Expression of postsynaptic density proteins of the ProSAP/Shank family in the thymus.

PSD95-DLG-ZO1 domain-containing proteins of the ProSAP/Shank family are major scaffolding proteins of the neuronal postsynaptic density which play a pivotal role in the linkage of membrane receptors to downstream signal effectors and the actin-based cytoskeleton. Recently, ProSAP1/Shank2 has also been localized in various non-neuronal cells where it may fulfill similar functions as in neurons. We now complement these data by the study of ProSAP/Shank expression at the mRNA and protein level in a primary lymphoid organ, i.e., the thymus. Transcripts for ProSAP1/Shank2, the spliceoform Shank2E, and ProSAP2/Shank3 could be clearly detected in the thymus. Western blot and immunocytochemical analyses verified the presence of ProSAP1/Shank2 and ProSAP2/Shank3 proteins in thymic tissue. Immunoreactivity was concentrated in the whole peripheral cytoplasm of thymocytes underneath the plasma membrane. Discrete subplasmalemmal areas of pronounced ProSAP/Shank immunoreactivity could be demonstrated inside several thymocytes by confocal laser scanning microscopy. Our results establish ProSAP/Shank as a constituent of the cell cortex of thymocytes and thus lead to the hypothesis that ProSAP/Shank proteins serve as a platform for the coordination of membrane receptor-dependent signal transduction in immune cells.