Alveolar macrophages from normal individuals and patients with interstitial lung diseases spontaneously expressed a 4.2-kilobase mRNA complementary to the c-sis gene, a proto-oncogene coding for one of the chains of platelet-derived growth factor (PDGF). Concomitantly, these cells released a mediator with the properties of PDGF, including: (a) chemotactic factor for smooth muscle cells whose activity was resistant to heat and acid, but sensitive to reduction; (b) mitogenic (competence) activity for fibroblasts; (c) ability to compete with PDGF for its receptor, and (d) precipitated by an anti-PDGF antibody. While blood monocytes did not contain c-sis mRNA transcripts, monocytes matured in vitro expressed c-sis, consistent with the concept that expression of c-sis occurs during the differentiation of monocytes into alveolar macrophages. Together with the known actions of PDGF, these observations suggest that the c-sis proto-oncogene and its PDGF product are part of the armamentarium available to the alveolar macrophages for normal lung defense and participation in lung inflammation.
Metabolic activating capacity of human livers for carcinogenic heterocyclic arylamines has been studied using a Salmonella mutagenesis test. A large individual variation was observed among 15 liver samples in the capacities of activation of Glu‐P‐1(2‐amino‐6‐methyldipyrido[1,2‐α:3′,2′‐d]imidazole), IQ (2‐amino‐3‐methylimidazo[4,5‐f]quinoline) and MeIQx (2‐amino‐3,8‐dimethyl‐3H‐imidazo[4,5‐f]quinoxaline). The average numbers of revertants induced by the three heterocyclic arylamines were nearly the same or rather higher in the presence of hepatic microsomes from human than those from rat. In high‐performance liquid chromatography, formation of N‐hydroxy‐Glu‐P‐1 was detected and accounted for more than 80% of the total mutagenicity observed in the human microsomal system with Glu‐P‐1, indicating that, similarly to experimental animals, N‐hydroxylation is a major activating step for heterocyclic arylamines in human. Addition of flavone or 7,8‐benzoflavone to human liver microsomes showed effective inhibition of the mutagenic activation of Glu‐P‐1, although the treatment rather enhanced microsomal benzo[a]pyrene hydroxylation in human livers. Mutagenic activation of Glu‐P‐1 by human liver microsomes was also decreased by the inclusion of anti‐rat P‐448‐H IgG, and was well correlated with the content of immunoreactive P‐448‐H in livers, suggesting the involvement of a human cytochrome P‐450, which shares immunochemical and catalytic properties with rat P‐448‐H, in the metabolic activation of heterocyclic arylamines in human livers.
Under some conditions, mononuclear phagocytes spontaneously synthesize and release fibronectin, an extracellular matrix glycoprotein with versatile effects on cell-matrix interactions. To gain insight into the processes that modulate the level of fibronectin secretion by these cells, we used monocytes, in vitro matured nonocytes and alveolar macrophages as models to compare fibronectin mRNA levels and fibronectin secretion in a variety of circumstances. Using Northern analysis and dot-blot analysis with a 32P-labeled human fibronectin cDNA probe, we evaluated steady-state mRNA levels and a human fibronectin-specific ELISA was used to evaluate fibronectin secretion. In all cases the amounts of fibronectin secreted paralleled fibronectin mRNA levels. Specifically (a) when fibronectin mRNA was undetectable, as in the case of normal blood monocytes, no fibronectin was secreted, but whenever fibronectin mRNA was present, as in normal alveolar macrophages, fibronectin was secreted by the cells; (b) as monocytes matured into macrophages in vitro, the cells began to express fibronectin mRNA and the cells secreted fibronectin; (c) when alveolar macrophages were activated with surface stimuli such as lipopolysaccharide (LPS) or immune complexes, fibronectin mRNA levels decreased and in parallel, the cells secreted less fibronectin; (d) in idiopathic pulmonary fibrosis (IPF), alveolar macrophages contained severalfold more fibronectin mRNA transcripts that normal and the cells spontaneously secreted severalfold more fibronectin than normal; and (e) when IPF alveolar macrophages were placed in culture the fibronectin mRNA levels in the cells decreased with time, and concurrently the amounts of fibronectin produced per unit time continually decreased. The observation of a strict concordance of fibronectin mRNA levels and fibronectin release by mononuclear phagocytes suggests that, at least in many circumstances, fibronectin secretion by mononuclear phagocytes is controlled by steady-state levels of fibronectin mRNA.
Characteristics of a typical male-dominant reaction, dealkylation of n-propoxycoumarin, in rat livers were studied in relation to microsomal testosterone 6 beta-hydroxylase. The depropylation was more than 10-fold higher in the liver of male than female adult rats, but the sex-related difference was eliminated by neonatal castration. Hypophysectomy of adult male rats, which decreased the rates of male-specific P-450-male-dependent reactions, increased the depropylation of propoxycoumarin, while the rate was decreased by either intermittent injection or continuous infusion of human growth hormone to hypophysectomized rats. With regard to age-related difference, microsomal depropylation was detectable at neonate and reached a maximal level at 14 to 20 d of age, but was abruptly diminished only in female rats at puberty. These changes are in good agreement with those of testosterone 6 beta-hydroxylation and the content of a male-specific P-450(6)beta-1/PB-1. In reconstituted systems using extracted microsomal lipids, P-450(6)beta-1/PB-1 and P-450-male catalyzed the depropylation of propoxycoumarin. However, the microsomal depropylation was inhibited by antibodies which recognize P-450(6)beta-1/PB-1, but not P-450-male. These results indicate that microsomal depropylation of propoxycoumarin is catalyzed mainly by a male-specific P-450(6)beta-1/PB-1 in livers of untreated rats.
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