Structural and functional characterization explains loss of dNTPase activity of the cancer-specific R366C/H mutant SAMHD1 proteins.

Abstract

Elevated intracellular levels of dNTPs have been shown to be a biochemical marker of cancer cells. Recently, a series of mutations in the multifunctional dNTP triphosphohydrolase (dNTPase), sterile alpha motif and histidine-aspartate domain-containing protein 1 (SAMHD1), have been reported in various cancers. Here, we investigated the structure and functions of SAMHD1 R366C/H mutants, found in colon cancer and leukemia. Unlike many other cancer-specific mutations, the SAMHD1 R366 mutations do not alter cellular protein levels of the enzyme. However, R366C/H mutant proteins exhibit a loss of dNTPase activity, and their X-ray structures demonstrate the absence of dGTP substrate in their active site, likely because of a loss of interaction with the γ-phosphate of the substrate. The R366C/H mutants failed to reduce intracellular dNTP levels and restrict HIV-1 replication, functions of SAMHD1 that are dependent on the ability of the enzyme to hydrolyze dNTPs. However, these mutants retain dNTPase-independent functions, including mediating dsDNA break repair, interacting with CtIP and cyclin A2, and suppressing innate immune responses. Finally, SAMHD1 degradation in human primary-activated/dividing CD4+ T cells further elevates cellular dNTP levels. This study suggests that the loss of SAMHD1 dNTPase activity induced by R366 mutations can mechanistically contribute to the elevated dNTP levels commonly found in cancer cells.

• Authors: Nicole E Bowen, Joshua Temple, Caitlin Shepard, Adrian Oo, Fidel Arizaga, Priya Kapoor-Vazirani, Mirjana Persaud, Corey H Yu, Dong-Hyun Kim, Raymond F Schinazi, Dmitri N Ivanov, Felipe Diaz-Griffero, David S Yu, Yong Xiong, Baek Kim
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 297 Issue 4 Pg. 101170 (10 2021) ISSN: 1083-351X [Electronic] United States
• PMID: 34492268 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, U.S. Gov't, Non-P.H.S.)
• Copyright: Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.

Chemical References

• Cyclin A2
• Neoplasm Proteins
• Endodeoxyribonucleases
• RBBP8 protein, human
• SAM Domain and HD Domain-Containing Protein 1
• SAMHD1 protein, human

Topics

• Amino Acid Substitution
• Cell Line
• Colonic Neoplasms (enzymology, genetics)
• Cyclin A2 (chemistry, genetics, metabolism)
• DNA Breaks, Double-Stranded
• DNA Repair
• Endodeoxyribonucleases (chemistry, genetics, metabolism)
• Humans
• Leukemia (enzymology, genetics)
• Mutation, Missense
• Neoplasm Proteins (chemistry, genetics, metabolism)
• SAM Domain and HD Domain-Containing Protein 1 (chemistry, genetics, metabolism)
• Structure-Activity Relationship