IFITM1 enhances nonenveloped viral RNA replication by facilitating cholesterol transport to the Golgi

IFITM1 as a modulator of surfaceome dynamics and aggressive phenotype in cervical cancer cells

Interferon‑induced transmembrane proteins (IFITMs) are frequently overexpressed in cancer cells, including cervical carcinoma cells, and play a role in the progression of various cancer types. However, their mechanisms of action remain incompletely understood. In the present study, by employing a combination of surface membrane protein isolation and quantitative mass spectrometry, it was comprehensively described how the IFITM1 protein influences the composition of the cervical cancer cell surfaceome. Additionally, the effects of interferon‑γ on protein expression and cell surface exposure were evaluated in the presence and absence of IFITM1. The IFITM1‑regulated membrane and membrane‑associated proteins identified are involved mainly in processes such as endocytosis and lysosomal transport, cell‑cell and cell‑extracellular matrix adhesion, antigen presentation and the immune response. To complement the proteomic data, gene expression was analyzed using reverse transcription‑quantitative PCR to distinguish whether the observed changes in protein levels were attributable to transcriptional regulation or differential protein dynamics. Furthermore, the proteomic and gene expression data are supported by functional studies demonstrating the impact of the IFITM1 and IFITM3 proteins on the adhesive, migratory and invasive capabilities of cervical cancer cells, as well as their interactions with immune cells.

Aichivirus A1 replicates in human intestinal epithelium and bronchial tissue: Lung-gut axis?

The role of aichivirus A1 (AiV-A1) in acute gastroenteritis remains controversial and in vitro data illustrating its pathogenesis in suitable human models are scarce. Here, we demonstrate that AiV-A1 isolate A846/88 replicates in ApoA1- (absorptive) and Ki-67-positive (proliferative) enterocytes in stem cell-derived human small intestinal epithelium (HIE) as well as in patient biopsy samples, but not in any of the tested human cell lines. The infection did not result in tissue damage and did not trigger type I and type III interferon (IFN) signalling, whereas the control, human coxsackievirus B3 (strain Nancy), triggered both IFNs. To investigate the tissue tropism, we infected a human tracheal/bronchial epithelium model (HTBE) with AiV-A1 isolates A846/88 and kvgh99012632/2010 and, as a control, with rhinovirus A2 (RV-A2). AiV-A1 isolate kvgh99012632/2010, but not isolate A846/88, replicated in HTBE and induced type III IFN and ISGs signalling. By using various pharmacological inhibitors, we elaborated that cellular entry of AiV-A1 depends on clathrin, dynamin, and lipid rafts and is strongly reliant on endosome acidification. Viral particles co-localised with Rab5a-positive endosomes and promoted leakage of endosomal content. Our data shed light on the early events of AiV-A1 infection and reveal that different isolates exhibit distinct tissue tropism. This supports its clinical importance as a human pathogen with the potential to evolve toward broader tissue specificity.

IFITM1 and IFITM3 Proteins Inhibit the Infectivity of Progeny HIV-1 without Disrupting Envelope Glycoprotein Clusters

Human interferon-induced transmembrane (IFITM) proteins inhibit the fusion of a broad spectrum of enveloped viruses, both when expressed in target cells and when present in infected cells. Upon expression in infected cells, IFITMs incorporate into progeny virions and reduce their infectivity by a poorly understood mechanism. Since only a few envelope glycoproteins (Envs) are present on HIV-1 particles, and Env clustering has been proposed to be essential for optimal infectivity, we asked if IFITM protein incorporation modulates HIV-1 Env clustering. The incorporation of two members of the IFITM family, IFITM1 and IFITM3, into HIV-1 pseudoviruses correlated with a marked reduction of infectivity. Super-resolution imaging of Env distribution on single HIV-1 pseudoviruses did not reveal significant effects of IFITMs on Env clustering. However, IFITM3 reduced the Env processing and incorporation into virions relative to the control and IFITM1-containing viruses. These results show that, in addition to interfering with the Env function, IFITM3 restricts HIV-1 Env cleavage and incorporation into virions. The lack of notable effect of IFITMs on Env clustering supports alternative restriction mechanisms, such as modification of the properties of the viral membrane.

A Proteomics-Based Approach Identifies the NEDD4 Adaptor NDFIP2 as an Important Regulator of Ifitm3 Levels

IFITMs are a family of highly related interferon-induced transmembrane proteins that interfere with the processes of fusion between viral and cellular membranes and are thus endowed with broad antiviral properties. A number of studies have shown how the antiviral potency of IFITMs is highly dependent on their steady-state levels, their intracellular distribution and a complex pattern of post-translational modifications, parameters that are overall tributary of a number of cellular partners. In an effort to identify additional protein partners involved in the biology of IFITMs, we devised a proteomics-based approach based on the piggyback incorporation of IFITM3 partners into extracellular vesicles. MS analysis of the proteome of vesicles bearing or not bearing IFITM3 identified the NDFIP2 protein adaptor protein as an important regulator of IFITM3 levels. NDFIP2 is a membrane-anchored adaptor protein of the E3 ubiquitin ligases of the NEDD4 family that have already been found to be involved in IFITM3 regulation. We show here that NDFIP2 acts as a recruitment factor for both IFITM3 and NEDD4 and mediates their distribution in lysosomal vesicles. The genetic inactivation and overexpression of NDFIP2 drive, respectively, lower and higher levels of IFITM3 accumulation in the cell, overall suggesting that NDFIP2 locally competes with IFITM3 for NEDD4 binding. Given that NDFIP2 is itself tightly regulated and highly responsive to external cues, our study sheds light on a novel and likely dynamic layer of regulation of IFITM3.