Neurobehavioral deficits in mice lacking the erythrocyte membrane cytoskeletal protein 4.1

Protein 4.1R regulates M1 macrophages polarization via glycolysis, alleviating sepsis-induced liver injury in mice

Acute liver injury (ALI) is a common clinical disease caused by sepsis, metabolic syndrome, hepatitis virus. Macrophage plays an important role in the development of ALI, which is characterized by polarization and inflammatory regulation. The polarization process of macrophages is related to membrane binding proteins and adaptors. Protein 4.1R acts as an adaptor, linking membrane proteins to the cytoskeleton, and is involved in cell activation and cytokine secretion. However, whether protein 4.1R is involved in regulating macrophage polarization and inflammation-induced liver injury remains unknown. In this study, protein 4.1R is identified with the special effect on macrophage M1 polarization. And it is further demonstrated that protein 4.1R deficiency significantly enhance glycolytic metabolism. Mechanistically, the regulation of protein 4.1R on pyruvate kinase M2 (PKM2) plays a key role in glycolysis metabolism. In addition, we found that protein 4.1R directly interacts with toll-like receptor 4 (TLR4), inhibits the activation of the AKT/HIF-1α signaling pathway. In conclusion, protein 4.1R targets HIF-1α mediated glycolysis regulates M1 macrophage polarization, indicating that protein 4.1R is a candidate for regulating macrophage mediated inflammatory response. In conclusion, we have revealed a novel function of protein 4.1R in macrophage polarization and ALI, providing important insights into the metabolic reprogramming, which is important for ALI therapy. We have revealed a novel function of protein 4.1R in macrophage polarization and ALI, providing important insights into the metabolic reprogramming, which is important for ALI therapy.

Are EPB41 and alpha-synuclein diagnostic biomarkers of sport-related concussion? Findings from the NCAA and Department of Defense CARE Consortium

BACKGROUND

Current protein biomarkers are only moderately predictive at identifying individuals with mild traumatic brain injury or concussion. Therefore, more accurate diagnostic markers are needed for sport-related concussion.

METHODS

This was a multicenter, prospective, case-control study of athletes who provided blood samples and were diagnosed with a concussion or were a matched non-concussed control within the National Collegiate Athletic Association-Department of Defense Concussion Assessment, Research, and Education Consortium conducted between 2015 and 2019. The blood was collected within 48 h of injury to identify protein abnormalities at the acute and subacute timepoints. Athletes with concussion were divided into 6 h post-injury (0-6 h post-injury) and after 6 h post-injury (7-48 h post-injury) groups. We applied a highly multiplexed proteomic technique that used a DNA aptamers assay to target 1305 proteins in plasma samples from athletes with and without sport-related concussion.

RESULTS

A total of 140 athletes with concussion (79.3% males; aged 18.71 ± 1.10 years, mean ± SD) and 21 non-concussed athletes (76.2% males; 19.14 ± 1.10 years) were included in this study. We identified 338 plasma proteins that significantly differed in abundance (319 upregulated and 19 downregulated) in concussed athletes compared to non-concussed athletes. The top 20 most differentially abundant proteins discriminated concussed athletes from non-concussed athletes with an area under the curve (AUC) of 0.954 (95% confidence interval: 0.922‒0.986). Specifically, after 6 h of injury, the individual AUC of plasma erythrocyte membrane protein band 4.1 (EPB41) and alpha-synuclein (SNCA) were 0.956 and 0.875, respectively. The combination of EPB41 and SNCA provided the best AUC (1.000), which suggests this combination of candidate plasma biomarkers is the best for diagnosing concussion in athletes after 6 h of injury.

CONCLUSION

Our data suggest that proteomic profiling may provide novel diagnostic protein markers and that a combination of EPB41 and SNCA is the most predictive biomarker of concussion after 6 h of injury.

Activity of Adenylyl Cyclase Type 6 Is Suppressed by Direct Binding of the Cytoskeletal Protein 4.1G

The G protein-coupled receptor (GPCR) signaling pathways mediated by trimeric G proteins have been extensively elucidated, but their associated regulatory mechanisms remain unclear. Parathyroid hormone (PTH)/PTH-related protein receptor (PTHR) is a GPCR coupled with G_s and G_q G_s activates adenylyl cyclases (ACs), which produces cAMP to regulate various cell fates. We previously showed that cell surface expression of PTHR was increased by its direct interaction with a subcortical cytoskeletal protein, 4.1G, whereas PTHR-mediated G_s/AC/cAMP signaling was suppressed by 4.1G through an unknown mechanism in human embryonic kidney (HEK)293 cells. In the present study, we found that AC type 6 (AC6), one of the major ACs activated downstream of PTHR, interacts with 4.1G in HEK293 cells, and the N-terminus of AC6 (AC6-N) directly and selectively binds to the 4.1/ezrin/radixin/moesin (FERM) domain of 4.1G (4.1G-FERM) in vitro. AC6-N was distributed at the plasma membrane, which was disturbed by knockdown of 4.1G. An AC6-N mutant, AC6-N-3A, in which three consecutive arginine residues are mutated to alanine residues, altered both binding to 4.1G-FERM and its plasma membrane distribution in vivo. Further, we overexpressed AC6-N to competitively inhibit the interaction of endogenous AC6 and 4.1G in cells. cAMP production induced by forskolin, an adenylyl cyclase activator, and PTH-(1-34) was enhanced by AC6-N expression and 4.1G-knockdown. In contrast, AC6-N-3A had no impact on forskolin- and PTH-(1-34)-induced cAMP productions. These data provide a novel regulatory mechanism that AC6 activity is suppressed by the direct binding of 4.1G to AC6-N, resulting in attenuation of PTHR-mediated G_s/AC6/cAMP signaling.

The physiological role of the amyloid precursor protein as an adhesion molecule in the developing nervous system

The amyloid precursor protein (APP) is a type I transmembrane glycoprotein better known for its participation in the physiopathology of Alzheimer disease as the source of the beta amyloid fragment. However, the physiological functions of the full length protein and its proteolytic fragments have remained elusive. APP was first described as a cell-surface receptor; nevertheless, increasing evidence highlighted APP as a cell adhesion molecule. In this review, we will focus on the current knowledge of the physiological role of APP as a cell adhesion molecule and its involvement in key events of neuronal development, such as migration, neurite outgrowth, growth cone pathfinding, and synaptogenesis. Finally, since APP is over-expressed in Down syndrome individuals because of the extra copy of chromosome 21, in the last section of the review, we discuss the potential contribution of APP to the neuronal and synaptic defects described in this genetic condition. Read the Editorial Highlight for this article on page 9. Cover Image for this issue: doi. 10.1111/jnc.13817.

Deletion of the intestinal plasma membrane calcium pump, isoform 1, Atp2b1, in mice is associated with decreased bone mineral density and impaired responsiveness to 1, 25-dihydroxyvitamin D3

The physiological importance of the intestinal plasma membrane calcium pump, isoform 1, (Pmca1, Atp2b1), in calcium absorption and homeostasis has not been previously demonstrated in vivo. Since global germ-line deletion of the Pmca1 in mice is associated with embryonic lethality, we selectively deleted the Pmca1 in intestinal absorptive cells. Mice with loxP sites flanking exon 2 of the Pmca1 gene (Pmca1(fl/fl)) were crossed with mice expressing Cre recombinase in the intestine under control of the villin promoter to give mice in which the Pmca1 had been deleted in the intestine (Pmca1(EKO) mice). Pmca1(EKO) mice were born at a reduced frequency and were small at the time of birth when compared to wild-type (Wt) littermates. At two months of age, Pmca1(EKO) mice fed a 0.81% calcium, 0.34% phosphorus, normal vitamin D diet had reduced whole body bone mineral density (P < 0.037), and reduced femoral bone mineral density (P < 0.015). There was a trend towards lower serum calcium and higher serum parathyroid hormone (PTH) and 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3) concentrations in Pmca1(EKO) mice compared to Wt mice but the changes were not statistically significant. The urinary phosphorus/creatinine ratio was increased in Pmca1(EKO) mice (P < 0.004). Following the administration of 200 ng of 1α,25(OH)2D3 intraperitoneally to Wt mice, active intestinal calcium transport increased ∼2-fold, whereas Pmca1(EKO) mice administered an equal amount of 1α,25(OH)2D3 failed to show an increase in active calcium transport. Deletion of the Pmca1 in the intestine is associated with reduced growth and bone mineralization, and a failure to up-regulate calcium absorption in response to 1α,25(OH)2D3.

Transcriptome analysis of neonatal larvae after hyperthermia-induced seizures in the contractile silkworm, Bombyx mori

The ability to respond quickly and efficiently to transient extreme environmental conditions is an important property of all biota. However, the physiological basis of thermotolerance in different species is still unclear. Here, we found that the cot mutant showed a seizure phenotype including contraction of the body, rolling, vomiting gut juice and a momentary cessation of movement, and the heartbeat rhythm of the dorsal vessel significantly increases after hyperthermia. To comprehensively understand this process at the molecular level, the transcriptomic profile of cot mutant, which is a behavior mutant that exhibits a seizure phenotype, was investigated after hyperthermia (42°C) that was induced for 5 min. By digital gene expression profiling, we determined the gene expression profile of three strains (cot/cot ok/ok, +/+ ok/ok and +/+ +/+) under hyperthermia (42°C) and normal (25°C) conditions. A Venn diagram showed that the most common differentially expressed genes (DEGs, FDR<0.01 and log2 Ratio≥1) were up-regulated and annotated with the heat shock proteins (HSPs) in 3 strains after treatment with hyperthermia, suggesting that HSPs rapidly increased in response to high temperature; 110 unique DEGs, could be identified in the cot mutant after inducing hyperthermia when compared to the control strains. Of these 110 unique DEGs, 98.18% (108 genes) were up-regulated and 1.82% (two genes) were down-regulated in the cot mutant. KEGG pathways analysis of these unique DEGs suggested that the top three KEGG pathways were “Biotin metabolism,” “Fatty acid biosynthesis” and “Purine metabolism,” implying that diverse metabolic processes are active in cot mutant induced-hyperthermia. Unique DEGs of interest were mainly involved in the ubiquitin system, nicotinic acetylcholine receptor genes, cardiac excitation–contraction coupling or the Notch signaling pathway. Insights into hyperthermia-induced alterations in gene expression and related pathways could yield hints for understanding the relationship between behaviors and environmental stimuli (hyperthermia) in insects.

Band 4.1 proteins are expressed in the retina and interact with both isoforms of the metabotropic glutamate receptor type 8

The function of the CNS depends on the correct regulation of neurotransmitter receptors by interacting proteins. Here, we screened a retinal cDNA library for proteins interacting with the intracellular C-terminus of the metabotropic glutamate receptor isoform 8a (mGluR8a). The band 4.1B protein binds to the C-termini of mGluR8a and mGluR8b, co-localizes with these glutamate receptors in transfected mammalian cells, facilitates their cell surface expression and inhibits the mGluR8 mediated reduction of intracellular cAMP concentrations. In contrast, no interaction with 4.1B was observed for other mGluRs tested. Amino acids encoded by exons 19 and 20 of 4.1B and a stretch of four basic amino acids present in the mGluR8 C-termini mediate the protein interaction. Besides binding to 4.1B, mGluR8 isoforms interact with 4.1G, 4.1N, and 4.1R. Because band 4.1 transcripts undergo extensive alternative splicing, we analyzed the splicing pattern of interacting regions and detected a 4.1B isoform expressed specifically in the retina. Within this tissue, mGluR8 and 4.1B, 4.1G, 4.1N, and 4.1R show a comparable distribution, being expressed in both synaptic layers and in somata of the ganglion cell layer. In summary, our studies identified band 4.1 proteins as new players for the mGluR8 mediated signal transduction.

Protein 4.1 and the control of ion channels

The classical function of 4.1R in red blood cells is to contribute to the mechanochemical properties of the membrane by promoting the interaction between spectrin and actin. More recently, it has been recognized that 4.1R is required for the stable cell surface accumulation of a number of erythrocyte membrane proteins. 4.1R is one member of the mammalian 4.1 family - the others being 4.1N, 4.1G and 4.1B - and is expressed in many cell types other than erythrocytes. Recently we have examined the phenotype of hearts from 4.1R knockout mice. Although they had a generally normal morphology, these hearts exhibited bradycardia, and prolongation of both action potentials and QT intervals. Electrophysiological analysis revealed anomalies in a range of ion channel activities. In addition, the immunoreactivity of voltage-gated Na(+) channel NaV1.5 was reduced, indicating a role for 4.1R in the cellular accumulation of this ion channel. 4.1 proteins also have roles in the accumulation of at least two other classes of ion channel. In epithelia, 4.1 interacts with the store-operated channel TRPC4. In neurons, the ligand-gated channels GluR1 and GluR4 require 4.1 proteins for cell surface accumulation. The spectrum of transmembrane proteins that bind to 4.1 proteins overlaps with that of ankyrin. A hypothesis to investigate in the future is that differential regulation of 4.1 and ankyrins (e.g. by PIP(2)) allows highly selective control of cell surface accumulation and transport activity of a specific range of ion channels.

Downregulation of protein 4.1R, a mature centriole protein, disrupts centrosomes, alters cell cycle progression, and perturbs mitotic spindles and anaphase

Centrosomes nucleate and organize interphase microtubules and are instrumental in mitotic bipolar spindle assembly, ensuring orderly cell cycle progression with accurate chromosome segregation. We report that the multifunctional structural protein 4.1R localizes at centrosomes to distal/subdistal regions of mature centrioles in a cell cycle-dependent pattern. Significantly, 4.1R-specific depletion mediated by RNA interference perturbs subdistal appendage proteins ninein and outer dense fiber 2/cenexin at mature centrosomes and concomitantly reduces interphase microtubule anchoring and organization. 4.1R depletion causes G(1) accumulation in p53-proficient cells, similar to depletion of many other proteins that compromise centrosome integrity. In p53-deficient cells, 4.1R depletion delays S phase, but aberrant ninein distribution is not dependent on the S-phase delay. In 4.1R-depleted mitotic cells, efficient centrosome separation is reduced, resulting in monopolar spindle formation. Multipolar spindles and bipolar spindles with misaligned chromatin are also induced by 4.1R depletion. Notably, all types of defective spindles have mislocalized NuMA (nuclear mitotic apparatus protein), a 4.1R binding partner essential for spindle pole focusing. These disruptions contribute to lagging chromosomes and aberrant microtubule bridges during anaphase/telophase. Our data provide functional evidence that 4.1R makes crucial contributions to the structural integrity of centrosomes and mitotic spindles which normally enable mitosis and anaphase to proceed with the coordinated precision required to avoid pathological events.

Neuroacanthocytosis associated with a defect of the 4.1R membrane protein

Background

Neuroacanthocytosis (NA) denotes a heterogeneous group of diseases that are characterized by nervous system abnormalities in association with acanthocytosis in the patients' blood. The 4.1R protein of the erythrocyte membrane is critical for the membrane-associated cytoskeleton structure and in central neurons it regulates the stabilization of AMPA receptors on the neuronal surface at the postsynaptic density. We report clinical, biochemical, and genetic features in four patients from four unrelated families with NA in order to explain the cause of morphological abnormalities and the relationship with neurodegenerative processes.

Case presentation

All patients were characterised by atypical NA with a novel alteration of the erythrocyte membrane: a 4.1R protein deficiency. The 4.1R protein content was significantly lower in patients (3.40 ± 0.42) than in controls (4.41 ± 0.40, P < 0.0001), reflecting weakened interactions of the cytoskeleton with the membrane. In patients IV:1 (RM23), IV:3 (RM15), and IV:6 (RM16) the 4.1 deficiency seemed to affect the horizontal interactions of spectrin and an impairment of the dimer self-association into tetramers was detected. In patient IV:1 (RM16) the 4.1 deficiency seemed to affect the skeletal attachment to membrane and the protein band 3 was partially reduced.

Conclusion

A decreased expression pattern of the 4.1R protein was observed in the erythrocytes from patients with atypical NA, which might reflect the expression pattern in the central nervous system, especially basal ganglia, and might lead to dysfunction of AMPA-mediated glutamate transmission.

Whirlin complexes with p55 at the stereocilia tip during hair cell development

Hearing in mammals depends upon the proper development of actin-filled stereocilia at the hair cell surface in the inner ear. Whirlin, a PDZ domain-containing protein, is expressed at stereocilia tips and, by virtue of mutations in the whirlin gene, is known to play a key role in stereocilia development. We show that whirlin interacts with the membrane-associated guanylate kinase (MAGUK) protein, erythrocyte protein p55 (p55). p55 is expressed in outer hair cells in long stereocilia that make up the stereocilia bundle as well as surrounding shorter stereocilia structures. p55 interacts with protein 4.1R in erythrocytes, and we find that 4.1R is also expressed in stereocilia structures with an identical pattern to p55. Mutations in the whirlin gene (whirler) and in the myosin XVa gene (shaker2) affect stereocilia development and lead to early ablation of p55 and 4.1R labeling of stereocilia. The related MAGUK protein Ca2+-calmodulin serine kinase (CASK) is also expressed in stereocilia in both outer and inner hair cells, where it is confined to the stereocilia bundle. CASK interacts with protein 4.1N in neuronal tissue, and we find that 4.1N is expressed in stereocilia with an identical pattern to CASK. Unlike p55, CASK labeling shows little diminution of labeling in the whirler mutant and is unaffected in the shaker2 mutant. Similarly, expression of 4.1N in stereocilia is unaltered in whirler and shaker2 mutants. p55 and protein 4.1R form complexes critical for actin cytoskeletal assembly in erythrocytes, and the interaction of whirlin with p55 indicates it plays a similar role in hair cell stereocilia.

PIKE GTPase signaling and function

PIKE (PI 3-Kinase Enhancer) is a recently identified brain specific nuclear GTPase, which binds PI 3-kinase and stimulates its lipid kinase activity. Nerve growth factor treatment leads to PIKE activation by triggering the nuclear translocation of phospholipase C-gamma1 (PLC-gamma1), which acts as a physiologic guanine nucleotide exchange factor (GEF) for PIKE through its SH3 domain. To date, three forms of PIKE have been characterized: PIKE-S, PIKE-L and PIKE-A. PIKE-S is initially identified shorter isoform. PIKE-L, a longer isoform of PIKE gene, differs from PIKE-S by C-terminal extension containing Arf-GAP (ADP ribosylation factor-GTPase Activating Protein) and two ankyrin repeats domains. In contrast to the exclusive nuclear localization of PIKE-S, PIKE-L occurs in both the nucleus and the cytoplasm. PIKE-L physiologically associates with Homer 1, an mGluR I binding adaptor protein. The Homer/PIKE-L complex couples PI 3-kinase to mGluR I and regulates a major action of group I mGluRs, prevention of neuronal apoptosis. More recently, a third PIKE isoform, PIKE-A was identified in human glioblastoma multiforme brain cancers. Unlike the brain specific PIKE-L and -S isoforms, PIKE-A distributes in various tissues. PIKE-A contains the same domains present in PIKE-L but lacks N-terminal proline-rich domain (PRD), which binds PI 3-kinase and PLC-gamma1. Instead, PIKE-A specifically binds to active Akt and upregulates its activity in a GTP-dependent manner, mediating human cancer cell invasion and preventing apoptosis. Thus, PIKE extends its roles from the nucleus to the cytoplasm, mediating cellular processes from cell invasion to programmed cell death.

Nectin-like molecule 1 is a protein 4.1N associated protein and recruits protein 4.1N from cytoplasm to the plasma membrane

Nectins are immunoglobulin superfamily adhesion molecules that participate in the organization of epithelial and endothelial junctions. Sharing high homology with the poliovirus receptor (PVR/CD155), nectins were also named poliovirus receptor-related proteins (PRRs). Four nectins and five nectin-like molecules have been identified. Here we describe the cloning and characterization of human and mouse nectin-like molecular 1 (NECL1). Human and mouse NECL1 share 87.3% identity at the amino acid level. NECL1 contains an ectodomain made of three immunoglobulin-like domains, and a cytoplasmic region homologous to those of glycophorin C and contactin-associated protein. RNA blot and in situ hybridization analysis showed that NECL1 predominantly expressed in the central nervous system, mainly in neuronal cell bodies in a variety of brain regions including the cerebellum, cerebral cortex and hippocampus. In vitro binding assay proved the association of NECL1 with protein 4.1N. NECL1 localizes to the cell-cell junctions and recruits protein 4.1N to the plasma membranes through its C-terminus, thus may regulate the function of the cell-cell junction. We propose that the NECL1 and protein 4.1N complex is involved in the morphological development, stability, and dynamic plasticity of the nervous system.

Putative tumor suppressor protein 4.1B is differentially expressed in kidney and brain via alternative promoters and 5' alternative splicing

Protein 4.1B has been reported as a tumor suppressor in brain, but not in kidney, despite high expression in both tissues. Here we demonstrate that N-terminal variability in kidney and brain 4.1B isoforms arises through an unusual coupling of RNA processing events in the 5' region of the gene. We describe two transcriptional promoters at far upstream alternative exons 1A and 1B, and show that their respective transcripts splice differentially to exon 2'/2 in a manner that determines mRNA coding capacity. The consequence of this unique processing is that exon 1B transcripts initiate translation at AUG1 (in exon 2') and encode larger 4.1B isoforms with an N-terminal extension; exon 1A transcripts initiate translation at AUG2 (in exon 4) and encode smaller 4.1B isoforms. Tissue-specific differences in promoter utilization may thus explain the abundance of larger 4.1B isoforms in brain but not in kidney. In cell studies, differentiation of PC12 cells was accompanied by translocation of large protein 4.1B isoforms into the nucleus. We propose that first exon specification is coupled to downstream splicing events, generating 4.1B isoforms with diverse roles in kidney and brain physiology, and potentially unique functions in cell proliferation and tumor suppression.

Hereditary haemolytic anaemias: unexpected sequelae of mutations in the genes for erythroid membrane skeletal proteins

Although the haemolytic anaemia may be the primary concern for hereditary spherocytosis and elliptocytosis patients, it is clear that their situation can be compromised by primary and secondary defects in erythroid and non-erythroid systems of the body. All seven of the red cell membrane skeletal proteins discussed in this review are also expressed in non-erythroid tissues, and mutations in their genes have the potential to cause non-erythroid defects. In some instances, such as the protein 4.1R and ANK1 neurological deficits, the diagnosis is clear. In other instances, because of the complex expression patterns involved, the non-erythroid effects may be difficult to assess. An example is the large multidomain, multifunctional band 3 protein. In this case, the location of the mutation can cause defects in one functional domain or isoform and not the other. In other cases, such as the beta-adducin null mutation, other isoforms may partially compensate for the primary deficiency. In such cases, it may be that the effects of the deficit are subtle but could increase under stress or with age. To be completely successful, treatment strategies must address both primary and secondary effects of the anaemia. If gene replacement therapy is to be used, the more that is known about the underlying genetic mechanisms producing the multiple isoforms the better we will be able to design the best replacement gene. The various animal models that are now available should be invaluable in this regard. They continue to contribute to our understanding of both the primary and the secondary effects and their treatment.

Differential domain evolution and complex RNA processing in a family of paralogous EPB41 (protein 4.1) genes facilitate expression of diverse tissue-specific isoforms

The EPB41 (protein 4.1) genes epitomize the resourcefulness of the mammalian genome to encode a complex proteome from a small number of genes. By utilizing alternative transcriptional promoters and tissue-specific alternative pre-mRNA splicing, EPB41, EPB41L2, EPB41L3, and EPB41L1 encode a diverse array of structural adapter proteins. Comparative genomic and transcript analysis of these 140- to 240-kb genes indicates several unusual features: differential evolution of highly conserved exons encoding known functional domains interspersed with unique exons whose size and sequence variations contribute substantially to intergenic diversity; alternative first exons, most of which map far upstream of the coding regions; and complex tissue-specific alternative pre-mRNA splicing that facilitates synthesis of functionally different complements of 4.1 proteins in various cells. Understanding the splicing regulatory networks that control protein 4.1 expression will be critical to a full appreciation of the many roles of 4.1 proteins in normal cell biology and their proposed roles in human cancer.

Inositol 1,4,5-trisphosphate receptors as signal integrators

The inositol 1,4,5 trisphosphate (IP3) receptor (IP3R) is a Ca2+ release channel that responds to the second messenger IP3. Exquisite modulation of intracellular Ca2+ release via IP3Rs is achieved by the ability of IP3R to integrate signals from numerous small molecules and proteins including nucleotides, kinases, and phosphatases, as well as nonenzyme proteins. Because the ion conduction pore composes only approximately 5% of the IP3R, the great bulk of this large protein contains recognition sites for these substances. Through these regulatory mechanisms, IP3R modulates diverse cellular functions, which include, but are not limited to, contraction/excitation, secretion, gene expression, and cellular growth. We review the unique properties of the IP3R that facilitate cell-type and stimulus-dependent control of function, with special emphasis on protein-binding partners.

Hereditary elliptocytosis: spectrin and protein 4.1R

Hereditary elliptocytosis (HE) is a common disorder of erythrocyte shape, occurring especially in individuals of African and Mediterranean ancestry, presumably because elliptocytes confer some resistance to malaria. The principle lesion in HE is mechanical weakness or fragility of the erythrocyte membrane skeleton due to defects in alpha-spectrin, beta-spectrin, or protein 4.1. Numerous mutations have been described in the genes encoding these proteins, including point mutations, gene deletions and insertions, and mRNA processing defects. Several mutations have been identified in a number of individuals on the same genetic background, suggesting a "founder effect." The majority of HE patients are asymptomatic, but some may experience hemolytic anemia, splenomegaly, and intermittent jaundice.

PIKE GTPase: a novel mediator of phosphoinositide signaling

Phosphoinositide (PI) 3-kinase enhancer (PIKE) is a brain-specific GTPase that binds to PI 3-kinase and stimulates its lipid kinase activity. It exists in two forms: the first to be identified, PIKE-S, is shorter and exclusively nuclear; by contrast, the longer form, PIKE-L, resides in multiple intracellular compartments. Nerve growth factor treatment leads to PIKE-S activation by triggering the nuclear translocation of phospholipase C (PLC)-γ1, which acts as a physiological guanine nucleotide exchange factor (GEF) for PIKE-S through its Src-homlogy 3 (SH3) domain. Cytoplasmic PI 3-kinase and its lipid product phosphatidylinositol (3,4,5)-trisphosphate [PtdIns(3,4,5)P3] regulate the membrane translocation and activation of many signaling molecules by binding to their pleckstrin homology (PH) domains. However, little is known about the physiological roles of their nuclear counterparts. The nuclear PLC-γ1/PIKE-S/PI 3-kinase signaling pathway seems to be an extension of the crosstalk between cytoplasmic PLC-γ1 and PI 3-kinase. PIKE-L contains a C-terminal extension consisting of an ADP ribosylation-GTPase-activating protein (ArfGAP) domain and two ankyrin repeats in addition to the N-terminal GTPase domain. PIKE-L could have additional, extranuclear functions, including regulation of postsynaptic signaling by metabotropic glutamate receptors.

Identification of a third Protein 4.1 tumor suppressor, Protein 4.1R, in meningioma pathogenesis

Meningiomas are common central nervous system tumors; however, the mechanisms underlying their pathogenesis are largely undefined. In this report, we demonstrate that a third Protein 4.1 family member, Protein 4.1R, functions as a meningioma tumor suppressor. We observed loss of Protein 4.1R expression in two meningioma cell lines (IOMM-Lee, CH157-MN) by Western blotting as well as in 6 of 15 sporadic meningiomas by immunohistochemistry and fluorescence in situ hybridization. In support of a meningioma tumor suppressor function, Protein 4.1R overexpression resulted in reduced IOMM-Lee and CH157-MN cell proliferation. Similar to the Protein 4.1B and merlin tumor suppressors, Protein 4.1R membrane localization increased significantly under conditions of growth arrest in vitro. Lastly, we show that Protein 4.1R interacted with a subset of merlin/Protein 4.1B interactors including CD44 and betaII-spectrin. Collectively, these results suggest that Protein 4.1R functions as an important tumor suppressor in the molecular pathogenesis of meningioma.

Alternative 5' exons and differential splicing regulate expression of protein 4.1R isoforms with distinct N-termini

Among the alternative pre-mRNA splicing events that characterize protein 4.1R gene expression, one involving exon 2' plays a critical role in regulating translation initiation and N-terminal protein structure. Exon 2' encompasses translation initiation site AUG1 and is located between alternative splice acceptor sites at the 5' end of exon 2; its inclusion or exclusion from mature 4.1R mRNA regulates expression of longer or shorter isoforms of 4.1R protein, respectively. The current study reports unexpected complexity in the 5' region of the 4.1R gene that directly affects alternative splicing of exon 2'. Identified far upstream of exon 2 in both mouse and human genomes were 3 mutually exclusive alternative 5' exons, designated 1A, 1B, and 1C; all 3 are associated with strong transcriptional promoters in the flanking genomic sequence. Importantly, exons 1A and 1B splice differentially with respect to exon 2', generating transcripts with different 5' ends and distinct N-terminal protein coding capacity. Exon 1A-type transcripts splice so as to exclude exon 2' and therefore utilize the downstream AUG2 for translation of 80-kDa 4.1R protein, whereas exon 1B transcripts include exon 2' and initiate at AUG1 to synthesize 135-kDa isoforms. RNA blot analyses revealed that 1A transcripts increase in abundance in late erythroblasts, consistent with the previously demonstrated up-regulation of 80-kDa 4.1R during terminal erythroid differentiation. Together, these results suggest that synthesis of structurally distinct 4.1R protein isoforms in various cell types is regulated by a novel mechanism requiring coordination between upstream transcription initiation events and downstream alternative splicing events.

Association of the type 1 inositol (1,4,5)-trisphosphate receptor with 4.1N protein in neurons

The type 1 inositol (1,4,5)-trisphosphate receptor (InsP(3)R1) is an intracellular calcium (Ca(2+)) release channel that plays an important role in neuronal function. In yeast two-hybrid screen of rat brain cDNA library with the InsP(3)R1 carboxy-terminal bait we isolated multiple clones of neuronal cytoskeletal protein 4.1N. We mapped the 4.1N-interaction site to a short fragment (50 amino acids) within the carboxy-terminal tail of the InsP(3)R1 and the InsP(3)R1-interaction site to the carboxy-terminal domain (CTD) of 4.1N. We established that InsP(3)R1 carboxy-terminal binds selectively to the CTDDelta alternatively spliced form of the 4.1N protein. In biochemical experiments we demonstrated that 4.1N and InsP(3)R1 specifically associate in vitro. We showed that both 4.1N and InsP(3)R1 were enriched in synaptic locations and immunoprecipitated the 4.1N-InsP(3)R1 complex from rat brain synaptosomes. In biochemical experiments we demonstrated a possibility of InsP(3)R1-4.1N-CASK-syndecan-2 quaternary complex formation. From our findings we hypothesize that InsP(3)R1-4.1N association may play a role in InsP(3)R1 localization or Ca(2+) signaling in neurons.

Mutational spectrum of the CHAC gene in patients with chorea-acanthocytosis

Chorea-acanthocytosis (ChAc) is an autosomal recessive neurological disorder whose characteristic features include hyperkinetic movements and abnormal red blood cell morphology. Mutations in the CHAC gene on 9q21 were recently found to cause chorea-acanthocytosis. CHAC encodes a large, novel protein with a yeast homologue implicated in protein sorting. In this study, all 73 exons plus flanking intronic sequence in CHAC were screened for mutations by denaturing high-performance liquid chromatography in 43 probands with ChAc. We identified 57 different mutations, 54 of which have not previously been reported, in 39 probands. The novel mutations comprise 15 nonsense, 22 insertion/deletion, 15 splice-site and two missense mutations and are distributed throughout the CHAC gene. Three mutations were found in multiple families within this or our previous study. The preponderance of mutations that are predicted to cause absence of gene product is consistent with the recessive inheritance of this disease. The high proportion of splice-site mutations found is probably a reflection of the large number of exons that comprise the CHAC gene. The CHAC protein product, chorein, appears to have a certain tolerance to amino-acid substitutions since only two out of nine substitutions described here appear to be pathogenic.

Syndecan-3-deficient mice exhibit enhanced LTP and impaired hippocampus-dependent memory

Syndecan-3 (N-syndecan) is a transmembrane heparan sulfate proteoglycan expressed predominantly in the nervous system in a developmentally regulated manner. Syndecan-3 has been suggested to play a role in the development and plasticity of neuronal connections by linking extracellular signals to the regulation of the cytoskeleton. To study its physiological functions, we produced mice deficient in syndecan-3 by gene targeting. The mutant animals are healthy, are fertile, and have no apparent defects in the structure of the brain. We focused on characterizing the functions of the hippocampus, a brain area where expression of syndecan-3 is prominent in adults. Mice lacking syndecan-3 exhibited an enhanced level of long-term potentiation (LTP) in area CA1, while basal synaptic transmission and short-term plasticity were similar to those in wild-type animals. Further, the mutant mice were not responsive to the syndecan-3 ligand heparin-binding growth-associated molecule, which inhibits LTP in area CA1 in wild-type animals. Behavioral testing of the syndecan-3-deficient mice revealed impaired performance in tasks assessing hippocampal functioning. We suggest that syndecan-3 acts as an important modulator of synaptic plasticity that influences hippocampus-dependent memory.

D2 and D3 dopamine receptor cell surface localization mediated by interaction with protein 4.1N

We identified protein 4.1N as a D2-like dopamine receptor-interacting protein in a yeast two-hybrid screen. Protein 4.1N is a neuronally enriched member of the 4.1 family of cytoskeletal proteins, which also includes protein 4.1R of erythrocytes and the 4.1G and 4.1B isoforms. The interaction of protein 4.1N was specific for the D2 and D3 dopamine receptors and was independently confirmed in pulldown and coimmunoprecipitation assays. Deletion mapping localized the site of dopamine receptor/protein 4.1N interaction to the N-terminal segment of the third intracellular domain of D2 and D3 receptors and the carboxyl-terminal domain of protein 4.1N. D2 and D3 receptors were also found to interact with the highly conserved carboxyl-terminal domain of proteins 4.1R, 4.1G, and 4.1B. Immunofluorescence studies show that protein 4.1N and D2 and D3 dopamine receptors are expressed at the plasma membrane of transfected human embryonic kidney 293 and mouse neuroblastoma Neuro2A cells. However, expression of D2 or D3 receptors with a protein 4.1N truncation fragment reduces the level of D2 and D3 receptor expression at the plasma membrane. These results suggest that protein 4.1N/dopamine receptor interaction is required for localization or stability of dopamine receptors at the neuronal plasma membrane.

Spectrin and ankyrin-based pathways: metazoan inventions for integrating cells into tissues

The spectrin-based membrane skeleton of the humble mammalian erythrocyte has provided biologists with a set of interacting proteins with diverse roles in organization and survival of cells in metazoan organisms. This review deals with the molecular physiology of spectrin, ankyrin, which links spectrin to the anion exchanger, and two spectrin-associated proteins that promote spectrin interactions with actin: adducin and protein 4.1. The lack of essential functions for these proteins in generic cells grown in culture and the absence of their genes in the yeast genome have, until recently, limited advances in understanding their roles outside of erythrocytes. However, completion of the genomes of simple metazoans and application of homologous recombination in mice now are providing the first glimpses of the full scope of physiological roles for spectrin, ankyrin, and their associated proteins. These functions now include targeting of ion channels and cell adhesion molecules to specialized compartments within the plasma membrane and endoplasmic reticulum of striated muscle and the nervous system, mechanical stabilization at the tissue level based on transcellular protein assemblies, participation in epithelial morphogenesis, and orientation of mitotic spindles in asymmetric cell divisions. These studies, in addition to stretching the erythrocyte paradigm beyond recognition, also are revealing novel cellular pathways essential for metazoan life. Examples are ankyrin-dependent targeting of proteins to excitable membrane domains in the plasma membrane and the Ca(2+) homeostasis compartment of the endoplasmic reticulum. Exciting questions for the future relate to the molecular basis for these pathways and their roles in a clinical context, either as the basis for disease or more positively as therapeutic targets.

The prototypical 4.1R-10-kDa domain and the 4.1g-10-kDa paralog mediate fodrin-actin complex formation

A complex family of 4.1R isoforms has been identified in non-erythroid tissues. In this study we characterized the exonic composition of brain 4.1R-10-kDa or spectrin/actin binding (SAB) domain and identified the minimal sequences required to stimulate fodrin/F-actin association. Adult rat brain expresses predominantly 4.1R mRNAs that carry an extended SAB, consisting of the alternative exons 14/15/16 and part of the constitutive exon 17. Exon 16 along with sequences carried by exon 17 is necessary and sufficient to induce formation of fodrin-actin-4.1R ternary complexes. The ability of the respective SAB domains of 4.1 homologs to sediment fodrin/actin was also investigated. 4.1G-SAB stimulates association of fodrin/actin, although with an approximately 2-fold reduced efficiency compared with 4.1R-10-kDa, whereas 4.1N and 4.1B do not. Sequencing of the corresponding domains revealed that 4.1G-SAB carries a cassette that shares significant homology with 4.1R exon 16, whereas the respective sequence is divergent in 4.1N and absent from brain 4.1B. An approximately 150-kDa 4.1R and an approximately 160-kDa 4.1G isoforms are present in PC12 lysates that occur in vivo in a supramolecular complex with fodrin and F-actin. Moreover, proteins 4.1R and 4.1G are distributed underneath the plasma membrane in PC12 cells. Collectively, these observations suggest that brain 4.1R and 4.1G may modulate the membrane mechanical properties of neuronal cells by promoting fodrin/actin association.

Protein 4.1 in forebrain postsynaptic density preparations: enrichment of 4.1 gene products and detection of 4.1R binding proteins

4.1 Proteins are a family of multifunctional cytoskeletal components (4.1R, 4.1G, 4.1N and 4.1B) derived from four related genes, each of which is expressed in the nervous system. Using subcellular fractionation, we have investigated the possibility that 4.1 proteins are components of forebrain postsynaptic densities, cellular compartments enriched in spectrin and actin, whose interaction is regulated by 4.1R. Antibodies to each of 4.1R, 4.1G, 4.1N and 4.1B recognize polypeptides in postsynaptic density preparations. Of these, an 80-kDa 4.1R polypeptide is enriched 11-fold in postsynaptic density preparations relative to brain homogenate. Polypeptides of 150 and 125 kDa represent 4.1B; of these, only the 125 kDa species is enriched (threefold). Antibodies to 4.1N recognize polypeptides of approximately 115, 100, 90 and 65 kDa, each enriched in postsynaptic density preparations relative to brain homogenate. Minor 225 and 200 kDa polypeptides are recognized selectively by specific anti-4.1G antibodies; the 200 kDa species is enriched 2.5-fold. These data indicate that specific isoforms of all four 4.1 proteins are components of postsynaptic densities. Blot overlay analyses indicate that, in addition to spectrin and actin, postsynaptic density polypeptides of 140, 115, 72 and 66 kDa are likely to be 4.1R-interactive. Of these, 72 kDa and 66 kDa polypeptides were identified as neurofilament L and alpha-internexin, respectively. A complex containing 80 kDa 4.1R, alpha-internexin and neurofilament L was immunoprecipitated with anti-4.1R antibodies from brain extract. We conclude that 4.1R interacts with the characteristic intermediate filament proteins of postsynaptic densities, and that the 4.1 proteins have the potential to mediate the interactions of diverse components of postsynaptic densities.

Type II brain 4.1 (4.1B/KIAA0987), a member of the protein 4.1 family, is localized to neuronal paranodes

Histochemical analyses of type II brain 4.1/4.1B/KIAA0987, a member of the protein 4.1 family, were carried out in rat brain. In situ hybridization (ISH) showed that type II brain 4.1 mRNA is expressed in a variety of neuronal cells. In particular, type II brain 4.1 mRNA was actively transcribed in the cells of the mesencephalon and the brainstem, which have large myelinated nerve fibers. Expression of type II brain 4.1 mRNA was not observed at least in glial cells distributed in nerve fiber tracts. In immunohistochemical studies using anti-type II brain 4.1-specific antibody, the major immunosignals appeared as brilliant pairs of dots along nerve fibers. Such immunosignals were detected throughout the brain, but were highly concentrated in nerve fiber tracts. These data suggested that type II brain 4.1 is predominantly localized to neuronal paranodes. Detailed analysis concentrating on the nodal region indicated that type II brain 4.1 is present at the paranodal membrane but not in the axoplasm. Weaker type II brain 4.1-specific immunosignals were observed along the internodal membrane of myelinated axons and in the cytoplasm of some neuronal cells. Finally, comparative immunohistochemical studies using antibodies against the other three protein 4.1 family members, type I brain 4.1/4.1N/KIAA0338, erythroid type 4.1 (4.1R) and 4.1G, demonstrated that each of these proteins is distributed in a unique pattern in the cerebellum. Our results are the first to show that type II brain 4.1 is the only member of the protein 4.1 family localized to neuronal paranodes.

Abnormal erythrocyte anion exchange in Alzheimer disease

CONTEXT

Several abnormalities have been described in red blood cells of patients with Alzheimer disease (AD), but to date none of these has been confirmed by a second, independent study. Erythrocyte anion exchange has been reported to be abnormal in AD; we have developed a new technique for measuring anion exchange.

OBJECTIVES

To confirm the abnormality of erythrocyte anion exchange in AD and to determine whether the phenomenon has potential for clinical utility.

DESIGN

Comparison of patients with probable AD to age-matched controls.

SETTING

University hospital and ambulatory clinic.

METHODS

Chloride-bicarbonate exchange was measured in erythrocyte ghosts resealed with a fluorescent probe of chloride concentration.

RESULTS

Erythrocyte anion exchange is abnormal in AD. This difference appears in citrate but not EDTA anticoagulant. Mahalanobis's generalized distance between the 2 populations is 1.7, and a discriminant function derived from our technique classifies 82% of the study population in accordance with the National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association criteria. Receiver operating characteristic analysis demonstrates the possibility of choosing cutoffs with high sensitivity and specificity.

CONCLUSIONS

Measurement of red blood cell anion exchange may be useful in classifying patients with AD. The dependence of this phenomenon on anticoagulant suggests the involvement of platelet activation or complement fixation.

A constitutive region is responsible for nuclear targeting of 4.1R: modulation by alternative sequences results in differential intracellular localization

Red blood cell protein 4.1, 4.1R, is an extreme variation on the theme of isoform multiplicity. The diverse 4.1R isoforms, mainly generated by alternative pre-mRNA splicing, are localized at different intracellular sites, including the nucleus. To characterize nonerythroid 4.1 proteins lacking the most upstream translation initiation site, analyze their intracellular localization and define specific domains involved in differential intracellular targeting of 4.1R, we cloned 4.1 cDNAs lacking that translation initiation site. Seven different 4.1R cDNAs were isolated. Four of these encoded 4.1R proteins localized predominantly to the nucleus and the other three localized to the cytoplasm. Three of the nuclear 4.1R isoforms did not contain the nuclear localization signal previously identified in the alternative exon 16. A comparative analysis of the exon composition of the naturally occurring 4.1R cDNAs cloned and of appropriate composite cDNA constructs, with the subcellular distribution of their respective products, demonstrated that a region encoded by constitutive exons, which is therefore common to all 4.1R isoforms and has been termed ‘core region’, had the capacity of localizing to the nucleus. This region was able to confer nuclear targeting to a cytosolic reporter. In protein 4.1R isoforms, the nuclear targeting of the core region is modulated by the expression of alternative exons. Thus, exon 5-encoded sequences eclipsed nuclear entry of the core region, resulting in 4.1R isoforms that predominantly distributed to the cytoplasm. Exon 5 was also able to confer cytoplasmic localization to a nuclear reporter. In protein 4.1R isoforms, when exons 5 and 16 were both expressed the nuclear targeting effect of exon 16 was dominant to the inhibitory effect observed by the expression of exon 5, yielding proteins that predominantly localized to the nucleus. Taken together, these results indicate that all 4.1R molecules contain a conserved region that is sufficient to target the protein to the nucleus, but that specific exon-encoded sequences modulate this capacity by acting in a hierarchical order.

The genetics of the protein 4.1 family: organizers of the membrane and cytoskeleton

Protein 4.1 (also called band 4.1 or simply 4.1) was originally identified as an abundant protein of the human erythrocyte, in which it stabilizes the spectrin/actin cytoskeleton. The protein and its relatives have since been found in many cell types of metazoan organisms and they are often concentrated in the nucleus, as well as in cell-cell junctions. They form multimolecular complexes with transmembrane and membrane-associated proteins, and these complexes may be important for both structural stability and signal transduction at sites of cell contact.

New insights into functions of erythroid proteins in nonerythroid cells

This article presents new insights into potential roles that three erythrocyte cytoskeletal proteins, protein 4.1, ankyrin, and spectrin, may play in nonerythroid nucleated cells. Each of these proteins is encoded by several closely related genes characterized by complex alternative splicing of their pre-mRNA, thus resulting in the cellular expression of a broad repertoire of isoforms that can adopt tissue- and cell-specific distribution. This could account for the presence of skeletal networks in intracellular organelles such as lysosomes, the Golgi apparatus, or the nucleus. In addition to providing structural support to cell membranes, these cytoskeletal proteins regulate the functions of various transmembrane proteins they interact with, in particular ion channels, as well as the activity of membrane-bound enzymes. Thus, they appear to be key players in major unsuspected cell functions such as protein sorting, dynamics of nuclear architecture during mitosis, or regulation of signal transduction pathways.

Stroke in estrogen receptor-alpha-deficient mice

BACKGROUND AND PURPOSE

Recent evidence suggests that endogenous estrogens or hormone replacement therapy can ameliorate brain damage from experimental stroke. Protective mechanisms involve enhanced cerebral vasodilation during ischemic stress as well as direct preservation of neuronal viability. We hypothesized that if the intracellular estrogen receptor subtype-alpha (ERalpha) is important to estrogen's signaling in the ischemic brain, then ERalpha-deficient (knockout) (ERalphaKO) female mice would sustain exaggerated cerebral infarction damage after middle cerebral artery occlusion.

METHODS

The histopathology of cresyl violet-stained tissues was evaluated after reversible middle cerebral artery occlusion (2 hours, followed by 22 hours of reperfusion) in ERalphaKO transgenic and wild-type (WT) mice (C57BL/6J background strain). End-ischemic cerebral blood flow mapping was obtained from additional female murine cohorts by using [(14)C]iodoantipyrine autoradiography.

RESULTS

Total hemispheric tissue damage was not altered by ERalpha deficiency in female mice: 51.9+/-10.6 mm(3) in ERalphaKO versus 60.5+/-5.0 mm(3) in WT. Striatal infarction was equivalent, 12.2+/-1.7 mm(3) in ERalphaKO and 13.4+/-1.0 mm(3) in WT mice, but cortical infarction was paradoxically smaller relative to that of the WT (20.7+/-4.5 mm(3) in ERalphaKO versus 30.6+/-4.1 mm(3) in WT). Intraocclusion blood flow to the parietal cortex was higher in ERalphaKO than in WT mice, likely accounting for the reduced infarction in this anatomic area. There were no differences in stroke outcomes by region or genotype in male animals.

CONCLUSIONS

Loss of ERalpha does not enhance tissue damage in the female animal, suggesting that estrogen inhibits brain injury by mechanisms that do not depend on activation of this receptor subtype.

Molecular and functional characterization of protein 4.1B, a novel member of the protein 4.1 family with high level, focal expression in brain

Brain-enriched isoforms of skeletal proteins in the spectrin and ankyrin gene families have been described. Here we characterize protein 4.1B, a novel homolog of erythrocyte protein 4.1R that is encoded by a distinct gene. In situ hybridization revealed high level, focal expression of 4.1B mRNA in select neuronal populations within the mouse brain, including Purkinje cells of the cerebellum, pyramidal cells in hippocampal regions CA1-3, thalamic nuclei, and olfactory bulb. Expression was also detected in adrenal gland, kidney, testis, and heart. 4.1B protein exhibits high homology to the membrane binding, spectrin-actin binding, and C-terminal domains of 4.1R, including motifs for interaction with NuMA and FKBP13. cDNA characterization and Western blot analysis revealed multiple spliceoforms of protein 4.1B, with functionally relevant heterogeneity in the spectrin-actin and NuMA binding domains. Regulated alternative splicing events led to expression of unique 4. 1B isoforms in brain and muscle; only the latter possessed a functional spectrin-actin binding domain. By immunofluorescence, 4. 1B was localized specifically at the plasma membrane in regions of cell-cell contact. Together these results indicate that 4.1B transcription is selectively regulated among neuronal populations and that alternative splicing regulates expression of 4.1B isoforms possessing critical functional domains typical of other protein 4.1 family members.

Protein 4.1N binding to nuclear mitotic apparatus protein in PC12 cells mediates the antiproliferative actions of nerve growth factor

Protein 4.1N is a neuronal selective isoform of the erythrocyte membrane cytoskeleton protein 4.1R. In the present study, we demonstrate an interaction between 4.1N and nuclear mitotic apparatus protein (NuMA), a nuclear protein required for mitosis. The binding involves the C-terminal domain of 4.1N. In PC12 cells treatment with nerve growth factor (NGF) elicits translocation of 4. 1N to the nucleus and promotes its association with NuMA. Specific targeting of 4.1N to the nucleus arrests PC12 cells at the G1 phase and produces an aberrant nuclear morphology. Inhibition of 4.1N nuclear translocation prevents the NGF-mediated arrest of cell division, which can be reversed by overexpression of 4.1N. Thus, nuclear 4.1N appears to mediate the antiproliferative actions of NGF by antagonizing the role of NuMA in mitosis.

Estrogen receptor antagonist ICI182,780 exacerbates ischemic injury in female mouse

Recent findings in animals emphasize that experimental ischemic brain damage can be strikingly reduced by estrogen: however, the neuroprotective mechanisms are not well understood. It was hypothesized that estrogen signaling via cognate estrogen receptors (ERs) within the vasculature is an important aspect of cerebral ischemic protection in the female brain, in part by amplifying intraischemic cerebral blood flow (CBF). In the present study, the hypothesis that chronic treatment with the pure ER antagonist ICI182,780 (ICI) would increase ischemic brain damage by a blood flow-mediated mechanism was investigated. Adult C57B1/6J mice were pretreated with either subcutaneous ICI (100 microg/day) or oil/ethanol vehicle for 1 week before 2 hours of middle cerebral artery occlusion (MCAO) and 22 hours of reperfusion. End-ischemic regional CBF was evaluated in additional cohorts using [14C]iodoantipyrine autoradiography. Infarction volume as measured by cresyl violet histology was greater in the striatum of ICI-treated females (70 +/- 3% of contralateral striatum vs. 40 +/- 12% in vehicle-treated females). Cortical injury was not enhanced relative to control animals (39 +/- 6% of contralateral cortex in ICI group vs. 27 +/- 8% in vehicle-treated group). Physiologic variables and ischemic reduction of the ipsilateral cortical laser-Doppler flow signal were similar between groups. Further, ICI treatment did not alter end-ischemic cortical or striatal CBF. The deleterious effect of ICI was limited to females, as there were no differences in stroke damage or CBF between male treatment groups. These data suggest that estrogen inhibits ischemic brain injury in striatum of the female by receptor-mediated mechanisms that are not linked to preservation of intraischemic CBF.

What do mouse gene knockouts tell us about the structure and function of the red cell membrane?

Recent development of knockout mice with targeted deletion of specific genes encoding various red cell membrane proteins has added valuable armamentarium to red cell membrane structure-function studies. In this chapter we will summarize the various recent developments regarding the structure and function of the red cell membrane derived from studies using knockout mice. In addition to being expressed in red cells, all major red cell membrane proteins are also expressed in cells of various tissues. The potential use of knockout mice to decipher the biological functions of red cell membrane proteins in non-erythroid cells is also explored.

A novel neuron-enriched homolog of the erythrocyte membrane cytoskeletal protein 4.1

We report the molecular cloning and characterization of 4.1N, a novel neuronal homolog of the erythrocyte membrane cytoskeletal protein 4.1 (4.1R). The 879 amino acid protein shares 70, 36, and 46% identity with 4.1R in the defined membrane-binding, spectrin-actin-binding, and C-terminal domains, respectively. 4.1N is expressed in almost all central and peripheral neurons of the body and is detected in embryonic neurons at the earliest stage of postmitotic differentiation. Like 4.1R, 4.1N has multiple splice forms as evidenced by PCR and Western analysis. Whereas the predominant 4.1N isoform identified in brain is approximately 135 kDa, a smaller 100 kDa isoform is enriched in peripheral tissues. Immunohistochemical studies using a polyclonal 4.1N antibody revealed several patterns of neuronal staining, with localizations in the neuronal cell body, dendrites, and axons. In certain neuronal locations, including the granule cell layers of the cerebellum and dentate gyrus, a distinct punctate-staining pattern was observed consistent with a synaptic localization. In primary hippocampal cultures, mouse 4.1N is enriched at the discrete sites of synaptic contact, colocalizing with the postsynaptic density protein of 95 kDa (a postsynaptic marker) and glutamate receptor type 1 (an excitatory postsynaptic marker). By analogy with the roles of 4.1R in red blood cells, 4.1N may function to confer stability and plasticity to the neuronal membrane via interactions with multiple binding partners, including the spectrin-actin-based cytoskeleton, integral membrane channels and receptors, and membrane-associated guanylate kinases.

Molecular characterization of a new member of the protein 4.1 family (brain 4.1) in rat brain

In addition to the well-known erythroid 4.1 gene, two human genes (KIAA0338 and 4.1G) have recently been identified as members of the protein 4.1 family of genes. We compared the expression levels of these three genes and found that the KIAA0338 gene was predominantly expressed in human brain. To further characterize this novel protein 4.1, called brain 4.1, we isolated rat brain 4.1 cDNA and analyzed its gene products in rat brain. The results indicated that the mRNA and protein products of the brain 4.1 gene were more abundant in brain compared to any other tissues examined. The brain 4.1 mRNA appeared as multiple bands with estimated sizes of 3.9 kb, 6.2 kb and 8.7 kb on RNA blotting analysis, and was found to consist of various alternative forms as reported previously for the erythroid 4. 1 gene. As for the brain 4.1 gene product, many isoforms discernible by immunoblotting analysis were also observed depending on the tissue type and the brain region. The existence of multiple forms of the brain 4.1 implies that it has multiple and diverse functions like the erythroid 4.1 gene product.