Subcellular localization of adenosine kinase in mammalian cells: The long isoform of AdK is localized in the nucleus.
Two isoforms of adenosine kinase (AdK) have been identified in mammalian organisms with the long isoform (AdK-long) containing extra 20-21 amino acids at the N-terminus (NTS). The subcellular localizations of these isoforms are not known and they contain no identifiable targeting sequence. Immunofluorescence labeling of mammalian cells expressing either only AdK-long or both isoforms with AdK-specific antibody showed only nuclear labeling or both nucleus and cytoplasmic labeling, respectively. The AdK-long and -short isoforms fused at the C-terminus with c-myc epitope also localized in the nucleus and cytoplasm, respectively. Fusion of the AdK-long NTS to green fluorescent protein also resulted in its nuclear localization. AdK-long NTS contains a cluster of conserved amino acids (PKPKKLKVE). Replacement of KK in this sequence with either AA or AD abolished its nuclear localization capability, indicating that this cluster likely serves as a nuclear localization signal. AdK in nucleus is likely required for sustaining methylation reactions.
Cui
Xianying Amy
XA
Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ont., Canada.
Singh
Bhag
B
Park
Jae
J
Gupta
Radhey S
RS
D021581:Active Transport, Cell Nucleus; D000248:Adenosine Kinase / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000201:enzymology*; D006801:Humans; D007527:Isoenzymes / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals / Q000235:genetics / Q000378:metabolism
D007527:Isoenzymes; D019913:Nuclear Localization Signals; D000248:Adenosine Kinase