SAMHD1 Phosphorylation Coordinates the Anti-HIV-1 Response by Diverse Interferons and Tyrosine Kinase Inhibition

Abstract

Macrophages are susceptible to human immunodeficiency virus type 1 (HIV-1) infection despite abundant expression of antiviral proteins. Perhaps the most important antiviral protein is the restriction factor sterile alpha motif domain and histidine/aspartic acid domain-containing protein 1 (SAMHD1). We investigated the role of SAMHD1 and its phospho-dependent regulation in the context of HIV-1 infection in primary human monocyte-derived macrophages and the ability of various interferons (IFNs) and pharmacologic agents to modulate SAMHD1. Here we show that stimulation by type I, type II, and to a lesser degree, type III interferons share activation of SAMHD1 via dephosphorylation at threonine-592 as a consequence of signaling. Cyclin-dependent kinase 1 (CDK1), a known effector kinase for SAMHD1, was downregulated at the protein level by all IFN types tested. Pharmacologic inhibition or small interfering RNA (siRNA)-mediated knockdown of CDK1 phenocopied the effects of IFN on SAMHD1. A panel of FDA-approved tyrosine kinase inhibitors potently induced activation of SAMHD1 and subsequent HIV-1 inhibition. The viral restriction imposed via IFNs or dasatinib could be overcome through depletion of SAMHD1, indicating that their effects are exerted primarily through this pathway. Our results demonstrate that SAMHD1 activation, but not transcriptional upregulation or protein induction, is the predominant mechanism of HIV-1 restriction induced by type I, type II, and type III IFN signaling in macrophages. Furthermore, SAMHD1 activation presents a pharmacologically actionable target through which HIV-1 infection can be subverted.

Pharmacological Modulation of SAMHD1 Activity by CDK4/6 Inhibitors Improves Anticancer Therapy

“…In addition, SAMHD1 function is inhibited by phosphorylation, a process controlled by cyclin-dependent kinases (CDK) and therefore tightly regulated during cell cycle progression [13][14][15]. Different pharmacological agents have been shown to block SAMHD1 phosphorylation, inducing SAMHD1 function and viral restriction [16][17][18][19][20].…”

The aryl hydrocarbon receptor and interferon gamma generate antiviral states via transcriptional repression

“…Indeed, immediately before submission of this manuscript another group reported that Type-I, II and III interferon can induce SAMHD1 dephosphorylation (Szaniawski et al, 2018). In principle, each of these signaling pathways could be activated as a consequence of infection by retroviruses or DNA viruses.…”

IFN-independent G0 arrest and SAMHD1 activation following TLR4 activation in macrophages

“…TLR4 activation stimulates production of interferons (IFN). In order to understand if IFN plays role in SAMHD1 activation/dephosphorylation after TLR4 activation as recently published 16, 22 , we used the JAK1/2 inhibitor Ruxolitinib (RUXO) that inhibits IFN signalling (Fig.1C) 23 . The inhibitor of IFN signalling could not restore infection and failed to reverse SAMHD1 phosphorylation at T592, suggesting that regulation of SAMHD1 phosphorylation is largely independent of IFN (Fig.1F).…”

“…We show here that human primary macrophages exit the cell cycle after exposure to exogenous IFNβ) and that this effect is dependent on JAK/STAT signalling. It has been shown that SAMHD1 can be activated/dephosphorylated by type I,II and III IFN 16, 22 in macrophages. We confirmed this observation and showed that SAMHD1 phosphorylation and HIV-1 infection can be rescued when JAK/STAT signalling is blocked after addition of exogenous IFNβ).…”

“…Type-I interferons are known to lead to dephosphorylation/activation of SAMHD1 in MDM 16, 22 . Whilst it has been proposed that LPS-stimulated macrophages can mediate HIV-1 restriction through IFN secretion, the role of SAMHD1 has not been established.…”