Abstract
Deoxynucleotide triphosphates (dNTPs) are essential for efficient hepatitis B virus (HBV) replication. Here, we investigated the influence of the restriction factor SAMHD1, a dNTP hydrolase (dNTPase) and RNase, on HBV replication. We demonstrated that silencing of SAMHD1 in hepatic cells increased HBV replication, while overexpression had the opposite effect. SAMHD1 significantly affected the levels of extracellular viral DNA as well as intracellular reverse transcription products, without affecting HBV RNAs or cccDNA. SAMHD1 mutations that interfere with the dNTPase activity (D137N) or in the catalytic center of the histidine-aspartate (HD) domain (D311A), and a phospho-mimetic mutation (T592E), abrogated the inhibitory activity. In contrast, a mutation diminishing the potential RNase but not dNTPase activity (Q548A) and a mutation disabling phosphorylation (T592A) did not affect antiviral activity. Moreover, HBV restriction by SAMHD1 was rescued by addition of deoxynucleosides. Although HBV infection did not directly affect protein level or phosphorylation of SAMHD1, the virus upregulated intracellular dATPs. Interestingly, SAMHD1 was dephosphorylated, thus in a potentially antiviral-active state, in primary human hepatocytes. Furthermore, SAMHD1 was upregulated by type I and II interferons in hepatic cells. These results suggest that SAMHD1 is a relevant restriction factor for HBV and restricts reverse transcription through its dNTPase activity.
Highlights
Deoxynucleotide triphosphates are essential for efficient hepatitis B virus (HBV) replication
The inhibitory mechanism against human immunodeficiency virus type-1 (HIV-1) was first linked to the dNTP hydrolase (dNTPase) activity of the protein, which lowers the intracellular Deoxynucleotide triphosphates (dNTPs) concentration to below the level needed for viral reverse transcription[20]
As a DNA virus, HBV depends on the availability of dNTPs in certain stages of its replication: in the early phase for completion of the incoming rc-DNA into closed circular DNA (cccDNA) and in the late phase for the maturation of newly infectious particles during reverse transcription
Summary
Deoxynucleotide triphosphates (dNTPs) are essential for efficient hepatitis B virus (HBV) replication. Its upregulation by interferon α(IFNα)was first shown in primary human monocytes[13] and in various cell lines[32,33,34], suggesting that its antiviral activity might not be limited to HIV-1 and could be involved in a broader antiviral defense In support of this idea, in addition to HIV-1, SAMHD1 has been shown to restrict other types of retroviruses, such as SIV, feline immunodeficiency virus and equine infectious anemia virus[18,35,36], and DNA viruses, such as vaccinia virus and herpes simplex virus[37,38], as well as LINE-1 and Alu/SVA retrotransposons[39]
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