Human deoxycytidine kinase is located in the cell nucleus

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Human deoxyribonucleoside kinases (dNKs) are crucial for activating anticancer and antiviral nucleoside analogs.
• Previous literature localized deoxycytidine kinase (dCK) and thymidine kinase 1 (TK1) to the cytosol, and deoxyguanosine kinase (DGK) and thymidine kinase 2 (TK2) to mitochondria.

Purpose of the Study:

• To determine the precise intracellular localization of the four human deoxyribonucleoside kinases in vivo.
• To investigate the functional implications of deoxycytidine kinase's nuclear localization for nucleoside analog activity.

Main Methods:

• Expression of human deoxyribonucleoside kinases as green fluorescent protein (GFP) fusion proteins.
• Intracellular localization studies using live-cell imaging.
• Site-directed mutagenesis of a putative nuclear targeting signal in deoxycytidine kinase.
• Functional assays using a deoxycytidine kinase-deficient cell line.

Main Results:

• Human deoxycytidine kinase (dCK) was localized to the cell nucleus, contrary to previous assumptions.
• Human deoxyguanosine kinase (DGK) was confirmed in the mitochondria.
• Thymidine kinases 1 (TK1) and 2 (TK2) were predominantly found in the cytosol.
• Mutation of the identified nuclear targeting signal in dCK abolished nuclear import.
• Restoration of dCK-deficient cells with nuclear dCK or mutant cytosolic dCK restored sensitivity to anticancer nucleoside analogs.

Conclusions:

• This study identifies the cell nucleus as a key localization for deoxycytidine kinase.
• The nuclear localization of dCK has significant implications for deoxyribonucleotide synthesis and the mechanism of action of nucleoside analog drugs.
• Revises the understanding of deoxyribonucleoside kinase distribution and its role in drug metabolism.