Authors

P AntequeraVM Castillo-Acosta¹; M Yague-Capilla¹; C Bosch-Navarrete¹; LM Ruiz-Perez¹; D gonzalez-pacanowska¹;  ¹ Instituto de Parasitologia y Biomedicina 'Lopez-Neyra', CSIC. Granada, Spain;  ² Instituto de Parasitología y Biomedicina , Spain

Discussion

DNA integrity, replication and repair depend on an appropriate homeostasis of dNTPs pool. Degradation of dNTPs takes place through catabolic pathways, where enzymes such as 5’-nucleotidases, nucleoside phosphorylases, and deaminases mediate the break-down of dNTPs to deoxynucleosides or nucleobases. dNTP break-down products can be reutilized in the salvage pathway or are transported to other organelles in order to maintain intracellular homeostasis. In humans, one of the most relevant proteins in the control of dNTP levels is sterile alpha motif and histidine-aspartic acid domain-containing protein 1 (SAMHD1), a triphosphohydrolase that catalyzes the degradation of the four canonical dNTPs to their corresponding nucleosides. SAM domains are known to function as protein interaction or RNA-binding modules, whereas several characterized HD domain proteins have been shown to possess phosphodiesterase, phosphatase, dGTP triphosphatase, or nuclease activities.  The purified HD of human SAMHD1 has been shown to possess dGTP-stimulated dNTP triphosphohydrolase activity. Two unique SAMHD1 putative orthologs have been identified in Trypanosoma brucei: TbHD82 and TbHD52, according to their molecular mass. While TbHD52 is mitochondrial, TbHD82 is a nuclear protein and both lack a canonical SAM domain. The quantification of dNTPs levels in bloodstream TbHD82-knockout cells revealed a significant accumulation of dATP and dCTP, which is reverted with the expression of an ectopic copy of the gene. Additionally, TbHD82-knockout cells present increased phosphorylation of trypanosomal histone H2A indicating the occurrence of DNA damage as a consequence of dNTP imbalance. Finally, in vivo analysis in mice evidenced that TbHD82 deficient cells are less infective that parental cells, which could be linked to a need for adequate dNTP levels during the early stages of infection. In conclusion, we suggest that TbHD82 plays a central role in dNTP homeostasis in Trypanosoma brucei and that while not essential for in vitro growth, its function is important for the progression of infection in animal models of the disease.