Inhibition of serotonergic raphe neurons is mediated by somatodendritic 5-HT1A autoreceptors, which may be increased in depressed patients. We report an association of the C(-1019)G 5-HT1A promoter polymorphism with major depression and suicide in separate cohorts. In depressed patients, the homozygous G(-1019) allele was enriched twofold versus controls (p = 0.0017 and 0.0006 for G/G genotype and G allele distribution, respectively), and in completed suicide cases the G(-1019) allele was enriched fourfold (p = 0.002 and 0.00008 for G/G genotype and G allele distribution, respectively). The C(-1019) allele was part of a 26 bp imperfect palindrome that bound transcription factors nuclear NUDR [nuclear deformed epidermal autoregulatory factor (DEAF-1)]/suppressin and Hairy/Enhancer-of-split-5 (Drosophila) (Hes5) to repress 5-HT1A or heterologous promoters, whereas the G(-1019) allele abolished repression by NUDR, but only partially impaired Hes5-mediated repression. Recombinant NUDR bound specifically to the 26 bp palindrome, and endogenous NUDR was present in the major protein-DNA complex from raphe nuclear extracts. Stable expression of NUDR in raphe cells reduced levels of endogenous 5-HT1A protein and binding. NUDR protein was colocalized with 5-HT1A receptors in serotonergic raphe cells, hippocampal and cortical neurons, and adult brain regions including raphe nuclei, indicating a role in regulating 5-HT1A autoreceptor expression. Our data indicate that NUDR is a repressor of the 5-HT1A receptor in raphe cells the function of which is abrogated by a promoter polymorphism. We suggest a novel transcriptional model in which the G(-1019) allele derepresses 5-HT1A autoreceptor expression to reduce serotonergic neurotransmission, predisposing to depression and suicide.

The serotonin system is implicated in major depression and suicide and is negatively regulated by somatodendritic 5-HT1A autoreceptors. Desensitization of 5-HT1A autoreceptors is implicated in the 2- to 3-week latency for antidepressant treatments. Alterations in 5-HT1A receptor levels are reported in depression and suicide, and gene knockout of the 5-HT1A receptor results in an anxiety phenotype, suggesting that abnormal transcriptional regulation of this receptor gene may underlie these disorders. The 5-HT1A receptor gene is negatively regulated in neurons by repressors including REST/NRSF, Freud-1, NUDR/Deaf-1, and Hes5. The association with major depression, suicide, and panic disorder of a new functional 5-HT1A polymorphism at C(-1019)G that selectively blocks repression of the 5-HT1A autoreceptor by NUDR further suggests a causative role for altered regulation of this receptor in predisposition to mental illness. The authors review evidence that altered transcription of the 5-HT1A receptor can affect the serotonin system and limbic and cortical areas, leading to predisposition to depression.

Altered regulation of 5-HT1A receptors is implicated in mood disorders such as anxiety and major depression. To provide insight into its transcriptional regulation, we previously identified a novel DNA element [14 bp 5'-repressor element (FRE)] of the 5-HT1A receptor gene that mediates repression in neuronal and non-neuronal cells (Ou et al., 2000). We have now cloned a novel DNA binding protein [five' repressor element under dual repression binding protein-1 (Freud-1)] that binds to FRE to mediate repression of the 5-HT1A receptor or heterologous promoters. Freud-1 is evolutionarily conserved and contains two DM-14 basic repeats, a predicted helix-loop-helix DNA binding domain, and a protein kinase C conserved region 2 (C2)/calcium-dependent lipid binding (CalB) calcium/phospholipid binding domain. An intact CalB domain was required for Freud-1-mediated repression. In serotonergic raphe cells, overexpression of Freud-1 repressed the 5-HT1A promoter and decreased 5-HT1A receptor protein levels, whereas transfection of antisense to Freud-1 derepressed the 5-HT1A gene and increased 5-HT1A receptor protein expression. Calcium-dependent signaling blocked Freud-1-FRE binding and derepressed the 5-HT1A promoter. Treatment with inhibitors of calmodulin or CAM-dependent protein kinase reversed calcium-mediated inhibition of Freud-1. Freud-1 RNA and protein were present in raphe nuclei, hippocampus, cortex, and hypothalamus, and Freud-1 protein was colocalized with 5-HT1A receptors, suggesting its importance in regulating 5-HT1A receptors in vivo. Thus, Freud-1 represents a novel calcium-regulated repressor that negatively regulates basal 5-HT1A receptor expression in neurons and may play a role in the altered regulation of 5-HT1A receptors associated with anxiety or major depression.

The serotonergic neurons of the raphe nuclei are the primary site of serotonin synthesis in the brain. They send projections to a wide variety of brain regions, including the hippocampus, cortex, limbic system, and hypothalamus (1). Activation of postsynaptic receptors in the above regions is associated with serotonergic regulation of memory, motivation, emotion, neuroendocrine stress response, etc. (2-4). The activity of serotonergic neurons of the raphe nuclei is regulated in part by presynaptic autoreceptors. The 5-HT1A autoreceptor is located at the cell body and dendrites of raphe serotonergic neurons (5, 6) and mediates negative feedback inhibition of the firing rate through recurrent activation of potassium channels via pertussis toxin-sensitive G proteins (7) to decrease serotonin release. Thus the 5-HT1A receptor plays a major role in controlling serotonergic outflow to the wide variety of brain regions that are innervated by the raphe nuclei.Abnormal regulation of 5-HT1A receptor expression is implicated in depression and anxiety disorders. 5-HT1A receptor knockout mice display increased anxiety-related behaviors (8 -10), suggesting that a loss of the 5-HT1A autoreceptors is correlated with symptoms of anxiety (3). On the other hand, 5-HT1A receptor levels are increased in the midbrain of suicide victims with major depression compared with nondepressed suicides (11). Down-regulation of the 5-HT1A autoreceptor by antidepressants (12, 13) disinhibits action potential firing of the raphe neuron, thereby enhancing serotonergic neurotransmission (14 -17). The prolonged (2-3 week) time course required for antidepressant action suggests an alteration in transcriptional activity of the 5-HT1A receptor.To investigate the mechanisms that regulate cell-specific and basal regulation of the 5-HT1A receptor, we have identified the transcriptional start site and examined the regulation of the transcriptional activity of a 2.719-kb 1 fragment of the rat 5-HT1A receptor gene in several cell lines, including 5-HT1A receptor-positive RN46A raphe and SN48 septal cells (18 -20) and receptor-negative L6 myoblast and C6 glioblastoma cells (21). We identified a region of the rat 5-HT1A receptor gene located upstream of an ubiquitously active promoter region that reduces transcriptional activity. In the present study, we have identified a 14-bp element in the 5Ј-flanking region of the 5-HT1A gene that mediates transcriptional repression in raphe cells, but is dispensable in receptor-negative cells where an adjacent 12-bp element maintains repression of the gene. In contrast to the single repressor-DNA complex present in 5-HT1A receptor-expressing cells that may modulate basal levels of receptor expression, the presence of two protein-DNA complexes in receptor-negative cell lines provides a dual mechanism to repress 5-HT1A receptor expression.

Antidepressants, such as serotonin or noradrenaline reuptake inhibitors (e.g. fluoxetine, nefadozone) or 5-HT1A agonists (flibanserin), desensitize the 5-HT1A autoreceptor, which may contribute to their clinical efficacy. The 5-HT1A receptor gene is repressed by NUDR/DEAF-1 in raphe cells at the C-, but not at the G-allele of the C(-1019)G polymorphism that is associated with major depression and suicide. Depressed patients (n=118) were treated with antidepressants including fluoxetine or nefadozone combined with pindolol or flibanserin alone. The severity of depression was assesssed using the Hamilton Rating Scale for Depression. Although patients had similar severity initially, those with the homozygous G(-1019) genotype responded significantly less to flibanserin (p=0.039) and in pooled antidepressant treatment groups (p=0.0497) and were approximately twice as likely to be non-responders as those with the C(-1019)C genotype. These results implicate the C(-1019)G 5-HT1A gene polymorphism as a potential marker for antidepressant response, suggesting a role for repression of the 5-HT1A gene.

The serotonin-1A (5-HT 1A ) receptor is the primary somatodendritic autoreceptor that inhibits the activity of serotonergic raphe neurons and is also expressed in nonserotonergic cortical and limbic neurons. Alterations in 5-HT 1A receptor levels are implicated in mood disorders, and a functional C(-1019)G 5-HT 1A promoter polymorphism has been associated with depression, suicide, and panic disorder. We examined the cell-specific activity of identified transcription factors, human nuclear deformed epidermal autoregulatory factor-1 (DEAF-1)-related (

Regulation of serotonin (5-HT)1A receptor expression in brain is implicated in mood disorders such as depression and anxiety. Transcriptional activity of the human 5-HT1A receptor gene was strongly repressed by a negative regulatory region containing a consensus repressor element-1 (RE-1) and two copies of the dual repressor element (DRE) identified in the rat 5-HT1A receptor gene. REST/NRSF, a silencer of neuronal genes, bound the 5-HT1A RE-1 and repressed the 5-HT1A promoter. Inactivation of RE-1 completely abolished RESTmediated repression, but resulted in only partial (15-50%) de-repression of basal 5-HT1A promoter activity. The human 5-HT1A DRE sequences bound specifically to the novel repressor Freud-1 (5¢repressor element under dual repression binding protein-1) and conferred repressor activity at 5-HT1A or SV40 promoters. In 5-HT1A-negative cells [L6, human embryonic kidney (HEK) 293], the histone deacetylase (HDAC) inhibitor trichostatin A (TSA) abolished repression mediated by both RE-1/REST and DRE/Freud-1, and induced almost complete de-repression of the 5-HT1A gene. By contrast, in 5-HT1A-expressing neuronal cells (RN46A, SN-48) TSA blocked RE-1/REST repression, but did not affect DRE/Freud-1-mediated repression. Thus in contrast to REST, Freud-1 mediates HDAC-independent repression of the 5-HT1A receptor promoter in neuronal 5-HT1A-positive cells, suggesting that HDAC recruitment might influence neuron-specific gene expression by further silencing expression in non-neuronal tissue.

The 5-HT1A receptor is implicated in depression and anxiety. This receptor couples to G i proteins to inhibit adenylyl cyclase (AC) activity but can stimulate AC in tissues (e.g. hippocampus) that express ACII. The role of ACII in receptor-mediated stimulation of cAMP formation was examined in HEK-293 cells transfected with the 5-HT1A receptor, which mediated inhibition of basal and G s -induced cAMP formation in the absence of ACII. In cells cotransfected with 5-HT1A receptor and ACII plasmids, 5-HT1A agonists induced a 1.5-fold increase in cAMP level. Cotransfection of 5-HT1A receptor, ACII, and G␣ i2 , but not G␣ i1 , G␣ i3 , or G␣ o , resulted in an agonist-independent 6-fold increase in the basal cAMP level, suggesting that G i2 preferentially coupled the receptor to ACII. The 5-HT1B receptor also constitutively activated ACII. Constitutive activity of the 5-HT1A receptor was blocked by pertussis toxin and the G␤␥ antagonist, ␤CT, suggesting an important role for G␤␥-mediated activation of ACII. The Thr-149 3 Ala mutation in the second intracellular domain of the 5-HT1A receptor disrupted G␤␥-selective activation of ACII. Spontaneous 5-HT1A receptor activity was partially attenuated by 5-HT1A receptor partial agonists with anxiolytic activity (e.g. buspirone and flesinoxan) but was not altered by full agonists or antagonists. Thus, anxiolytic activity may involve inhibition of spontaneous 5-HT1A receptor activity.The 5-HT1A receptor functions as an inhibitory somatodendritic autoreceptor on serotonergic neurons of the raphe nuclei and as a post-synaptic receptor in a variety of serotonergic targets (1-4). A number of partial agonists of the 5-HT1A receptor have been shown to synergize with serotonin reuptake blockers in treatment of depression (1, 4 -7). The antidepressant action of these compounds appears to involve both agonistmediated down-regulation of presynaptic 5-HT1A receptors and activation of the post-synaptic receptors (that are resistant to desensitization) to result in enhanced serotonergic neurotransmission. By contrast, the anxiolytic actions of 5-HT1A partial agonists may involve inhibition of serotonergic activity by enhancing autoreceptor activation and reducing post-synaptic receptor action. Homozygous null 5-HT1A receptor mutant mice display enhanced serotonin release and anxiety-associated behaviors (8 -10), consistent with the idea that hyperactivity of the serotonin system by reduction in 5-HT1A autoreceptor activity results in anxiety disorders.The 5-HT1A receptor mediates inhibitory signaling by coupling to pertussis toxin-sensitive (PTX-sensitive) 1 G proteins (G i and G o ) to mediate a variety of intracellular changes including inhibition of cAMP accumulation, activation of potassium channels, and inactivation of calcium channels (2, 3). However, in hippocampal membrane preparations, 5-HT1A receptor activation stimulates adenylyl cyclase activity (11-13), an action that can be blocked by the specific antagonist WAY100,135 (11). Activation of the G i -coupled 5-HT1A or GABA-B rece...