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Expression profile and role of sterile alpha motif domain-and histidine domain-containing protein 1 (SAMHD1) in restriction of feline immunodeficiency virus (FIV)

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Title: Expression profile and role of sterile alpha motif domain-and histidine domain-containing protein 1 (SAMHD1) in restriction of feline immunodeficiency virus (FIV)
Author: Asadian, Peyman
Department: Department of Pathobiology
Program: Pathobiology
Advisor: Bienzle, Dorothee
Abstract: SAMHD1 is one of the type-I interferon-induced proteins known collectively as “restriction factors”. The triphosphohydrolase activity of SAMHD1 reduces the cellular dNTP pool in non-dividing myeloid cells and resting CD4+ T cells to levels below that required for efficient HIV-1 cDNA synthesis. SAMHD1 also has putative exonuclease activity that degrades ssRNA and ssDNA. The feline genome encodes a SAMHD1 orthologue, but neither expression nor physiologic or antiviral functions are known. Using a feline whole-body tissue microarray with 24 tissues for comprehensive immunohistochemical analysis, SAMHD1 protein was identified in a wide range of tissues with most concentrated detection at sites of viral entry and replication. Nuclear and cytoplasmic immunoreactivity were variable among tissues. Among six commonly used feline cell lines, SAMHD1 protein and mRNA were most abundant in the lymphocyte cell line (FeTJ) with the highest rate of replication. Subsequently, the response of SAMHD1 to different types of interferon was examined through several experimental approaches. SAMHD1 mRNA in FeTJ cells increased in a dose-related manner in response to IFNγ treatment concurrent with increased nuclear localization and phosphorylation. In contrast, IFNα treatment induced SAMHD1 mRNA but did not significantly alter SAMHD1 protein detection, phosphorylation or nuclear translocation. In purified primary feline CD4+ lymphocytes, interleukin-2 supplementation increased SAMHD1 expression, but addition of IFNγ did not further alter SAMHD1 protein expression or nuclear localization. These findings imply that while SAMH1 was inducible by IFNγ, overall activity was cell type- and compartment-specific. Promoter methylation regulates SAMHD1 transcription. When the promoter is non-methylated and accessible to transcription factor binding and recruitment of RNA polymerases, gene transcription is enabled. However, the methylated promoter is inaccessible to transcription factors. Azacytidine reduced DNA methylation in feline lymphocytes, resulting in increased cellular and nuclear SAMHD1 protein without an increase in phosphorylated SAMHD1. These findings suggest that the antiviral activity of SAMHD1 may be augmented by promoter demethylation with compounds such as Azacytidine. In summary, tissue-, cell- and subcellular compartment-specific expression of SAMHD1, responsiveness to IFNγ stimulation, and transcriptional regulation by demethylation, suggest that SAMHD1 has unique functions in viral restriction and regulation of nucleotide availability.
URI: https://hdl.handle.net/10214/24733
Date: 2021-04
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Related Publications: Asadian, P., Bienzle, D., & Finnie, G. (2018). The expression profile of sterile alpha motif and histidine-aspartate domain-containing protein 1 (SAMHD1) in feline tissues. Veterinary Immunology and Immunopathology, 195, 7-18. doi:http://dx.doi.org.subzero.lib.uoguelph.ca/10.1016


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