Mapping of protein phosphatase-6 association with its SAPS domain regulatory subunit using a model of helical repeats.

BACKGROUND: Helical repeat motifs are common among regulatory subunits for type-1 and type-2A protein Ser/Thr phosphatases. Yeast Sit4 is a distinctive type-2A phosphatase that has dedicated regulatory subunits named Sit4-Associated Proteins (SAPS). These subunits are conserved, and three human SAPS-related proteins are known to associate with PP6 phosphatase, the Sit4 human homologue. RESULTS: Here we show that endogenous SAPS subunit PP6R3 co-precipitates half of PP6 in cell extracts, and the SAPS region of PP6R3 is sufficient for binding PP6. The SAPS domain of recombinant GST-PP6R3 is relatively resistant to trypsin despite having many K and R residues, and the purified SAPS domain (residues 1-513) has a circular dichroic spectrum indicative of mostly alpha helical structure. We used sequence alignments and 3D-jury methods to develop alternative models for the SAPS domain, based on available structures of other helical repeat proteins. The models were used to select sites for charge-reversal substitutions in the SAPS domain of PP6R3 that were tested by co-precipitation of endogenous PP6c with FLAG-tagged PP6R3 from mammalian cells. Mutations that reduced binding with PP6 suggest that SAPS adopts a helical repeat similar to the structure of p115 golgin, but distinct from the PP2A-A subunit. These mutations did not cause perturbations in overall PP6R3 conformation, evidenced by no change in kinetics or preferential cleavage by chymotrypsin. CONCLUSION: The conserved SAPS domain in PP6R3 forms helical repeats similar to those in golgin p115 and negatively charged residues in interhelical loops are used to associate specifically with PP6. The results advance understanding of how distinctive helical repeat subunits uniquely distribute and differentially regulate closely related Ser/Thr phosphatases.

The Role of the Nuclear Factor-κB Transcriptional Complex in Cortical Immune Activation in Schizophrenia.

BACKGROUND: Transcript levels for cytokines and the viral restriction factor interferon-induced transmembrane protein are markedly higher in the prefrontal cortex in schizophrenia. These gene products are regulated by the nuclear factor-κB (NF-κB) transcriptional complex. NF-κB activity, which requires the formation of NF-κB family member heterodimers, is regulated by activation receptors, kinases, and inhibitors. Whether any of these factors are altered in schizophrenia is not known. It is also unclear whether NF-κB-related disturbances reflect ongoing cortical immune activation or a long-lasting response to a prenatal immune-related insult. METHODS: Transcript levels for NF-κB pathway markers were assessed using quantitative polymerase chain reaction in the prefrontal cortex from 1) 62 matched pairs of schizophrenia and unaffected comparison subjects, 2) antipsychotic-exposed monkeys, and 3) adult mice exposed prenatally to maternal immune activation or in adulthood to the immune stimulant polyinosinic-polycytidylic acid. RESULTS: In schizophrenia subjects, but not antipsychotic-exposed monkeys, we found higher messenger RNA levels for 1) most NF-κB family members, 2) all NF-κB activation receptors, 3) several kinases, and 4) one inhibitor (IκBα) whose transcript level is itself regulated by NF-κB activity. A similar pattern of elevated NF-κB-related messenger RNA levels was seen in adult mice that received daily polyinosinic-polycytidylic acid injections, but not in adult mice subjected to maternal immune activation in utero. CONCLUSIONS: Higher NF-κB activity, evidenced by elevated transcript levels for NF-κB family members, activation receptors, and kinases, may contribute to increased markers of cortical immune activation in schizophrenia.

Altered brain cannabinoid 1 receptor mRNA expression across postnatal development in the MAM model of schizophrenia.

Altered cannabinoid 1 receptor (CB1R) expression has been reported in the brain of subjects with schizophrenia, a developmental mental illness that usually emerges in late adolescence/early adulthood. However, the developmental period at which changes in the CB1R expression appear in schizophrenia is unknown. To gain insight into this factor, we assessed the postnatal developmental trajectory of CB1R expression in the methylazoxymethanol (MAM) model of schizophrenia. Using in situ hybridization with film and grain analyses, CB1R messenger RNA (mRNA) levels were quantified in multiple brain regions, including the medial prefrontal cortex (mPFC), secondary motor cortex, dorsomedial and dorsolateral striatum, dorsal subregions and ventral subiculum of the hippocampus, of MAM-treated rats and normal controls at three developmental periods [juvenile - postnatal day (PD) 30; adolescence - PD45; and adulthood - PD85]. In all brain regions studied, CB1R mRNA levels were highest in juveniles and then decreased progressively toward adolescent and adult levels in control and MAM-treated rats. However, in MAM-treated rats, CB1R mRNA levels were lower in the mPFC at PD85 and higher in the dorsolateral striatum at PD45 and PD85 relative to controls. Cellular analyses confirmed the changes in CB1R mRNA expression in MAM-treated rats. These findings are in accordance with previous studies showing a decrease in the CB1R mRNA expression from juvenile period to adolescence to adulthood in cortical, striatal, and hippocampal regions. Additionally, similar to most of the schizophrenia-like signs observed in the MAM model, embryonic exposure to MAM leads to schizophrenia-related changes in CB1R mRNA expression that only emerge later in development.

Altered expression of developmental regulators of parvalbumin and somatostatin neurons in the prefrontal cortex in schizophrenia.

Dysfunction of prefrontal cortex (PFC) inhibitory neurons that express the calcium-binding protein parvalbumin or the neuropeptide somatostatin in schizophrenia may be related to disturbances in the migration, phenotypic specification, and/or maturation of these neurons. These pre- and postnatal developmental stages are regulated in a cell type-specific manner by various transcription factors and co-activators, fibroblast growth factor receptors (FgfR), and other molecular markers. Consequently, we used quantitative PCR to quantify mRNA levels for these developmental regulators in the PFC of 62 schizophrenia subjects in whom parvalbumin and somatostatin neuron disturbances were previously reported, and in antipsychotic-exposed monkeys. Relative to unaffected comparison subjects, subjects with schizophrenia exhibited elevated mRNA levels for 1) the transcription factor MafB, which is expressed by parvalbumin and somatostatin neurons as they migrate from the medial ganglionic eminence to the cortex, 2) the transcriptional coactivator PGC-1α, which is expressed postnatally by parvalbumin neurons to maintain parvalbumin levels and inhibitory function, and 3) FgfR1, which is required for the migration and phenotypic specification of parvalbumin and somatostatin neurons. Elevations in these markers were most prominent in younger schizophrenia subjects and were not present in antipsychotic-exposed monkeys. Finally, expression levels of other important developmental regulators (i.e. Dlx1, Dlx5, Dlx6, SATB1, Sip1/Zeb2, ST8SIA4, cMaf, Nkx6.2, and Arx) were not altered in schizophrenia. The over-expression of a subset of molecular markers with distinct roles in the pre- and postnatal development of parvalbumin and somatostatin neurons might reflect compensatory mechanisms to sustain the development of these neurons in the face of other insults.

Chemokine receptors and cortical interneuron dysfunction in schizophrenia.

Alterations in inhibitory (GABA) neurons, including deficiencies in the GABA synthesizing enzyme GAD67, in the prefrontal cortex in schizophrenia are pronounced in the subpopulations of neurons that contain the calcium-binding protein parvalbumin or the neuropeptide somatostatin. The presence of similar illness-related deficits in the transcription factor Lhx6, which regulates prenatal development of parvalbumin and somatostatin neurons, suggests that cortical GABA neuron dysfunction may be related to disturbances in utero. Since the chemokine receptors CXCR4 and CXCR7 guide the migration of cortical parvalbumin and somatostatin neurons from their birthplace in the medial ganglionic eminence to their final destination in the neocortex, we sought to determine whether altered CXCR4 and/or CXCR7 mRNA levels were associated with disturbances in GABA-related markers in schizophrenia. Quantitative PCR was used to quantify CXCR4 and CXCR7 mRNA levels in the prefrontal cortex of 62 schizophrenia and 62 healthy comparison subjects that were previously characterized for markers of parvalbumin and somatostatin neurons and in antipsychotic-exposed monkeys. We found elevated mRNA levels for CXCR7 (+29%; p<.0001) and CXCR4 (+14%, p=.052) in schizophrenia subjects but not in antipsychotic-exposed monkeys. CXCR7 mRNA levels were inversely correlated with mRNA levels for GAD67, parvalbumin, somatostatin, and Lhx6 in schizophrenia but not in healthy subjects. These findings suggest that higher mRNA levels for CXCR7, and possibly CXCR4, may represent a compensatory mechanism to sustain the migration and correct positioning of cortical parvalbumin and somatostatin neurons in the face of other insults that disrupt the prenatal development of cortical GABA neurons in schizophrenia.

Molecular mechanisms and timing of cortical immune activation in schizophrenia.

OBJECTIVE: Immune-related abnormalities are commonly reported in schizophrenia, including higher mRNA levels for the viral restriction factor interferon-induced transmembrane protein (IFITM) in the prefrontal cortex. The authors sought to clarify whether higher IFITM mRNA levels and other immune-related disturbances in the prefrontal cortex are the consequence of an ongoing molecular cascade contributing to immune activation or the reflection of a long-lasting maladaptive response to an in utero immune-related insult. METHOD: Quantitative polymerase chain reaction was employed to measure mRNA levels for immune-related cytokines and transcriptional regulators, including those reported to regulate IFITM expression, in the prefrontal cortex from 62 schizophrenia and 62 healthy subjects and from adult mice exposed prenatally to maternal immune activation or in adulthood to the immune stimulant poly(I:C). RESULTS: Schizophrenia subjects had markedly higher mRNA levels for interleukin 6 (IL-6) (+379%) and interferon-ß (+29%), which induce IFITM expression; lower mRNA levels for Schnurri-2 (-10%), a transcriptional inhibitor that lowers IFITM expression; and higher mRNA levels for nuclear factor-κB (+86%), a critical transcription factor that mediates cytokine regulation of immune-related gene expression. In adult mice that received daily poly(I:C) injections, but not in offspring with prenatal exposure to maternal immune activation, frontal cortex mRNA levels were also markedly elevated for IFITM (+304%), multiple cytokines including IL-6 (+493%), and nuclear factor-κB (+151%). CONCLUSIONS: These data suggest that higher prefrontal cortex IFITM mRNA levels in schizophrenia may be attributable to adult, but not prenatal, activation of multiple immune markers and encourage further investigation into the potential role of these and other immune markers as therapeutic targets in schizophrenia.

Cortical inhibitory neuron disturbances in schizophrenia: role of the ontogenetic transcription factor Lhx6.

Disturbances in parvalbumin- and somatostatin-containing neurons, including deficits in the gamma-aminobutyric acid (GABA)-synthesizing enzyme GAD67 in the prefrontal cortex (PFC) in schizophrenia, may be related to disrupted pre- and/or postnatal development. Deficits in the transcription factor Lhx6, which regulates parvalbumin and somatostatin neuron development, are associated with GAD67 deficits in schizophrenia. Therefore, we investigated the potential pre- and postnatal roles of Lhx6 in GABA-related disturbances using qPCR and/or in situ hybridization to quantify PFC levels of (1) Lhx6 mRNA in a new cohort of schizophrenia subjects; (2) Lhx6 mRNA in monkeys across postnatal development; (3) GABA-related mRNAs in Lhx6 heterozygous (Lhx6+/−) mice, which model Lhx6 deficits in schizophrenia; and (4) Lhx6 mRNA in GAD67+/− mice, which model GAD67 deficits in schizophrenia. Lhx6 mRNA levels were lower (−15%) in schizophrenia and correlated with lower GAD67 mRNA levels. In addition, Lhx6 mRNA levels declined 24% from the perinatal to prepubertal periods then stabilized in monkeys. Finally, GAD67, parvalbumin, and somatostatin mRNAs were not altered in Lhx6+/− mice, and Lhx6 mRNA was not altered in GAD67+/− mice. These data suggest that PFC Lhx6 and GAD67 mRNA deficits are common components of GABA neuron pathology in schizophrenia. An excessive early postnatal decline in Lhx6 mRNA might contribute to Lhx6 mRNA deficits in schizophrenia. However, a partial loss of Lhx6 is not sufficient in isolation to produce deficits in GAD67 mRNA and vice versa, suggesting that the concurrence of Lhx6 and GAD67 mRNA deficits in schizophrenia may instead be the consequence of a common upstream factor.

Elevated viral restriction factor levels in cortical blood vessels in schizophrenia.

BACKGROUND: Higher tissue transcript levels of immune-related markers-including the recently discovered viral restriction factor interferon-induced transmembrane protein (IFITM), which inhibits viral entry and replication-have been reported in the prefrontal cortex in schizophrenia. Interestingly, mouse models of neuroinflammation have higher IFITM levels and deficits in γ-aminobutyric acid (GABA)-related markers that are similar to findings in schizophrenia, suggesting that a shared pathogenetic process might underlie diverse cortical pathology in the disorder. However, the cell types that overexpress IFITM messenger RNA (mRNA) in schizophrenia are unknown, and it is unclear whether higher IFITM mRNA levels are associated with lower GABA-related marker levels in the same schizophrenia subjects. METHODS: We used quantitative polymerase chain reaction and in situ hybridization with film and grain counting analyses to quantify IFITM mRNA levels in prefrontal cortex area 9 of 57 schizophrenia and 57 healthy comparison subjects and in antipsychotic-exposed monkeys. RESULTS: Quantitative polymerase chain reaction and in situ hybridization film analysis revealed markedly elevated IFITM mRNA levels (+114% and +117%, respectively) in prefrontal gray matter in schizophrenia. Interestingly, emulsion-dipped, Nissl-stained sections from schizophrenia and comparison subjects revealed IFITM mRNA expression in pia mater and blood vessels. The IFITM grain density over blood vessels was 71% higher in schizophrenia. The IFITM mRNA levels were negatively correlated with GABA-related mRNAs in the same schizophrenia subjects. CONCLUSIONS: The finding that schizophrenia subjects with higher IFITM mRNA levels in cortical blood vessels have greater disturbances in cortical GABA neurons suggests that these cell-type distinct pathological disturbances might be influenced by a shared upstream insult that involves immune activation.

The Discodermia calyx toxin calyculin a enhances cyclin D1 phosphorylation and degradation, and arrests cell cycle progression in human breast cancer cells.

Cyclin D1 is a key regulator of the cell cycle that is over expressed in more than half of breast cancer patients. The levels of cyclin D1 are controlled primarily through post-translational mechanisms and phosphorylation of cyclin D1 at T286 induces its proteasomal degradation. To date, no studies have explored the involvement of phosphatases in this process. Here we treated human breast cancer cells with the structurally distinct toxins calyculin A, okadaic acid, and cantharidin, which are known to inhibit Ser/Thr phosphatases of the PPP family. At low nanomolar concentrations calyculin A induced T286 phosphorylation and degradation of cyclin D1 via the proteosome in MDA-MB-468 and MDA-MB-231 cells. Cyclin D1 degradation also was dose-dependently induced by okadaic acid and catharidin, implicating a negative regulatory role for type-2A phosphatases. These effects occurred without increasing phosphorylation of p70S6K, cyclin D3, or myosin light chain that were used as endogenous reporters of cellular PP2A and PP1 activity. A reverse phase phosphoprotein array analysis revealed increased phosphorylation of only 6 out of 33 Ser/Thr phosphosites, indicating selective inhibition of phosphatases by calyculin A. Calyculin A treatment induced cell cycle arrest in MDA-MB-468 and MCF-7 breast cancer cells. These findings suggest that a specific pool of type-2A phosphatase is inhibited by calyculin A leading to the degradation of cyclin D1 in human breast cancer cells. The results highlight the utility of toxins as pharmacological probes and points to the T286 cyclin D1 phosphatase inhibited by calyculin A as a possible target for chemotherapy to treat triple negative breast cancer.