WFDC1/ps20: a host factor that influences the neutrophil response to murine hepatitis virus (MHV) 1 infection

Molecular structure, gene expression and functional role of WFDC1 in angiogenesis and cancer

Whey acidic proteins (WAP) perform a diverse range of important biological functions, including proteinase activity, calcium transport and bacterial growth. The WAP four-disulphide core domain protein 1 (WFDC1) gene (also called PS20), encodes the 20 kDa prostate stromal protein (ps20), which is a member of the WAP-type four-disulphide core domain family of proteins, and exhibits characteristics of serine protease inhibitors, such as elafin and secretory leukocyte protease inhibitor. Molecular structural analysis reveals that ps20 consists of four-disulphide bonds formed by eight cysteine residues located at the carboxyl terminus of the protein. Wfdc1-null mice were found to display no overt developmental phenotype, suggesting a dispensable role in organ growth and development. However, WFDC1 was able to mediate endothelial cell migration and pericyte stabilization, which are vital for the formation of functional vascular structures. WFDC1 was also found to be downregulated in cancers and exhibited a regulatory effect on cell proliferation. In addition, it was involved in the modulation of memory T cells during human immunodeficiency virus infection. Gaining a solid understanding of the mechanisms by which WFDC1 regulates tissue homeostasis and disease processes, in a tissue specific manner, will be an important move towards the development of WFDC1/ps20 as potential therapeutic targets.

Residues F103 and M106 within the influenza A virus NS1 CPSF4-binding region regulate interferon-stimulated gene translation initiation

Influenza A virus (IAV) non-structural protein 1 (NS1) suppresses host innate immune responses by inhibiting type I interferon (IFN) production. We provide evidence that residues F103 and M106 in the CPSF4-binding domain of A/HK/1/68 [H3N2] NS1 contribute to post-transcriptional inhibition of antiviral IFN-stimulated genes (ISGs), thereby suppressing an antiviral type I IFN response. Recombinant (r) IAVs encoding F103L and M106I mutations in NS1 replicate to significantly lower viral titers in human A549 lung epithelial cells and primary type II alveolar cells. In A549 cells, rIAVs encoding these mutant NS1s induce higher levels of IFN-β production and are more sensitive to the antiviral effects of IFN-β treatment. qPCR characterization of polysomal mRNA, in the presence or absence of IFN-β treatment, identified a greater proportion of heavy polysome-associated ISGs including EIF2AK2, OAS1, and MxA in A549 cells infected with rIAVs encoding these CPSF4-binding mutant NS1s, in contrast to rIAV encoding wildtype NS1.

A Conserved Residue, Tyrosine (Y) 84, in H5N1 Influenza A Virus NS1 Regulates IFN Signaling Responses to Enhance Viral Infection

The non-structural protein, NS1, is a virulence factor encoded by influenza A viruses (IAVs). In this report, we provide evidence that the conserved residue, tyrosine (Y) 84, in a conserved putative SH2-binding domain in A/Duck/Hubei/2004/L-1 [H5N1] NS1 is critical for limiting an interferon (IFN) response to infection. A phenylalanine (F) substitution of this Y84 residue abolishes NS1-mediated downregulation of IFN-inducible STAT phosphorylation, and surface IFNAR1 expression. Recombinant IAV (rIAV) [H1N1] expressing A/Grey Heron/Hong Kong/837/2004 [H5N1] NS1-Y84F (rWSN-GH-NS1-Y84F) replicates to lower titers in human lung epithelial cells and is more susceptible to the antiviral effects of IFN-β treatment compared with rIAV expressing the intact H5N1 NS1 (rWSN-GH-NS1-wt). Cells infected with rWSN-GH-NS1-Y84F express higher levels of IFN stimulated genes (ISGs) associated with an antiviral response compared with cells infected with rWSN-GH-NS1-wt. In mice, intranasal infection with rWSN-GH-NS1-Y84F resulted in a delay in onset of weight loss, reduced lung pathology, lower lung viral titers and higher ISG expression, compared with mice infected with rWSN-GH-NS1-wt. IFN-β treatment of mice infected with rWSN-GH-NS1-Y84F reduced lung viral titers and increased lung ISG expression, but did not alter viral titers and ISG expression in mice infected with rWSN-GH-NS1-wt. Viewed altogether, these data suggest that the virulence associated with this conserved Y84 residue in NS1 is, in part, due to its role in regulating the host IFN response.

Interferon-Stimulated Gene Expression as a Preferred Biomarker for Disease Activity in Aicardi-Goutières Syndrome

Aicardi-Goutières syndrome (AGS) is an early-onset, genetic disease characterized by recurrent fever, multifocal lesions of the brain, and systemic autoimmunity. We report on 3 AGS patients, 2 siblings with an RNASEH2A gene mutation and 1 patient with a SAMHD1 gene mutation. Serial analysis of peripheral blood from all 3 AGS patients showed consistently elevated expression of the interferon-stimulated genes (ISGs): ISG15, RSAD2, and IFI27, not observed in unaffected family members. Enumeration of circulating white blood cells and platelets and examination of C-reactive protein showed no significant deviation from the normal range for Patient 2 with the RNASEH2A mutation and Patient 3 with the SAMHD1 mutation, even when Patient 2 had magnetic resonance imaging abnormalities and ongoing febrile episodes. Erythrocyte sedimentation rates fluctuated within the normal range for Patient 2, with some elevation, yet, were in the normal range during the second febrile episode when there were accompanying neurological abnormalities. These preliminary data suggest that ISG expression may be a more specific indicator of disease activity in comparison to standard inflammatory markers.

Cathepsin-L and transglutaminase dependent processing of ps20: A novel mechanism for ps20 regulation via ECM cross-linking

Whey-acidic-protein (WAP) four-disulphide core (WFDC) proteins have important roles in the regulation of innate immunity, anti-microbial function, and the inhibition of inflammatory proteases at mucosal surfaces. It was recently demonstrated that the WFDC protein, prostate stromal 20 (ps20), encoded by the WFDC1 gene, is a potent growth inhibitory factor, and shares with other WFDC proteins the ability to modulate wound healing processes and immune responses to viral infections. However, ps20 remains relatively uncharacterised at the protein level. Using a panel of ps20 antibodies for western-blotting (WB), ELISA and immunoaffinity purification, we isolated, biochemically characterised and tested ps20 preparations for three biological properties: (i) interactions with glycosaminoglycans (GAG) (ii) inhibition of cell proliferation, and (iii) transglutaminase2 (TG2) mediated crosslinking of ps20 to fibronectin, a process implicated in wound healing. We show herein that ps20 preparations contain multiple molecular forms including full-length ps20 (resolving at ≈27 kDa), an exon 3 truncated form (≈22 kDa) that lacks aa113-140, and variable amounts of a putatively cleaved lower MW (≈15-17 kDa) species. Untagged purified ps20 preparations containing a mixture of these forms are biologically active in significantly suppressing prostate cell proliferation. We show that one mechanism by which lower LMW forms of ps20 arise is through cathepsin L (CL) cleavage, and confirm that CL cleaves ps20 at the C-terminus, but this does not inhibit its growth inhibitory function. However, CL cleavage abrogated the interaction between ps20 and solid-phase fibronectin. Therefore, we demonstrate for the first time that LMW forms of ps20 that lack a C-terminal immunogenic epitope can arise through CL cleavage and this cleavage impairs multimerisation and potential capacity to cross-link to ECM, but not the capacity of ps20 to inhibit cell proliferation. We propose that ps20 like other WFDC proteins can become associated with GAGs and the ECM. Furthermore, we suggest post-translational processing and cleavage of ps20 is required to generate functional protein species, and TG2 mediated crosslinking and CL cleavage form components of a ps20 regulatory apparatus.

WFDC1 is a key modulator of inflammatory and wound repair responses

WFDC1/ps20 is a whey acidic protein four-disulfide core member that exhibits diverse growth and immune-associated functions in vitro. In vivo functions are unknown, although WFDC1 is lower in reactive stroma. A Wfdc1-null mouse was generated to assess core functions. Wfdc1-null mice exhibited normal developmental and adult phenotypes. However, homeostasis challenges affected inflammatory and repair processes. Wfdc1-null mice infected with influenza A exhibited 2.75-log-fold lower viral titer relative to control mice. Wfdc1-null infected lungs exhibited elevated macrophages and deposition of osteopontin, a potent macrophage chemokine. In wounding studies, Wfdc1-null mice exhibited an elevated rate of skin closure, and this too was associated with elevated deposition of osteopontin and macrophage recruitment. Wfdc1-null fibroblasts exhibited impaired spheroid formation, elevated adhesion to fibronectin, and an increased rate of wound closure in vitro. This was reversed by neutralizing antibody to osteopontin. Osteopontin mRNA and cleaved protein was up-regulated in Wfdc1-null cells treated with lipopolysaccharide or polyinosinic-polycytidylic acid coordinate with constitutively active matrix metallopeptidase-9 (MMP-9), a protease that cleaves osteopontin. These data suggest that WFDC1/ps20 modulates core host response mechanisms, in part, via regulation of osteopontin and MMP-9 activity. Release from WFDC1 regulation is likely a key component of inflammatory and repair response mechanisms, and involves the processing of elevated osteopontin by activated MMP-9, and subsequent macrophage recruitment.