The clinical picture of severe acute respiratory syndrome (SARS) is characterized by an over-exuberant immune response with lung lymphomononuclear cells infilteration and proliferation that may account for tissue damage more than the direct effect of viral replication. To understand how cells response in the early stage of virus-host cell interaction, in this study, a purified recombinant S protein was studied for stimulating murine macrophages (RAW264.7) to produce proinflammatory cytokines (IL-6 and TNF-alpha) and chemokine IL-8. We found that direct induction of IL-6 and TNF-alpha release in the supernatant in a dose-, time-dependent manner and highly spike protein-specific, but no induction of IL-8 was detected. Further experiments showed that IL-6 and TNF-alpha production were dependent on NF-kappaB, which was activated through I-kappaBalpha degradation. These results suggest that SARS-CoV spike protein may play an important role in the pathogenesis of SARS, especially in inflammation and high fever.

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Severe acute respiratory syndrome coronavirus (SARS-CoV) infects many organs, such as lung, liver, and immune organs and causes life-threatening atypical pneumonia, SARS causes high morbidity and mortality rates. The molecular mechanism of SARS pathogenesis remains elusive. Inflammatory stimuli can activate IkappaB kinase (IKK) signalsome and subsequently the nuclear factor kappa B (NF-kappaB), which influences gene expression of cyclooxygenase-2 (Cox-2) along with other transcription factors. In this work, we found that the membrane (M) protein of SARS-CoV physically interacted with IKKbeta using a co-immunoprecipitation assay (IPA). Expression of M suppressed tumor necrosis factor alpha (TNF-alpha) induced NF-kappaB activation using a luciferase reporter assay. Further investigation showed M protein suppressed Cox-2 expression using a luciferase reporter gene assay, RT-PCR and Western blot analysis. The carboxyl terminal of M protein was sufficient for the M protein function. Together, these results indicate that SARS-CoV M suppresses NF-kappaB activity probably through a direct interaction with IKKbeta, resulting in lower Cox-2 expression. Suppression of NF-kappaB activity and Cox-2 expression may contribute to SARS pathogenesis.

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Encoded by Kaposi's sarcoma-associated herpesvirus, viral macrophage-inflammatory protein-II (VMIP-II) is unique among CC chemokines in that it has been shown to bind to the CXC chemokine receptor CXCR4 as well as to a variety of CC chemokine receptors. This unique binding ability allows vMIP-II to block infection by a wide range of human immunodeficiency virus type I (HIV-1) strains, but the structural and dynamic basis for this broad range of binding is not known. 15N T1, T2 and 15N[-HN] nuclear Overhauser effect (NOE) values of vMIP-II, determined through a series of heteronuclear multidimensional nuclear magnetic resonance (NMR) experiments, were used to obtain information about the backbone dynamics of the protein. Whereas almost all chemokine structures reveal a dimer or multimer, vMIP-II has a rotational correlation time (tauc) of 4.7 +/- 0.3 ns, which is consistent with a monomeric chemokine. The rotational diffusion anisotropy, D parallel/D perpendicular, is approximately 1.5 +/- 0.1. The conformation of vMIP-II is quite similar to other known chemokines, containing an unstructured N-terminus followed by an ordered turn, three beta-strands arranged in an antiparallel fashion, and one C-terminal alpha-helix that lies across the beta-strands. Most of the protein is well-ordered on a picosecond time scale, with an average order parameter S2 (excluding the N-terminal 13 amino acids) of 0.83 +/- 0. 09, and with even greater order in regions of secondary structure. The NMR data reveal that the N-terminus, which in other chemokines has been implicated in receptor binding, extends like a flexible tail in solution and possesses no secondary structure. The region of the ordered turn, including residues 25-28, experiences conformational exchange dynamics. The implications of these NMR data to the broad receptor binding capability of vMIP-II are discussed.