Intramolecular backfolding of the carboxyl-terminal end of MxA protein is a prerequisite for its oligomerization.

Mx proteins are large GTPases, which play a pivotal role in the interferon type I-mediated response against viral infections. The human MxA inhibits the replication of several RNA viruses and is organized in oligomeric structures. Using two different experimental approaches, the mammalian two-hybrid system and an interaction dependent nuclear translocation approach, three domains in the carboxyl-terminal moiety were identified that are involved in the oligomerization of MxA. The first consists of a carboxyl-terminal amphipathic helix (LZ1), which binds to a more proximal part of the same molecule. This intramolecular backfolding is a prerequisite for the formation of an intermolecular complex. This intermolecular interaction is mediated by two domains, a poorly defined region generated by the intramolecular interaction and a domain located between amino acids 363 and 415. Co-expression of wild-type MxA with various mutant fragments thereof revealed that the presence of the carboxyl-terminal region comprising the amphipathic helices LZ1 and LZ2 is necessary and sufficient to exert a dominant negative effect. This finding suggests that the functional interference of the carboxyl-terminal region is due to competition for binding of an as yet unidentified cellular or viral target molecules.

Human MxA protein protects mice lacking a functional alpha/beta interferon system against La crosse virus and other lethal viral infections.

The human MxA protein is part of the antiviral state induced by alpha/beta interferon (IFN-alpha/beta). MxA inhibits the multiplication of several RNA viruses in cell culture. However, its antiviral potential in vivo has not yet been fully explored. We have generated MxA-transgenic mice that lack a functional IFN system by crossing MxA-transgenic mice constitutively expressing MxA with genetically targeted (knockout) mice lacking the beta subunit of the IFN-alpha/beta receptor (IFNAR-1(-/-) mice). These mice are an ideal animal model to investigate the unique antiviral activity of human MxA in vivo, because they are unable to express other IFN-induced proteins. Here, we show that MxA confers resistance to Thogoto virus, La Crosse virus, and Semliki Forest virus. No Thogoto virus progeny was detectable in MxA-transgenic mice, indicating an efficient block of virus replication at the primary site of infection. In the case of La Crosse virus, MxA restricted invasion of the central nervous system. In contrast, Semliki Forest virus multiplication in the brain was detectable in both MxA-expressing and nonexpressing IFNAR-1(-/-) mice. However, viral titers were clearly reduced in MxA-transgenic mice. Our results demonstrate that MxA does not need the help of other IFN-induced proteins for activity but is a powerful antiviral agent on its own. Moreover, the results suggest that MxA may protect humans from potential fatal infections by La Crosse virus and other viral pathogens.

Human MxA protein confers resistance to Semliki Forest virus and inhibits the amplification of a Semliki Forest virus-based replicon in the absence of viral structural proteins.

Mx proteins form a small family of interferon (IFN)-induced GTPases with potent antiviral activity against various negative-strand RNA viruses. To examine the antiviral spectrum of human MxA in homologous cells, we stably transfected HEp-2 cells with a plasmid directing the expression of MxA cDNA. HEp-2 cells are permissive for many viruses and are unable to express endogenous MxA in response to IFN. Experimental infection with various RNA and DNA viruses revealed that MxA-expressing HEp-2 cells were protected not only against influenza virus and vesicular stomatitis virus (VSV) but also against Semliki Forest virus (SFV), a togavirus with a single-stranded RNA genome of positive polarity. In MxA-transfected cells, viral yields were reduced up to 1,700-fold, and the degree of inhibition correlated well with the expression level of MxA. Furthermore, expression of MxA prevented the accumulation of 49S RNA and 26S RNA, indicating that SFV was inhibited early in its replication cycle. Very similar results were obtained with MxA-transfected cells of the human monocytic cell line U937. The results demonstrate that the antiviral spectrum of MxA is not restricted to negative-strand RNA viruses but also includes SFV, which contains an RNA genome of positive polarity. To test whether MxA protein exerts its inhibitory activity against SFV in the absence of viral structural proteins, we took advantage of a recombinant vector based on the SFV replicon. The vector contains only the coding sequence for the viral nonstructural proteins and the bacterial LacZ gene, which was cloned in place of the viral structural genes. Upon transfection of vector-derived recombinant RNA, expression of the beta-galactosidase reporter gene was strongly reduced in the presence of MxA. This finding indicates that viral components other than the structural proteins are the target of MxA action.

Adrenomedullary function in depressed patients.

In this paper from the Collaborative Depression Study (CDS)--Biological, a set of data analyses are presented which indicate that depressed states and perhaps depressed mood are associated with a greater activation of the adrenomedullary system than the sympathetic nervous system [as measured by norepinephrine (NE) and normetanephrine excretion]. For the most part this finding of predominant activation of the adrenomedullary system is seen in unipolar and not bipolar patients.

Serotonin function and the mechanism of antidepressant action. Reversal of antidepressant-induced remission by rapid depletion of plasma tryptophan.

Brain serotonin content is dependent on plasma levels of the essential amino acid tryptophan. We investigated the behavioral effects of rapid tryptophan depletion in patients in antidepressant-induced remission. Twenty-one patients who were depressed by DSM-III-R criteria received a 24-hour, 160-mg/d, low-tryptophan diet followed the next morning by a 16-amino acid drink, in a double-blind, placebo-controlled (acute tryptophan depletion and control testing), crossover fashion. Total and free tryptophan levels decreased 87% and 91%, respectively, during acute tryptophan depletion. Fourteen of the 21 remitted depressed patients receiving antidepressants experienced a depressive relapse after the tryptophan-free amino acid drink, with gradual (24 to 48 hours) return to the remitted state on return to regular food intake. Control testing produced no significant behavioral effects. Free plasma tryptophan level was negatively correlated with depression score during acute tryptophan depletion. The therapeutic effects of some antidepressant drugs may be dependent on serotonin availability.

Neuroendocrine and behavioral effects of dietary tryptophan restriction in healthy subjects.

The neuroendocrine and behavioral effects of gradual dietary tryptophan (TRP) depletion, utilizing two magnitudes of a 10-day TRP-restriction diet (700 mg/day and 200 mg/day), were studied in 22 healthy subjects. The prolactin response to a 7 gm L-TRP infusion was measured prior to and on day 10 of the diet. Both diets significantly reduced fasting total plasma TRP by 15 to 20%, but only the 200 mg/day TRP diet led to an enhancement of the prolactin response to intravenous L-TRP. Female subjects demonstrated a more robust increase in plasma prolactin following L-TRP infusion pre-diet and exhibited a larger decrease in plasma TRP following dietary TRP restriction compared to males. There were no significant behavioral effects of either diet. Gradual dietary TRP depletion leads to an enhancement of the prolactin response to L-TRP infusion, suggestive of postsynaptic serotonin receptor supersensitivity.

Biochemistry and suicidal behavior in depressed patients.

The present study was undertaken in order to further explore the relationship between monoamine levels and hypothalamic-pituitary-adrenocortical (HYPAC) functioning and suicidal behavior in depressed patients. One hundred and thirty-two depressed inpatients participated in the NIMH Collaborative Study on the Psychobiology of Depression. Similar to previous reports, our suicide attempters were younger, more likely to be bipolar, had an earlier age at onset, and displayed more psychotic features. No correlation between cortisol hypersecretion or Dexamethasone Suppression Test (DST) nonsuppression and suicide attempts were found. Only the pre-DST evening plasma cortisol distinguished the groups, being lower in the attempter group. We were unable to confirm the previously reported correlation between cerebrospinal fluid (CSF) 5-hydroxyindoleacetic acid (5-HIAA) and suicide attempts. Of the monoamines examined, only urinary and plasma 3-methoxy-4-hydroxphenylglycol (MHPG) differed between suicide attempters and nonattempters, showing lower levels in the attempter group. There was a trend for CSF MHPG in the same direction. This latter reduction was restricted to the bipolar group.

Abrupt discontinuation of tricyclic antidepressant drugs: evidence for noradrenergic hyperactivity.

The effect of abrupt discontinuation of amitriptyline, desipramine, or imipramine) on norepinephrine turnover and specific symptoms in seven depressed patients was examined. Turnover, as determined by plasma and urinary 3 methoxy-4-hydroxy-phenylethylene glycol (MHPG), was increased to a peak during the second week following discontinuation. There were no changes in blood pressure or heart rate. Two of the seven patients experienced clear increases in anxiety. The implications for the role of noradrenergic function is discussed.

The occurrence of free vs. conjugated MHPG in non-human and human primate brain.

It has been found that in the brain of the non-human primate (Macaca arctoides) MHPG occurs principally if not exclusively in the free rather than the conjugated form. It has also been found that in all areas of human brain examined MHPG is present in the free form rather than the conjugated form. The quantity of free MHPG present in various structures of human brain ranged from 46.4 to 69.8 microng/gm of tissue.