Autoimmunity to beta IV spectrin in paraneoplastic lower motor neuron syndrome

Interest of rare autoantibodies in autoimmune encephalitis and paraneoplastic neurological syndromes: the utility (or futility) of rare antibody discovery

PURPOSE OF REVIEW

The increasing recognition and diagnosis of autoimmune encephalitis (AE) and paraneoplastic neurological syndromes (PNS) is partly due to neural autoantibody testing and discovery. The past two decades witnessed an exponential growth in the number of identified neural antibodies. This review aims to summarize recent rare antibody discoveries in the context of central nervous system (CNS) autoimmunity and evaluate the ongoing debate about their utility.

RECENT FINDINGS

In the last 5 years alone 15 novel neural autoantibody specificities were identified. These include rare neural antibody biomarkers of autoimmune encephalitis, cerebellar ataxia or other movement disorders, including multifocal presentations.

SUMMARY

Although the clinical applications of these rare antibody discoveries may be limited by the low number of positive cases, they still provide important diagnostic, prognostic, and therapeutic insights.

Contribution of Axon Initial Segment Structure and Channels to Brain Pathology

Brain channelopathies are a group of neurological disorders that result from genetic mutations affecting ion channels in the brain. Ion channels are specialized proteins that play a crucial role in the electrical activity of nerve cells by controlling the flow of ions such as sodium, potassium, and calcium. When these channels are not functioning properly, they can cause a wide range of neurological symptoms such as seizures, movement disorders, and cognitive impairment. In this context, the axon initial segment (AIS) is the site of action potential initiation in most neurons. This region is characterized by a high density of voltage-gated sodium channels (VGSCs), which are responsible for the rapid depolarization that occurs when the neuron is stimulated. The AIS is also enriched in other ion channels, such as potassium channels, that play a role in shaping the action potential waveform and determining the firing frequency of the neuron. In addition to ion channels, the AIS contains a complex cytoskeletal structure that helps to anchor the channels in place and regulate their function. Therefore, alterations in this complex structure of ion channels, scaffold proteins, and specialized cytoskeleton may also cause brain channelopathies not necessarily associated with ion channel mutations. This review will focus on how the AISs structure, plasticity, and composition alterations may generate changes in action potentials and neuronal dysfunction leading to brain diseases. AIS function alterations may be the consequence of voltage-gated ion channel mutations, but also may be due to ligand-activated channels and receptors and AIS structural and membrane proteins that support the function of voltage-gated ion channels.

Spectrins: molecular organizers and targets of neurological disorders

Spectrins are cytoskeletal proteins that are expressed ubiquitously in the mammalian nervous system. Pathogenic variants in SPTAN1, SPTBN1, SPTBN2 and SPTBN4, four of the six genes encoding neuronal spectrins, cause neurological disorders. Despite their structural similarity and shared role as molecular organizers at the cell membrane, spectrins vary in expression, subcellular localization and specialization in neurons, and this variation partly underlies non-overlapping disease presentations across spectrinopathies. Here, we summarize recent progress in discerning the local and long-range organization and diverse functions of neuronal spectrins. We provide an overview of functional studies using mouse models, which, together with growing human genetic and clinical data, are helping to illuminate the aetiology of neurological spectrinopathies. These approaches are all critical on the path to plausible therapeutic solutions.

Dual ankyrinG and subpial autoantibodies in a man with well-controlled HIV infection with steroid-responsive meningoencephalitis: A case report

Neuroinvasive infection is the most common cause of meningoencephalitis in people living with human immunodeficiency virus (HIV), but autoimmune etiologies have been reported. We present the case of a 51-year-old man living with HIV infection with steroid-responsive meningoencephalitis whose comprehensive pathogen testing was non-diagnostic. Subsequent tissue-based immunofluorescence with acute-phase cerebrospinal fluid revealed anti-neural antibodies localizing to the axon initial segment (AIS), the node of Ranvier (NoR), and the subpial space. Phage display immunoprecipitation sequencing identified ankyrinG (AnkG) as the leading candidate autoantigen. A synthetic blocking peptide encoding the PhIP-Seq-identified AnkG epitope neutralized CSF IgG binding to the AIS and NoR, thereby confirming a monoepitopic AnkG antibody response. However, subpial immunostaining persisted, indicating the presence of additional autoantibodies. Review of archival tissue-based staining identified candidate AnkG autoantibodies in a 60-year-old woman with metastatic ovarian cancer and seizures that were subsequently validated by cell-based assay. AnkG antibodies were not detected by tissue-based assay and/or PhIP-Seq in control CSF (N = 39), HIV CSF (N = 79), or other suspected and confirmed neuroinflammatory CSF cases (N = 1,236). Therefore, AnkG autoantibodies in CSF are rare but extend the catalog of AIS and NoR autoantibodies associated with neurological autoimmunity.

Pathology of Initial Axon Segments in Chronic Inflammatory Demyelinating Polyradiculoneuropathy and Related Disorders

The diagnosis of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is based on a combination of clinical, electrodiagnostic and laboratory features. The different entities of the disease include chronic immune sensory polyradiculopathy (CISP) and autoimmune nodopathies. It is debatable whether CIDP occurring in the course of other conditions, i.e., monoclonal IgG or IgA gammopathy, should be treated as a separate disease entity from idiopathic CIDP. This study aims to evaluate the molecular differences of the nodes of Ranvier and the initial axon segment (AIS) and juxtaparanode region (JXP) as the potential cause of phenotypic variation of CIDP while also seeking new pathomechanisms since JXP is sequestered behind the paranode and autoantibodies may not access the site easily. The authors initially present the structure of the different parts of the neuron and its functional significance, then discuss the problem of whether damage to the juxtaparanodal region, Schwann cells and axons could cause CIDP or if these damages should be separated as separate disease entities. In particular, AIS's importance for modulating neural excitability and carrying out transport along the axon is highlighted. The disclosure of specific pathomechanisms, including novel target antigens, in the heterogeneous CIDP syndrome is important for diagnosing and treating these patients.

βIV-Spectrin Autoantibodies in 2 Individuals With Neuropathy of Possible Paraneoplastic Origin: A Case Series

OBJECTIVE

To identify the autoantigen in 2 individuals with possible seronegative paraneoplastic neuropathy.

METHODS

Serum and CSF were screened by tissue-based assay and panned for candidate autoantibodies by phage display immunoprecipitation sequencing (PhIP-Seq). The candidate antigen was validated by immunostaining knockout tissue and HEK 293T cell-based assay.

RESULTS

Case 1 presented with gait instability, distal lower extremity numbness, and paresthesias after a recent diagnosis of serous uterine and fallopian carcinoma. Case 2 had a remote history of breast adenocarcinoma and presented with gait instability, distal lower extremity numbness, and paresthesias that progressed to generalized weakness. CSF and serum from both patients immunostained the axon initial segment (AIS) and node of Ranvier (NoR) of mice and enriched βIV-spectrin by PhIP-Seq. Patient CSF and serum failed to immunostain NoRs in dorsal root sensory neurons from βI/βIV-deficient mice. βIV-spectrin autoantibodies were confirmed by overexpression of AIS and nodal βIV-spectrin isoforms Σ1 and Σ6 by a cell-based assay. βIV-spectrin was not enriched in a combined 4,815 PhIP-Seq screens of healthy and other neurologic disease patients.

DISCUSSION

Therefore, βIV-spectrin autoantibodies may be a marker of paraneoplastic neuropathy.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that βIV-spectrin antibodies are specific autoantibody biomarkers for paraneoplastic neuropathy.

Reorganization of Destabilized Nodes of Ranvier in βIV Spectrin Mutants Uncovers Critical Timelines for Nodal Restoration and Prevention of Motor Paresis

Disorganization of nodes of Ranvier is associated with motor and sensory dysfunctions. Mechanisms that allow nodal recovery during pathological processes remain poorly understood. A highly enriched nodal cytoskeletal protein βIV spectrin anchors and stabilizes the nodal complex to actin cytoskeleton. Loss of murine βIV spectrin allows the initial nodal organization, but causes gradual nodal destabilization. Mutations in human βIV spectrin cause auditory neuropathy and impairment in motor coordination. Similar phenotypes are caused by nodal disruption due to demyelination. Here we report on the precise timelines of nodal disorganization and reorganization by following disassembly and reassembly of key nodal proteins in βIV spectrin mice of both sexes before and after βIV spectrin re-expression at specifically chosen developmental time points. We show that the timeline of nodal restoration has different outcomes in the PNS and CNS with respect to nodal reassembly and functional restoration. In the PNS, restoration of nodes occurs within 1 month regardless of the time of βIV spectrin re-expression. In contrast, the CNS nodal reorganization and functional restoration occurs within a critical time window; after that, nodal reorganization diminishes, leading to less efficient motor recovery. We demonstrate that timely restoration of nodes can improve both the functional properties and the ultrastructure of myelinated fibers affected by long-term nodal disorganization. Our studies, which indicate a critical timeline for nodal restoration together with overall motor performance and prolonged life span, further support the idea that nodal restoration is more beneficial if initiated before any axonal damage, which is critically relevant to demyelinating disorders.SIGNIFICANCE STATEMENT Nodes of Ranvier are integral to efficient and rapid signal transmission along myelinated fibers. Various demyelinating disorders are characterized by destabilization of the nodal molecular complex, accompanied by severe reduction in nerve conduction and the onset of motor and sensory dysfunctions. This study is the first to report in vivo reassembly of destabilized nodes with sequential improvement in overall motor performance. Our study reveals that nodal restoration is achievable before any axonal damage, and that long-term nodal destabilization causes irreversible axonal structural changes that prevent functional restoration. Our studies provide significant insights into timely restoration of nodal domains as a potential therapeutic approach in treatment of demyelinating disorders.

Antibodies to TRIM46 are associated with paraneoplastic neurological syndromes

Paraneoplastic neurological syndromes (PNS) are often characterized by the presence of antineuronal antibodies in patient serum or cerebrospinal fluid. The detection of antineuronal antibodies has proven to be a useful tool in PNS diagnosis and the search for an underlying tumor. Here, we describe three patients with autoantibodies to several epitopes of the axon initial segment protein tripartite motif 46 (TRIM46). We show that anti‐TRIM46 antibodies are easy to detect in routine immunohistochemistry screening and can be confirmed by western blotting and cell‐based assay. Anti‐TRIM46 antibodies can occur in patients with diverse neurological syndromes and are associated with small‐cell lung carcinoma.

Isoforms of Spectrin and Ankyrin Reflect the Functional Topography of the Mouse Kidney

The kidney displays specialized regions devoted to filtration, selective reabsorption, and electrolyte and metabolite trafficking. The polarized membrane pumps, channels, and transporters responsible for these functions have been exhaustively studied. Less examined are the contributions of spectrin and its adapter ankyrin to this exquisite functional topography, despite their established contributions in other tissues to cellular organization. We have examined in the rodent kidney the expression and distribution of all spectrins and ankyrins by qPCR, Western blotting, immunofluorescent and immuno electron microscopy. Four of the seven spectrins (αΙΙ, βΙ, βΙΙ, and βΙΙΙ) are expressed in the kidney, as are two of the three ankyrins (G and B). The levels and distribution of these proteins vary widely over the nephron. αΙΙ/βΙΙ is the most abundant spectrin, found in glomerular endothelial cells; on the basolateral membrane and cytoplasmic vesicles in proximal tubule cells and in the thick ascending loop of Henle; and less so in the distal nephron. βΙΙΙ spectrin largely replaces βΙΙ spectrin in podocytes, Bowman’s capsule, and throughout the distal tubule and collecting ducts. βΙ spectrin is only marginally expressed; its low abundance hinders a reliable determination of its distribution. Ankyrin G is the most abundant ankyrin, found in capillary endothelial cells and all tubular segments. Ankyrin B populates Bowman’s capsule, podocytes, the ascending thick loop of Henle, and the distal convoluted tubule. Comparison to the distribution of renal protein 4.1 isoforms and various membrane proteins indicates a complex relationship between the spectrin scaffold, its adapters, and various membrane proteins. While some proteins (e.g. ankyrin B, βΙΙΙ spectrin, and aquaporin 2) tend to share a similar distribution, there is no simple mapping of different spectrins or ankyrins to most membrane proteins. The implications of this data are discussed.

Reactive protoplasmic and fibrous astrocytes contain high levels of calpain-cleaved alpha 2 spectrin

Calpain, a family of calcium-dependent neutral proteases, plays important roles in neurophysiology and pathology through the proteolytic modification of cytoskeletal proteins, receptors and kinases. Alpha 2 spectrin (αII spectrin) is a major substrate for this protease family, and the presence of the αII spectrin breakdown product (αΙΙ spectrin BDP) in a cell is evidence of calpain activity triggered by enhanced intracytoplasmic Ca(2+) concentrations. Astrocytes, the most dynamic CNS cells, respond to micro-environmental changes or noxious stimuli by elevating intracytoplasmic Ca(2+) concentration to become activated. As one measure of whether calpains are involved with reactive glial transformation, we examined paraffin sections of the human cerebral cortex and white matter by immunohistochemistry with an antibody specific for the calpain-mediated αΙΙ spectrin BDP. We also performed conventional double immunohistochemistry as well as immunofluorescent studies utilizing antibodies against αΙΙ spectrin BDP as well as glial fibrillary acidic protein (GFAP). We found strong immunopositivity in selected protoplasmic and fibrous astrocytes, and in transitional forms that raise the possibility of some of fibrous astrocytes emerging from protoplasmic astrocytes. Immunoreactive astrocytes were numerous in brain sections from cases with severe cardiac and/or respiratory diseases in the current study as opposed to our previous study of cases without significant clinical conditions that failed to reveal such remarkable immunohistochemical alterations. Our study suggests that astrocytes become αΙΙ spectrin BDP immunopositive in various stages of activation, and that spectrin cleavage product persists even in fully reactive astrocytes. Immunohistochemistry for αΙΙ spectrin BDP thus marks reactive astrocytes, and highlights the likelihood that calpains and their proteolytic processing of spectrin participate in the morphologic and physiologic transition from resting protoplasmic astrocytes to reactive fibrous astrocytes.

Brca1 is expressed in human microglia and is dysregulated in human and animal model of ALS

Background

There is growing evidence that microglia are key players in the pathological process of amyotrophic lateral sclerosis (ALS). It is suggested that microglia have a dual role in motoneurone degeneration through the release of both neuroprotective and neurotoxic factors.

Results

To identify candidate genes that may be involved in ALS pathology we have analysed at early symptomatic age (P90), the molecular signature of microglia from the lumbar region of the spinal cord of hSOD1^G93A mice, the most widely used animal model of ALS. We first identified unique hSOD1^G93A microglia transcriptomic profile that, in addition to more classical processes such as chemotaxis and immune response, pointed toward the potential involvement of the tumour suppressor gene breast cancer susceptibility gene 1 (Brca1). Secondly, comparison with our previous data on hSOD1^G93A motoneurone gene profile substantiated the putative contribution of Brca1 in ALS. Finally, we established that Brca1 protein is specifically expressed in human spinal microglia and is up-regulated in ALS patients.

Conclusions

Overall, our data provide new insights into the pathogenic concept of a non-cell-autonomous disease and the involvement of microglia in ALS. Importantly, the identification of Brca1 as a novel microglial marker and as possible contributor in both human and animal model of ALS may represent a valid therapeutic target. Moreover, our data points toward novel research strategies such as investigating the role of oncogenic proteins in neurodegenerative diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-015-0023-x) contains supplementary material, which is available to authorized users.

Is there a paraneoplastic ALS?

Our objective was to examine the strength of evidence in support of the paraneoplastic syndrome (PNS) as one cause of ALS and, if the association appears more likely than chance, determine which features of ALS imply concurrent malignancy. We reviewed the literature on concurrent ALS and neoplasia assessing the strength of evidence for the association. Most accounts of ALS and neoplasm are case reports or small uncontrolled series. In order of strength of evidence, three clinical situations that support a paraneoplastic aetiology for ALS are: 1) laboratory evidence of well-characterized onconeuronal antibodies, most often anti-Hu, anti-Yo or anti-Ri; 2) co-occurrence of ALS and a neoplasm known to cause PNS, usually lymphoma or cancer of the breast; and 3) combined ALS and a neoplasm not classically associated with PNS, without detectable onconeuronal antibodies. Clinical features that warrant evaluation of neoplasm include upper motor neuron disease in elderly females, rapid progression, non-motor signs, and young onset. In conclusion, most examples of ALS and neoplasm do not constitute a classically established PNS. Rare instances of elevated onconeuronal antibody titres or typical neoplasm, implies that, albeit rare, the PNS is one of a multitude of causes of ALS.

Paraneoplastic neuropathies

PURPOSE OF REVIEW

This review describes relevant advances in paraneoplastic neuropathies with emphasis on particular syndromes and the impact of new therapies.

RECENT FINDINGS

Sensory neuronopathy may present with symptoms that do not raise the suspicion of a paraneoplastic origin. A recent study on sensory neuronopathies of different causes identified paraneoplastic cases in a group of older (>60 years) male patients with subacute onset early pain, and frequent involvement of the arms. Paraneoplastic sensorimotor polyneuropathies may be confused with chronic inflammatory demyelinating polyneuropathy (CIDP) and in lymphomas with direct infiltration of nerves (neurolymphomatosis). Recent neurophysiological studies indicate that the polyneuropathy of POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, M component, and skin changes) can be differentiated from CIDP by the presence of diffuse demyelination and more severe axonal loss. Neuropathy in Waldenström macroglobulinemia is heterogeneous. Up to 38% have demyelinating features and the rest show axonal degeneration due to different causes (dysimmune, amyloidosis, or tumoral infiltration). Isolated case reports suggest that the combination of cyclophosphamide and rituximab may be effective in paraneoplastic neuronopathies. Lenalidomide and dexamethasone are effective to control the neuropathy of POEMS patients who are not suitable for or progress after autologous stem cell transplantation.

SUMMARY

Clinical and neurophysiological studies are helpful to correctly identify particular paraneoplastic neuropathies.

Node of Ranvier disruption as a cause of neurological diseases

Dysfunction and/or disruption of nodes of Ranvier are now recognized as key contributors to the pathophysiology of various neurological diseases. One reason is that the excitable nodal axolemma contains a high density of Nav (voltage-gated Na⁺ channels) that are required for the rapid and efficient saltatory conduction of action potentials. Nodal physiology is disturbed by altered function, localization, and expression of voltage-gated ion channels clustered at nodes and juxtaparanodes, and by disrupted axon–glial interactions at paranodes. This paper reviews recent discoveries in molecular/cellular neuroscience, genetics, immunology, and neurology that highlight the critical roles of nodes of Ranvier in health and disease.

Paraneoplastic neuropathy

Recent progress in serological screening of paraneoplastic antibodies and in diagnostic imaging techniques to detect malignancies has enabled a broadening of the concept of paraneoplastic neurological syndromes by integrating nonclassic clinical features. The peripheral nervous system is frequently involved in patients with paraneoplastic syndrome and may be seen alone or in combination with involvement of other areas of the nervous system. Destruction of dorsal root ganglion cells due to lymphocytic infiltration, especially with CD8-positive cytotoxic T cells, has been postulated to mediate the classic syndrome of subacute sensory neuronopathy. However, the motor and autonomic nervous systems are frequently affected. Indeed, patients can develop clinical features compatible with Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy, or brachial plexopathy. Other forms of paraneoplastic neuropathy are vasculitic neuropathy, autoimmune autonomic ganglionopathy, and chronic intestinal pseudo-obstruction. Various onconeural antibodies, including anti-Hu, anti-CV2/CRMP-5, and anti-ganglionic acetylcholine receptor antibodies, are associated with neuropathy. Somatic neuropathy is the most common manifestation in patients with anti-Hu and anti-CV2/CRMP-5 antibodies, while anti-ganglionic acetylcholine receptor antibody is associated with autonomic neuropathies. A whole-body fluorodeoxyglucose positron emission tomography scan may be useful to detect malignancy in patients with unremarkable conventional radiological findings. Recognition and diagnosis of paraneoplastic neuropathy is important, as neuropathic symptoms usually precede the identification of the primary tumor, and treatment at an earlier stage provides better chances of good outcomes.

A new paraneoplastic encephalomyelitis autoantibody reactive with the axon initial segment

Serum from a patient with paraneoplastic encephalomyelitis (PEM) and small cell lung cancer (SCLC) showed high titer immunohistochemical staining of the axon initial segment (AIS) on rat and human brain sections. EM studies showed that the antigen was localized in close proximity of the microtubules in the AIS. Double labeling experiments and absence of staining at the nodes of Ranvier excluded the previously identified betaIV spectrin as autoantigen. Screening a rat hippocampal cDNA library resulted in the isolation of ubiquitin-conjugating enzyme E2E1 (UBE2E1). However, blocking and elution experiments excluded UBE2E1 as the AIS autoantigen.

Ankyrin facilitates intracellular trafficking of alpha1-Na+-K+-ATPase in polarized cells

Defects in ankyrin underlie many hereditary disorders involving the mislocalization of membrane proteins. Such phenotypes are usually attributed to ankyrin's role in stabilizing a plasma membrane scaffold, but this assumption may not be accurate. We found in Madin-Darby canine kidney cells and in other cultured cells that the 25-residue ankyrin-binding sequence of alpha(1)-Na(+)-K(+)-ATPase facilitates the entry of alpha(1),beta(1)-Na(+)-K(+)-ATPase into the secretory pathway and that replacement of the cytoplasmic domain of vesicular stomatitis virus G protein (VSV-G) with this ankyrin-binding sequence bestows ankyrin dependency on the endoplasmic reticulum (ER) to Golgi trafficking of VSV-G. Expression of the ankyrin-binding sequence of alpha(1)-Na(+)-K(+)-ATPase alone as a soluble cytosolic peptide acts in trans to selectively block ER to Golgi transport of both wild-type alpha(1)-Na(+)-K(+)-ATPase and a VSV-G fusion protein that includes the ankyrin-binding sequence, whereas the trafficking of other proteins remains unaffected. Similar phenotypes are also generated by small hairpin RNA-mediated knockdown of ankyrin R or the depletion of ankyrin in semipermeabilized cells. These data indicate that the adapter protein ankyrin acts not only at the plasma membrane but also early in the secretory pathway to facilitate the intracellular trafficking of alpha(1)-Na(+)-K(+)-ATPase and presumably other selected proteins. This novel ankyrin-dependent assembly pathway suggests a mechanism whereby hereditary disorders of ankyrin may be manifested as diseases of membrane protein ER retention or mislocalization.

Spectrin and ankyrin-based cytoskeletons at polarized domains in myelinated axons

In myelinated nerve fibers, action potential initiation and propagation requires that voltage-gated ion channels be clustered at high density in the axon initial segments and nodes of Ranvier. The molecular organization of these subdomains depends on specialized cytoskeletal and scaffolding proteins such as spectrins, ankyrins, and 4.1 proteins. These cytoskeletal proteins are considered to be important for 1) formation, localization, and maintenance of specific integral membrane protein complexes, 2) a barrier restricting the diffusion of both cytoplasmic and membrane proteins to distinct regions or compartments of the cell, and 3) stabilization of axonal membrane integrity. Increased insights into the role of the cytoskeleton could provide important clues about the pathophysiology of various neurological disorders.

Breast cancer and motor neuron disease: clinical study of seven cases

We report seven women, aged 52-78 years, with motor neuron disease (MND) associated with breast cancer. In five, cancer preceded MND by 30 years to 24 months, while in the remaining two it occurred from 8.5 years to one month after MND onset. Three patients were considered cured of their cancer at the time of the study. Four patients have died, one from associated colonic cancer, and three from MND. As in a previous report, the clinical pattern of MND in these patients was that of predominant upper motor neuron involvement in 6/7 cases. Three had frontotemporal dementia. No anti-neuronal antibodies were found. Although there is no recognized pathophysiological link between breast cancer and UMN-predominant MND we suggest there may be comorbidity between the two diseases.

Peripheral nervous system involvement in patients with cancer

Involvement of the peripheral nervous system (PNS) is common in patients with cancer and any part, including motor neurons, sensory ganglia, nerve roots, plexuses, cranial and peripheral nerves, and neuromuscular junctions, can be affected. Different mechanisms can initiate damage associated with cancer-related PNS disorders. These include tumour infiltration, toxicity of treatments, metabolic and nutritional perturbations, cachexia, virus infections, and paraneoplastic neurological syndromes. The type of cancer, lymphoma, or solid tumour is a further determinant of a PNS disorder. In this Review we discuss the different causes and mechanisms of disorders of the PNS in patients with cancer and we will focus on their assessment and diagnosis.

Atomistic and Coarse-grained Analysis of Double Spectrin Repeat Units: The Molecular Origins of Flexibility

Spectrin is an ubiquitous protein in metazoan cells, and its flexibility is one of the keys to maintaining cellular structure and organization. Both alpha-spectrin and beta-spectrin polypeptides consist primarily of triple coiled-coil modular repeat units, and two important factors that determine spectrin flexibility are the bending flexibility between two consecutive repeat units and the conformational flexibility of individual repeat units. Atomistic molecular dynamics (MD) simulations are used here to study double spectrin repeat units (DSRUs) from the human erythrocyte beta-spectrin (HEbeta89) and the chicken brain alpha-spectrin (CBalpha1617). From the results of MD simulations, a highly conserved Trp residue in the A-helix of most repeat units that has been suggested to be important in conferring stability to the coiled-coil structures is found not to have a significant effect on the conformational flexibility of individual repeat units. Characterization of the bending flexibility for two consecutive repeats of spectrin via atomistic simulations and coarse-grained (CG) modeling indicate that the bending flexibility is governed by the interactions between the AB-loop of the first repeat unit, the BC-loop of the second repeat unit and the linker region. Specifically, interactions between residues in these regions can lead to a strong directionality in the bending behavior of two repeat units. The biological implications of these finding are discussed.

Paraneoplastic syndromes affecting the nervous system

The paraneoplastic neurologic disorders (PND) are a diverse group of diseases characterized by the presence of neurologic dysfunction in the setting of a remote cancer. PND can affect almost any part of the nervous system, and are most commonly associated with lung cancer (small cell) and gynecologic tumors. Laboratory studies have demonstrated that an autoimmune response links the neurologic disorder and the cancer, and established a model whereby the cancer is believed to initiate the syndrome by expressing a protein antigen normally expressed in the nervous system, leading to anti-tumor immune response followed by autoimmune neurologic symptoms. We review the currently known PND and their pathogenesis.

Paraneoplastic syndromes of the peripheral nerves

PURPOSE OF REVIEW

To describe the paraneoplastic disorders of the motor and sensory nerves and neurons, and their immunologic associations.

RECENT FINDINGS

Recently proposed diagnostic criteria for paraneoplastic disorders may assist in determining the likelihood a given neuropathy or neuronopathy is related to an underlying malignancy. Of this group of disorders, paraneoplastic sensory neuronopathies are the most frequent; many of these patients have anti-Hu antibodies and small-cell lung cancer. There is often motor, autonomic, or central nervous system involvement, and electrophysiological studies may demonstrate not only sensory changes, but also motor abnormalities. While cancer has been found more frequently than expected in patients with Guillain-Barré syndrome, this association is extremely rare. A limited number of reports have described chronic inflammatory demyelinating polyradiculoneuropathy, multifocal motor neuropathy with conduction block, vasculitic neuropathies, and motor neuron disease as paraneoplastic disorders. Anti-CV2 antibodies are frequently associated with a paraneoplastic sensorimotor axonal neuropathy and small-cell lung cancer. Peripheral nerve hyperexcitability may occur with or without a cancer association, and in both instances patients often have antibodies to voltage-gated potassium channels; thymoma and small-cell lung cancer are the most common underlying tumors. Plasma cell proliferative disorders are frequently associated with neuropathies, particularly demyelinating ones.

SUMMARY

There is increasing recognition of an extensive variety of paraneoplastic disorders of the peripheral nerves. In many of these disorders onconeuronal antibodies are absent. Whole body fluorodeoxyglucose positron emission tomography scanning helps uncover the associated tumor, and recently proposed criteria may assist in the diagnosis. In many instances, prompt treatment of the tumor and immunotherapy result in symptom stabilization or neurologic improvement.

BetaIVSigma1 spectrin stabilizes the nodes of Ranvier and axon initial segments

Saltatory electric conduction requires clustered voltage-gated sodium channels (VGSCs) at axon initial segments (AIS) and nodes of Ranvier (NR). A dense membrane undercoat is present at these sites, which is thought to be key for the focal accumulation of channels. Here, we prove that βIVΣ1 spectrin, the only βIV spectrin with an actin-binding domain, is an essential component of this coat. Specifically, βIVΣ1 coexists with βIVΣ6 at both AIS and NR, being the predominant spectrin at AIS. Removal of βIVΣ1 alone causes the disappearance of the nodal coat, an increased diameter of the NR, and the presence of dilations filled with organelles. Moreover, in myelinated cochlear afferent fibers, VGSC and ankyrin G clusters appear fragmented. These ultrastructural changes can explain the motor and auditory neuropathies present in βIVΣ1 −/− mice and point to the βIVΣ1 spectrin isoform as a master-stabilizing factor of AIS/NR membranes.

Naturally occurring B-cell responses to breast cancer

As demonstrated by the effectiveness of trastuzumab, antibodies against breast cancer antigens are a potentially potent mechanism of tumor control. While trastuzumab is administered exogenously, its efficacy suggests that induction of very high titer antibody responses in vivo might also be therapeutic. Both naturally occurring and vaccine-induced antibody responses to some breast cancer antigens are associated with improved survival in some cases. However, the improvement in survival associated with antibody responses to breast cancer is modest, and tumor regression is not known to be associated with the natural antitumor antibody response, indicating a need for improved understanding of the natural antitumor antibody response. Naturally occurring B-cell responses in the form of serum antibody, tumor reactive lymph node B cells, and tumor-infiltrating B cells have been described, and a variety of breast tumor-associated antigens have been identified based on reactivity of patient antibodies. This review discusses current knowledge of humoral immunity to breast cancer with regard to specific antigens and the basis for their immunogenicity, and the contexts (tumor, lymph node, serum) in which responses are observed. With few exceptions, "tumor-associated antigens" identified with naturally occurring antibodies may be overexpressed on tumor but are in fact nonspecific autoantigens. This suggests that while overexpression or aberrant processing can increase immunogenicity in some cases, the immunogenicity of many or even most tumor-associated antigens is a function of expression in tumor or the result of ancillary tumor factors.

Paraneoplastic neurological syndromes: an update on diagnosis, pathogenesis, and therapy

Since the discovery of the first clinically relevant anti neuronal antibody specific for a paraneoplastic aetiology in 1985, the number of such reactivities has grown at a rate of about one per year. Clinicians can now diagnose a paraneoplastic syndrome much more easily. This ability is especially important because, typically, the neurological symptoms occur before the cancer is diagnosed. Early tumour diagnosis is essential, because effective treatment of the cancer still seems to be the most efficient treatment option for the neurological symptoms. Immuno modulatory therapy should, nevertheless, be initiated as early as possible and seems especially helpful for peripheral syndromes and limbic encephalitis. The recent fundamental advances in understanding of the autoimmune pathology of these disorders, especially the role of cytotoxic T cells, should eventually lead to more effective treatment options.

Antigen-driven oligoclonal expansion of tumor-infiltrating B cells in infiltrating ductal carcinoma of the breast

The objective of this study was to determine whether tumor-infiltrating B cells (TIL-B) of infiltrating ductal carcinoma (IDC) of the breast represent a tumor-specific humoral immune response. Immunohistochemical analysis of three Her-2/neu-negative IDC tumors from geriatric patients showed that TIL-B cluster in structures similar to germinal centers containing CD20(+) B lymphocyte and CD3(+) T lymphocyte zones with interdigitating CD21(+) follicular dendritic cells, suggesting an in situ immune response. A total of 29, 31, and 58 IgG1 H chain clones was sequenced from the three IDC tumors, respectively. Intratumoral oligoclonal expansion of TIL-B was demonstrated by a preponderance (45-68%) of clonal B cells. In contrast, only 7% of tumor-draining lymph node and 0% of healthy donor PBL IgG H chains were clonal, consistent with the larger repertoires of node and peripheral populations. Patterns and levels of TIL-B IgG H chain somatic hypermutation suggested affinity maturation in intratumoral germinal centers. To examine the specificity of TIL-B Ig, a phage-displayed Fab library was generated from the TIL-B of one IDC tumor. Panning with an allogeneic breast cancer cell line enriched Fab binding to breast cancer cells, but not nonmalignant cell lines tested. However, panning with autologous tumor tissue lysate increased binding of Fab to both tumor tissue lysate and healthy breast tissue lysate. These data suggest an in situ Ag-driven oligoclonal B cell response to a variety of tumor- and breast-associated Ags.