Viral Interactions with Adaptor-Protein Complexes: A Ubiquitous Trait among Viral Species.

Numerous viruses hijack cellular protein trafficking pathways to mediate cell entry or to rearrange membrane structures thereby promoting viral replication and antagonizing the immune response. Adaptor protein complexes (AP), which mediate protein sorting in endocytic and secretory transport pathways, are one of the conserved viral targets with many viruses possessing AP-interacting motifs. We present here different mechanisms of viral interference with AP complexes and the functional consequences that allow for efficient viral propagation and evasion of host immune defense. The ubiquity of this phenomenon is evidenced by the fact that there are representatives for AP interference in all major viral families, covered in this review. The best described examples are interactions of human immunodeficiency virus and human herpesviruses with AP complexes. Several other viruses, like Ebola, Nipah, and SARS-CoV-2, are pointed out as high priority disease-causative agents supporting the need for deeper understanding of virus-AP interplay which can be exploited in the design of novel antiviral therapies.

Cytomegalovirus protein m154 perturbs the adaptor protein-1 compartment mediating broad-spectrum immune evasion.

Cytomegaloviruses (CMVs) are ubiquitous pathogens known to employ numerous immunoevasive strategies that significantly impair the ability of the immune system to eliminate the infected cells. Here, we report that the single mouse CMV (MCMV) protein, m154, downregulates multiple surface molecules involved in the activation and costimulation of the immune cells. We demonstrate that m154 uses its cytoplasmic tail motif, DD, to interfere with the adaptor protein-1 (AP-1) complex, implicated in intracellular protein sorting and packaging. As a consequence of the perturbed AP-1 sorting, m154 promotes lysosomal degradation of several proteins involved in T cell costimulation, thus impairing virus-specific CD8+ T cell response and virus control in vivo. Additionally, we show that HCMV infection similarly interferes with the AP-1 complex. Altogether, we identify the robust mechanism employed by single viral immunomodulatory protein targeting a broad spectrum of cell surface molecules involved in the antiviral immune response.

Galectin-3 Deficiency Facilitates TNF-α-Dependent Hepatocyte Death and Liver Inflammation in MCMV Infection.

Galectin-3 (Gal-3) has a role in multiple inflammatory pathways. Various, opposite roles of Gal-3 in liver diseases have been described but there are no data about the role of Gal-3 in development of hepatitis induced with cytomegalovirus infection. In this study we aimed to clarify the role of Gal-3 in murine cytomegalovirus (MCMV)-induced hepatitis by using Gal-3-deficient (Gal-3 KO) mice. Here we provide the evidence that Gal-3 has the protective role in MCMV-induced hepatitis. Enhanced hepatitis manifested by more inflammatory and necrotic foci and serum level of ALT, enhanced apoptosis and necroptosis of hepatocytes and enhanced viral replication were detected in MCMV-infected Gal-3 deficient mice. NK cells does not contribute to more severe liver damage in MCMV-infected Gal-3 KO mice. Enhanced expression of TNF-α in the hepatocytes of Gal-3 KO mice after MCMV infection, abrogated hepatocyte death, and attenuated inflammation in the livers of Gal-3 KO mice after TNF-α blockade suggest that TNF-α plays the role in enhanced disease in Gal-3 deficient animals. Treatment with recombinant Gal-3 reduces inflammation and especially necrosis of hepatocytes in the livers of MCMV-infected Gal-3 KO mice. Our data highlight the protective role of Gal-3 in MCMV-induced hepatitis by attenuation of TNF-α-mediated death of hepatocytes.

Gallium enhances reconstructive properties of a calcium phosphate bone biomaterial.

Calcium phosphate (CaP)-based biomaterials are commonly used in bone reconstructive surgery to replace the damaged tissue, and can also serve as vectors for local drug delivery. Due to its inhibitory action on osteoclasts, the semi-metallic element gallium (Ga) is used for the systemic treatment of disorders associated with accelerated bone resorption. As it was demonstrated that Ga could be incorporated in the structure of CaP biomaterials, we investigated the biological properties of Ga-loaded CaP biomaterials. Culturing bone cells on Ga-CaP, we observed a decrease in osteoclast number and a downregulation of late osteoclastic markers expression, while Ga-CaP upregulated the expression of osteoblastic marker genes involved in the maturation of bone matrix. We next investigated in vivo bone reconstructive properties of different Ga-loaded biomaterials using a murine bone defect healing model. All implanted biomaterials showed a good osseointegration into the surrounding host tissue, accompanied by a successful bone ingrowth and bone marrow reconstruction, as evidenced by histological analysis. Moreover, quantitative micro-computed tomography analysis of implants revealed that Ga enhanced total defect filling. Lastly, we took advantage for the first time of a particular mode of non-linear microscopy (second harmonic generation) to quantify in vivo bone tissue reconstruction within a CaP bone substitute. By doing so, we showed that Ga exerted a positive impact on mature organized collagen synthesis. As a whole, our data support the hypothesis that Ga represents an attractive additive to CaP biomaterials for bone reconstructive surgery. Copyright © 2017 John Wiley & Sons, Ltd.

Gallium, a promising candidate to disrupt the vicious cycle driving osteolytic metastases.

Bone metastases of breast cancer typically lead to a severe osteolysis due to an excessive osteoclastic activity. On the other hand, the semi-metallic element gallium (Ga) displays an inhibitory action on osteoclasts, and therefore on bone resorption, as well as antitumour properties. Thus, we explored in vitro Ga effects on osteoclastogenesis in an aggressive bone metastatic environment based on the culture of pre-osteoclast RAW 264.7 cells with conditioned medium from metastatic breast tumour cells, i.e. the breast tumour cell line model MDA-MB-231 and its bone-seeking clone MDA-231BO. We first observed that Ga dose-dependently inhibited the tumour cells-induced osteoclastic differentiation of RAW 264.7 cells. To mimic a more aggressive environment where pro-tumourigenic factors are released from bone matrix due to osteoclastic resorption, metastatic breast tumour cells were stimulated with TGF-ß, a mayor cytokine in bone metastasis vicious cycle. In these conditions, we observed that Ga still inhibited cancer cells-driven osteoclastogenesis. Lastly, we evidenced that Ga affected directly and strongly the proliferation/viability of both cancer cell lines, as well as the expression of major osteolytic factors in MDA-231BO cells. With the exception of two small scale clinical studies from 1980s, this is the first time that antitumour properties of Ga have been specifically studied in the context of bone metastases. Our data strongly suggest that, through its action against the vicious cycle involving bone cells and tumour cells, Ga represents a relevant and promising candidate for the local treatment of bone metastases in patients with breast cancer.