Reciprocal expression of the TNF family receptor herpes virus entry mediator and its ligand LIGHT on activated T cells: LIGHT down-regulates its own receptor

The TNF receptor (TNFR) family plays a central role in the development of the immune response. Here we describe the reciprocal regulation of the recently identified TNFR superfamily member herpes virus entry mediator (HVEM) (TR2) and its ligand LIGHT (TL4) on T cells following activation and the mechanism of this process. T cell activation resulted in down-regulation of HVEM and up-regulation of LIGHT, which were both more pronounced in CD8(+) than CD4(+) T lymphocytes. The analysis of HVEM and LIGHT mRNA showed an increase in the steady state level of both mRNAs following stimulation. LIGHT, which was present in cytoplasm of resting T cells, was induced both in cytoplasm and at the cell surface. For HVEM, activation resulted in cellular redistribution, with its disappearance from cell surface. HVEM down-regulation did not rely on de novo protein synthesis, in contrast to the partial dependence of LIGHT induction. Matrix metalloproteinase inhibitors did not modify HVEM expression, but did enhance LIGHT accumulation at the cell surface. However, HVEM down-regulation was partially blocked by a neutralizing mAb to LIGHT or an HVEM-Fc fusion protein during activation. As a model, we propose that following stimulation, membrane or secreted LIGHT binds to HVEM and induces receptor down-regulation. Degradation or release of LIGHT by matrix metalloproteinases then contributes to the return to baseline levels for both LIGHT and HVEM. These results reveal a self-regulating ligand/receptor system that contributes to T cell activation through the interaction of T cells with each other and probably with other cells of the immune system.     

Elimination of Fc receptor-dependent effector functions of a modified IgG4 monoclonal antibody to human CD4

Several CD4 mAbs have entered the clinic for the treatment of autoimmune diseases or transplant rejection. Most of these mAbs caused CD4 cell depletion, and some were murine mAbs which were further hampered by human anti-mouse Ab responses. To obviate these concerns, a primatized CD4 mAb, clenoliximab, was generated by fusing the V domains of a cynomolgus macaque mAb to human constant regions. The heavy chain constant region is a modified IgG4 containing two single residue substitutions designed to ablate residual Fc receptor binding activity and to stabilize heavy chain dimer formation. This study compares and contrasts the in vitro properties of clenoliximab with its matched IgG1 derivative, keliximab, which shares the same variable regions. Both mAbs show potent inhibition of in vitro T cell responses, lack of binding to complement component C1q, and inability to mediate complement-dependent cytotoxicity. However, clenoliximab shows markedly reduced binding to Fc receptors and therefore does not mediate Ab-dependent cell-mediated cytotoxicity or modulation/loss of CD4 from the surface of T cells, except in the presence of rheumatoid factor or activated monocytes. Thus, clenoliximab retains the key immunomodulatory attributes of keliximab without the liability of strong Fcgamma receptor binding. In initial clinical trials, these properties have translated to a reduced incidence of CD4+ T cell depletion.     

TRPM7 regulates quiescent/proliferative metabolic transitions in lymphocytes

A unique property of lymphocytes among all body tissues is their capacity for rapid proliferation in the context of responding to infectious challenges. Lymphocyte proliferation involves a transition from a quiescent metabolic state adjusted to maintain cellular energy homeostasis, to a proliferative metabolic state in which aerobic glycolysis is used to generate energy and biosynthetic precursors necessary for the accumulation of cell mass. Here we show that modulation of TRPM7 channel function in tumor B lymphocytes directly induces quiescent/proliferative metabolic transitions. As TRPM7 is widely expressed outside of the immune system, our results suggest that TRPM7 may play an active role in regulating metabolic transitions associated with rapid cellular proliferation and malignancy.Key words: aerobic glycolysis, lymphocyte, metabolism, quiescence, TRPM7     

Altered Synthesis and Composition of Cell Wall of Grape (Vitis vinifera L.) Leaves during Expansion and Growth-Inhibiting Water Deficits

The rate and composition of cell wall polysaccharide synthesisduring development and growth-inhibiting water deficits wereinvestigated in leaves of grape (Vitis vinifera L.). The rateof leaf expansion was monitored as plant water status was manipulatedby modulating the supply of irrigation water to potted plantsover several days. The corresponding wall synthesis was determinedby incubating leaf tissue with [¹⁴C]glucose and quantifyingincorporation into wall components. Samples were obtained fromrapidly expanding and mature leaves before, during, and following(recovery from) moderate water deficits. Uptake was approximately2-fold greater for mature leaf tissue than for rapidly expandingtissue at both high and low water status. In contrast, incorporationinto cell wall polysaccharides was 18 to 41% (under low andhigh water status) of uptake in expanding leaves but less than4% in mature tissue. Incorporation of precursor into wall polysaccharideswas insensitive to plant water status in mature leaves, butwas inhibited to less than 50% of well-watered controls in expandingleaves at low water potential. Incorporation of label into cellulose,uronic acid, and neutral sugar fractions was differentiallyaffected by water deficits, with cellulose synthesis apparentlyexhibiting the greatest sensitivity to low water status. Afterrewatering, growth, as well as uptake and incorporation of labelrecovered, although the latter did not attain prestress rates.The results indicate a high sensitivity of wall polysaccharide(particularly cellulose) synthesis to growth-inhibiting waterdeficits. ¹ Supported by United States Department of Agriculture, CompetitiveResearch grant GAM 8502539. (Received November 15, 1989; Accepted January 17, 1990)     

PDE-10A inhibitors as insulin secretagogues

Modulation of cAMP levels has been linked to insulin secretion in preclinical animal models and in humans. The high expression of PDE-10A in pancreatic islets suggested that inhibition of this enzyme may provide the necessary modulation to elicit increased insulin secretion. Using an HTS approach, we have identified quinoline-based PDE-10A inhibitors as insulin secretagogues in vitro. Optimized compounds were evaluated in vivo where improvements in glucose tolerance and increases in insulin secretion were measured.     

Zebrafish atoh1 genes: classic proneural activity in the inner ear and regulation by Fgf and Notch

Hair cells of the inner ear develop from an equivalence group marked by expression of the proneural gene Atoh1. In mouse, Atoh1 is necessary for hair cell differentiation, but its role in specifying the equivalence group (proneural function) has been questioned and little is known about its upstream activators. We have addressed these issues in zebrafish. Two zebrafish homologs, atoh1a and atoh1b, are together necessary for hair cell development. These genes crossregulate each other but are differentially required during distinct developmental periods, first in the preotic placode and later in the otic vesicle. Interactions with the Notch pathway confirm that atoh1 genes have early proneural function. Fgf3 and Fgf8 are upstream activators of atoh1 genes during both phases, and foxi1, pax8 and dlx genes regulate atoh1b in the preplacode. A model is presented in which zebrafish atoh1 genes operate in a complex network leading to hair cell development.