Dopamine neurotransmission has long been thought be altered in schizophrenic brain, mainly since dopamine antagonists are the primary treatment for schizophrenic patients.  A number of proteins have been identified as putative modulators and amplifiers of the intracellular signaling cascades initiated by dopamine binding to a receptor. Among these are DARPP-32, spinophilin, and calcyon. To determine if these dopamine-interacting molecules are abnormal in schizophrenic brain, we compared the amount of mRNA for these proteins in two regions of the schizophrenic and control frontal cortex.  This study found no difference in DARPP-32 mRNA, but altered spinophilin and calcyon mRNA, in schizophrenic brain.

Both calcyon mRNA and protein have consistently been found to be increased in schizophrenic brain.  Although calcyon has been hypothesized to be involved in receptor crosstalk, the specific function of this molecule is not well understood.  Calcyon, a 24 kD membrane protein, has been reported in vitro to associate with the D1 dopamine receptor, putatively coupling D1 receptor activation to potentiated intracellular calcium release when Gq/11 signaling pathways are co-stimulated. This is hypothesized as a means for dopamine signaling to modulate crosstalk with other neurotransmitter receptor systems. We used in situ hybridization to characterize the distribution of calcyon in primate brain, compared to that of dopamine- and glutamate-associated signaling molecules. Moderately dense, diffuse signal of calcyon mRNA is found in all areas of cerebral cortex, with stronger labeling present in pyramidal cell layers of medial prefrontal and anterior cingulate cortex.  The distribution of calcyon is not consistent with localization exclusively to dopamine-receptive regions, but is similar to the distribution of ionotropic glutamate receptors.

 In order to shed light on the specific function of calcyon, we undertook a yeast two-hybrid screen to find proteins that bind to calcyon.  This screen yielded ~10 putative calcyon-binding proteins.  We are currently utilizing additional techniques (such as co-immunoprecipitation of in vitro synthesized proteins) to confirm the results of the yeast two-hybrid screen.  

Karen Baracskay