Alternative RNA Splicing Generates a Glycosylphosphatidylinositol-anchored Form of Ceruloplasmin in Mammalian Brain*
- From the Center for Research in Neuroscience, The Montreal General Hospital Research Institute and McGill University, Montreal, Quebec H3G 1A4, Canada
Abstract
Ceruloplasmin is a copper-containing ferroxidase that is essential for normal iron homeostasis. Whereas ceruloplasmin in plasma is produced and secreted by hepatocytes, in the brain a glycosylphosphatidylinositol (GPI)-anchored form of ceruloplasmin is expressed on the surface of astrocytes. By using a cDNA cloning approach, we have now determined that the GPI-anchored form of ceruloplasmin is generated by alternative RNA splicing. The splicing occurs downstream of exon 18 and replaces the C-terminal 5 amino acids of the secreted form with an alternative 30 amino acids that signal GPI anchor addition. RNase protection analysis demonstrates that the GPI-anchored form is the major form in the brain, whereas the secreted form predominates in the liver. Individuals with aceruloplasminemia, a hereditary deficiency of ceruloplasmin, have severe iron deposition in a number of organs, including the brain where it results in neurodegeneration. Therefore, this novel GPI-anchored form of ceruloplasmin is likely to play an important role in iron metabolism in the central nervous system.
Footnotes
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↵* This work was supported by a grant from the Canadian Medical Research Council (to S. D.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) (ra+ GPI-anchored ceruloplasmin).
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↵‡ Recipient of studentships from the National Centers of Excellence NeuroScience Network and the David and Dorothy Lam Award from the NeuroScience Canada Foundation.
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↵§ To whom correspondence should be addressed: Center for Research in Neuroscience, Montreal General Hospital Research Institute, 1650 Cedar Ave., Montreal, Quebec H3G 1A4, Canada. Tel.: 514-937-6011 (ext. 4240); Fax: 514-934-8265; E-mail: mcsl@musica.mcgill.ca.
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↵2 B. N. Patel and S. David, unpublished observations.
- Abbreviations:
- CNS
-
central nervous system
- GPI
-
glycosylphosphatidylinositol
- ORF
-
open reading frame
- HEK 293T
-
human embryonic kidney 293T
- mAb
-
monoclonal antibody
- PI-PLC
-
phosphatidylinositol-specific phospholipase C
- RT-PCR
-
reverse transcriptase-polymerase chain reaction
- nt
-
nucleotide
- kb
-
kilobase pair
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- Received July 9, 1999.
- Revision received November 8, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
