The cytoplasmic Purkinje onconeural antigen cdr2 down-regulates c-Myc function: implications for neuronal and tumor cell survival

Woong-Yang Park

Laboratory of Molecular Neuro-Oncology, The Rockefeller University, New York, NY10021, USA and Department of Biochemistry and Molecular Biology, Seoul National University College of Medicine, Seoul 110-799, KOREA

e-mail: parkw@mail.rockefeller.edu

Paraneoplastic neurological degenerations (PNDs) are neurological disorders that develop in patients with cancer. PNDs are triggered by an effective antitumour immune response against neuronal antigens that are expressed in cancer cells, which subsequently develops into autoimmune neurodegenerative disease. Paraneoplastic cerebellar degeneration (PCD) is a disorder in which breast or ovarian tumors express an onconeural antigen termed cdr2, which normally is expressed in cerebellar Purkinje neurons. This leads to an immune response to cdr2 that is associated with tumor immunity and autoimmune cerebellar degeneration. We have found that cdr2, a cytoplasmic protein harboring a helix–leucine zipper (HLZ) motif, interacts specifically with the HLZ motif of c-Myc. Both proteins colocalize in the cytoplasm of adult cerebellar Purkinje neurons, and coimmunoprecipitate from tumor cell lines and cerebellar extracts. cdr2 down–regulates c-Myc-dependent transcription in cotransfection assays, and redistributes Myc protein in the cytoplasm. Disease antisera from six of six PCD patients specifically blocked the interaction between cdr2 and c-Myc in vitro. These data indicate that cdr2 normally sequesters c-Myc in the neuronal cytoplasm, thereby down-regulating c-Myc activity, and suggest a mechanism whereby inhibition of cdr2 function by autoantibodies in PCD may contribute to Purkinje neuronal death.