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Published ahead of print on October 6, 2005, doi:10.1165/rcmb.2005-0273OC

Am. J. Respir. Cell Mol. Biol., Volume 34, Number 2, February 2006, 204-212

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Submitted on July 19, 2005
Revised on October 3, 2005

Oxygen and Glucocorticoids Modulate {alpha}ENaC mRNA Translation in Fetal Distal Lung Epithelium

Gail Otulakowski1*, Bijan Rafii2, Michael Harris2, and Hugh O'Brodovich3

1 CIHR Group in Lung Development, Programme in Lung Biology Research, Hospital for Sick Children Research Institute, Toronto, Ontario, Canada; Department of Paediatrics, University of Toronto, Toronto, Ontario, Canada, 2 CIHR Group in Lung Development, Programme in Lung Biology Research, Hospital for Sick Children Research Institute, Toronto, Ontario, Canada, 3 CIHR Group in Lung Development, Programme in Lung Biology Research, Hospital for Sick Children Research Institute, Toronto, Ontario, Canada; Department of Paediatrics, University of Toronto, Toronto, Ontario, Canada; Department of Physiology, University of Toronto, Toronto, Ontario, Canada

* To whom correspondence should be addressed. E-mail: gail.otulakowski{at}sickkids.ca.

It is known that glucocorticoid hormones play an important role in fetal lung maturation; however, it is unknown how they interact with changes in oxygen tension which play an important role in converting the lung from a fluid-secreting to a fluid-absorbing organ at birth. Airspace fluid absorption arises from active transepithelial Na+ transport with the amiloride-sensitive epithelial Na channel (ENaC), consisting of {alpha}, {beta} and {gamma} subunits, representing the rate-limiting step under non-pathological conditions. We investigated the individual and combined effects of dexamethasone and pO2 on {alpha}ENaC mRNA levels, rate of {alpha}ENaC protein synthesis, and amiloride-sensitive short-circuit current in primary cultures of rat fetal distal lung epithelial cells. Dexamethasone significantly induced {alpha}ENaC mRNA in both fetal (3%) and postnatal (21%) O2, but increases in {alpha}ENaC protein synthesis and function only occurred when epithelia were grown under a postnatal pO2. Sucrose density gradient analyses showed that dexamethasone treatment of cells cultured at 3% O2 decreased association of {alpha}ENaC mRNA with large polysomes and enhanced association with small polysomes. Conversely, incubation of dexamethasone-treated cells in 21% O2 restored {alpha}ENaC mRNA association with large polysomes. No significant changes were seen in the overall polyribosome profiles, or in the distribution of mRNAs encoding {beta} and {gamma} subunits of ENaC or cytokeratin 18, indicating specific modulation of {alpha}ENaC mRNA translation. These data suggest that postnatal O2 exposure may be important for efficient translation of the {alpha}ENaC mRNA.




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