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The cytoplasmic Purkinje onconeural antigen cdr2 down-regulates c-Myc function: implications for neuronal and tumor
H J Okano1, W Y Park, J P Corradi
1Laboratory of Molecular Neuro-Oncology, The Rockefeller University, New York, New York 10021 USA.
Abstract:
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.
Insights
Paraneoplastic cerebellar degeneration (PCD) involves an immune response to the cdr2 protein, which interacts with c-Myc. Autoantibodies against cdr2 may disrupt this interaction, potentially causing neuronal death.
Area of Science:
- Neuroscience
- Immunology
- Oncology
Background:
- Paraneoplastic cerebellar degeneration (PCD) is linked to breast or ovarian tumors expressing the onconeural antigen cdr2.
- cdr2 is normally found in cerebellar Purkinje neurons, and its expression by tumors triggers an immune response.
- This immune response is associated with both tumor immunity and autoimmune cerebellar degeneration.
Purpose of the Study:
- To investigate the interaction between the onconeural antigen cdr2 and c-Myc.
- To elucidate the role of cdr2-c-Myc interaction in the pathogenesis of paraneoplastic cerebellar degeneration.
Main Methods:
- Co-immunoprecipitation assays to detect cdr2-c-Myc interaction in tumor cell lines and cerebellar extracts.
- Co-localization studies in adult cerebellar Purkinje neurons.
- Cotransfection assays to assess cdr2's effect on c-Myc-dependent transcription.
- In vitro assays using patient disease antisera to block cdr2-c-Myc interaction.
Main Results:
- cdr2, a cytoplasmic protein with a helix-leucine zipper (HLZ) motif, specifically interacts with the HLZ motif of c-Myc.
- Both cdr2 and c-Myc colocalize in the cytoplasm of cerebellar Purkinje neurons and coimmunoprecipitate.
- cdr2 down-regulates c-Myc-dependent transcription and redistributes Myc protein in the cytoplasm.
- Disease antisera from all tested PCD patients blocked the cdr2-c-Myc interaction in vitro.
Conclusions:
- cdr2 normally sequesters c-Myc in the neuronal cytoplasm, down-regulating c-Myc activity.
- Autoantibodies in PCD patients may inhibit cdr2 function.
- This inhibition of cdr2 function by autoantibodies could contribute to Purkinje neuronal death in paraneoplastic cerebellar degeneration.