Publications

We characterized T3 efflux in primary cultures of cells derived from human placenta, neonatal rat cardiac myocytes, and rat inner medullary collecting ducts (IMCD). The T3 efflux rate was highest in placenta cells, followed by ventriculocytes, atriocytes, and IMCD cells. Verapamil reversibly blocked [125I]T3 efflux in these cells in a manner that correlated with their T3 efflux rate. Thus, verapamil inhibition of [125I]T3 efflux in placenta cells led to a 432% increase in the [125I]T3 content compared with 33% increase in IMCD cells. Several unlabeled iodothyronines, but not TRIAC, differentially blocked [125I]T3 efflux such as (T4 > T3 > rT3 = D-T3 > D-T4) in placenta cells and (T4 > rT3 = D-T4 = T3 > D-T3) in ventriculocytes, suggesting tissue-specific differences in the carriers/transporters responsible for T3 efflux. This hypothesis draws further support from the fact that D-T3 inhibited [125I]T3 efflux in placenta cells, but not in ventriculocytes. TRIAC did not affect T3 efflux in ventriculocytes or placenta cells, but it greatly inhibited [125I]T3 uptake in these cells, suggesting that [125I]T3 uptake and efflux mechanisms are distinct and appear to be mediated by distinct carrier/transporter proteins. Collectively, these data suggest that differences in thyroid hormone transport in target cells may provide an important mechanism for regulating hormone action in a tissue-specific fashion.

Infection by field strains of Foot-and-mouth disease virus (FMDV) is initiated by binding to certain species of arginine-glycine-aspartic acid (RGD)-dependent integrin including alphavbeta3 and the epithelial integrin alphavbeta6. In this report we show that the integrin alphavbeta1, when expressed as a human/hamster heterodimer on transfected CHOB2 cells, is a receptor for FMDV. Virus binding and infection mediated by alphavbeta1 was inefficient in the presence of physiological concentrations of calcium and magnesium but were significantly enhanced by reagents that activate the integrin and promote ligand binding. The ability of chimeric alpha5/alphav integrin subunits, in association with the beta1 chain, to bind FMDV and mediate infection matched the ligand binding specificity of alphavbeta1, not alpha5beta1, thus providing further evidence for the receptor role of alphavbeta1. In addition, data are presented suggesting that amino acid residues near the RGD motif may be important for differentiating between the binding specificities of alphavbeta1 and alphavbeta6.

Airway inflammation and airway hyperresponsiveness (AHR) are hallmarks of asthma. Cytokines produced by T helper type 2 (Th2) lymphocytes have been implicated in both processes. There is strong support for the idea that Th2 cytokines can produce AHR indirectly by promoting the recruitment of inflammatory cells. Less attention has been given to the possibility that Th2 cytokines might induce AHR by acting directly on resident airway cells. To investigate this, we polarized and activated CD4(+) T cells in vitro and analyzed airway function after administration of lymphocyte-conditioned media to the airways of naive mice. Th2-lymphocyte-conditioned medium induced AHR within 6 h. This finding was reproduced in mast-cell-deficient and in T- and B-lymphocyte-deficient mice. AHR did not occur when Th2-lymphocyte-conditioned medium was administered to mice lacking the IL-4 receptor alpha subunit or Stat6, suggesting a critical role for interleukin (IL)-4 and/or IL-13. This was confirmed by the finding that recombinant IL-4 and IL-13 both induced AHR within 6 h. The induction of AHR occurred in the absence of inflammatory cell recruitment or mucus production. These results strongly suggest that products of activated Th2 lymphocytes can rapidly perturb airway function through direct effects on resident airway cells.

We reported previously that mast cell tryptase is a growth factor for dog tracheal smooth muscle cells. The goals of our current experiments were to determine if tryptase also is mitogenic in cultured human airway smooth muscle cells, to compare its strength as a growth factor with that of other mitogenic serine proteases, and to determine whether its proteolytic actions are required for mitogenesis. Highly purified preparations of human lung beta-tryptase (1-30 nM) caused dose-dependent increases in DNA synthesis in human airway smooth muscle cells. Maximum tryptase-induced increases in DNA synthesis far exceeded those occurring in response to coagulation cascade proteases, such as thrombin, factor Xa, or factor XII, or to other mast cell proteases, such as chymase or mastin. Irreversibly abolishing tryptase's catalytic activity did not alter its effects on increases in DNA synthesis. We conclude that beta-tryptase is a potent mitogenic serine protease in cultured human airway smooth muscle cells. However, its growth stimulatory effects in these cells occur predominantly via nonproteolytic actions.