Global modulation of cellular transcription by human cytomegalovirus is initiated by viral glycoprotein B

Human cytomegalovirus (HCMV) infection alters the expression of many cellular genes, including IFN-stimulated genes (ISGs) [Zhu, H., Cong, J.-P., Mamtora, G., Gingeras, T. & Shenk, T. (1998) Proc. Natl. Acad. Sci. USA 95, 14470–14475]. By using high-density cDNA microarrays, we show that the HCMV-regulated gene expression profile in fibroblasts does not differ substantially from the response generated by IFN. Furthermore, we identified the specific viral component triggering this response as the envelope glycoprotein B (gB). Cells treated with gB, but not other herpesviral glycoproteins, exhibited the same transcriptional profile as HCMV-infected cells. Thus, the interaction of gB with its as yet unidentified cellular receptor is the principal mechanism by which HCMV alters cellular gene expression early during infection. These findings highlight a pioneering paradigm for the consequences of virus–receptor interactions.

Expression of a Soybean Hydroxyproline-Rich Glycoprotein Gene Is Correlated with Maturation of Roots1

A novel extensin gene has been identified in soybean (Glycine max L.) that encodes a hydroxyproline-rich glycoprotein (SbHRGP3) with two different domains. In this study expression of SbHRGP3 was investigated during soybean root development. SbHRGP was expressed in roots of mature plants, as well as seedlings, and showed a distinct pattern of expression during root development. The expression of SbHRGP3 increased gradually during root development of seedlings and reached a maximum while the secondary roots were maturing. The maximum expression level was contributed mainly by the secondary roots rather than by the primary root. Furthermore, expression of SbHRGP3 was preferentially detected in the regions undergoing maturation of the primary and secondary roots. These results imply that the expression of SbHRGP3 is regulated in an organ- and development-specific manner and that in soybean SbHRGP3 expression may be required for root maturation, presumably for the cessation of root elongation. Wounding and sucrose in combination enhanced expression of SbHRGP3 in roots, whereas both wounding and sucrose were required for the expression of SbHRGP3 in leaves.

Fas (CD95) expression and death-mediating function are induced by CD4 cross-linking on CD4+ T cells.

The CD4 receptor contributes to T-cell activation by coligating major histocompatibility complex class II on antigen presenting cells with the T-cell receptor (TCR)/CD3 complex, and triggering a cascade of signaling events including tyrosine phosphorylation of intracellular proteins. Paradoxically, CD3 cross-linking prior to TCR stimulation results in apoptotic cell death, as does injection of anti-CD4 antibodies in vivo of CD4 ligation by HIV glycoprotein (gp) 120. In this report we investigate the mechanism by which CD4 cross-linking induces cell death. We have found that CD4 cross-linking results in a small but rapid increase in levels of cell surface Fas, a member of the tumor necrosis factor receptor family implicated in apoptotic death and maintenance of immune homeostasis. Importantly, CD4 cross-linking triggered the ability of Fas to function as a death molecule. Subsequent to CD4 cross-linking, CD4+ splenocytes cultured overnight became sensitive to Fas-mediated death. Death was Fas-dependent, as demonstrated by cell survival in the absence of plate-bound anti-Fas antibody, and by the lack of CD4-induced death in cells from Fas-defective lymphoproliferative (lpr) mice. We demonstrate here that CD4 regulates the ability of Fas to induce cell death in Cd4+ T cells.

Expression of the CD36 homolog (FAT) in fibroblast cells: effects on fatty acid transport.

An adipocyte membrane glycoprotein, (FAT), homologous to human CD36, has been previously implicated in the binding/transport of long-chain fatty acids. It bound reactive derivatives of long-chain fatty acids and binding was specific and associated with significant inhibition of fatty acid uptake. Tissue distribution of the protein and regulation of its expression were also consistent with its postulated role. In this report, we have examined the effects of FAT expression on rates and properties of fatty acid uptake by Ob17PY fibroblasts lacking the protein. Three clones (P21, P22, and P25) were selected based on FAT mRNA and protein levels. Cell surface labeling could be demonstrated with the anti-CD36 antibody FITC-OKM5. In line with this, the major fraction of immunoreactive FAT was associated with the plasma membrane fraction. Assays of oleate and/or palmitate uptake demonstrated higher rates in the three FAT-expressing clones, compared to cells transfected with the empty vector. Clone P21, which had the highest protein levels on Western blots, exhibited the largest increase in transport rates. Fatty acid uptake in FAT-expressing P21 cells reflected two components, a phloretin-sensitive high-affinity saturable component with a Km of 0.004 microM and a basal phloretin-insensitive component that was a linear function of unbound fatty acid. P21 cells incorporated more exogenous fatty acid into phospholipids, indicating that binding of fatty acids was followed by their transfer into the cell and that both processes were increased by FAT expression. The data support the interpretation that FAT/CD36 functions as a high-affinity membrane receptor/transporter for long-chain fatty acids.

Leukemia inhibitory factor (LIF) and LIF receptor expression in human endometrium suggests a potential autocrine/paracrine function in regulating embryo implantation.

The uterine expression of leukemia inhibitory factor (LIF) is essential for embryo implantation in the mouse. Here, we describe the expression of LIF, related members of this group of cytokines, oncostatin M and ciliary neurotrophic factor, and the LIF receptor beta and glycoprotein gp130 in normal human tissues and in the endometrium of fertile women. Our results show that LIF is the only one of these factors expressed at detectable levels in the endometrium of women of proven fertility. LIF expression is restricted to the endometrial glands during the secretory/postovulatory phase but is not present in the endometrium during the proliferative/preovulatory phase. The LIF receptor beta is expressed during the proliferative and secretory phases of the cycle and is restricted to the luminal epithelium. The associated signal-transducing component of the LIF receptor, gp130, is also expressed in both the luminal and glandular epithelium throughout the cycle. These results suggest that uterine expression of LIF in humans, like mice, may have a role in regulating embryo implantation, possibly through an autocrine/paracrine interaction between LIF and its receptor at the luminal epithelium.

A pregnancy-specific glycoprotein is expressed in the brain and serves as a receptor for mouse hepatitis virus.

Mouse hepatitis virus (MHV), a murine coronavirus known to cause encephalitis and demyelination, uses murine homologues of carcinoembryonic antigens as receptors. However, the expression of these receptors is extremely low in the brain. By low-stringency screening of a mouse brain cDNA library, we have identified a member of the pregnancy-specific glycoprotein (PSG) subgroup of the carcinoembryonic antigen gene family. Unlike other PSG that are expressed in the placenta, it is expressed predominantly in the brain. Transfection of the cDNA into COS-7 cells, which lack a functional MHV receptor, conferred susceptibility to infection by some MHV strains, including A59, MHV-2, and MHV-3, but not JHM. Thus, this is a virus strain-specific receptor. The detection of multiple receptors for MHV suggests the flexibility of this virus in receptor utilization. The identification of this virus in receptor utilization. The identification of a PSG predominantly expressed in the brain also expands the potential functions of these molecules.

Artificial regulation of gene expression in Escherichia coli by RNase P.

Plasmids encoding various external guide sequences (EGSs) were constructed and inserted into Escherichia coli. In strains harboring the appropriate plasmids, the expression of fully induced beta-galactosidase and alkaline phosphatase activity was reduced by more than 50%, while no reduction in such activity was observed in strains with non-specific EGSs. The inhibition of gene expression was virtually abolished at restrictive temperatures in strains that were temperature-sensitive for RNase P (EC 3.1.26.5). Northern blot analysis showed that the steady-state copy number of EGS RNAs was several hundred per cell in vivo. A plasmid that contained a gene for M1 RNA covalently linked to a specific EGS reduced the level of expression of a suppressor tRNA that was encoded by a separate plasmid. Similar methods can be used to regulate gene expression in E. coli and to mimic the properties of cold-sensitive mutants.