Biomedical subjects

M A Sikorski

Publications and source records attributed to M A Sikorski.

6 recordsLinked to original sources

PubMed1998

Cyclic AMP, PKA, and the physiological regulation of adiposity.

The major regulator of lipolysis in white adipocytes and brown adipocytes is cAMP and the actions of cAMP are mediated by protein kinase A (PKA). Multiple subunits of PKA, including RII beta, R1 alpha, C alpha, and C beta 1, are expressed in fat cells but the major holoenzyme assembled under normal conditions contains RII beta and C alpha. Targeted disruption of the RII beta gene in mice revealed that both white and brown adipocytes are capable of compensating by increasing the level of RI alpha. Nevertheless, the mice display a lean phenotype, have an elevated metabolic rate due to activation and induction of uncoupling protein in brown fat, and are resistant to diet-induced obesity and insulin resistance. Although the metabolic disturbances in white and brown fat tissue may explain most of the phenotypic changes, the loss of neuronal expression of RII beta may also contribute to the alterations in energy balance. Specific neuronal defects have been characterized that prevent the normal changes in gene expression seen with drugs that act through the dopaminergic pathway. The RII beta mutant mouse provides an interesting model of obesity resistance and demonstrates that chronic changes in the PKA signaling system can lead to stable alterations in energy storage and utilization.

Adipose Tissue↗

PubMed1996

Protease-resistant L-selectin mutants. Down-modulation by cross-linking but not cellular activation.

The adhesion molecule L-selectin (CD62L) is rapidly shed from the plasma membrane during leukocyte activation as a result of proteolytic cleavage between Lys321 and Ser322 within the extracellular domain. L-selectin is also down-modulated from the surface in response to cross-linking, possibly through a similar mechanism. To further characterize the mechanism of down-modulation, several L-selectin mutants were generated and transfected into COS cells. Wild-type L-selectin as well as mutants with one or two amino acid substitutions at the cleavage site were nearly quantitatively shed into the culture supernatant. However, mutants in which a nine-amino acid stretch that included the protease-sensitive site was either deleted or replaced with a polyglycine spacer or a comparable region of E-selectin were retained on the cell surface and not detected in the supernatant. These results are consistent with other reports describing protease resistant L-selectin mutants. We also demonstrate that when expressed in L1-2 pre-B cells, the L-selectin nine-amino acid deletion mutant (321del.9), but not wild-type L-selectin, is resistant to down-regulation induced by PMA. However, both wild-type and mutant 321del.9 are completely lost from the cell surface in response to cross-linking with an L-selectin Ab. PMA-induced- but not L-selectin cross-linking-induced down-modulation was inhibited by staurosporine. These data are consistent with the idea that the L-selectin protease(s) can tolerate minor structural alterations at the cleavage site, and that L-selectin down-modulation can be induced by more than one mechanism, at least one of which (cross-linking) is protein kinase C independent.

Amino Acid Sequence↗

PubMed1996

L-selectin crosslinking induces integrin-dependent adhesion: evidence for a signaling pathway involving PTK but not PKC.

L-selectin mediates the initial contact of leukocytes with the endothelium prior to extravasation. Here we demonstrate that L-selectin engagement can induce rapid and avid integrin-dependent T cell adhesion to recombinant immobilized cell adhesion molecules (CAMs) including ICAM-1, ICAM-3, and VCAM-1, as well as to the extracellular matrix protein fibronectin (FN). L-selectin-induced adhesion to these integrin ligands shares characteristics with CD3 mAb- or phorbol ester-induced adhesion in requiring metabolic energy, tyrosine kinase and ligand-stimulated Ca2+ channel activity. However, L-selectin-induced adhesion is distinct from that induced by phorbol ester or CD3 crosslinking in being relatively independent of protein kinase C (PKC) activity and actin polymerization. Consistent with the higher levels of L-selectin expression on CD45RA+ (naive) cells, L-selectin crosslinking induces a greater proportion of naive relative to memory cell binding to CAMs and FN. In contrast, exposure to phorbol ester or CD3 crosslinking is more effective in inducing CD45RO+ (memory) cell adhesion. Thus, in addition to its role in leukocyte capture and rolling on the endothelium, L-selectin may contribute to beta 1 and beta 2 integrin-dependent binding and arrest.

Cell Adhesion↗

PubMed1992

CD43 interferes with T-lymphocyte adhesion.

CD43 is a cell-surface sialoglycoprotein of uncertain physiologic function expressed to various degrees by most leukocytes. We tested whether or not CD43 participates in intercellular adhesion by comparing the binding of human T lymphocytes to transfected HeLa cells stably expressing CD43 and sham-transfected HeLa cells (CD43-negative). Significantly fewer T lymphocytes adhered to the CD43-positive HeLa cells than to the CD43-negative HeLa cells. Diminished T-cell adherence to the CD43-positive HeLa cells was seen for all T lymphocytes tested, irrespective of their source or derivation. Antibody-blocking experiments revealed that CD43 interference with T-cell adhesion largely represented interference with T-cell leukocyte function-associated antigen 1 binding to HeLa cell intercellular adhesion molecule 1. The CD43 anti-adhesion effect was not overcome by treating cells with phorbol 12-myristate 13-acetate, a chemical that increases the binding avidity of leukocyte function-associated antigen 1 for intercellular adhesion molecule 1. However, neuraminidase treatment of the HeLa cell transfectants diminished the CD43 antiadhesion effect. These data indicate that CD43 expression by opposing cells can interfere with cell-cell adhesion. The data also suggest that CD43 might regulate T-cell adhesion by interfering with leukocyte function-associated 1 binding to intercellular adhesion molecule 1, a major activation-induced adhesion pathway among lymphocytes.

Antigens, CD↗

PubMed1990

Human immunodeficiency virus type 1-infected individuals make autoantibodies that bind to CD43 on normal thymic lymphocytes.

Sera from human immunodeficiency virus type 1 (HIV-1)-infected and -noninfected individuals were screened for antibodies that could bind to native T cell differentiation antigens. Antibodies that could immunoprecipitate CD43 (sialophorin, leukosialin) from a T cell lymphoma line were detected in sera from 27% of patients, and antibodies that could bind specifically to transfected cells expressing CD43 were detected in 47% of patients. The anti-CD43 antibodies were related to HIV-1 infection in that no patients with other chronic viral infections or systemic lupus erythematosus contained such antibodies in their sera. The anti-CD43 autoantibodies bound to a partially sialylated form of CD43 expressed by normal human thymocytes, but not by normal, circulating T lymphocytes. However, the determinant(s) recognized by the anti-CD43 autoantibodies was present on a large proportion of circulating T lymphocytes, but masked from antibody recognition by sialic acid residues. These results demonstrate that HIV-1 infection is specifically associated with the production of autoantibodies that bind to a native T cell surface antigen.

Antigens, CD↗

PubMed1987

Does ethanol inhibit LH secretion in the rat?

A prevailing view among those studying neuroendocrine effects of ethanol is that acute doses suppress luteinizing hormone releasing hormone (LHRH) secretion, and consequently inhibit luteinizing hormone (LH) release in the rat. This phenomenon has not been observed in primates, and has been thought to be a species difference. The experimental procedures, however, have involved ethanol administration by oral or intragastric (ig) routes in humans and monkeys, but intraperitoneal (ip) or carotid artery injection in rats. It has also been suggested that inhibition of LH secretion by ethanol in rats is mediated by endogenous opioid peptides (EOP), because the effect can be reversed by the opiate antagonist naloxone. An alternative explanation is that ip ethanol injection might stress rats sufficiently to activate hypothalamic-pituitary-adrenocortical (H-P-A) and EOP systems that are well known to inhibit hormonal activities of the hypothalamic-pituitary-gonadal (H-P-G) axis. Presented here are preliminary results from experiments with male rats. When ethanol is administered ig, under relatively stress-free conditions, it does not inhibit LH secretion in gonadally intact or castrated males. In contrast, ip injection of the same ethanol dose (2.0 g/kg body wt) causes pronounced inhibition of LH secretion and concomitant increases in plasma prolactin (PRL) and corticosterone--indicative of a stress response. Furthermore, when ip ethanol administration is preceded by intracerebroventricular (icv) injection of a corticotropin releasing factor (CRF) antagonist (alpha-helical ovine CRF residues 9 to 41), the effects of ethanol on LH and corticosterone are blocked. These results indicate that it may be stress, rather than ethanol per se, that inhibits LHRH and LH secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗