Publications

Activation of T lymphocytes infected with the human immunodeficiency virus-1 (HIV-1) results in enhancement of viral replication mediated in part by activation of cellular NF kappa B capable of binding directly to sequences in the viral long terminal repeat, or LTR. Together with CD4+ T cells, macrophages constitute a major target for infection by HIV-1. Unlike lymphocytes, however, stimulation of mononuclear phagocytes is not associated with cell division and proliferation. Human monocyte-derived macrophages transfected with HIV-LTR-CAT constructs demonstrated down-regulation of CAT activity after stimulation with bacterial lipopolysaccharide (LPS) that mapped to a region distinct from NF kappa B binding sites. In contrast, fresh monocytes and the promonocytic U937 cell line both demonstrated up-regulation of HIV-LTR-CAT expression by LPS. Differentiation of U937 by PMA to establish a nondividing phenotype resulted in down-regulation of transfected HIV-LTR-CAT activity by LPS similar to that in mature macrophages. Human monocyte-derived macrophages infected with HIV-1 in vitro demonstrated a decrease in viral p24 release after incubation in LPS that was comparable to the negative regulation that occurred in the transient transfection assays. Factors controlling HIV replication may differ in dividing and nondividing hematopoietic cells and may contribute to restricted viral expression in nondividing cells.

Cultured glomerular mesangial cells (MC) respond to low concentrations of bacterial endotoxin (ET) by secreting prostaglandins and interleukin-1. To evaluate further the nature of ET-induced mesangial cell activation, the authors evaluated the effects of this agent on MC morphology and cytoskeletal organization. Bacterial ET, in concentrations as low as I ng/ml, induced reversible membrane ruffling, cellular rounding, and extension of many filopodia and lamellopodia. Augmented fluid-phase pinocytosis occurred in parallel, as determined by transmission electron microscopy and tritiated sucrose uptake. These cellular morphologic and functional changes were associated with an extensive, but reversible, depolymerization of actin microfilaments. Actin gene expression was also modified by ET. At 4 to 6 hours after ET exposure, Northern blot analysis showed a twofold to fourfold increase in actin mRNA levels. In situ hybridizations of ET-stimulated cells at the light and electron microscopic levels demonstrated a markedly asymmetric distribution of actin mRNA, which was localized in the cellular periphery at filopodial and lamellopodial extensions, presumably sites of new actin protein synthesis. It is concluded that ET effects on MC are distinct from the nonspecific lytic or 'toxic' actions described for other cell types. Endotoxin induces a global activation of this cell type associated with major changes in membrane structure, cytoskeletal organization, and gene expression, which resemble in many respects the responses to peptide mitogens.

Cells lining the respiratory tract form an interface between the organism and the external environment and are repeatedly exposed to physical, chemical, and metabolic stresses. We examined the response of cultured guinea pig tracheal epithelial cells and alveolar macrophages to various forms of stress, including clinically and environmentally relevant metabolic stresses such as ozone and acid exposure. Classic stress treatments such as heat shock and sodium arsenite treatment induced the synthesis of 28, 32, 72, 73, 90, and 110 kD stress proteins similar to those observed in other cell types. In contrast, no significant changes in the pattern of protein synthesis were detected after exposure to ambient concentrations of ozone, although ozone exposure caused significant cytotoxicity to both cell types. Another potent oxidant, hydrogen peroxide, similarly did not induce appreciable stress protein synthesis. However, surface acidification of tracheal epithelial cells and alveolar macrophages caused the induction of 72 and 78 kD stress proteins. While stress proteins may play a role in the response of respiratory cells to certain injuries such as hyperthermia and surface acidification, they may not be important in the defense against ozone or other forms of oxidative injury.