The cortactin-binding postsynaptic density protein ProSAP1 in non-neuronalcells

Proline-rich synapse-associated protein-1 (ProSAP1) is a neuronal PDZ domai n-containing protein that has recently been identified as an essential elem ent of the postsynaptic density. Via its interaction with the actin-binding protein cortactin and its integrative function in the organization of neur otransmitter receptors, ProSAP1 is believed to be involved in the linkage o f the postsynaptic signaling machinery to the actin-based cytoskeleton, and may play a role in the cytoskeletal rearrangements that underlie synaptic plasticity. As a result of our ongoing studies on the distribution and func tion of this novel PDZ domain protein, we now report that the expression of ProSAP1 is restricted neither to neurons and interneuronal junctions nor t o the nervous system. Using immunohistochemical technniques in conjunction with specific antibodies, we found that, in the CNS, ProSAP1 can be detecte d in certain glial cells, such as ependymal cells, tanycytes, subpial/radia l astrocytes, and in the choroid plexus epithelium. Moreover, our immunohis tochemical analyses revealed the presence of ProSAP1 in endocrine cells of the adenohypophysis and of the pancreas, as well as in non-neuronal cell ty pes of other organs. In the pancreas, ProSAP1 immunoreactivity was also loc alized in the duct system of the exocrine parenchyma. Our findings demonstr ate that, in addition to neurons, ProSAP1 is present in various non-neurona l cells, in which it may play a crucial role in the dynamics of the actin-b ased cytoskeleton.