Identification and chromosomal localisation by fluorescence in situ hybridisation of human gene of phosphoinositide-specific phospholipase C beta(1)

Phosphoinositide-specific Phospholipase C β1 gene deletion in bipolar disorder affected patient

The involvement of phosphoinositides (PI) signal transduction pathway and related molecules, such as the Phosphoinositide-specific Phospholipase C (PI-PLC) enzymes, in the pathophysiology of mood disorders is corroborated by a number of recent evidences. Our previous works identified the deletion of PLCB1 gene, which codifies for the PI-PLC β1 enzyme, in 4 out 15 patients affected with schizophrenia, and no deletion both in major depression affected patients and in normal controls. By using interphase fluorescent in situ hybridization methodology, we analyzed PLCB1 in paraffin embedded samples of orbito-frontal cortex of 15 patients affected with bipolar disorder. Deletion of PLCB1 was identified in one female patient.

Cellular neurochemical characterization and subcellular localization of phospholipase C β1 in rat brain

The present study describes a complete and detailed neuroanatomical distribution map of the phospholipase C beta1 (PLCβ1) isoform along the adult rat neuraxis, and defines the phenotype of cells expressing PLCβ1, along with its subcellular localization in cortical neurons as assessed by double-immunofluorescence staining and confocal laser scanning. Immunohistochemical labeling revealed a considerable morphological heterogeneity among PLCβ1-positive cells in the cortex, even though there was a marked predominance of pyramidal morphologies. As an exception to the general non-matching distribution of GFAP and PLCβ1, a high degree of co-expression was observed in radial glia-like processes of the spinal cord white matter. In the somatosensory cortex, the proportion of GABAergic neurons co-stained with PLCβ1 was similar (around 2/3) in layers I, II-III, IV and VI, and considerably lower in layer V (around 2/5). Double immunofluorescence against PLCβ1 and nuclear speckle markers SC-35 and NeuN/Fox3 in isolated nuclei from the rat cortex showed a high overlap of both markers with PLCβ1 within the nuclear matrix. In contrast, there was no apparent co-localization with markers of the nuclear envelope and lamina. Finally, to assess whether the subcellular expression pattern of PLCβ1 involved specifically one of the two splice variants of PLCβ1, we carried out Western blot experiments in cortical subcellular fractions. Notably, PLCβ1a/1b ratios were statistically higher in the cytoplasm than in the nuclear and plasma membrane fractions. These results provide a deeper knowledge of the cellular distribution of the PLCβ1 isoform in different cell subtypes of the rat brain, and of its presence in the neuronal nuclear compartment.

Deletion of PLCB1 gene in schizophrenia-affected patients

A prevalence of 1% in the general population and approximately 50% concordance rate in monozygotic twins was reported for schizophrenia, suggesting that genetic predisposition affecting neurodevelopmental processes might combine with environmental risk factors. A multitude of pathways seems to be involved in the aetiology and/or pathogenesis of schizophrenia, including dopaminergic, serotoninergic, muscarinic and glutamatergic signalling. The phosphoinositide signal transduction system and related phosphoinositide-specific phospholipase C (PI-PLC) enzymes seem to represent a point of convergence in these networking pathways during the development of selected brain regions. The existence of a susceptibility locus on the short arm of chromosome 20 moved us to analyse PLCB1, the gene codifying for PI-PLC β1 enzyme, which maps on 20p12. By using interphase fluorescent in situ hybridization methodology, we found deletions of PLCB1 in orbito-frontal cortex samples of schizophrenia-affected patients.

Molecular cytogenetic interphase analysis of Phosphoinositide-specific Phospholipase C β1 gene in paraffin-embedded brain samples of major depression patients

Mood disorders represent a major medical need, as their chronic treatments are not effective in all patients. Literature data suggested that phosphoinositides (PI) signal transduction pathway and related molecules such as the Phosphoinositide-specific Phospholipase C (PI-PLC) enzymes, might be involved in the pathophysiology of mood disorders, including major depression. By using interphase fluorescent in situ hybridization methodology, we analyzed PLCB1 gene, which codifies for the PI-PLC β1 enzyme, in paraffin embedded samples of orbito-frontal cortex of 15 patients affected with major depression and in 15 normal controls. No deletions of PLCB1 were identified with the methodology used, which allows to exclude wide gene deletions. The results, the technical aspects of the FISH methodology, and its limitations are discussed.

Nuclear PI-PLC β1 and Myelodysplastic syndromes: from bench to clinics

Myelodysplastic syndromes (MDS), clonal hematopoietic stem-cell disorders mainly affecting older adult patients, show ineffective hematopoiesis in one or more of the lineages of the bone marrow. A number of MDS progresses to acute myeloid leukemia (AML) with the involvement of genetic and epigenetic mechanisms affecting PI-PLC β1. The molecular mechanisms underlying the MDS evolution to AML are still unclear, even though it is now clear that the nuclear signaling elicited by PI-PLC β1, Cyclin D3, and Akt plays an important role in the control of the balance between cell cycle progression and apoptosis in both normal and pathologic conditions. Moreover, a correlation between other PI-PLCs, such as PI-PLC β3, kinases and phosphatases has been postulated in MDS pathogenesis. Here, we review the findings hinting at the role of nuclear lipid signaling pathways in MDS, which could become promising therapeutic targets.

Nuclear phosphoinositides: location, regulation and function

Lipid signalling in human disease is an important field of investigation and stems from the fact that phosphoinositide signalling has been implicated in the control of nearly all the important cellular pathways including metabolism, cell cycle control, membrane trafficking, apoptosis and neuronal conduction. A distinct nuclear inositide signalling metabolism has been identified, thus defining a new role for inositides in the nucleus, which are now considered essential co-factors for several nuclear processes, including DNA repair, transcription regulation, and RNA dynamics. Deregulation of phoshoinositide metabolism within the nuclear compartment may contribute to disease progression in several disorders, such as chronic inflammation, cancer, metabolic, and degenerative syndromes. In order to utilize these very druggable pathways for human benefit there is a need to identify how nuclear inositides are regulated specifically within this compartment and what downstream nuclear effectors process and integrate inositide signalling cascades in order to specifically control nuclear function. Here we describe some of the facets of nuclear inositide metabolism with a focus on their relationship to cell cycle control and differentiation.

Physiology and pathology of nuclear phospholipase C β1

The existence and function of inositide signaling in the nucleus is well documented and we know that the existence of the inositide cycle inside the nucleus has a biological role. An autonomous lipid-dependent signaling system, independently regulated from its plasma membrane counterpart, acts in the nucleus and modulates cell cycle progression and differentiation.We and others focused on PLCβ1, which is the most extensively investigated PLC isoform in the nuclear compartment. PLCβ1 is a key player in the regulation of nuclear inositol lipid signaling, and, as discussed above, its function could also be involved in nuclear structure because it hydrolyses PtdIns(4,5)P2, a well accepted regulator of chromatin remodelling. The evidence, in a number of patients with myelodysplastic syndromes, that the mono-allelic deletion of PLCβ1 is associated with an increased risk of developing acute myeloid leukemia paves the way for an entirely new field of investigation. Indeed the genetic defect evidenced, in addition to being a useful prognostic tool, also suggests that altered expression of this enzyme could have a role in the pathogenesis of this disease, by causing an imbalance between proliferation and apoptosis. The epigenetics of PLCβ1 expression in MDS has been reviewed as well.

Phospholipase C beta 1 deficiency is associated with early-onset epileptic encephalopathy

The epileptic encephalopathies of infancy and childhood are a collection of epilepsy disorders characterized by refractory, severe seizures and poor neurological outcome, in which the mechanism of disease is poorly understood. We report the clinical presentation and evolution of epileptic encephalopathy in a patient, associated with a loss-of-function mutation in the phospholipase C-β 1 gene. We ascertained a consanguineous family containing a male infant who presented with early-onset epileptic encephalopathy for detailed clinical phenotyping and molecular genetic investigation. In addition, a cohort of 12 consanguineous families of children with infantile spasms were analysed for linkage to the phospholipase C-β 1 gene locus. The male infant presented with tonic seizures in early infancy and subsequently developed infantile spasms. Over time, he developed drug-resistant epilepsy associated with severe neurological regression and failure to thrive. Molecular genetic investigation revealed a homozygous loss-of-function 0.5-Mb deletion, encompassing the promoter element and exons 1, 2 and 3 of phospholipase C-β 1 in the index case. Linkage to the phospholipase C-β 1 locus was excluded in the 12 other consanguineous families, consistent with genetic heterogeneity in this disorder. Although phospholipase C-β 1 deficiency has not previously been reported in humans, the Plcb1 homozygote knockout mouse displays early-onset severe tonic seizures and growth retardation, thus recapitulating the human phenotype. Phospholipase C-β 1 has important functions in both hippocampal muscarinic acetylcholine receptor signalling and in cortical development. Thus, the discovery of a phospholipase C-β 1 mutation allows us to propose a novel potential underlying mechanism in early-onset epileptic encephalopathy.

Gqalpha-linked phospholipase Cbeta1 and phospholipase Cgamma are essential components of the pheromone biosynthesis activating neuropeptide (PBAN) signal transduction cascade

Sex pheromone production for most moths is regulated by pheromone biosynthesis activating neuropeptide (PBAN). In Bombyx mori, PBAN binding triggers the opening of store-operated Ca(2+) channels, suggesting the involvement of a receptor-activated phospholipase C (PLC). In this study, we found that PLC inhibitors U73122 and compound 48/80 reduced sex pheromone production and that intracellular levels of (3)H-inositol phosphate species increased following PBAN stimulation. In addition, we amplified cDNAs from pheromone glands corresponding to PLCbeta1, PLCbeta4, PLCgamma and two G protein alpha subunits, Go and Gq. In vivo RNA interference-mediated knockdown analyses revealed that BmPLCbeta1, BmGq1, and unexpectedly, BmPLCgamma, are part of the PBAN signal transduction cascade.

Nuclear inositide signaling in myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are defined as clonal hematopoietic stem-cell disorders characterized by ineffective hematopoiesis in one or more of the lineages of the bone marrow. Although distinct morphologic subgroups exist, the natural history of MDS is progression to acute myeloid leukemia (AML). However, the molecular the mechanisms the underlying MDS evolution to AML are not completely understood. Inositides are key cellular second messengers with well-established roles in signal transduction pathways, and nuclear metabolism elicited by phosphoinositide-specific phospholipase C (PI-PLC) beta1 and Akt plays an important role in the control of the balance between cell cycle progression and apoptosis in both normal and pathologic conditions. Recent findings evidenced the role played by nuclear lipid signaling pathways, which could become promising therapeutic targets in MDS. This review will provide a concise and updated revision of the state of art on this topic.

Phosphoinositide-Phospholipase C β1 Mono-Allelic Deletion Is Associated With Myelodysplastic Syndromes Evolution Into Acute Myeloid Leukemia

Purpose

To evaluate the association between the presence of phosphoinositide-phospholipase C β1 (PI-PLCβ1) mono-allelic deletion with the clinical outcome of myelodysplastic syndromes (MDS) patients.

Methods

PI-PLCβ1, PI-PLCβ4, and PI-PLCγ1 cytogenetic investigations were performed on 80 newly diagnosed MDS patients (18 low risk, 26 intermediate 1, 18 intermediate 2, 18 high risk) comparing the results with the clinical outcome of the patients. Moreover, fluorescent in situ hybridization results were validated by real-time polymerase chain reaction (PCR). Finally, PI-PLCβ1 gene and protein expression were assessed by both real-time PCR and immunocytochemical experiments.

Results

Collectively, 35 (43.75%) of 80 of the MDS patients showed a specific mono-allelic deletion of PI-PLCβ1. Kaplan-Meier analysis revealed a significant association (P < .0001) between the PI-PLCβ1 mono-allelic deletion and a higher risk of evolution into acute myeloid leukemia (AML), since 23 of 35 MDS patients (65.7%) bearing the PI-PLCβ1 mono-allelic deletion evolved into AML. Even in multivariate analysis, the PI-PLCβ1 mono-allelic deletion retained a higher significance, with a P < .001, as a prognostic factor of evolution into AML (odds ratio [OR] 1.83; 95% CI, 2.26 to 17.24; P = .00045). Finally, PI-PLCβ1 deletion was related to an altered gene and protein expression.

Conclusion

PI-PLCβ1 mono-allelic deletion is associated with a worse clinical outcome in MDS patients, hinting at the identification of a new group at higher risk of AML evolution and representing a reliable prognostic tool. Moreover, targeting PI-PLCβ1 pathways might emerge as a new therapeutic strategy for MDS.

Nuclear inositol lipid metabolism: more than just second messenger generation?

A distinct polyphosphoinositide cycle is present in the nucleus, and growing evidence suggests its importance in DNA replication, gene transcription, and apoptosis. Even though it was initially thought that nuclear inositol lipids would function as a source for second messengers, recent findings strongly indicate that lipids present in the nucleus also fulfil other roles. The scope of this review is to highlight the most intriguing advances made in the field over the last few years, such as the possibility that nuclear phosphatidylinositol (4,5) bisphosphate is involved in maintaining chromatin in a transcriptionally active conformation, the new emerging roles for intranuclear phosphatidylinositol (3,4,5) trisphosphate and phosphoinositide 3-kinase, and the evidence which suggests a tight relationship between a decreased level of nuclear phosphoinositide specific phospholipase C-beta1 and the evolution of myelodisplastic syndrome into acute myeloid leukemia.

Nuclear phospholipase C beta1, regulation of the cell cycle and progression of acute myeloid leukemia

A large number of observations have hinted at the fact that location impinges on function of some of the main players of nuclear inositol lipid cycle. PLC beta1 is a well-known example, given that it has been shown that only the enzyme located in the nucleus targets the cyclin D3/cdk4 complex, playing, in turn, a key role in the control of normal progression through the G1 phase of the cell cycle. The PLC beta1 gene, which is constituted of 36 small exons and large introns, maps on the short arm of human chromosome 20 (20pl2, nearby markers D20S917 and D20S177) with the specific probe (PAC clone HS881E24) spanning from exon 19 to 32 of the gene itself. The chromosome band 20pl2 has been shown to be rearranged in human diseases such as solid tumors without a more accurate definition of the alteration, maybe because of the absence of candidate genes or specific probes. Moreover, non-specific alterations in chromosome 20 have been found in patients affected by MDS and acute myeloid leukemia AML. MDS is an adult hematological disease that evolves into AML in about 30% of the cases. The availability of a highly specific probe gave an opportunity to perform in patients affected with MDS/AML, associated with normal karyotype, painting and FISH analysis aimed to check the PLC beta1 gene, given that this signaling molecule is a key player in the control of some checkpoints of the normal progression through the cell cycle. FISH analysis disclosed in a small group of MDS/AML patients with normal karyotype the monoallelic deletion of the PLC beta1 gene. In contrast, PLC beta4, another gene coding for a signaling molecule, located on 20pl2.3 at a distance as far as less than 1 Mb from PLC beta1, is unaffected in MDS patients with the deletion of PLC beta1 gene, hinting at an interstitial deletion. The MDS patients, bearing the deletion, rapidly evolved to AML, whilst the normal karyotype MDS patients, showing non-deletion of PLC beta1 gene, are still alive at least 24 months after the diagnosis. The immunocytochemical analysis using an anti PLC beta1 monoclonal antibody showed that all the AML/MDS patients who were normal at FISH analysis also had normal staining of the nucleus, which is a preferential site for PLC beta1. In contrast, the monoallelic deletion gave rise to a dramatic decrease of the nuclear staining suggesting a decreased expression of the nuclear PLC beta1. The reported data strengthen the contention of a key role played by PLC beta1 in the nucleus, suggest a possible involvement of PLC beta1 in the progression of MDS to AML and pave the way for a larger investigation aimed at identifying a possible high risk group among MDS patients with a normal karyotype.

Inositide-specific phospholipase c β1 gene deletion in the progression of myelodysplastic syndrome to acute myeloid leukemia

Myelodysplastic syndrome (MDS) is an adult hematological disease that evolves into acute myeloid leukemia (AML) in about 30% of the cases. The availability of a highly specific probe moved us to perform in patients affected with MDS/AML, associated with normal karyotype, painting and fluorescence in situ hybridization (FISH) analysis aimed to check the inositide-specific phospholipase C (PI-PLC) beta1 gene, a player in the control of some checkpoints of the cell cycle. Here we present a preliminary observation in which FISH analysis disclosed in a small group of MDS/AML patients with normal karyotype the monoallelic deletion of the PI-PLCbeta1 gene. On the contrary, PI-PLC beta4, another gene coding for a signaling molecule, located on 20p12.3 at a distance as far as less than 1Mb from PI-PLCbeta1, is unaffected in MDS patients with the deletion of PI-PLC beta1 gene, hinting at an interstitial deletion. The MDS patients, bearing the deletion, rapidly evolved to AML. The data suggest the possible involvement of PI-PLCbeta1 in the progression of the disease and pave the way for a larger investigation aimed at identifying a possible high-risk group among MDS patients with a normal karyotype.

Chromosome 11 rearrangements and specific MLL amplification revealed by spectral karyotyping in a patient with refractory anaemia with excess of blasts (RAEB)

A patient with refractory anaemia with excess of blasts (RAEB) had a complex karyotype with multiple markers. Spectral karyotyping (SKY) showed rearrangements including three different der(11), containing a very high number of MLL gene copies, shown by fluorescence in situ hybridization (FISH) analysis. Fibre-FISH experiments disclosed the presence of chromatin fibres with multiple MLL copies with a head-to-tail pattern. Apparently, no other region flanking the MLL site was present in the three der(11). MLL amplification was confirmed by the reverse transcription polymerase chain reaction (RT-PCR). The patient died 6 months after diagnosis, supporting the severe prognosis of sole MLL amplification.

Molecular characterization of the human PLC beta1 gene

Inositide-specific phospholipase C (PLC) signaling constitutes a central intermediate in a number of cellular functions among which the control of cell growth raises a particular interest. Indeed, we have previously shown that nuclear phospholipase C beta1 (PLC beta1) is central for the regulation of mitogen-induced cell growth. We have also assigned by fluorescence in situ hybridization (FISH) analysis the PLC beta1 to human chromosome 20p12. In this study, we have carried out a detailed analysis of the human gene, showing the existence of alternative splicing, which gives rise, besides the two forms (1a and 1b) already shown in rodents, to a new 600 bp smaller form coding for a 110 kDa protein. We have also identified a new exon at the 5', showing no homology with the rodent sequence. Here we provide the complete determination of the exon/intron structure of the gene spanning 250 kb of DNA. We found that the exons are quite small, ranging from 49 to 222 bp, while the introns vary between 108 bp and 34,400 bp. The availability of the understanding of the genome organization of this inositide-specific PLC, which represents a key step of the cell cycle related signaling, could actually pave the way for further genetic analysis of p12 region of human chromosome 20 in diseases involving alterations of the control of cell growth such as malignancies.

Cloning and characterization of the human phosphoinositide-specific phospholipase C-beta 1 (PLC beta 1)

Phospholipase C-beta (PLC beta) catalyses the generation of inositol 1,4,5-trisphosphate (IP(3)) and diacylglycerol (DAG) from phosphatidylinositol 4,5-bisphosphate (IP(2)), a key step in the intracellular transduction of a large number of extracellular signals, including neurotransmitters and hormones modulating diverse developmental and functional aspects of the mammalian central nervous system. Four mammalian isozymes are known (PLC beta 1-4), which differ in their function and expression patterns in vivo. We have characterized the human PLC beta 1 genomic locus (PLC beta 1), cloned two distinct PLC beta 1 cDNAs (PLC beta 1a and b) and analysed their respective expression patterns in a comprehensive panel of human tissues using quantitative TaqMan technology. The two cDNAs derive from transcripts generated through alternative splicing at their 3' end, and are predicted to encode for PLC beta 1 isoforms differing at their carboxy-terminus. The human PLC beta 1 isoforms are co-expressed in the same tissues with a distinctly CNS-specific profile of expression. Quantitative differences in PLC beta 1 isoform expression levels are observed in some tissues. Transient expression of epitope-tagged versions of the two isoforms followed by immunofluorescence revealed localization of the proteins to the cytoplasm and the inner side of the cell membrane. Finally, we characterized the structure of the PLC beta 1 locus and confirmed its mapping to human chromosome 20.