Human DCTPP1 (
dCTP pyrophosphatase 1), also known as XTP3-transactivated
protein A, belongs to MazG-like
nucleoside triphosphate pyrophosphatase (NTP-PPase) superfamily. Being a newly identified
pyrophosphatase, its relevance to
tumorigenesis and the mechanisms are not well investigated. In the present study, we have confirmed our previous study that DCTPP1 was significantly hyperexpressed in
breast cancer and further demonstrated its strong association with
tumor progression and poor prognosis in
breast cancer. Knockdown of DCTPP1 in
breast cancer cell line MCF-7 cells remarkably retarded proliferation and colony formation in vitro. The capacity of mammosphere formation of MCF-7 was suppressed with the silence of DCTPP1, which was consistent with the enhanced mammosphere-forming ability in DCTPP1-overexpressed MDA-MB-231 cells. To further dissect the mechanisms of DCTPP1 in promoting
tumor cell growth and stemness maintenance, its biochemical properties and
biological functions were investigated. DCTPP1 displayed bioactive form with tetrameric structure similar to other MazG domain-containing
pyrophosphatases based on structure simulation. A substrate preference for
dCTP and its methylated or
halogen-modified derivatives over the other canonical (deoxy-) NTPs was demonstrated from enzymatic assay. This substrate preference was also proved in
breast cancer cells that the intracellular
5-methyl-dCTP level increased in DCTPP1-deficient MCF-7 cells but decreased in DCTPP1-overexpressed MDA-MB-231 cells. Moreover, global methylation level was elevated in DCTPP1-knockdown MCF-7 cells or mammosphere-forming MCF-7 cells but decreased significantly in DCTPP1-overexpressed MDA-MB-231 cells and its mammospheres. Our results thus indicated that human DCTPP1 was capable of modulating the concentration of intracellular
5-methyl-dCTP. This in turn affected global methylation, contributing to a known phenomenon of hypomethylation related to the
cancer cell growth and stemness maintenance. Our current investigations point to the pathological functions of DCTPP1 overexpression in
breast cancer cells with aberrant
dCTP metabolism and epigenetic modification.