Cloning, physical mapping and structural characterization of the human alpha(A)-adaptin gene

AP2A2 mutation and defective endocytosis in a Malian family with hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) comprises a large group of neurogenetic disorders characterized by progressive lower extremity spasticity. Neurological evaluation and genetic testing were completed in a Malian family with early-onset HSP. Three children with unaffected consanguineous parents presented with symptoms consistent with childhood-onset complicated HSP. Neurological evaluation found lower limb weakness, spasticity, dysarthria, seizures, and intellectual disability. Brain MRI showed corpus callosum thinning with cortical and spinal cord atrophy, and an EEG detected slow background in the index patient. Whole exome sequencing identified a homozygous missense variant in the adaptor protein (AP) complex 2 alpha-2 subunit (AP2A2) gene. Western blot analysis showed reduced levels of AP2A2 in patient-iPSC derived neuronal cells. Endocytosis of transferrin receptor (TfR) was decreased in patient-derived neurons. In addition, we observed increased axon initial segment length in patient-derived neurons. Xenopus tropicalis tadpoles with ap2a2 knockout showed cerebral edema and progressive seizures. Immunoprecipitation of the mutant human AP-2-appendage alpha-C construct showed defective binding to accessory proteins. We report AP2A2 as a novel genetic entity associated with HSP and provide functional data in patient-derived neuron cells and a frog model. These findings expand our understanding of the mechanism of HSP and improve the genetic diagnosis of this condition.

Alpha adaptins show isoform-specific association with neurofibrillary tangles in Alzheimer's disease

AIMS

The heterotetrameric assembly protein complex 2 (AP-2) is a central hub for clathrin-dependent endocytosis. The AP-2 α-adaptin subunit has two major isoforms, encoded by two separate genes: AP2A1 and AP2A2. Endocytosis has been implicated in the pathogenesis of neurodegenerative disease, and recent studies linked α-adaptins (gene variants, splicing defects and altered expression) with late-onset Alzheimer's disease (LOAD) risk. Here, we used multiple antibodies to investigate α-adaptin isoforms and their localization in human brains.

METHODS

The specificities of 10 different α-adaptin antibodies were evaluated using immunoblots after human AP2A1 and AP2A2 plasmid transfection in cultured cells. Additional immunoblot analyses were then performed on protein homogenates from control and LOAD subjects. Formalin-fixed, paraffin-embedded brain sections from control and LOAD subjects were immunohistochemically stained, and immunofluorescence experiments were performed for quantitation of colocalisation with digital image analysis.

RESULTS

Eight of the 10 evaluated antibodies recognised transfected α-adaptin proteins on immunoblots. The α-adaptin subspecies were relatively uniformly expressed in five different human brain regions. The α-adaptins were present in the detergent-insoluble fraction from cognitively impaired, but less so in control, brains. Immunohistochemical analyses showed colocalisation of AP2A1 with tau pathology in LOAD brains. By contrast, AP2A2 colocalised with microglial cells.

CONCLUSIONS

These observations provide evidence of isoform-specific changes of α-adaptins in the brains of LOAD subjects. Antibodies that were verified to recognise AP2A1, but not AP2A2, labelled neurofibrillary tangles of LOAD patients. The findings extend our understanding of AP-2 proteins in the human brain in healthy and diseased states.

The adaptor-related protein complex 2, alpha 2 subunit (AP2α2) gene is a peroxisome proliferator-activated receptor cardiac target gene

A peroxisome proliferator-actived receptor (PPAR) response element (RE) in the promoter region of the adaptor-related protein complex 2, alpha 2 subunit (AP2α2) of mouse heart has been identified. The steroid hormone nuclear PPARs and the retinoid X receptors (RXRs) are important transcriptional factors that regulate gene expression, cell differentiation and lipid metabolism. They form homo- (RXR) and hetero- (PPAR-RXR) dimers that bind DNA at various REs. The AP2α2 gene is part of complex and process that transports lipids and proteins from the plasma membrane to the endosomal system. A PPAR activator (Wy14643) and DMSO (vehicle) was introduced into control and δ337T thyroid hormone receptor (TRβ1) transgenic mice. Heart tissue was extracted and AP2α2 gene expression was compared using Affymetrix expression arrays and qRT PCR among four groups [control, control with Wy14643, δ337T TRβ1 and δ337T TRβ1 with Wy14643]. The gene expression of AP2α2 in the Wy14643 control and transgenic mouse groups was significantly up regulated over the vehicle mouse groups in both the array (p < 0.01) and qRT PCR (p < 0.01) studies. Duplex oligo DNAs containing the PPAR/RXR motif (AGGTCA/TCCAGT) from the AP2α2 promoter were used in EMSA to verify binding of the PPAR and RXR receptors to their REs. pGL4.0 [Luc] constructs of the AP2α2 promoter with and without the PPAR/RXR motifs were co-transfected with mouse PPARα, β or γ1 into HepG2 cells and used in lucerifase assays to verify gene activation. In conclusion our study revealed that PPARα regulates the mouse cardiac AP2α2 gene in both the control and transgenic mouse.

An evaluation of molecular markers for improved detection of breast cancer metastases in sentinel nodes

BACKGROUND AND OBJECTIVES

In patients with breast cancer (BC), the sentinel node (SN) is the first node in the axillary basin that receives the primary lymphatic flow and can be used to accurately assess the axillary nodal status without removal of the axillary contents. Currently, histology and/or immunohistochemistry are the routine methods of SN analysis. The primary objective of this study was to develop a reproducible reverse transcription (RT) PCR assay, with emphasis on achieving high specificity for accurate detection of BC micrometastases in the SN. To correct for the heterogeneity of BC cells, a multimarker approach was followed, with the further aim of improving the detection rate of the assay.

METHODS

In total, 73 markers were evaluated, of which 7 were breast epithelial markers and 66 were either cancer testis or tumour associated antigens. Twelve BC cell lines and 30 SNs (from 30 patients) were analysed using RT-PCR to determine the in vitro and in vivo detection rates for each of the markers. In addition, 20 axillary nodes obtained from a patient with brain death were used as controls to optimise the PCR cycle numbers for all the markers.

RESULTS

Of the 30 SNs, 37% (11/30) were positive on haematoxylin and eosin analysis. Extensive immunohistochemical (IHC) analyses of the haematoxylin and eosin negative nodes confirmed the presence of very small numbers of BC cells in an additional 40% (12/30) of SNs. Molecular analysis with the hMAM-A alone identified metastases in 70% (21/30) of SNs. Using MAGE-A3 in combination with hMAM-A identified metastases in 90% (27/30) of patients. Seven SNs (23%) were negative for micrometastases (with haematoxylin and eosin and IHC) but RT-PCR positive for either hMAM-A or MAGE-A3.

CONCLUSIONS

As IHC analysis resulted in a 77% detection rate compared with 37% for haematoxylin and eosin analysis, we consider that IHC is essential in order not to miss SN micrometastases. Molecular analysis with hMAM-A and MAGE-A3 allows detection of BC micrometastases with a 90% detection rate. However, the clinical value of histologically negative but RT-PCR positive SNs can only be determined with long term follow up.

mRNA expression analysis of a variety of apoptosis-related genes, including the novel gene of the BCL2-family, BCL2L12, in HL-60 leukemia cells after treatment with carboplatin and doxorubicin

Apoptosis is a type of programmed cell death involved in many crucial biological processes. It represents the basic mechanism for the action of chemotherapeutic agents, such as doxorubicin and carboplatin. Both are able to cause cell death through the induction of apoptosis in the human leukemic cell line HL-60. We investigated the possible alterations in the expression of apoptosis-related genes, including the novel BCL2L12 gene, which was recently cloned in our group. The kinetics of apoptosis induction and cell toxicity was investigated by DNA laddering and by the MTT method, respectively. Total RNA was extracted and cDNA was prepared by reverse transcription. BCL2 , BAX , FAS , caspase-9, caspase-3 and BCL2L12 were amplified by PCR. Overexpression of FAS , BCL2L12 and caspase-3 was observed after treatment of HL-60 cells for 3 or 6 h with carboplatin, while their expression was decreased after a 12-h treatment, demonstrating that these genes may take part in the early stages of apoptosis. Overexpression of the same genes was also observed after 6 h of treatment with doxorubicin (concomitantly with DNA laddering). In the case of carboplatin-induced apoptosis we detected down-regulation of BAX , BCL2 and caspase-9, whereas in the case of doxorubicin, BAX and BCL2 remained at control levels and caspase-9 was increased.

SCN5A–linked disease syndromes: complex monogenic disorders of cardiac rhythm

Significant advances in the field of molecular biology have enabled the identification of genes that confer susceptibility to disease. Inherited arrhythmia syndromes resulting from genetic alterations of various cardiac ion channels and proteins have been invaluable to further our understanding of the molecular basis of cardiac excitability. Mutations in SCN5A, the gene encoding the pore-forming subunit of the cardiac sodium channel, have been associated with distinct life-threatening cardiac rhythm syndromes. While electrophysiological characterization of mutant sodium channels in dissociated systems have revealed abnormalities in channel function, significant overlap between aberrant rhythm phenotypes suggests a complex relationship between mutations and disease phenotype. These new insights not only enhance our understanding of the structure-–unction relationships of ion channels, but also highlight the complexities involved in linking single mutations, ion-channel behavior, and cardiac rhythm.