Interferon-induced transmembrane 3 binds osteopontin in vitro: expressed in vivo IFITM3 reduced OPN expression

Abstract

Osteopontin is a secreted, integrin-binding and phosphorylated acidic glycoprotein, which has an important role in tumour progression. We have shown that Wnt, Ets, AP-1, c-jun and b-catenin/Lef-1/Tcf-1 stimulates OPN transcription in rat mammary carcinoma cells by binding to a specific promoter sequence. However, co-repressors of OPN have not been identified. In this study, we have used the bacterial two-hybrid system to isolate cDNA-encoding proteins that bind to OPN and modulate its role in malignant transformation. Using this approach we isolated interferon-induced transmembrane protein 3 gene (IFITM3) as a potential protein partner. We show that IFITM3 and OPN interact in vitro and in vivo and that IFITM3 reduces osteopontin (OPN) mRNA expression, possibly by affecting OPN mRNA stability. Stable transfection of IFITM3 inhibits OPN, which mediates anchorage-independent growth, cell adhesion and cell invasion. Northern blot analysis revealed an inverse mRNA expression pattern of IFITM3 and OPN in human mammary cell lines. Inhibition of IFITM3 by antisense RNA promoted OPN protein expression, enhanced cell invasion by parental benign non-invasive Rama 37 cells, indicating that the two proteins interact functionally as well. We also identified an IFITM3 DNA-binding domain, which interacts with OPN, deletion of which abolished its inhibitive effect on OPN. This work has shown for the first time that IFITM3 physically interacts with OPN and reduces OPN mRNA expression, which mediates cell adhesion, cell invasion, colony formation in soft agar and metastasis in a rat model system.

The role of IFITM3 in the growth and migration of human glioma cells

“…For instance, El-Tanani et al [32] found that IFITM3 in breast cancer physically interacts with OPN and reduces OPN mRNA expression, which mediates cancer cell adhesion, cell invasion and colony formation. Similar situation has come under observation in human melanoma, and it is deemed dynamic promoter methylation adds an additional layer of complexity to the IFN-α key response genes like IFITM3 be required for comprehensive control of the IFN-α response [33,34].…”

Important role of integrins in the cancer biology

“…In vitro and in vivo studies have revealed that interferon-induced transmembrane protein 3 gene interacts with OPN and reduces its mRNA expression to reduce metastases [62]. Interestingly, expression analysis indicates that the osteopontin expression may serve as a prognostic biomarker [63].…”

Role of osteopontin in the pathophysiology of cancer

“…Hedley et al reported that OPN downregulation by BRMS1 may be responsible, at least in part, for BRMS1-mediated metastasis suppression by sensitizing cancer cells to stress induced apoptosis (Hedley et al, 2008). The El-Tanani lab identified interferon-induced transmembrane protein 3 gene (IFITM3) as a potential protein partner of OPN that reduces OPN mRNA expression and negatively impacts cell adhesion, cell invasion, colony formation in soft agar and preclinical metastasis (El-Tanani et al, 2010). RUNX3 is a transcriptional repressor of OPN and loss of RUNX3 upregulates OPN, which promotes migration in gastric cancer cells (Cheng et al, 2013).…”