J Biol Chem, Vol. 274, Issue 40, 28405-28412, October 1, 1999
Intracellular Localization of Human Cytidine Deaminase
IDENTIFICATION OF A FUNCTIONAL NUCLEAR LOCALIZATION SIGNAL
Angelika
Somasekaram
,
Adam
Jarmuz
,
Alan
How
,
James
Scott¶, and
Naveenan
Navaratnam
From the
MRC Molecular Medicine Group, Clinical
Science Centre and ¶ Division of National Heart and Lung
Institute, Imperial College School of Medicine, Hammersmith Hospital,
Du Cane Road, London W12 ONN, United Kingdom
The cytidine deaminases belong to the family of
multisubunit enzymes that catalyze the hydrolytic deamination of their
substrate to a corresponding uracil product. They play a major role in
pyrimidine nucleoside and nucleotide salvage. The intracellular
distribution of cytidine deaminase and related enzymes has previously
been considered to be cytosolic. Here we show that human cytidine
deaminase (HCDA) is present in the nucleus. A highly specific, affinity purified polyclonal antibody against HCDA was used to analyze the
intracellular localization of native HCDA in a variety of mammalian
cells by in situ immunochemistry. Native HCDA was found to
be present in the nucleus as well as the cytoplasm in several cell
types. Indirect immunofluorescence microscopy indicated a predominantly
nuclear localization of FLAG-tagged HCDA overexpressed in these cells.
We have identified an amino-terminal bipartite nuclear localization
signal that is both necessary and sufficient to direct HCDA and a
non-nuclear reporter protein to the nucleus. We also show HCDA binding
to the nuclear import receptor, importin
. Similar putative
bipartite nuclear localization sequences are found in other
cytidine/deoxycytidylate deaminases. The results presented here suggest
that the pyrimidine nucleotide salvage pathway may operate in the
nucleus. This localization may have implications in the regulation of
nucleoside and nucleotide metabolism and nucleic acid biosynthesis.
Copyright © 1999 by The American Society for Biochemistry and Molecular Biology, Inc.