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A more recent version of this article appeared on July 1, 2004
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Submitted on March 16, 2004
Accepted on April 27, 2004
1-subunit increases the translation efficiency of the
1-subunit in MSV-MDCK cells
1 Department of Pathology and Laboratory Medicine, David Geffen School of Medicine at UCLA, Los Angeles, California, CA 90095
2 Nemours Biomedical Research, Alfred I duPont Hospital for Children, Wilmington, DE 19803
* Corresponding author. E-mail address: arajasekaran{at}mednet.ucla.edu.
The Na,K-ATPase consists of an
- and
-subunit. Moloney sarcoma virus-transformed MDCK cells (MSV-MDCK) express low levels of Na,K-ATPase
1-subunit. Ectopic expression of Na,K-ATPase
1-subunit in these cells increased the protein levels of the
1-subunit of Na,K-ATPase. This increase was not due to altered transcription of the
1-subunit gene or half-life of the
1-subunit protein since both
1-subunit mRNA levels and half-life of the
1-subunit protein were comparable in MSV-MDCK and
1-subunit expressing MSV-MDCK cells. However, short pulse labeling revealed that the initial translation rate of the
1-subunit in
1-subunit expressing MSV-MDCK cells was six- to sevenfold higher compared with MSV-MDCK cells. The increased translation was specific to
1-subunit since translation rates of occludin and
-catenin, membrane and cytosolic proteins, respectively, were not altered. In vitro cotranslation/translocation experiments using rabbit reticulocyte lysate and rough microsomes revealed that the
1-subunit mRNA is more efficiently translated in the presence of
1-subunit. Furthermore, sucrose density gradient analysis revealed significantly more
1-subunit transcript associated with the polysomal fraction in
1-subunit expressing MSV-MDCK cells compared with MSV-MDCK cells indicating that in mammalian cells the Na,K-ATPase
1-subunit is involved in facilitating the translation of the
1-subunit mRNA in the endoplasmic reticulum.
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