Paraneoplastic Antigens Research Articles

Low titre autoantibodies against recoverin in sera of patients with small cell lung cancer but without a loss of vision

To date, many authors have described the presence of autoantibodies against various neuronal proteins, paraneoplastic antigens (PNA), in a serum of patients with different kinds of malignant tumors located outside the nervous system. These autoantibodies may cross-react with the corresponding PNA or their epitops present in neurons and thus initiate the development of a variety of neurological disorders, paraneoplastic syndromes (PNS), even though the primary tumor and its metastases have not invaded the nervous system. Cancer-associated retinopathy (CAR) is a rare ocular PNS induced by autoantibodies against several retinal antigens, one of which is a photoreceptor calcium-binding protein, recoverin. Only several CAR patients with a few kinds of cancer (endothelial carcinoma, breast cancer, epithelial ovarian carcinoma) have so far been found to contain autoantibodies against recoverin in their sera. As for lung cancer, the majority of CAR cases mediated by anti-recoverin autoantibodies have been revealed in patients with the most malignant lung cancer, small cell lung carcinoma (SCLC), and only one similar case has been described for a patient with non-small lung carcinoma. The common feature of all these anti-recoverin-positive patients, irrespective of the type of cancer, is the presence of both the CAR syndrome and high titres (as a rule, more than 1:1000) of the underlying autoantibodies in their serum. In this study, we have used recombinant myristoylated recoverin to screen serum samples of 50 patients with SCLC by Western blot and revealed 5 individuals with low titres of anti-recoverin antibodies, who have no manifestation of a loss of vision. To our knowledge, this is the first report on the presence of low titre autoantibodies against recoverin in a serum of patients with cancer, but without visual dysfunction.

Paraneoplastic neurologic disease antigens: RNA-binding proteins and signaling proteins in neuronal degeneration.

Studies of the disorders known as paraneoplastic neurologic degenerations exemplify the successful application of modern molecular biological techniques to diseases, yielding, even for these extremely rare disorders, wide-ranging insight into basic neurobiology, tumor immunity, and autoimmune neurologic disease. Immune responses to paraneoplastic neurologic degeneration antigens, also called onconeural antigens, have been exploited to clone and characterize a number of neuron-specific proteins, including several RNA-binding proteins and new kinds of signaling molecules. The biology and functions of these proteins are reviewed, and a model in which their functions are related to the pathogenesis of autoimmune neurologic disease is discussed.

A brain-enriched polypyrimidine tract-binding protein antagonizes the ability of Nova to regulate neuron-specific alternative splicing.

The Nova paraneoplastic antigens are neuron-specific RNA binding proteins that participate in the control of alternative splicing. We have used the yeast two-hybrid system to isolate Nova interacting proteins and identify an RNA binding protein that is closely related to the polypyrimidine tract-binding protein (PTB). The expression of this protein, brPTB, is enriched in the brain, where it is expressed in glia and neurons. brPTB interacts with Nova proteins in cell lines and colocalizes with Nova within neuronal nuclei. We previously found that Nova binds to a pyrimidine-rich RNA element present upstream of an alternatively spliced exon, E3A, in glycine receptor alpha2 (GlyRalpha2) pre-mRNA, and this binding is implicated in Nova-dependent regulation of splicing. Cotransfection assays with a GlyRalpha2 minigene demonstrate that brPTB antagonizes the action of Nova to increase utilization of GlyRalpha2 E3A. brPTB binds to a 90-nt GlyRalpha2 RNA adjacent to the Nova binding site, but with an affinity that is more than 10-fold lower than Nova. When a putative binding site for brPTB on the GlyRalpha2 RNA is mutated, binding is abolished and the inhibitory effect on Nova-dependent exon selection disappears. These results suggest that brPTB is a tissue-restricted RNA binding protein that interacts with and inhibits the ability of Nova to activate exon selection in neurons.

ANOVA, a putative astrocytic RNA-binding protein gene that maps to chromosome 19q13.3.

Exon amplification from cosmids mapping to the glioma tumor suppressor gene candidate region on chromosome 19q13.3 yielded an exon with high homology to a portion of the NOVA1 gene, which encodes a neuron-specific RNA-binding protein recognized by the paraneoplastic syndrome antibody anti-Ri. Screening of a human brain cDNA library with this exon identified a 1.9 kb cDNA with extensive homology to NOVA1, including three nearly identical KH domains characteristic of a subtype of RNA-binding proteins. Northern blots demonstrated expression of a 2.5 kb mRNA in brain, but in no other tissues. In situ hybridization on human cerebral cortex showed mRNA expression restricted to astrocytes. We have therefore named the gene ANOVA, for astrocytic NOVA1-like gene. Southern blotting and single strand conformation polymorphism analyses did not show tumor-specific alterations of this gene in gliomas and RT-PCR studies showed expression in glioma cell lines, suggesting that ANOVA is not the chromosome 19q glioma tumor suppressor gene. Given that two cloned paraneoplastic antigens are neuronal RNA-binding proteins and that glial proteins may act as paraneoplastic antigens, the ANOVA product may be a target antigen in one of the undefined human paraneoplastic syndromes.

Paraneoplastic nervous system syndromes.

Recent progress in the understanding of the paraneoplastic neurologic syndromes has included further deliniation of the clinical syndromes and their treatment, attempts at standardization of the diagnostic nomenclature, investigations of pathogenetic mechanisms, and molecular characterization of the paraneoplastic antigens with implications as to their biologic relevance. Despite more than 30 years of investigation, the pathogenesis of these presumably autoimmune conditions remains unclear. Furthermore, no effective therapy has been identified for these conditions, with the possible exception of the opsoclonus-myoclonus ataxia and Lambert-Eaton myasthenic syndromes. Future investigations must focus on the disrupted genetic regulatory events involved in generation and propagation of the autoimmune response, antigen presentation and processing; target cell destruction, and consideration of alternative pathologic causes. Effective management strategies are most likely to develop from a better understanding of the disease pathogenesis, the development of animal model systems, and a creative look beyond the usual therapies employed in autoimmune conditions.

Specific detection of anti-cell surface antibodies in herpes gestationis sera.

We examined 42 herpes gestationis sera with immunofluorescence of normal human skin sections, and found that anti-keratinocyte cell surface antibodies were detected specifically in 10 herpes gestationis sera. The diagnosis of these herpes gestationis cases was confirmed by detecting antibodies against the 180 kD bullous pemphigoid antigen with immunoblotting of its fusion protein. The results of immunoadsorption assay using baculoproteins of both pemphigus vulgaris and pemphigus foliaceus antigens indicated that the herpes gestationis sera did not recognize common pemphigus antigens. Immunoblotting of human epidermal extracts and immunofluorescence of various tissues also suggested that the sera did not recognize any other desmosomal components or paraneoplastic pemphigus antigens. The significance of this reactivity is unclear. However, because no control bullous pemphigoid sera showed this reactivity, it may suggest a different pathophysiology between herpes gestationis and bullous pemphigoid.

Paraneoplastic Encephalomyelitis Antigens Bind to the AU-rich Elements of mRNA

The Hu antigens are composed of a family of neuronal-specific, RNA-binding proteins encoded by at least three distinct genes. All three gene products, HuD, HuC/ple21, and Hel-N1, are human homologues of Elav, a Drosophila protein required for neuronal development and maintenance. Although the three proteins are very similar in structure, they are differentiated by alternative splicing of their mRNAs. We report here that the Hu antigens bind avidly to the AU-rich element resident in many mRNAs that regulate cell proliferation. This interaction suggests that the Hu antigens promote neuronal differentiation by suppressing the neuroblast cell cycle. Such a mechanism provides a plausible model for the role of the Hu antigens in tumorigenesis, neuronal differentiation, and paraneoplastic neurologic disorders.