Interferon-inducible Transmembrane Protein Family Research Articles

IFITM1 promotes the metastasis of human colorectal cancer via CAV-1

Interferon-induced transmembrane protein 1 (IFITM1) is one of the interferon-induced transmembrane protein family members. In this study, we reported that the elevated IFITM1 expression in human colorectal cancer (CRC) significantly correlated with CRC lymph node and distance metastasis as well as a more advanced clinical stage. Importantly, elevated IFITM1 expression is an independent prognostic factor for poor survival. To investigate the molecular mechanisms, we showed that over-expression of IFITM1 in CRC cells promoted, whereas knockdown of IFITM1 expression inhibited, cell migration/invasion and tumorigenicity in vitro. Furthermore, we identified Caveolin-1 (CAV1) as a downstream target of IFITM1-induced cell invasion, as knockdown of CAV1 abrogated siIFITM1 mediated inhibition of cell invasion in CRC cells. In addition, in a CRC cohort of 229 patients, the expression of IFITM1 inversely correlated with the expression of CAV1. These results suggested that IFITM1 promotes the aggressiveness of CRC cells, and it is a potential prognostic marker and therapeutic target for CRC.

Abstract 4617: Targeting interferon-induced transmembrane protein 1: a novel strategy to treat inflammatory breast cancer

Abstract Inflammatory breast cancer (IBC) is a very rare and aggressive form of breast cancer that accounts for about 1 to 5% of all breast cancers diagnosed in the United States. IBC is characterized by absence of a discrete mass, coupled with very rapid progression and dermal lymphatic invasion, which makes it the most lethal of the breast cancers. IBC is currently treated by a multimodal approach involving systemic chemotherapy, surgery, followed by radiation therapy; however, this strategy has yielded a 5-year survival outcome of only 20 to 30%. There is an urgent need to better understand the molecular mechanism that contributes to the development of IBC and to use that knowledge to identify novel targets that can be manipulated to enhance treatment options for IBC patients. In the present study, we have examined the role of human interferon-inducible transmembrane protein 1 (IFITM1) in the proliferation and invasion of inflammatory breast cancer. IFITM1 is a member of the interferon-inducible transmembrane protein family, which is involved in many cellular functions, including the transduction of antiproliferative and homotypic adhesion signals in lymphocytes, inhibition of viral replication, and promotion of cell invasion. At present, however, very little is known about the function of IFITM1 in inflammatory breast cancer. Our in vitro studies were performed in human inflammatory breast cancer cell lines; SUM149, SUM190, MDA-IBC-3, and non-inflammatory MCF-7 breast cancer cells. We found that IFITM1 mRNA and protein levels were constitutively overexpressed in SUM149 and MDA-IBC-3 cell lines but not expressed in non-inflammatory MCF-7 cells. Functional analysis of IFITM1 by silencing of its expression with small-interfering RNA showed that the loss of IFITM1 significantly inhibited the proliferation and invasiveness of SUM149 and MDA-IBC-3 cells and it completely blocked the ability of these cells to form colonies in soft agar assays. Interestingly, we found that interferon (IFN-α) significantly induced IFITM1 expression in all three of the IBC cell lines; however, IFN-α treatment inhibited the proliferation and invasiveness of the IBC cells. Our data also showed that several other interferon-regulated genes, including STAT1, PLSCR1, and STAT6 were elevated in inflammatory SUM149, MDA-IBC-3, and SUM190 cells but not in non-inflammatory MCF-7 cells. Overall, these results demonstrate that IFITM1 plays an important role in the proliferation and invasiveness of IBC cells and they suggest that targeting IFITM1 might be a novel strategy to treat inflammatory breast cancer. Citation Format: Joshua W. Ogony, Joan Lewis-Wambi. Targeting interferon-induced transmembrane protein 1: a novel strategy to treat inflammatory breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4617. doi:10.1158/1538-7445.AM2014-4617

P0001 Over-expression of interferon-inducible transmembrane protein family in human gastric carcinoma and its clinicopathological significance

<h3>Background</h3> Gastric cancer is the second most common cancer and the sixth leading cause of cancer-related death in Taiwan. Identification of useful biomarkers for early diagnosis and prognosis are necessary to improve patient survival outcome. Interferon-inducible transmembrane protein family (IFITM protein family) was identified by using iTRAQ labelling combined with LTQ-Orbitrap mass spectrometry analysis. IFITM1, IFITM2, and IFITM3 belong to the human interferon-inducible transmembrane gene family and are highly inducible by both type I (αβ) and type II (γ) interferons. The 14kDa IFITM protein family is involved in the homotypic cell adhesion functions of interferons. However, the role of IFITM protein family in gastric carcinogenesis remains unclear. <h3>Methods</h3> IFITM protein family expression level of gastric cancer tissue was validated by qRT-PCR, western blotting, and immunohistochemistry analysis (IHC). <h3>Findings</h3> In qRT-PCR, we found IFITM family mRNA transcripts are highly upregulated in 76.3% of gastric cancer patients (<i>n</i>=76) compared with adjacent non-tumour tissues. In IHC, IFITM protein family is significantly over-expressed in 94.57% of gastric cancer patients (<i>n</i>=122) when compared to their counterparts (<i>p</i><0.0001). To better understand the function of the IFITM protein family in human gastric cancer cells, IFITM protein depletion stable clones were established. After IFITM protein depletion, the proliferation rate, cell migration, or colony number were significantly reduced. Moreover, IFITM protein family depletion cells show more sensitivity to cisplatin-induced cell death. <h3>Interpretation</h3> Taken together, overexpressed IFITM protein family in gastric cancer cells may be involved in the cell proliferation, cell motility, and resistance to anticancer drugs. IFITM protein may play a role in the progression of gastric cancer.

IFITM Proteins Restrict Viral Membrane Hemifusion

The interferon-inducible transmembrane (IFITM) protein family represents a new class of cellular restriction factors that block early stages of viral replication; the underlying mechanism is currently not known. Here we provide evidence that IFITM proteins restrict membrane fusion induced by representatives of all three classes of viral membrane fusion proteins. IFITM1 profoundly suppressed syncytia formation and cell-cell fusion induced by almost all viral fusion proteins examined; IFITM2 and IFITM3 also strongly inhibited their fusion, with efficiency somewhat dependent on cell types. Furthermore, treatment of cells with IFN also markedly inhibited viral membrane fusion and entry. By using the Jaagsiekte sheep retrovirus envelope and influenza A virus hemagglutinin as models for study, we showed that IFITM-mediated restriction on membrane fusion is not at the steps of receptor- and/or low pH-mediated triggering; instead, the creation of hemifusion was essentially blocked by IFITMs. Chlorpromazine (CPZ), a chemical known to promote the transition from hemifusion to full fusion, was unable to rescue the IFITM-mediated restriction on fusion. In contrast, oleic acid (OA), a lipid analog that generates negative spontaneous curvature and thereby promotes hemifusion, virtually overcame the restriction. To explore the possible effect of IFITM proteins on membrane molecular order and fluidity, we performed fluorescence labeling with Laurdan, in conjunction with two-photon laser scanning and fluorescence-lifetime imaging microscopy (FLIM). We observed that the generalized polarizations (GPs) and fluorescence lifetimes of cell membranes expressing IFITM proteins were greatly enhanced, indicating higher molecularly ordered and less fluidized membranes. Collectively, our data demonstrated that IFITM proteins suppress viral membrane fusion before the creation of hemifusion, and suggested that they may do so by reducing membrane fluidity and conferring a positive spontaneous curvature in the outer leaflets of cell membranes. Our study provides novel insight into the understanding of how IFITM protein family restricts viral membrane fusion and infection.

Identification of Common and Distinctive Mechanisms of Resistance to Different Anti-IGF-IR Agents in Ewing's Sarcoma

IGF system contributes significantly to many human malignancies. Targeting IGF-I receptor (IGF-IR) has been reported to be active against several tumors, but particular efficacy was observed only against a minority of Ewing's sarcoma patients. Identification of mechanisms of acquired resistance to anti-IGF-IR agents is mandatory to individualize their use in clinics and optimize cure costs. In this study, we compared gene expression profiles of cells made resistant with three different anti-IGF-IR drugs (human antibodies AVE1642, Figitumumab, or tyrosine kinase inhibitor NVP-AEW541) to highlight common and distinctive mechanisms of resistance. Among common mechanisms, we identified two molecular signatures that distinguish sensitive from resistant cells. Annotation analysis indicated some common altered pathways, such as insulin signaling, MAPK pathway, endocytosis, and modulation of some members of the interferon-induced transmembrane protein family. Among distinctive pathways/processes, resistance to human antibodies involves mainly genes regulating neural differentiation and angiogenesis, whereas resistance to NVP-AEW541 is mainly associated with alterations in genes concerning inflammation and antigen presentation. Evaluation of the common altered pathways indicated that resistant cells seem to maintain intact the IGF-IR internalization/degradation route of sensitive cells but constantly down-regulated its expression. In resistant cells, the loss of proliferative stimulus, normally sustained by IGF-I/IGF-IR autocrine loop in Ewing's sarcoma cells, is compensated by transcriptional up-regulation of IGF-II and insulin receptor-A; this signaling seems to favor the MAPK pathway over the v-akt murine thymoma viral oncogene homolog 1 pathway. Overall, complexity of IGF system requires analytical evaluation of its components to select those patients that may really benefit from this targeted therapy and support the idea of cotargeting IGF-IR and insulin receptor-A to increase the efficacy.

IFITM3 Inhibits Influenza A Virus Infection by Preventing Cytosolic Entry

To replicate, viruses must gain access to the host cell's resources. Interferon (IFN) regulates the actions of a large complement of interferon effector genes (IEGs) that prevent viral replication. The interferon inducible transmembrane protein family members, IFITM1, 2 and 3, are IEGs required for inhibition of influenza A virus, dengue virus, and West Nile virus replication in vitro. Here we report that IFN prevents emergence of viral genomes from the endosomal pathway, and that IFITM3 is both necessary and sufficient for this function. Notably, viral pseudoparticles were inhibited from transferring their contents into the host cell cytosol by IFN, and IFITM3 was required and sufficient for this action. We further demonstrate that IFN expands Rab7 and LAMP1-containing structures, and that IFITM3 overexpression is sufficient for this phenotype. Moreover, IFITM3 partially resides in late endosomal and lysosomal structures, placing it in the path of invading viruses. Collectively our data are consistent with the prediction that viruses that fuse in the late endosomes or lysosomes are vulnerable to IFITM3's actions, while viruses that enter at the cell surface or in the early endosomes may avoid inhibition. Multiple viruses enter host cells through the late endocytic pathway, and many of these invaders are attenuated by IFN. Therefore these findings are likely to have significance for the intrinsic immune system's neutralization of a diverse array of threats.