Rab1 GTPase promotes expression of beta-adrenergic receptors in rat pulmonary microvascular endothelial cells.

It is known that Rab1 regulates the expression and function of beta-adrenoceptors (beta-ARs) in many cells. However, the effect of these changes in rat pulmonary microvascular endothelial cells (RPMVECs) is not known. In the present study, we investigated the role of Rab1, a Ras-like GTPase that coordinates protein transport from the endoplasmic reticulum (ER) to the Golgi body and regulates the cell-surface targeting and function of endogenous beta-ARs in RPMVECs in the presence of lipopolysaccharide (LPS). We found that lentivirus-driven expression of wild-type Rab1 (Rab1WT) in RPMVECs strongly enhanced the amount of beta-ARs on the cell surface, whereas the dominant-negative mutant Rab1N124I significantly attenuated beta-ARs expression on the cell surface. In addition, LPS stimulation significantly reduced beta-ARs expression on the cell surface in RPMVECs; however, this effect was reversed by over-expression of wild-type Rab1WT. Fluorescent microscopy analysis demonstrated that expression of Rab1N124I and Rab1 small interfering RNA (siRNA) significantly induced the accumulation of green fluorescent protein (GFP)-tagged beta(2)-AR in the ER. Consistent with their effects on beta-ARs export, Rab1WT and Rab1N124I differentially modified the beta-AR-mediated activation of extracellular signal-regulated kinase1/2 (ERK1/2). Importantly, over-expression of Rab1WT markedly reduced LPS-induced hyper-permeability of RPMVECs by increasing the expression of beta(2)-AR on the cell surface. These data reveal that beta-ARs function in RPMVECs could be modulated by manipulating beta-ARs traffic from the ER to the Golgi body. We propose the ER-to-Golgi transport as a regulatory site for control of permeability of RPMVECs. Copyright 2010 Elsevier Ltd. All rights reserved.