Viruses are strictly dependent on cells to propagate and many incorporate host proteins in their viral particles, but the significance of this incorporation is poorly understood. Recently, we performed the first comprehensive characterization of the mature herpes simplex virus type 1 (HSV-1) in which up to 49 distinct cellular proteins were identified by mass spectrometry. In the present study, we sought to identify if these cellular factors are relevant for the HSV-1 life cycle. To this end, we performed a small interfering RNA functional screen and found that 15 of these host proteins altered HSV-1 proliferation in cell culture, without any significant effect on cell viability. Moreover, the siRNA used had no negative consequences for Adenovirus type 5 propagation (with one exception) indicating that the modulation was specific for HSV-1 and not merely due to unhealthy cells. The positive host proteins include several Rab GTPases and other intracellular transport components as well as proteins involved in signal transduction, gene regulation and immunity. Remarkably, in most cases when virions were depleted for one of the above proteins, they replicated more poorly in subsequent infections in wild type cells. This highlights for the first time that both the cellular and virion-associated pools of many of these proteins actively contribute to viral propagation. Altogether, these findings underscore the power and biological relevance of combining proteomics and RNA interference to identify novel host-pathogen interactions.

Staphylococcus aureus is a Gram-positive bacterium that is carried by a quarter of the healthy human population and that can cause severe infections. This pathobiosis has been linked to a balance between Toll-like receptor 2 (TLR2)-dependent pro-and anti-inflammatory responses. The relationship between these two types of responses is unknown. Analysis of 16 nasal isolates of S. aureus showed heterogeneity in their capacity to induce pro-and anti-inflammatory responses, suggesting that these two responses are independent of each other. Uncoupling of these responses was corroborated by selective signaling through phosphoinositol 3-kinase (PI3K)-AktmTOR and extracellular signal-regulated kinase (ERK) for the anti-inflammatory response and through p38 for the proinflammatory response. Uncoupling was also observed at the level of phagocytosis and phagosomal processing of S. aureus, which were required solely for the proinflammatory response. Importantly, the anti-inflammatory properties of an S. aureus isolate correlated with its ability to modulate T cell immunity. Our results suggest the presence of anti-inflammatory TLR2 ligands in the staphylococcal cell wall, whose identification may provide templates for novel immunomodulatory drugs.

The human protein DDX3X is a DEAD box ATP-dependent RNA helicase that regulates transcription, mRNA maturation, and mRNA export and translation. DDX3X concomitantly modulates the replication of several RNA viruses and promotes innate immunity. We previously showed that herpes simplex virus 1 (HSV-1), a human DNA virus, incorporates DDX3X into its mature particles and that DDX3X is required for optimal HSV-1 infectivity. Here, we show that viral gene expression, replication, and propagation depend on optimal DDX3X protein levels. Surprisingly, DDX3X from incoming viral particles was not required for the early stages of the HSV-1 infection, but, rather, the protein controlled the assembly of new viral particles. This was independent of the previously reported ability of DDX3X to stimulate interferon type I production. Instead, both the lack and overexpression of DDX3X disturbed viral gene transcription and thus subsequent genome replication. This suggests that in addition to its effect on RNA viruses, DDX3X impacts DNA viruses such as HSV-1 by an interferon-independent pathway. IMPORTANCE Viruses interact with a variety of cellular proteins to complete their life cycle. Among them is DDX3X, an RNA helicase that participates in most aspects of RNA biology, including transcription, splicing, nuclear export, and translation. Several RNA viruses and a limited number of DNA viruses are known to manipulate DDX3X for their own benefit. In contrast, DDX3X is also known to promote interferon production to limit viral propagation. Here, we show that DDX3X, which we previously identified in mature HSV-1 virions, stimulates HSV-1 gene expression and, consequently, virion assembly by a process that is independent of its ability to promote the interferon pathway. KEYWORDS DDX3X, helicase, herpes, host-pathogen interaction, DNA virus, RNA virus, interferon, herpes simplex virus, host-pathogen interactions, transcriptional regulation, translational control T he human DDX3 protein is a member of a large family of DEAD box ATP-dependent RNA helicases. In humans, it is encoded by the X (DDX3X) and Y (DDX3Y) chromosomes, albeit the latter is restricted to testes (1). It participates in different stages of cellular gene expression, such as transcription, mRNA maturation, and mRNA export and translation (2). Given these crucial roles in RNA biology, several RNA viruses interact with DDX3X, often with important consequences for viral replication. This includes hepatitis C virus (HCV), norovirus, West Nile virus, and Japanese encephalitis virus (3-7). This is also the case for HIV and hepatitis B virus (HBV), a peculiar DNA virus that relies on an RNA template and reversed transcription to replicate its genome (8,9). Furthermore, DDX3X also contributes to innate immunity against these viruses. For instance, DDX3X stimulates interferon (IFN) type I production by binding IKK (IB kinase epsilon) and TBK1 (tank-binding kinase 1), leading to IRF3 phosphorylation and activation (10,

Activation of LCK is required for canonical TCR signaling leading to T cell responses. LCK activation also initiates a negative feedback loop mediated by the phosphatase SHP-1 that turns off TCR signaling. In this article, we report that the thousand-and-one amino acid kinase 3 (TAOK3) is a key regulator of this feedback. TAOK3 is a serine/threonine kinase expressed in many different cell types including T cells. TAOK3-deficient human T cells had impaired LCK-dependent TCR signaling resulting in a defect in IL-2 response to canonical TCR signaling but not to bacterial superantigens, which use an LCK-independent pathway. This impairment was associated with enhanced interaction of LCK with SHP-1 after TCR engagement and rapid termination of TCR signals, a defect corrected by TAOK3 reconstitution. Thus, TAOK3 is a positive regulator of TCR signaling by preventing premature SHP-1–mediated inactivation of LCK. This mechanism may also regulate signaling by other Src family kinase-dependent receptors.