated. Protein ASC was detected in 38% of the patients. A correlation to the disease spectrum of leprosy was apparent: polar lepromatous cases, 64% positive; borderline lepromatous, 50%; borderline tuberculoid, 36%; subpolar tuberculoid, 17%; and polar tuberculoid, negative. Antibody activity against the a antigen of Mycobacterium leprae was also determined, showing a similar correlation to the disease spectrum. Serum samples from 23 apparently healthy Ethiopians serving as controls showed a protein ASC incidence of 22%. This figure is significantly higher than the frequency found by others among healthy Norwegian blood donors. Immunoglobulin M levels among patients were elevated in the borderline lepromatous and poplar lepromatous groups. The three tuberculoid groups did not differ in this respect from the control group but were all elevated as compared to a normal Caucasian serum pool. Although raised immunoglobulin M levels seemed to parallel increased frequencies of protein ASC in the patient groups as well as in controls, this correlation might be only secondary to a primary derangement in T-cell function.

Adult↗

PubMed2025

Evolutionary and Functional Analysis of Caspase-8 and ASC Interactions to Drive Lytic Cell Death, PANoptosis.

Caspases are evolutionarily conserved proteins essential for driving cell death in development and host defense. Caspase-8, a key member of the caspase family, is implicated in nonlytic apoptosis, as well as lytic forms of cell death. Recently, caspase-8 has been identified as an integral component of PANoptosomes, multiprotein complexes formed in response to innate immune sensor activation. Several innate immune sensors can nucleate caspase-8-containing PANoptosome complexes to drive inflammatory lytic cell death, PANoptosis. However, how the evolutionarily conserved and diverse functions of caspase-8 drive PANoptosis remains unclear. To address this, we performed evolutionary, sequence, structural, and functional analyses to decode caspase-8's complex-forming abilities and its interaction with the PANoptosome adaptor ASC. Our study distinguished distinct subgroups within the death domain superfamily based on their evolutionary and functional relationships, identified homotypic traits among subfamily members, and captured key events in caspase evolution. We also identified critical residues defining the heterotypic interaction between caspase-8's death effector domain and ASC's pyrin domain, validated through cross-species analyses, dynamic simulations, and in vitro experiments. Overall, our study elucidated recent evolutionary adaptations of caspase-8 that allowed it to interact with ASC, improving our understanding of critical molecular associations in PANoptosome complex formation and the underlying PANoptotic responses in host defense and inflammation. These findings have implications for understanding mammalian immune responses and developing new therapeutic strategies for inflammatory diseases.

Caspase 8↗

PubMed1992

Effects of tumor necrosis factor on system ASC-mediated glutamine transport by human fibroblasts.

The effects of tumor necrosis factor-alpha (TNF) on glutamine GLN transport by cultured human fibroblasts were studied. Uptake of 3H-GLN was assayed in both the presence and absence of sodium in order to differentiate Na(+)-dependent and Na(+)-independent transport systems. GLN transport was linear (r = 0.99) for at least 15 min and occurred predominantly via a single Na(+)-dependent pathway, consistent with System ASC. Incubation of fibroblasts with TNF (1000 units/ml) for 12 hr resulted in a significant decrease in system ASC-mediated glutamine transport activity. TNF did not alter cell morphology or protein content. Kinetic studies indicated that the decrease in carrier-mediated Na(+)-dependent GLN transport was not due to a change in transporter affinity (Km = 117 +/- 23 microM in controls vs 86 +/- 23 microM in TNF, P = NS), but instead to a 45% decrease in maximal transport rate (Vmax = 4088 +/- 354 pmole/mg protein/30 sec in controls vs 2230 +/- 510 in TNF, P less than 0.05). TNF also decreased Na(+)-independent transport by 50% (mean uptake of 50 microM GLN = 94 +/- 13 pmole/mg protein/30 sec in controls vs 46 +/- 6 in TNF, P less than 0.02). In human fibroblasts, the activity of System ASC, which has generally been viewed as a hormonally unresponsive carrier, is decreased by TNF. This impairment in glutamine transport may result in inadequate amounts of intracellular glutamine to support fibroblast metabolism and possibly function.

Amino Acid Transport Systems↗

PubMed1992

Characterization of a novel variant of amino acid transport system asc in erythrocytes from Przewalski's horse (Equus przewalskii).

In thoroughbred horses, red blood cell amino acid transport activity is Na(+)-independent and controlled by three codominant genetic alleles (h, l, s), coding for high-affinity system asc1 (L-alanine apparent Km for influx at 37 degrees C congruent to 0.35 mM), low-affinity system asc2 (L-alanine Km congruent to 14 mM), and transport deficiency, respectively. The present study investigated amino acid transport mechanisms in red cells from four wild species: Przewalski's horse (Equus przewalskii), Hartmann's zebra (Zebra hartmannae), Grevy's zebra (Zebra grevyi), and onager (Equus hemonius). Red blood cell samples from different Przewalski's horses exhibited uniformly high rates of L-alanine uptake, mediated by a high-affinity asc1-type transport system. Mean apparent Km and Vmax values (+/- SE) for L-alanine influx at 37 degrees C in red cells from 10 individual animals were 0.373 +/- 0.068 mM and 2.27 +/- 0.11 mmol (L cells.h), respectively. As in thoroughbreds, the Przewalski's horse transporter interacted with dibasic as well as neutral amino acids. However, the Przewalski asc1 isoform transported L-lysine with a substantially (6.4-fold) higher apparent affinity than its thoroughbred counterpart (Km for influx 1.4 mM at 37 degrees C) and was also less prone to trans-stimulation effects. The novel high apparent affinity of the Przewalski's horse transporter for L-lysine provides additional key evidence of functional and possible structural similarities between asc and the classical Na(+)-dependent system ASC and between these systems and the Na(+)-independent dibasic amino acid transport system y+. Unlike Przewalski's horse, zebra red cells were polymorphic with respect to L-alanine transport activity, showing high-affinity or low-affinity saturable mechanisms of L-alanine uptake. Onager red cells transported this amino acid with intermediate affinity (apparent Km for influx 3.0 mM at 37 degrees C). Radiation inactivation analysis was used to estimate the target size of system asc in red cells from Przewalski's horse. The transporter's in situ apparent molecular weight was 158,000 +/- 2500 (SE).

Alanine↗

PubMed1979