Hypercapnia Induces Cleavage and Nuclear Localization of RelB Protein, Giving Insight into CO2 Sensing and Signaling

Kathryn M Oliver,Colin R Lenihan,Ulrike Bruning,Alex Cheong,John G Laffey,Paul Mcloughlin,Cormac T Taylor,Eoin P Cummins

doi:10.1074/jbc.m112.347971

Kathryn M Oliver, Colin R Lenihan + Show 6 more

Open Access

https://doi.org/10.1074/jbc.m112.347971

Copy DOI

Abstract

Carbon dioxide (CO(2)) is increasingly being appreciated as an intracellular signaling molecule that affects inflammatory and immune responses. Elevated arterial CO(2) (hypercapnia) is encountered in a range of clinical conditions, including chronic obstructive pulmonary disease, and as a consequence of therapeutic ventilation in acute respiratory distress syndrome. In patients suffering from this syndrome, therapeutic hypoventilation strategy designed to reduce mechanical damage to the lungs is accompanied by systemic hypercapnia and associated acidosis, which are associated with improved patient outcome. However, the molecular mechanisms underlying the beneficial effects of hypercapnia and the relative contribution of elevated CO(2) or associated acidosis to this response remain poorly understood. Recently, a role for the non-canonical NF-κB pathway has been postulated to be important in signaling the cellular transcriptional response to CO(2). In this study, we demonstrate that in cells exposed to elevated CO(2), the NF-κB family member RelB was cleaved to a lower molecular weight form and translocated to the nucleus in both mouse embryonic fibroblasts and human pulmonary epithelial cells (A549). Furthermore, elevated nuclear RelB was observed in vivo and correlated with hypercapnia-induced protection against LPS-induced lung injury. Hypercapnia-induced RelB processing was sensitive to proteasomal inhibition by MG-132 but was independent of the activity of glycogen synthase kinase 3β or MALT-1, both of which have been previously shown to mediate RelB processing. Taken together, these data demonstrate that RelB is a CO(2)-sensitive NF-κB family member that may contribute to the beneficial effects of hypercapnia in inflammatory diseases of the lung.

Highlights

The molecular mechanisms underpinning how CO2 affects cell signaling and gene transcription are not well understood
We demonstrate that in cells exposed to elevated CO2, the NF-␬B family member RelB was cleaved to a lower molecular weight form and translocated to the nucleus in both mouse embryonic fibroblasts and human pulmonary epithelial cells (A549)
Elevated CO2 Induces Cleavage and Nuclear Localization of RelB—We have previously demonstrated that the key NF-␬B signaling protein IKK␣ translocates to the nucleus in response to elevated CO2 in mammalian cells, leading to suppression of inflammatory gene expression through inhibition of canonical NF-␬B signaling [15]

Summary

Background

The molecular mechanisms underpinning how CO2 affects cell signaling and gene transcription are not well understood. The molecular mechanisms underlying the beneficial effects of hypercapnia and the relative contribution of elevated CO2 or associated acidosis to this response remain poorly understood. Hypercapnia-induced RelB processing was sensitive to proteasomal inhibition by MG-132 but was independent of the activity of glycogen synthase kinase 3␤ or MALT-1, both of which have been previously shown to mediate RelB processing Taken together, these data demonstrate that RelB is a CO2-sensitive NF-␬B family member that may contribute to the beneficial effects of hypercapnia in inflammatory diseases of the lung. We demonstrate that under conditions of elevated CO2, RelB is cleaved to a low molecular weight form that translocates to the nucleus, where it impacts upon the expression of proinflammatory genes. We provide mechanistic insight into RelB processing in response to CO2

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION