Abstract
ClC-3 is a Cl(-)/H(+) antiporter required for cytokine-induced intraendosomal reactive oxygen species (ROS) generation by Nox1. ClC-3 current is distinct from the swelling-activated chloride current (ICl(swell)), but overexpression of ClC-3 can activate currents that resemble ICl(swell). Because H(2)O(2) activates ICl(swell) directly, we hypothesized that ClC-3-dependent, endosomal ROS production activates ICl(swell). Whole-cell perforated patch clamp methods were used to record Cl(-) currents in cultured aortic vascular smooth muscle cells from wild type (WT) and ClC-3 null mice. Under isotonic conditions, tumor necrosis factor-alpha (TNF-alpha) (10 ng/ml) activated outwardly rectifying Cl(-) currents with time-dependent inactivation in WT but not ClC-3 null cells. Inhibition by tamoxifen (10 microm) and by hypertonicity (340 mosm) identified them as ICl(swell). ICl(swell) was also activated by H(2)O(2) (500 microm), and the effect of TNF-alpha was completely inhibited by polyethylene glycol-catalase. ClC-3 expression induced ICl(swell) in ClC-3 null cells in the absence of swelling or TNF-alpha, and this effect was also blocked by catalase. ICl(swell) activation by hypotonicity (240 mosm) was only partially inhibited by catalase, and the size of these currents did not differ between WT and ClC-3 null cells. Disruption of endosome trafficking with either mutant Rab5 (S34N) or Rab11 (S25N) inhibited TNF-alpha-mediated activation of ICl(swell). Thrombin also activates ROS production by Nox1 but not in endosomes. Thrombin caused H(2)O(2)-dependent activation of ICl(swell), but this effect was not ClC-3- or Rab5-dependent. Thus, activation of ICl(swell) by TNF-alpha requires ClC-3-dependent endosomal H(2)O(2) production. This demonstrates a functional link between two distinct anion currents, ClC-3 and ICl(swell).
Highlights
22864 JOURNAL OF BIOLOGICAL CHEMISTRY mode of ClC-3 activity may account for the native acid-activated current in HEK293 cells [3]
A current similar to that induced by TNF-␣ was elicited by IL-1 (10 ng/ml, n ϭ 4; data not shown), which causes endosomal reactive oxygen species (ROS) production [21]
In vascular smooth muscle (VSM) cells, TNF-␣ activates ClϪ currents that are indistinguishable from those elicited by hypotonic conditions
Summary
Cell Culture and Modification of ClC-3 Expression—Murine aortic VSM cells were prepared from ClC-3 wild type and null mice using established methods [19, 21]. Adenoviruses were infected in serum-free Dulbecco’s modified Eagle’s medium for 16 h prior to being returned to their standard serum concentration They were allowed to express for 24 – 48 h prior to experimentation. Due to the relatively low efficiency of plasmid uptake by cultured VSM cells, plasmid expressing Myc-tagged dominant negative Rab11b (S25N Rab11-Myc) was co-transfected with an independent plasmid expressing enhanced GFP (1 g of each plasmid/well in 6-well plates containing ϳ106 cells/well) using Lipofectamine 2000 (5 l/ml) in 2% serum. Currents were sampled at 5 kHz and filtered at 1 kHz. Standard bath solution contained 120 mM NaCl, 2.5 mM MgCl2, 2.5 mM CaCl2, 10 mM HEPES, 5.5 mM glucose, pH 7.35, with NaOH. A p value of Ͻ0.05 was considered to be statistically significant
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