Social stress and the reactivation of latent herpes simplex virus type 1

Psychological stress is thought to contribute to reactivation of latent herpes simplex virus (HSV). Although several animal models have been developed in an effort to reproduce different pathogenic aspects of HSV keratitis or labialis, until now, no good animal model existed in which application of a psychological laboratory stressor results in reliable reactivation of the virus. Reported herein, disruption of the social hierarchy within colonies of mice increased aggression among cohorts, activated the hypothalamic-pituitary-adrenal axis, and caused reactivation of latent HSV type 1 in greater than 40% of latently infected animals. However, activation of the hypothalamic-pituitary-adrenal axis using restraint stress did not activate the latent virus. Thus, the use of social stress in mice provides a good model in which to investigate the neuroendocrine mechanisms that underlie behaviorally mediated reactivation of latent herpesviruses.

The cysteine-rich frizzled domain of Frzb-1 is required and sufficient for modulation of Wnt signaling

Convincing evidence has accumulated to identify the Frizzled proteins as receptors for the Wnt growth factors. In parallel, a number of secreted frizzled-like proteins with a conserved N-terminal frizzled motif have been identified. One of these proteins, Frzb-1, binds Wnt-1 and Xwnt-8 proteins and antagonizes Xwnt-8 signaling in Xenopus embryos. Here we report that Frzb-1 blocks Wnt-1 induced cytosolic accumulation of β-catenin, a key component of the Wnt signaling pathway, in human embryonic kidney cells. Structure/function analysis reveals that complete removal of the frizzled domain of Frzb-1 abolishes the Wnt-1/Frzb-1 protein interaction and the inhibition of Wnt-1 mediated axis duplication in Xenopus embryos. In contrast, removal of the C-terminal portion of the molecule preserves both Frzb-Wnt binding and functional inhibition of Wnt signaling. Partial deletions of the Frzb-1 cysteine-rich domain maintain Wnt-1 interaction, but functional inhibition is lost. Taken together, these findings support the conclusion that the frizzled domain is necessary and sufficient for both activities. Interestingly, Frzb-1 does not block Wnt-5A signaling in a Xenopus functional assay, even though Wnt-5A coimmunoprecipitates with Frzb-1, suggesting that coimmunoprecipitation does not necessarily imply inhibition of Wnt function.

Multiple loop structures critical for ligand binding of the integrin α4 subunit in the upper face of the β-propeller mode 1

A non-I-domain integrin, α4β1, recognizes vascular cell adhesion molecule 1 (VCAM-1) and the IIICS portion of fibronectin. To localize regions of α4 critical for ligand binding, we swapped several predicted loops within or near the putative ligand-binding site of α4 (which spans repeats 2–5 of the seven N-terminal repeats) with the corresponding regions of α5. Swapping residues 112–131 in repeat 2, or residues 237–247 in repeat 4, completely blocked adhesion to immobilized VCAM-1 and connecting segment 1 (CS-1) peptide. However, swapping residues 40–52 in repeat 1, residues 151–164 in repeat 3, or residues 282–288 (which contain a putative cation binding motif) in repeat 5 did not affect or only slightly reduced adhesion to these ligands. The binding of several function-blocking antibodies is blocked by swapping residues 112–131, 151–164, and 186–191 (which contain previously identified residues critical for ligand binding, Tyr-187 and Gly-190). These results are consistent with the recently published β-propeller folding model of the integrin α4 subunit [Springer, T. A. (1997) Proc. Natl. Acad. Sci. USA 94, 65–72], in which seven four-stranded β-sheets are arranged in a torus around a pseudosymmetric axis. The regions of α4 critical for ligand binding are adjacent to each other and are located in the upper face, the predicted ligand-binding site, of the β-propeller model, although they are not adjacent in the primary structure.

Potentially predictive and manipulable blood serum correlates of aging in the healthy human male: Progressive decreases in bioavailable testosterone, dehydroepiandrosterone sulfate, and the ratio of insulin-like growth factor 1 to growth hormone

A cross-sectional survey was made in 56 exceptionally healthy males, ranging in age from 20 to 84 years. Measurements were made of selected steroidal components and peptidic hormones in blood serum, and cognitive and physical tests were performed. Of those blood serum variables that gave highly significant negative correlations with age (r > −0.6), bioavailable testosterone (BT), dehydroepiandrosterone sulfate (DHEAS), and the ratio of insulin-like growth factor 1 (IGF-1) to growth hormone (GH) showed a stepwise pattern of age-related changes most closely resembling those of the age steps themselves. Of these, BT correlated best with significantly age-correlated cognitive and physical measures. Because DHEAS correlated well with BT and considerably less well than BT with the cognitive and physical measures, it seems likely that BT and/or substances to which BT gives rise in tissues play a more direct role in whatever processes are rate-limiting in the functions measured and that DHEAS relates more indirectly to these functions. The high correlation of IGF-1/GH with age, its relatively low correlation with BT, and the patterns of correlations of IGF-1/GH and BT with significantly age-correlated cognitive and physical measures suggest that the GH–IGF-1 axis and BT play independent roles in affecting these functions. Serial determinations made after oral ingestion of pregnenolone and data from the literature suggest there is interdependence of steroid metabolic systems with those operational in control of interrelations in the GH–IGF-1 axis. Longitudinal concurrent measurements of serum levels of BT, DHEAS, and IGF-1/GH together with detailed studies of their correlations with age-correlated functional measures may be useful in detecting early age-related dysregulations and may be helpful in devising ameliorative approaches.

Regulation of dorsal fate in the neuraxis by Wnt-1 and Wnt-3a

Members of the Wnt family of signaling molecules are expressed differentially along the dorsal–ventral axis of the developing neural tube. Thus we asked whether Wnt factors are involved in patterning of the nervous system along this axis. We show that Wnt-1 and Wnt-3a, both of which are expressed in the dorsal portion of the neural tube, could synergize with the neural inducers noggin and chordin in Xenopus animal explants to generate the most dorsal neural structure, the neural crest, as determined by the expression of Krox-20, AP-2, and slug. Overexpression of Wnt-1 or Wnt-3a in the neuroectoderm of whole embryos led to a dramatic increase of slug and Krox-20-expressing cells, but the hindbrain expression of Krox-20 remained unaffected. Enlargement in the neural crest population could occur even when cell proliferation was inhibited. Wnt-5A and Wnt-8, neither of which is expressed in the dorsal neuroectoderm, failed to induce neural crest markers. Overexpression of glycogen synthase kinase 3, known to antagonize Wnt signaling, blocked the neural-crest-inducing activity of Wnt-3a in animal explants and inhibited neural crest formation in whole embryos. We suggest that Wnt-1 and Wnt-3a have a role in patterning the neural tube along its dorsoventral axis and function in the differentiation of the neural crest.

A point mutation in the HIV-1 Tat responsive element is associated with postintegration latency.

Study of the mechanism of HIV-1 postintegration latency in the ACH2 cell line demonstrates that these cells failed to increase HIV-1 production following treatment with exogenous Tat. Reasoning that the defect in ACH2 cells involves the Tat response, we analyzed the sequence of tat cDNA and Tat responsive element (TAR) from the virus integrated in ACH2. Tat cDNA sequence is closely related to that of HIV LAI, and the encoded protein is fully functional in terms of long terminal repeat (LTR) transactivation. Cloning of a region corresponding to the 5'-LTR from ACH2, however, identified a point mutation (C37 -> T) in TAR. This mutation impaired Tat responsiveness of the LTR in transient transfection assays, and the measured defect was complemented in cells that had been treated with tetradecanoyl phorbol acetate or tumor necrosis factor type alpha (TNF-alpha). A compensatory mutation in TAR (G28 -> A), designed to reestablish base pairing in the TAR hairpin, restored wild-type Tat responsiveness. When the (C37 -> T) mutation was introduced in an infectious clone of HIV-1, no viral production was measured in the absence of TNF-alpha, whereas full complementation was observed when the infection was conducted in the presence of TNF-alpha or when a compensatory mutation (G28 -> A) was introduced into TAR. These experiments identify a novel mutation associated with HIV-1 latency and suggest that alterations in the Tat-TAR axis can be a crucial determinant of the latent phenotype in infected individuals.

Involvement of Ras/Raf/AP-1 in BMP-4 signaling during Xenopus embryonic development.

Previously, we elucidated the role of bone morphogenetic protein 4 (BMP-4) in the dorsal-ventral patterning of the Xenopus embryo by using a dominant negative mutant of the BMP-4 receptor (DN-BR). The present paper describes the involvement of Ras, Raf, and activator protein 1 (AP-1) in BMP-4 signaling during Xenopus embryonic development. The AP-1 activity was determined by injecting an AP-1-dependent luciferase reporter gene into two-cell-stage Xenopus embryos and measuring the luciferase activity at various developmental stages. We found that injection of BMP-4 mRNA increased AP-1 activity, whereas injection of DN-BR mRNA inhibited AP-1 activity. Similar inhibitory effects were seen with injection of mRNAs encoding dominant negative mutants of c-Ha-Ras, c-Raf, or c-Jun. These results suggest that the endogenous AP-1 activity is regulated by BMP-4/Ras/Raf/Jun signals. We next investigated the effects of Ras/Raf/AP-1 signals on the biological functions of BMP-4. DN-BR-induced dorsalization of the embryo, revealed by the formation of a secondary body axis or dorsalization of the ventral mesoderm explant analyzed by histological and molecular criteria, was significantly reversed by coinjection of [Val12]Ha-Ras, c-Raf, or c-Jun mRNA. Furthermore, the BMP-4-stimulated erythroid differentiation in the ventral mesoderm was substantially inhibited by coinjection with the dominant negative c-Ha-Ras, c-Raf, or c-Jun mutant. Our results suggest the involvement of Ras/Raf/AP-1 in the BMP-4 signaling pathway.

A type 1 serine/threonine kinase receptor that can dorsalize mesoderm in Xenopus.

We have cloned a type I serine/threonine kinase receptor, XTrR-I, from Xenopus. XTrR-I (Xenopus transforming growth factor beta-related receptor type I) is expressed in all regions of embryos throughout early development. Overexpression of this receptor does not affect ectoderm or endoderm but dorsalizes the mesoderm such that muscle appears in ventral mesoderm and notochord appears in lateral mesoderm normally fated to become muscle. In addition, overexpression of XTrR-I in UV-treated embryos is able to cause formation of a partial dorsal axis. These results suggest that XTrR-I encodes a receptor which responds in normal development to a transforming growth factor beta-like ligand so as to promote dorsalization. Its function would therefore be to direct mesodermalized tissue into muscle or notochord.

Anterior axis duplication in Xenopus induced by the over-expression of the cadherin-binding protein plakoglobin.

Plakoglobin interacts with both classical and desmosomal cadherins. It is closely related to Drosophila aramadillo (arm) gene product; arm acts in the wingless (wg)-signaling pathway to establish segment polarity. In Xenopus, homologs of wg--i.e., wnts, can produce anterior axis duplications by inducing dorsal mesoderm. Studies in Drosophila suggest that wnt acts by increasing the level of cytoplasmic armadillo protein (arm). To test whether simply increasing the level of plakoglobin mimics the effects of exogenous wnts in Xenopus, we injected fertilized eggs with RNA encoding an epitope-tagged form of plakoglobin; this induced both early radial gastrulation and anterior axis duplication. Exogenous plakoglobin accumulates in the nuclei of embryonic cells. Plakoglobin binds to the tail domain of the desmosomal cadherin desmoglein 1. When RNA encoding the tail domain of desmoglein was coinjected with plakoglobin RNA, both the dorsalizing effect and nuclear accumulation of plakoglobin were suppressed. Mutational analysis indicates that the central arm repeat region of plakoglobin is sufficient to induce axis duplication and that this polypeptide accumulates in the nuclei of embryonic cells. These data show that increased plakoglobin levels can, by themselves, generate the intracellular signals involved in the specification of dorsal mesoderm.