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Molecular Neuro-oncology
Summary: Robert Darnell studies degenerative brain disorders that are provoked by an immune response to certain cancers.
The study of disease allows the pursuit of mechanism while maintaining a narrow focus on questions directly relevant to human biology. The main effort of my laboratory is directed at developing a basic understanding of a group of rare brain diseases, the paraneoplastic neurologic syndromes (PNDs). These studies are producing insights into tumor immunology, autoimmunity, and neuronal cell biology.
PNDs are believed to arise when tumors outside of the nervous system express proteins that are normally made only in the brain (termed onconeural antigens). The serum and cerebrospinal fluid of PND patients harbor high titers of antibodies to specific onconeural antigens. This immune response is associated with clinically effective tumor suppression and neuronal cell death. Immunologic questions under study include the following: How are these proteins perceived as foreign by the immune system in tumor cells? What is the relationship between neuronal degeneration and the "immune-privileged" status of neurons? Why do some patients react with tumors expressing PND antigens, while others do not?
Immunologic studies of PND patient material have provided the first insight into how killer T cells mediate tumor immunity in humans. We have found that tumor cell suicide (apoptotic death) serves as a potent trigger to initiate this killer T cell immune response in PND patients. In small-scale clinical research studies performed at the Rockefeller University Hospital, we are working to recapitulate this process in cancer patients. The goal of these clinical studies is to apply our understanding of the effective tumor immunity observed in PND to the general population of cancer patients.
A second focus of study is an exploration of the nature of the onconeural antigens. Our laboratory has helped pioneer the use of PND antibodies to define new onconeural antigens by Western blot, histochemistry, and expression vector cDNA cloning. The function of these target antigens in the brain and cancer is of particular interest because of their expression patterns, which are strictly limited to neurons and specific tumor types. We are investigating several groups of onconeural antigens, particularly those associated with cerebellar degeneration and neuronal RNA-binding proteins (n-RBPs). The cerebellar degeneration gene CDR2 is normally expressed in cerebellar Purkinje neurons and ectopically expressed in gynecologic tumors. The CDR2 gene encodes a new kind of signaling protein—a leucine zipper protein that interacts with c-Myc. A second cerebellar degeneration gene, β-NAP, encodes a neuron-specific vesicle coat protein.
Two n-RBP families, the NOVA and HU genes, encode targets in a diverse set of PNDs. Nova is a target antigen in a motor degeneration associated with breast and lung cancer. NOVA genes encode a family of highly conserved RNA-binding proteins related to hnRNP K and FMRP (the fragile X mental retardation protein), while the HU genes are homologs of a Drosophila n-RBP termed elav.
We have combined biochemical, structural, and genetic approaches, ranging from RNA selection to protein:RNA crystallization to the generation of mouse knockouts, to identify RNA targets of Nova and FMRP and to determine that Nova regulates neuron-specific alternative splicing. In recent studies, we have added bioinformatics to this mix of approaches, revealing an unanticipated map of the genome-wide rules by which Nova regulates alternative splicing. These studies lay out, for the first time, an approach to developing global insight into how alternative splicing is regulated by one disease-associated protein, Nova. With this map in hand, scientists may be able to begin to put together a comprehensive understanding of human diseases that result from dysregulation of RNA metabolism.
Identification of the set of RNAs that Nova regulates has also revealed that it is not a random set but a highly coherent subset of brain transcripts. As a group, these RNAs encode synaptic functions, indicating that Nova, in regulating their alternative exon usage, can help shape the quality of the proteins that are present in the synapse. This work is beginning to provide new links between the regulation of gene expression and the modulation of synaptic function. Ongoing studies exploring the functional consequences of Nova's action are allowing us to begin to develop a framework for understanding the role of n-RBPs in neurons, tumors, and paraneoplastic neurologic disease.
This work is also supported by grants from the National Institutes of Health, the Goldhirsh Foundation, and the Dextra Baldwin McGonagle Foundation.
Last updated: November 9, 2007
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