The catechol-O-methyltransferase (COMT) Val158Met genotype modulates working memory-related dorsolateral prefrontal response and performance in bipolar disorder.

OBJECTIVES: Cognitive dysfunction affects a substantial proportion of patients with bipolar disorder (BD), and genetic-imaging paradigms may aid in the elucidation of mechanisms implicated in this symptomatic domain. The Val allele of the functional Val158Met polymorphism of the catechol-O-methyltransferase (COMT) gene is associated with reduced prefrontal cortex dopamine and exaggerated working memory-related prefrontal activity. This functional magnetic resonance imaging (fMRI) study investigated for the first time whether the COMT Val158Met genotype modulates prefrontal activity during spatial working memory in BD. METHODS: Sixty-four outpatients with BD in full or partial remission were stratified according to COMT Val158Met genotype (ValVal [n=13], ValMet [n=34], and MetMet [n=17]). The patients completed a spatial n-back working memory task during fMRI and the Cambridge Neuropsychological Test Automated Battery (CANTAB) Spatial Working Memory test outside the scanner. RESULTS: During high working memory load (2-back vs 1-back), Val homozygotes displayed decreased activity relative to ValMet individuals, with Met homozygotes displaying intermediate levels of activity in the right dorsolateral prefrontal cortex (dlPFC) (P=.016). Exploratory whole-brain analysis revealed a bilateral decrease in working memory-related dlPFC activity in the ValVal group vs the ValMet group which was not associated with differences in working memory performance during fMRI. Outside the MRI scanner, Val carriers performed worse in the CANTAB Spatial Working Memory task than Met homozygotes (P≤.006), with deficits being most pronounced in Val homozygotes. CONCLUSIONS: The association between Val allelic load, dlPFC activity and WM impairment points to a putative role of aberrant PFC dopamine tonus in the cognitive impairments in BD.

Point mutation increases a form of the NK1 receptor with high affinity for neurokinin A and B and septide.

1. The binding modalities of substance P and neurokinin A on the wild type and Gly166 to-Cys mutant NK1 receptors expressed on CHO cells were investigated in homologous and heterologous binding experiments using both radiolabelled substance P and neurokinin A. 2. On the wild type NK1 receptor NKA displaces radiolabelled substance P with very low apparent affinity, despite its high-affinity binding constant (determined in homologous binding experiments). The Gly166 to-Cys substitution in the NK1 tachykinin receptor greatly enhances the apparent affinity of neurokinin A in competition for radiolabelled substance P, but it does not change the binding constant of neurokinin A. The mutation, thereby, eliminates the discrepancy between the low apparent affinity and the high binding constant of neurokinin A. 3. On the wild type receptor the binding capacity of neurokinin A is significantly smaller than that of substance P. In contrast, the two tachykinins bind to approximately the same number of sites on the mutant receptor. 4. Simultaneous mass action law analysis of binding data in which multiple radioligands were employed in parallel demonstrated that a one-site model was unable to accommodate all the experimental data, whereas a two-site model provided a dramatically better description. 5. These two receptor-sites display equally high affinity for substance P, while neurokinin A strongly discriminates between a high and a low affinity component. The binding affinities of neurokinin A are not affected by the mutation, which instead specifically alters the distribution between receptor sites in favour of a high affinity neurokinin A binding form. 6. The low apparent affinity and binding capacity of neurokinin A on the wild type receptor results from neurokinin A binding with high affinity only to a fraction of the sites labelled by substance P. The mutation increases the proportion of this site, and consequently enhances the apparent affinity and binding capacity of neurokinin A. 7. The binding modalities of septide-like ligands (i.e. neurokinin B, SP(6-11), SP-methyl ester) are affected similarly to neurokinin A and are better resolved into two sites. The mutation leaves the affinity of these ligands for the two receptor forms unchanged, but increases the fraction of high-affinity sites. On the other hand, the binding of non-peptide and peptide antagonists (SR140.333 and FK888) behaved similarly to substance P with a single high affinity site that is unaffected by the mutation. 8. These findings may suggest that the NK1 receptor exists in two different forms with similar affinity for substance P and NK1 antagonists, but with a high and a low affinity for neurokinin A and septide-like ligands. Hence, the Gly166 in the NK1 receptor would seem to control the distribution between a pan-reactive form and a substance P-selective form of the receptor.

Gly166 in the NK1 receptor regulates tachykinin selectivity and receptor conformation.

We have studied the pharmacological properties of genetically engineered human NK1 tachykinin receptors in which residues at the extracellular surface of the fourth transmembranal domain were substituted with the corresponding amino acids from the NK2 receptor. We show that substitution of G166C:Y167F in the human NK1 receptor induces high affinity binding of a group of tachykinin ligands, known as 'septides' (i.e. neurokinin A, neurokinin B, [pGlu6,Pro9]-substance P6-11 and substance P-methylester). In contrast, binding of substance P and non-peptide antagonists is unaffected by these mutations. This effect parallels that found on the rat receptor and is therefore species specific. Second, we demonstrate that mutation of Gly166 to Cys alone is both necessary and sufficient to create this pan-reactive tachykinin receptor, whereas replacement of Tyr167 by Phe has no detectable effect on the pharmacological properties of the receptor. Furthermore, analysis of the effect of N-ethylmaleimide and dithiothreitol on binding of radiolabelled substance P documents differences in the mode in which this ligand interacts with wild-type and mutant receptors and supports the existence of a mutational induced change in the conformational status of the NK1 receptor.

A mutation changes ligand selectivity and transmembrane signaling preference of the neurokinin-1 receptor.

We studied the biochemical properties of a genetically engineered neurokinin-1 receptor (NK1R) in which two residues lying on the extracellular edge of the fourth transmembrane domain were replaced by equivalently located elements of the neurokinin-2 receptor (G166C, Y167F NK1R mutant). The mutation produced two effects. The first is enhancement of the apparent binding affinity for heterologous tachykinins (substance K and neurokinin B) and for N- or C-terminal modified analogues of substance P, but not for substance P itself, its full-length analogues, and several peptide and nonpeptide antagonists. Only two antagonists, as exceptions, were found to exhibit a diminished affinity for the mutant receptor. The second effect is a shift in NK1R preference for distinct G protein-mediated signaling pathways. NK1R-mediated phosphoinositide hydrolysis was enhanced both in transiently and permanently transfected cells, while stimulation of cAMP accumulation did not change in transient expression experiments and was reduced in permanently expressing cells. The effect of the mutation on ligand affinity was not related to any obvious structural commonality, nor to the selectivity for different neurokinin receptors or the agonistic/antagonistic nature of the ligand. However, all ligands responding to the mutation appear to share the ability to induce phosphoinositide signaling more efficiently than cAMP responses when binding to NK1R. We suggest that the mutation shifts the internal equilibria of different functional forms of NK1R. A theoretical analysis according to a multistate allosteric model suggests that the link between binding and biological changes can result from altered stability constants of substates in the conformational space of the receptor.

Identifying a putative common binding site shared by substance P receptor and an anti-substance P monoclonal antibody.

Substance P G-protein coupled receptor and the antigen recognition site of a monoclonal antibody raised against substance P share a stretch of five contiguous identical amino acids. This observation prompted us to build an atomic model of both the receptor and the antibody and to analyse their common features. In particular, we report here that a pocket of similar size and composition is present in both proteins, strongly suggesting a similarity in the mode of binding of both macromolecules to substance P. From the analysis of our models, the available data on the mode of binding of the antibody to substance P and recent data on substance P receptor mutants, we concluded that the pocket is very likely to be involved in binding of the C-terminal 'message sequence' of the tachykinin. This allowed us to suggest specific site-directed mutants of the receptor which should shed some light on the mechanism of peptide recognition by G-protein coupled receptors.

Apoptosis in cerebellar granule cells is blocked by high KCl, forskolin, and IGF-1 through distinct mechanisms of action: the involvement of intracellular calcium and RNA synthesis.

Cerebellar granule cells deprived of depolarizing concentration of extracellular potassium, [K+]o, undergo apoptosis. We here report that this apoptotic process is associated with an immediate and permanent decrease in the levels of free intracellular calcium, [Ca2+]i. Although forskolin and IGF-1 are both able to prevent apoptosis, only forskolin is able to counteract the instantaneous decrease of [Ca2+]i. However, the early effect of forskolin on [Ca2+]i is lost after longer incubation in low [K+]o. The calcium antagonist nifedipine is able to inhibit the survival effect of high [K+]o, while not affecting forskolin and IGF-1 promoted survival, as assessed by viability and genomic DNA analysis. Accordingly, the L-type calcium channels agonist Bay K8644 significantly enhanced the survival of low KCl treated neurons. To temporally characterize the signal transduction events and the essential transcriptional step in cerebellar granule cells apoptosis, we determined the time course of the rescue capacity of high [K+]o, forskolin, IGF-1, and actinomycin D. Addition of high KCl, forskolin, or IGF-1 6 hr after the initial KCl deprivation saves 50% of cells. Remarkably, 50% of neurons loss the potential to be rescued by actinomycin D after only 1 hr in low [K+]o. Finally, we show that the survival promoting activities of high [K+]o, forskolin, and IGF-1 do not require RNA synthesis. We conclude that [Ca2+]i is involved in the survival promoting activity exerted by high [K+]o but not in those of forskolin and IGF-1, and that all three agents, although rescuing neurons from apoptosis through distinct mechanisms of action, do not necessitate RNA transcription.

Intracellular single chain Fv antibody inhibits Ras activity in T-cell antigen receptor stimulated Jurkat cells.

A mammalian expression vector directing the synthesis of a cytoplasmic single chain Fv version of the Y13-259 anti-Ras antibody was constructed and co-transfected into the human lymphoid cell line Jurkat together with a reporter construct containing the bacterial gene for chloramphenicol acetyl transferase under the transcriptional control of several copies of the binding site for the transcription factor NF-AT. The Ras specific antibody interferes with NF-AT activation upon direct activation of the T-cell antigen receptor, whereas activation by direct protein kinase C stimulation is less sensitive to the anti-Ras antibody. Furthermore, the observed inhibition is dependent on the ratio of antibody to reporter plasmid utilized in the transfection experiments.

Identification of an epitope in the substance P receptor important for recognition of the common carboxyl-terminal tachykinin sequence.

The substance P receptor and the anti-substance P antibody NC1 share the ability to bind to the COOH terminus of substance P. Sequence analysis identified a direct noninterrupted homology of 5 residues in the two molecules. Replacement of Gly166 and Tyr167 in this epitope of the substance P receptor by the corresponding substance K receptor amino acids (Cys and Phe) increases the affinity toward substance P 2-fold and toward substance K and neurokinin B 11- and 21-fold, respectively. A significantly larger effect of the mutation is observed for the hexapeptides of substance P and substance K which show a mutation-induced increase in binding energy of more than 2 kcal/mol. Hence, the NH2 terminus of substance P and, to a lesser extent, of substance K masks the effect of the mutation. I conclude that the epitope is important for recognition of the common COOH terminus of the tachykinins and for preservation of selectivity. The data furthermore suggest that formation of the peptide-receptor complex occurs through a composite set of interactions which are not adequately described by the two-site/no cooperativity "address-message" model.

A recombinant cell line expressing a form of the Y13-259 anti-p21ras antibody which binds protein A and may be produced as ascites.

We have recently reported the molecular cloning of the immunoglobulin genes encoding the variable regions of the rat anti-p21ras antibody, Y13-259. These genes were reassembled into expression vectors supplying DNA sequences encoding human gamma 1 and kappa constant domains, as well as the leader sequence for antibody secretion, thus yielding Hu-Y13-259, a secretory anti-p21ras antibody containing human constant regions. We now report the creation of a recombinant cell line, NS0/Hu-Y13-259/B6, secreting high levels of the Hu-Y13-259 Ig. The antigen specificity of this recombinant antibody was demonstrated to be identical to that of the parental Y13-259, i.e. the amino acid sequence 60-76 of the p21ras protein. Unlike the parental cell line, the recombinant cells could be grown as ascites in mice, allowing the production of large quantities of the protein A-binding Hu-Y13-259 antibody.

Neuroantibodies: molecular cloning of a monoclonal antibody against substance P for expression in the central nervous system.

We present a strategy to study functional and/or developmental processes occurring in the nervous system, as well as in other systems, of mice. This strategy is based on the local expression of specific monoclonal antibodies (mAbs) by cells of the nervous system. As an application of this strategy, we report the cloning of the anti-substance P rat mAb NC1/34HL. Functional substance P-binding antibodies were reconstituted from the cloned variable domains by using vectors for expression in myeloma cells. With these and other vectors a general system for the cloning and expression of mAbs under a series of promoters (of the rat VGF8a gene, the neurofilament light-chain gene, and the methallothionein gene) has been created. The activity of these plasmids was confirmed by expressing the recombinant NC1/34HL mAb in GH3 pituitary cells, PC12 pheochromocytoma cells, and COS cells. DNA from the described constructs can be used to target the expression of the NC1/34HL mAb to the central nervous system of transgenic mice. This procedure will allow us to perturb substance P activity in a controlled way in order to dissect its multiple roles.

Intracellular immunization. Cloning and intracellular expression of a monoclonal antibody to the p21ras protein.

Following the demonstration that intracellular expression of antibodies ('intracellular immunization') may be utilized to engineer new traits in mammalian cells, we undertook experiments to perturb the function of p21ras proteins, by engineering the intracellular expression of the anti-p21ras antibody Y13-259. The variable regions of this antibody have been cloned and, after verifying their antigen binding activity, expressed in general purpose vectors for the intracellular expression of antibodies. The results confirmed that the cloned antibody has been efficiently expressed both in the secretory and the intracellular forms. Thus, intracellular immunization of mammalian cells against p21ras, or any other antigen for which a monoclonal antibody is available, can now be performed.