P326	The serum- and glucocorticoid-regulated kinase Sgk-1 is involved in pulmonary vascular remodeling: role in redox-sensitive regulation of tissue factor by thrombin.
1R.S.Belaiba, 1T.Djordjevic, 1S.Bonello, 2F.Lang, 1J.Hess, 1A.Görlach
1Experimentelle Kinderkardiologie, Deutsches Herzzentrum München an der TU München, München, DE; 2Institut für Physiologie, Universität Tübingen, Tübingen, DE.

Increased levels of thrombin are frequently associated with pulmonary hypertension (PH), and a procoagulant state has been suggested to play a prominent role in vascular remodeling. Thrombin has been shown to increase tissue factor (TF) expression, the regulator of the extrinsic coagulation cascade which is also the major regulator of thrombin generation. However, the signaling pathways supporting such a thrombogenic cycle in the pulmonary vasculature are poorly understood. The serum- and glucocorticoid-inducible kinase Sgk-1 is known as a stress-responsive kinase which is involved in osmoregulation and cell survival. The role of Sgk-1 in vascular remodeling and thrombosis, the two major determinants of PH, has not been elucidated. We investigated the role of Sgk-1 in thrombin signaling, TF expression and activity in pulmonary artery smooth muscle cells (PASMC). Thrombin rapidly increased Sgk-1 activity as well as mRNA and protein expression. This response was decreased by inhibitors of phosphatidylinositol-3 kinase (PI3K) and p38-MAP kinase (p38MAPK), by kinase-deficient phosphoinositide-dependent kinase-1 (PDK1), by kinase-deficient mitogen-activated protein kinase kinase-3 (MKK3), by antioxidants or by dominant-negative RacT17N. In contrast, expression of constitutively active PDK1, MKK3 or RacG12V or exposure to H2O2 increased Sgk-1 expression. Thrombin or overexpression of Sgk-1 enhanced TF expression and activity whereas kinase-deficient Sgk-1 prevented these responses. Consistently, thrombin-induced TF protein was not detectable in fibroblasts from sgk-1 knock-out mice. Furthermore, Sgk-1 was found to activate the nuclear factor kappa B (NFkB) pathway by interacting with IkB kinase inducing IkB degradation and p50 nuclear translocation. Inhibition of NFkB by expressing an IkB repressor prevented thrombin/Sgk-1-induced TF expression. Moreover, Sgk-1 protein was present in the media of pulmonary vessels in lung tissue with pulmonary vascular disease associated with pulmonary hypertension. These data show that thrombin induces Sgk-1 involving Rac, reactive oxygen species as well as PI3K, PDK1 and p38MAPK. Sgk-1 stimulates NFkB and upregulates TF expression and activity. Since thrombin and TF can promote vascular remodeling and Sgk-1 is present in the media of remodeled pulmonary vessels, Sgk-1 may play a critical role in vascular remodeling in PH.

Copyright © 2005 S. Karger AG, Basel. Any further use of this abstract requires written permission from the publisher.