Tài liệu Báo cáo khoa học: Caveolin-1 influences P2X7 receptor expression and localization in mouse

Caveolin-1 influences P2X7 receptor expression and

localization in mouse lung alveolar epithelial cells

K. Barth1,*, K. Weinhold1,*, A. Guenther1

, M. T. Young2

, H. Schnittler3 and M. Kasper1

1 Institute of Anatomy, Medical Faculty ‘Carl Gustav Carus’, Dresden University of Technology, Germany

2 Faculty of Life Sciences, University of Manchester, UK

3 Institute of Physiology, Medical Faculty ‘Carl Gustav Carus’, Dresden University of Technology, Germany

Extracellular nucleotide signaling in vertebrate cells is

mediated by plasma membrane P2 receptors, which

may be divided into two categories: G-protein-coupled

receptors (P2Y) and ion channels (P2X) [1]. P2X

receptors are ATP-gated nonselective cation channels,

seven members of which (P2X1)7) have been cloned

and characterized in humans, rats and mice [2]. P2X

receptors display a unique topology among ion chan￾nels. The functional channel is a trimer, with each sub￾unit consisting of two transmembrane spans, a large

extracellular loop, and cytoplasmic N- and C-termini

[2]. The extracellular loop contains 10 conserved cys￾teine residues that form five disulfide bonds, some of

which are essential for appropriate trafficking of the

receptor to the cell surface [3]. Additionally, the extra￾cellular loop of P2X receptors contains a number of

putative N-glycosylation sites. N-glycosylation of P2X

receptors has been shown to be essential for their cor￾rect folding, trafficking and function [4–8].

The intracellular C-terminal tail of P2X7 is consider￾ably longer than those of other members of the P2X

family, and contains multiple potential protein and

lipid interaction motifs [9]. Uniquely for P2X7, ion

channel activity is coupled through the C-terminus to

downstream events, including membrane blebbing,

interleukin-1b release and pore formation [10–13]. The

presence of two discrete populations of P2X7 has been

demonstrated in the plasma membrane of rat subman￾dibular glands [14] and in mouse lymphoma cells [15],

leading to the suggestion that P2X7 may be distributed

Keywords

alveolar epithelium; Caveolin-1; mouse lung;

P2X7 receptor

Correspondence

M. Kasper, Institute of Anatomy, Medical

Faculty Carl Gustav Carus, Dresden

University of Technology, Fiedlerstr. 42,

D-01307 Dresden, Germany

Fax: +49 351 458 6303

Tel: +49 351 458 6080

E-mail: [email protected]

*These authors contributed equally to this

work

(Received 3 January 2007, revised 11 April

2007, accepted 16 April 2007)

doi:10.1111/j.1742-4658.2007.05830.x

The P2X7 receptor has recently been described as a marker for lung alveo￾lar epithelial type I cells. Here, we demonstrate both the expression of

P2X7 protein and its partition into lipid rafts in the mouse lung alveolar

epithelial cell line E10. A significant degree of colocalization was observed

between P2X7 and the raft marker protein Caveolin-1; also, P2X7 protein

was associated with caveolae. A marked reduction in P2X7 immunoreacti￾vity was observed in lung sections prepared from Caveolin-1-knockout

mice, indicating that Caveolin-1 expression was required for full expression

of P2X7 protein. Indeed, suppression of Caveolin-1 protein expression in

E10 cells using short hairpin RNAs resulted in a large reduction in P2X7

protein expression. Our data demonstrate a potential interaction between

P2X7 protein and Caveolin-1 in lipid rafts, and provide a basis for further

functional and biochemical studies to probe the physiologic significance of

this interaction.

Abbreviations

b-Cop, b-coatomer protein; Flo-1, flotillin-1; PDI, protein disulfide isomerase; sh, short hairpin; TfR, ransferrin receptor; TRCP1, transient

receptor potential channel protein.

FEBS Journal 274 (2007) 3021–3033 ª 2007 The Authors Journal compilation ª 2007 FEBS 3021