The mental retardation gene CC2D1A/Freud-1 encodes a long isoform that binds conserved DNA elements to repress gene transcription

CC2D1A causes ciliopathy, intellectual disability, heterotaxy, renal dysplasia, and abnormal CSF flow

Intellectual and developmental disabilities result from abnormal nervous system development. Over a 1,000 genes have been associated with intellectual and developmental disabilities, driving continued efforts toward dissecting variant functionality to enhance our understanding of the disease mechanism. This report identified two novel variants in CC2D1A in a cohort of four patients from two unrelated families. We used multiple model systems for functional analysis, including Xenopus, Drosophila, and patient-derived fibroblasts. Our experiments revealed that cc2d1a is expressed explicitly in a spectrum of ciliated tissues, including the left-right organizer, epidermis, pronephric duct, nephrostomes, and ventricular zone of the brain. In line with this expression pattern, loss of cc2d1a led to cardiac heterotaxy, cystic kidneys, and abnormal CSF circulation via defective ciliogenesis. Interestingly, when we analyzed brain development, mutant tadpoles showed abnormal CSF circulation only in the midbrain region, suggesting abnormal local CSF flow. Furthermore, our analysis of the patient-derived fibroblasts confirmed defective ciliogenesis, further supporting our observations. In summary, we revealed novel insight into the role of CC2D1A by establishing its new critical role in ciliogenesis and CSF circulation.

CaMKIV-Mediated Phosphorylation Inactivates Freud-1/CC2D1A Repression for Calcium-Dependent 5-HT1A Receptor Gene Induction

Calcium calmodulin-dependent protein kinase (CaMK) mediates calcium-induced neural gene activation. CaMK also inhibits the non-syndromic intellectual disability gene, Freud-1/CC2D1A, a transcriptional repressor of human serotonin-1A (5-HT1A) and dopamine-D2 receptor genes. The altered expression of these Freud-1-regulated genes is implicated in mental illnesses such as major depression and schizophrenia. We hypothesized that Freud-1 is blocked by CaMK-induced phosphorylation. The incubation of purified Freud-1 with either CaMKIIα or CaMKIV increased Freud-1 phosphorylation that was partly prevented in Freud-1-Ser644Ala and Freud-1-Thr780Ala CaMK site mutants. In human SK-N-SH neuroblastoma cells, active CaMKIV induced the serine and threonine phosphorylation of Freud-1, and specifically increased Freud-1-Thr780 phosphorylation in transfected HEK-293 cells. The activation of purified CaMKIIα or CaMKIV reduced Freud-1 binding to its DNA element on the 5-HT1A and dopamine-D2 receptor genes. In SK-N-SH cells, active CaMKIV but not CaMKIIα blocked the Freud-1 repressor activity, while Freud-1 Ser644Ala, Thr780Ala or dual mutants were resistant to inhibition by activated CaMKIV or calcium mobilization. These results indicate that the Freud-1 repressor activity is blocked by CaMKIV-induced phosphorylation at Thr780, resulting in the up-regulation of the target genes, such as the 5-HT1A receptor gene. The CaMKIV-mediated inhibition of Freud-1 provides a novel de-repression mechanism to induce 5-HT1A receptor expression for the regulation of cognitive development, behavior and antidepressant response.

A nonsense CC2D1A variant is associated with congenital anomalies, motor delay, hypotonia, and slight deformities

Background

Autosomal recessive intellectual developmental disorder-3 is caused by homozygous or compound heterozygous mutations in the CC2D1A gene. The disorder is characterized by intellectual disability (ID) and autism spectrum disorder (ASD). To date, 39 patients from 17 families with CC2D1A -related disorders have been reported worldwide, in whom only six pathogenic or likely pathogenic loss-of-function variants and three variants of uncertain significance (VUS) in the CC2D1A gene have been identified in these patients.

Methods

We described a patient with ID from a non-consanguineous Chinese family and whole-exome sequencing (WES) was used to identify the causative gene.

Results

The patient presented with severe ID and ASD, speech impairment, motor delay, hypotonia, slight facial anomalies, and finger deformities. Threatened abortion and abnormal fetal movements occurred during pregnancy with the proband but not his older healthy sister. WES analysis identified a homozygous nonsense variant, c.736C > T (p.Gln246Ter), in the CC2D1A gene. In addition, six novel likely pathogenic CC2D1A variants were identified by a retrospective review of the in-house database.

Conclusions

This study expands the genetic and clinical spectra of CC2D1A-associated disorders, and may aid in increasing awareness of this rare condition. Our findings have provided new insights into the clinical heterogeneity of the disease and further phenotype-genotype correlation, which could help to offer scope for more accurate genetic testing and counseling to affected families.

Genetic Background Underlying 5-HT1A Receptor Functioning Affects the Response to Fluoxetine

The influence of genetic background on sensitivity to drugs represents a topical problem of personalized medicine. Here, we investigated the effect of chronic (20 mg/kg, 14 days, i.p.) antidepressant fluoxetine treatment on recombinant B6-M76C mice, differed from control B6-M76B mice by CBA-derived 102.73–110.56 Mbp fragment of chromosome 13 and characterized by altered sensitivity of 5-HT_1A receptors to chronic 8-OH-DPAT administration and higher 5-HT_1A receptor mRNA levels in the frontal cortex and hippocampus. Significant changes in the effects of fluoxetine treatment on behavior and brain 5-HT system in recombinant B6-M76C mice were revealed. In contrast to B6-M76B mice, in B6-M76C mice, fluoxetine produced pro-depressive effects, assessed in a forced swim test. Fluoxetine decreased 5-HT_1A receptor mRNA levels in the cortex and hippocampus, reduced 5-HT_1A receptor protein levels and increased receptor silencer Freud-1 protein levels in the hippocampus of B6-M76C mice. Fluoxetine increased mRNA levels of the gene encoding key enzyme for 5-HT synthesis in the brain, tryptophan hydroxylase-2, but decreased tryptophan hydroxylase-2 protein levels in the midbrain of B6-M76B mice. These changes were accompanied by increased expression of the 5-HT transporter gene. Fluoxetine reduced 5-HT and 5-HIAA levels in cortex, hippocampus and midbrain of B6-M76B and in cortex and midbrain of B6-M76C; mice. These data demonstrate that changes in genetic background may have a dramatic effect on sensitivity to classic antidepressants from the Selective Serotonin Reuptake Inhibitors family. Additionally, the results provide new evidence confirming our idea on the disrupted functioning of 5-HT_1A autoreceptors in the brains of B6-M76C mice, suggesting these mice as a model of antidepressant resistance.

Abrogated Freud-1/Cc2d1a Repression of 5-HT1A Autoreceptors Induces Fluoxetine-Resistant Anxiety/Depression-Like Behavior

Freud-1/Cc2d1a represses the gene transcription of serotonin-1A (5-HT1A) autoreceptors, which negatively regulate 5-HT tone. To test the role of Freud-1 in vivo, we generated mice with adulthood conditional knock-out of Freud-1 in 5-HT neurons (cF1ko). In cF1ko mice, 5-HT1A autoreceptor protein, binding and hypothermia response were increased, with reduced 5-HT content and neuronal activity in the dorsal raphe. The cF1ko mice displayed increased anxiety- and depression-like behavior that was resistant to chronic antidepressant (fluoxetine) treatment. Using conditional Freud-1/5-HT1A double knock-out (cF1/1A dko) to disrupt both Freud-1 and 5-HT1A genes in 5-HT neurons, no increase in anxiety- or depression-like behavior was seen upon knock-out of Freud-1 on the 5-HT1A autoreceptor-negative background; rather, a reduction in depression-like behavior emerged. These studies implicate transcriptional dysregulation of 5-HT1A autoreceptors by the repressor Freud-1 in anxiety and depression and provide a clinically relevant genetic model of antidepressant resistance. Targeting specific transcription factors, such as Freud-1, to restore transcriptional balance may augment response to antidepressant treatment.SIGNIFICANCE STATEMENT Altered regulation of the 5-HT1A autoreceptor has been implicated in human anxiety, major depression, suicide, and resistance to antidepressants. This study uniquely identifies a single transcription factor, Freud-1, as crucial for 5-HT1A autoreceptor expression in vivo Disruption of Freud-1 in serotonin neurons in mice links upregulation of 5-HT1A autoreceptors to anxiety/depression-like behavior and provides a new model of antidepressant resistance. Treatment strategies to reestablish transcriptional regulation of 5-HT1A autoreceptors could provide a more robust and sustained antidepressant response.

Recruitment by the Repressor Freud-1 of Histone Deacetylase-Brg1 Chromatin Remodeling Complexes to Strengthen HTR1A Gene Repression

Five-prime repressor element under dual repression binding protein-1 (Freud-1)/CC2D1A is genetically linked to intellectual disability and implicated in neuronal development. Freud-1 represses the serotonin-1A (5-HT1A) receptor gene HTR1A by histone deacetylase (HDAC)-dependent or HDAC-independent mechanisms in 5-HT1A-negative (e.g., HEK-293) or 5-HT1A-expressing cells (SK-N-SH), respectively. To identify the underlying mechanisms, Freud-1-associated proteins were affinity-purified from HEK-293 nuclear extracts and members of the Brg1/SMARCCA chromatin remodeling and Sin3A-HDAC corepressor complexes were identified. Pull-down assays using recombinant proteins showed that Freud-1 interacts directly with the Brg1 carboxyl-terminal domain; interaction with Brg1 required the carboxyl-terminal of Freud-1. Freud-1 complexes in HEK-293 and SK-N-SH cells differed, with low levels of BAF170/SMARCC2 and BAF57/SMARCE1 in HEK-293 cells and low-undetectable BAF155/SMARCC1, Sin3A, and HDAC1/2 in SK-N-SH cells. Similarly, by quantitative chromatin immunoprecipitation, Brg1-BAF170/57 and Sin3A-HDAC complexes were observed at the HTR1A promoter in HEK-293 cells, whereas in SK-N-SH cells, Sin3A-HDAC proteins were not detected. Quantifying 5-HT1A receptor mRNA levels in cells treated with siRNA to Freud-1, Brg1, or both RNAs addressed the functional role of the Freud-1-Brg1 complex. In HEK-293 cells, 5-HT1A receptor mRNA levels were increased only when both Freud-1 and Brg1 were depleted, but in SK-N-SH cells, depletion of either protein upregulated 5-HT1A receptor RNA. Thus, recruitment by Freud-1 of Brg1, BAF155, and Sin3A-HDAC complexes appears to strengthen repression of the HTR1A gene to prevent its expression inappropriate cell types, while recruitment of the Brg1-BAF170/57 complex is permissive to 5-HT1A receptor expression. Alterations in Freud-1-Brg1 interactions in mutants associated with intellectual disability could impair gene repression leading to altered neuronal development.

5-HT1A receptor gene silencers Freud-1 and Freud-2 are differently expressed in the brain of rats with genetically determined high level of fear-induced aggression or its absence

Serotonin 5-HT1A receptor is known to play a crucial role in the mechanisms of genetically defined aggression. In its turn, 5-HT1A receptor functional state is under control of multiple factors. Among others, transcriptional factors Freud-1 and Freud-2 are known to be involved in the repression of 5-HT1A receptor gene expression. However, implication of these factors in the regulation of behavior is unclear. Here, we investigated the expression of 5-HT1A receptor and silencers Freud-1 and Freud-2 in the brain of rats selectively bred for 85 generations for either high level of fear-induced aggression or its absence. It was shown that Freud-1 and Freud-2 levels were different in aggressive and nonaggressive animals. Freud-1 protein level was decreased in the hippocampus, whereas Freud-2 protein level was increased in the frontal cortex of highly aggressive rats. There no differences in 5-HT1A receptor gene expression were found in the brains of highly aggressive and nonaggressive rats. However, 5-HT1A receptor protein level was decreased in the midbrain and increased in the hippocampus of highly aggressive rats. These data showed the involvement of Freud-1 and Freud-2 in the regulation of genetically defined fear-induced aggression. However, these silencers do not affect transcription of the 5-HT1A receptor gene in the investigated rats. Our data indicate the implication of posttranscriptional rather than transcriptional regulation of 5-HT1A receptor functional state in the mechanisms of genetically determined aggressive behavior. On the other hand, the implication of other transcriptional regulators for 5-HT1A receptor gene in the mechanisms of genetically defined aggression could be suggested.

Phosphodiesterase activity is regulated by CC2D1A that is implicated in non-syndromic intellectual disability

Background

Cyclic adenosine 3^′,5^′-monophosphate (cAMP) is a key regulator of many cellular processes, including in the neuronal system, and its activity is tuned by Phosphodiesterase (PDE) activation. Further, the CC2D1A protein, consisting of N-Terminal containing four DM14 domains and C-terminal containing C2 domain, was shown to regulate the cAMP-PKA pathway. A human deletion mutation lacking the fourth DM14 and the adjacent C2 domain results in Non Syndromic Intellectual Disability (NSID) also referred to as Non Syndromic Mental Retardation (NSMR).

Findings

Here we demonstrate that in Mouse Embryonic Fibroblasts (MEF) CC2D1A co-localizes with PDE4D in the cytosol before cAMP stimulation and on the periphery after stimulation, and that the movement to the periphery requires the full-length CC2D1A. In CC2D1A mouse mutant cells, the absence of three of the four DM14 domains abolishes migration of the complex to the periphery and causes constitutive phosphorylation of PDE4D Serine 126 (S¹²⁶) via the cAMP-dependent protein kinase A (PKA) resulting in PDE4D hyperactivity. Suppressing PDE4D activity with Rolipram in turn restores the down-stream phosphorylation of the “cAMP response element-binding protein” (CREB) that is defective in mouse mutant cells.

Conclusion

Our findings suggest that CC2D1A is a novel regulator of PDE4D. CC2D1A interacts directly with PDE4D regulating its activity and thereby fine-tuning cAMP-dependent downstream signaling. Based on our in vitro evidence we propose a model which links CC2D1A structure and function to cAMP homeostasis thereby affecting CREB phosphorylation. We speculate that CC2D1A and/or PDE4D may be promising targets for therapeutic interventions in many disorders with impaired PDE4D function such as NSID.

Transcriptional regulation of the 5-HT1A receptor: implications for mental illness

The serotonin-1A (5-HT(1A)) receptor is an abundant post-synaptic 5-HT receptor (heteroreceptor) implicated in regulation of mood, emotion and stress responses and is the major somatodendritic autoreceptor that negatively regulates 5-HT neuronal activity. Based on animal models, an integrated model for opposing roles of pre- and post-synaptic 5-HT(1A) receptors in anxiety and depression phenotypes and response to antidepressants is proposed. Understanding differential transcriptional regulation of pre- versus post-synaptic 5-HT(1A) receptors could provide better tools for their selective regulation. This review examines the transcription factors that regulate brain region-specific basal and stress-induced expression of the 5-HT(1A) receptor gene (Htr1a). A functional polymorphism, rs6295 in the Htr1a promoter region, blocks the function of specific repressors Hes1, Hes5 and Deaf1, resulting in increased 5-HT(1A) autoreceptor expression in animal models and humans. Its association with altered 5-HT(1A) expression, depression, anxiety and antidepressant response are related to genotype frequency in different populations, sample homogeneity, disease outcome measures and severity. Preliminary evidence from gene × environment studies suggests the potential for synergistic interaction of stress-mediated repression of 5-HT(1A) heteroreceptors, and rs6295-induced upregulation of 5-HT(1A) autoreceptors. Targeted therapeutics to inhibit 5-HT(1A) autoreceptor expression and induce 5-HT(1A) heteroreceptor expression may ameliorate treatment of anxiety and major depression.

CC2D1A is a regulator of ESCRT-III CHMP4B

Endosomal sorting complexes required for transport (ESCRTs) regulate diverse processes ranging from receptor sorting at endosomes to distinct steps in cell division and budding of some enveloped viruses. Common to all processes is the membrane recruitment of ESCRT-III that leads to membrane fission. Here, we show that CC2D1A is a novel regulator of ESCRT-III CHMP4B function. We demonstrate that CHMP4B interacts directly with CC2D1A and CC2D1B with nanomolar affinity by forming a 1:1 complex. Deletion mapping revealed a minimal CC2D1A-CHMP4B binding construct, which includes a short linear sequence within the third DM14 domain of CC2D1A. The CC2D1A binding site on CHMP4B was mapped to the N-terminal helical hairpin. Based on a crystal structure of the CHMP4B helical hairpin, two surface patches were identified that interfere with CC2D1A interaction as determined by surface plasmon resonance. Introducing these mutations into a C-terminal truncation of CHMP4B that exerts a potent dominant negative effect on human immunodeficiency virus type 1 budding revealed that one of the mutants lost this effect completely. This suggests that the identified CC2D1A binding surface might be required for CHMP4B polymerization, which is consistent with the finding that CC2D1A binding to CHMP4B prevents CHMP4B polymerization in vitro. Thus, CC2D1A might act as a negative regulator of CHMP4B function.

17β-estradiol-induced regulation of the novel 5-HT1A-related transcription factors NUDR and Freud-1 in SH SY5Y cells

Nuclear deformed epidermal autoregulatory factor-1 (NUDR/Deaf-1) and five prime repressor element under dual repression (Freud-1) are novel transcriptional regulators of the 5-HT(1A) receptor, a receptor that has been implicated in the pathophysiology of various psychiatric illnesses. The antidepressant effect of 17β-Estradiol (17βE(2)) is purported to involve the downregulation of this receptor. We investigated the possible role of NUDR and Freud-1 in 17βE(2)-induced downregulation of the 5-HT(1A) receptor in the neuroblastoma cell line SH SY5Y. Cells were treated with 10 nM of 17βE(2) for 3 or 48 h, followed by a 24-h withdrawal period. Proteins were isolated and analyzed by western blotting. 17βE(2) treatment increased NUDR immunoreactivity while Freud-1 and the 5-HT(1A) receptor showed significant decreases. Upon withdrawal of 17βE(2), protein expression returned to control levels, except for NUDR, which remained significantly elevated in the 3-h treatment. Taken together, these data support a non-genomic downregulation of 5-HT(1A) receptor protein by 17βE(2), which does not involve NUDR and Freud-1. Rather, changes in both transcription factors seem to be compensatory/homeostatic responses to changes in 5-HT(1A) receptor induced by 17βE(2). These observations further highlight the importance of NUDR and Freud-1 in regulating 5-HT(1A) receptor expression.

Positive association of CC2D1A and CC2D2A gene haplotypes with mental retardation in a Han Chinese population

The CC2D1A and CC2D2A genes are involved in Ca(2+)-regulated signaling pathways and have recently been implicated in the etiology of mental retardation (MR). The aim of this study was to investigate whether CC2D1A and CC2D2A polymorphisms are associated with susceptibility to MR in a Han Chinese population using a family based association approach. The sample included 172 trios (parents and offspring), and all subjects were genotyped for several single-nucleotide polymorphisms covering CC2D1A and CC2D2A. Linkage disequilibrium (LD) analysis revealed that the rs6511901 and rs10410239 polymorphisms of CC2D1A were in strong LD (D'=0.865), and haplotype analysis showed evidence for over-transmission from parents to MR offspring (p=0.0009). The LD analysis also revealed that CC2D2A single-nucleotide polymorphisms rs10025837, rs13116304, and rs7661102 were in strong LD (D'=0.848), and haplotype analysis showed significant transmission disequilibrium (p=0.0004). The results suggest the involvement of CC2D1A and CC2D2A in MR in the Han Chinese population, and some specific haplotypes may be susceptible or protective.

Region-specific regulation of 5-HT1A receptor expression by Pet-1-dependent mechanisms in vivo

Serotonin (5-hydroxytryptamine, 5-HT) neurotransmission is negatively regulated by 5-HT1A autoreceptors on raphe neurons, and is implicated in mood disorders. Pet-1/FEV is an ETS transcription factor expressed exclusively in serotonergic neurons and is essential for serotonergic differentiation, although its regulation of 5-HT receptors has not yet been studied. Here, we show by electrophoretic mobility shift assay that recombinant human Pet-1/FEV binds directly to multiple Pet-1 elements of the human 5-HT1A receptor promoter to enhance its transcriptional activity. In luciferase reporter assays, mutational analysis indicated that while several sites contribute, the Pet-1 site at -1406 bp had the greatest effect on 5-HT1A promoter activity. To address the effect of Pet-1 on 5-HT1A receptor regulation in vivo, we compared the expression of 5-HT1A receptor RNA and protein in Pet-1 null and wild-type littermate mice. In the raphe nuclei of Pet-1-/- mice tryptophan hydroxylase 2 (TPH2) RNA, and 5-HT and TPH immunostaining were greatly reduced, indicating a deficit in 5-HT production. Raphe 5-HT1A RNA and protein levels were also reduced in Pet-1-deficient mice, consistent with an absence of Pet-1-mediated transcriptional enhancement of 5-HT1A autoreceptors in serotonergic neurons. Interestingly, 5-HT1A receptor expression was up-regulated in the hippocampus, but down-regulated in the striatum and cortex. These data indicate that, in addition to transcriptional regulation by Pet-1 in raphe neurons, 5-HT1A receptor expression is regulated indirectly by alterations in 5-HT neurotransmission in a region-specific manner that together may contribute to the aggressive/anxiety phenotype observed in Pet-1 null mice.

TBK1-associated protein in endolysosomes (TAPE) is an innate immune regulator modulating the TLR3 and TLR4 signaling pathways

The innate immune system elicits the first wave of immune responses against pathogen infection. Its operational modes are complex and have yet to be defined. Here, we report the identification of an innate immune regulator termed TAPE (TBK1-associated protein in endolysosomes), previously known as CC2D1A/Freud-1/Aki-1, which modulates the TLR3 and TLR4 pathways. We found that TAPE activated the TBK1, NF-κB, and ERK pathways leading to IFN-β and inflammatory cytokine induction. TAPE was shown to colocalize with endosomal marker Rab5 and lysosomal marker LAMP1 in mammalian cells, suggesting that TAPE resided in endolysosomes. Knockdown of TAPE selectively impaired the TLR3 and endocytic TLR4 pathways to IFN-β induction. Furthermore, TAPE interacted and synergized with Trif to activate IFN-β. TAPE knockdown failed to block Trif-mediated IFN-β induction, whereas Trif knockdown impaired the TLR3 and TAPE cooperation on IFN-β induction, suggesting that TAPE acts upstream of Trif. Together, our data demonstrate a central role for TAPE in linking TLR3 and TLR4 to innate immune defenses at an early step.

Freud-2/CC2D1B mediates dual repression of the serotonin-1A receptor gene

The serotonin-1A (5-HT1A) receptor functions as a pre-synaptic autoreceptor in serotonin neurons that regulates their activity, and is also widely expressed on non-serotonergic neurons as a post-synaptic heteroreceptor to mediate serotonin action. The 5-HT1A receptor gene is strongly repressed by a dual repressor element (DRE), which is recognized by two proteins: Freud-1/CC2D1A and another unknown protein. Here we identify mouse Freud-2/CC2D1B as the second repressor of the 5-HT1A-DRE. Freud-2 shares 50% amino acid identity with Freud-1, and contains conserved structural domains. Mouse Freud-2 bound specifically to the rat 5-HT1A-DRE adjacent to, and partially overlapping, the Freud-1 binding site. By supershift assay using nuclear extracts from L6 myoblasts, Freud-2-DRE complexes were distinguished from Freud-1-DRE complexes. Freud-2 mRNA and protein were detected throughout mouse brain and peripheral tissues. Freud-2 repressed 5-HT1A promoter-reporter constructs in a DRE-dependent manner in non-neuronal (L6) or 5-HT1A-expressing neuronal (NG108-15, RN46A) cell models. In NG108-15 cells, knockdown of Freud-2 using a specific short-interfering RNA reduced endogenous Freud-2 protein levels and decreased Freud-2 bound to the 5-HT1A-DRE as detected by chromatin immunoprecipitation assay, but increased 5-HT1A promoter activity and 5-HT1A protein levels. Taken together, these data show that Freud-2 is the second component that, with Freud-1, mediates dual repression of the 5-HT1A receptor gene at the DRE.

Decreased expression of Freud-1/CC2D1A, a transcriptional repressor of the 5-HT1A receptor, in the prefrontal cortex of subjects with major depression

Serotonin1A (5-HT(1A)) receptors are reported altered in the brain of subjects with major depressive disorder (MDD). Recent studies have identified transcriptional regulators of the 5-HT(1A) receptor and have documented gender-specific alterations in 5-HT(1A) transcription factor and 5-HT(1A) receptors in female MDD subjects. The 5' repressor element under dual repression binding protein-1 (Freud-1) is a calcium-regulated repressor that negatively regulates the 5-HT(1A) receptor gene. This study documented the cellular expression of Freud-1 in the human prefrontal cortex (PFC) and quantified Freud-1 protein in the PFC of MDD and control subjects as well as in the PFC of rhesus monkeys chronically treated with fluoxetine. Freud-1 immunoreactivity was present in neurons and glia and was co-localized with 5-HT(1A) receptors. Freud-1 protein level was significantly decreased in the PFC of male MDD subjects (37%, p=0.02) relative to gender-matched control subjects. Freud-1 protein was also reduced in the PFC of female MDD subjects (36%, p=0.18) but was not statistically significant. When the data was combined across genders and analysed by age, the decrease in Freud-1 protein level was greater in the younger MDD subjects (48%, p=0.01) relative to age-matched controls as opposed to older depressed subjects. Similarly, 5-HT(1A) receptor protein was significantly reduced in the PFC of the younger MDD subjects (48%, p=0.01) relative to age-matched controls. Adult male rhesus monkeys administered fluoxetine daily for 39 wk revealed no significant change in cortical Freud-1 or 5-HT(1A) receptor proteins compared to vehicle-treated control monkeys. Reduced protein expression of Freud-1 in MDD subjects may reflect dysregulation of this transcription factor, which may contribute to the altered regulation of 5-HT(1A) receptors observed in subjects with MDD. These data may also suggest that reductions in Freud-1 protein expression in the PFC may be associated with early onset of MDD.

Human Freud-2/CC2D1B: a novel repressor of postsynaptic serotonin-1A receptor expression

BACKGROUND

Altered expression of serotonin-1A (5-HT1A) receptors, both presynaptic in the raphe nuclei and post-synaptic in limbic and cortical target areas, has been implicated in mood disorders such as major depression and anxiety. Within the 5-HT1A receptor gene, a powerful dual repressor element (DRE) is regulated by two protein complexes: Freud-1/CC2D1A and a second, unknown repressor. Here we identify human Freud-2/CC2D1B, a Freud-1 homologue, as the second repressor.

METHODS

Freud-2 distribution was examined with Northern and Western blot, reverse transcriptase polymerase chain reaction, and immunohistochemistry/immunofluorescence; Freud-2 function was examined by electrophoretic mobility shift, reporter assay, and Western blot.

RESULTS

Freud-2 RNA was widely distributed in brain and peripheral tissues. Freud-2 protein was enriched in the nuclear fraction of human prefrontal cortex and hippocampus but was weakly expressed in the dorsal raphe nucleus. Freud-2 immunostaining was co-localized with 5-HT1A receptors, neuronal and glial markers. In prefrontal cortex, Freud-2 was expressed at similar levels in control and depressed male subjects. Recombinant hFreud-2 protein bound specifically to 5' or 3' human DRE adjacent to the Freud-1 site. Human Freud-2 showed strong repressor activity at the human 5-HT1A or heterologous promoter in human HEK-293 5-HT1A-negative cells and neuronal SK-N-SH cells, a model of postsynaptic 5-HT1A receptor-positive cells. Furthermore, small interfering RNA knockdown of endogenous hFreud-2 expression de-repressed 5-HT1A promoter activity and increased levels of 5-HT1A receptor protein in SK-N-SH cells.

CONCLUSIONS

Human Freud-2 binds to the 5-HT1A DRE and represses the human 5-HT1A receptor gene to regulate its expression in non-serotonergic cells and neurons.

Freud-1/Aki1, a novel PDK1-interacting protein, functions as a scaffold to activate the PDK1/Akt pathway in epidermal growth factor signaling

The phosphoinositide 3-kinase (PI3K)/3-phosphoinositide-dependent protein kinase 1 (PDK1)/Akt pathway regulates various cellular functions, especially cell survival and cell cycle progression. In contrast to other survival pathways, there have been few reports of scaffold proteins that regulate signaling cascade specificity in this pathway. Here we identify a 5' repressor element under dual-repression binding protein 1 (Freud-1)/Akt kinase-interacting protein 1 (Aki1) as a novel scaffold for the PDK1/Akt pathway. Freud-1/Aki1 (also known as CC2D1A) expression induced formation of a PDK1/Akt complex and regulated Akt activation in a concentration-dependent biphasic manner. Freud-1/Aki1 also associated with epidermal growth factor (EGF) receptor in response to EGF stimulation and was required for Akt activation induced by EGF, but not by insulin-like growth factor 1. Freud-1/Aki1 gene silencing decreased Akt kinase activity, resulting in induction of apoptosis and increased sensitivity toward chemotherapeutic agents. Our results suggest that Freud-1/Aki1 is a novel receptor-selective scaffold protein for the PDK1/Akt pathway and present a new activation mechanism of Akt.