Silencing CD36 gene expression results in the inhibition of latent-TGF-β1 activation and suppression of silica-induced lung fibrosis in the rat

<p>Abstract</p> <p>Background</p> <p>The biologically active form of transforming growth factor-β1 (TGF-β1) plays a key role in the development of lung fibrosis. CD36 is involved in the transformation of latent TGF-β1 (L-TGF-β1) to active TGF-β1. To clarify the role of CD36 in the development of silica-induced lung fibrosis, a rat silicosis model was used to observe both the inhibition of L-TGF-β1 activation and the antifibrotic effect obtained by lentiviral vector silencing of CD36 expression.</p> <p>Methods</p> <p>The rat silicosis model was induced by intratracheal injection of 10 mg silica per rat and CD36 expression was silenced by administration of a lentiviral vector (Lv-shCD36). The inhibition of L-TGF-β1 activation was examined using a CCL-64 mink lung epithelial growth inhibition assay, while determination of hydroxyproline content along with pathological and immunohistochemical examinations were used for observation of the inhibition of silica-induced lung fibrosis.</p> <p>Results</p> <p>The lentiviral vector (Lv-shCD36) silenced expression of CD36 in alveolar macrophages (AMs) obtained from bronchoalveolar lavage fluid (BALF) and the activation of L-TGF-β1 in the BALF was inhibited by Lv-shCD36. The hydroxyproline content of silica+Lv-shCD36 treated groups was significantly lower than in other experimental groups. The degree of fibrosis in the silica+Lv-shCD36-treated groups was less than observed in other experimental groups. The expression of collagen I and III in the silica+Lv-shCD36-treated group was significantly lower than in the other experimental groups.</p> <p>Conclusion</p> <p>These results indicate that silencing expression of CD36 can result in the inhibition of L-TGF-β1 activation in a rat silicosis model, thus further preventing the development of silica-induced lung fibrosis.</p

J. Biol. Chem.

Rap1 is a small GTPase that is involved in signal transduction cascades. It is highly homologous to Ras but it is down- regulated by its own set of GTPase activating proteins (GAPs). To investigate the mechanism of the GTP-hydrolysis reaction catalyzed by Rap1GAP, a catalytically active fragment was expressed in Escherichia coli and characterized by kinetic and mutagenesis studies. The GTPase reaction of Rap1 is stimulated 10(5)-fold by Rap1GAP and has a k(cat) of 6 s(-1) at 25 degreesC. The catalytic effect of GAPs from Ras, Rho, and Rabs depends on a crucial arginine which is inserted into the active site. However, all seven highly conserved arginines of Rap1GAP can be mutated without dramatically reducing V-max of the GTP- hydrolysis reaction. We found instead two lysines whose mutations reduce catalysis 25- and 100-fold, most likely by an affinity effect. Rap1GAP does also not supply the crucial glutamine that is missing in Rap proteins at position 61. The Rap1(G12V) mutant which in Ras reduces catalysis 10(6)-fold is shown to be efficiently down-regulated by Rap1GAP. As an alternative, Rap1(F64A) is shown by kinetic and cell biological studies to be a Rap1GAP-resistant mutant. This study supports the notion of a completely different mechanism of the Rap1GAP- catalyzed GTP-hydrolysis reaction on Rap1

Evaluation studies of cross-cultural training programs: A Review of the Literature From 1988-2000.

The field of international human resource management (IHRM) is a relative new-comer in the social sciences. Despite its nascency, this field has seen massive growth in the research generated by scholars in the past decade (Mendenhall, Kuhlmann, Stahl, & Osland, 2002). One area within the IHRM field that has experienced explosive growth over the past 20 years is that of expatriation. Numerous scholars have focused on a variety of aspects of expatriation during this time period: selection, adjustment, training, relationship to global leadership development, family relationships, reentry issues, national and gender differences (for examples, see Black, Gregersen, Mendenhall, & Stroh, 1999; Church, 1982; Cui & Awa, 1992; Furnham & Bochner, 1986; Gertsen, 1990; Kealey & Ruben, 1983; Mendenhall, Kuhlmann, & Stahl, 2001; Mendenhall & Oddou, 1985; Torbiörn, 1982; Tung, 1981, 1982)