The role of PSD-95 in the rearrangement of Kv1.3 channels to the immunological synapse.

Establishment of the immunological synapse (IS) between T lymphocytes and antigen-presenting cells is a key step in the adaptive immune response. Several proteins accumulate in the IS, such as the Kv1.3 potassium channel; however, the mechanism of this translocation is unknown. PSD-95 and SAP97 are adaptor proteins that regulate the polarized cell surface expression and localization of Kv1 channels in neurons. We investigated whether these proteins affect the redistribution of Kv1.3 into the IS in non-excitable human T cells. We show here that PSD-95 and SAP97 are expressed in Jurkat and interact with the C terminus of Kv1.3. Disruption of the interaction between PSD-95 or SAP97 and Kv1.3 in Jurkat was realized by the expression of a C-terminal truncated Kv1.3, which lacks the binding domain for these proteins, or by the knockdown of the expression of PSD-95 or SAP97 using specific shRNA. Expression of the truncated Kv1.3 or knockdown of PSD-95, but not the knockdown of SAP97, inhibited the recruitment of Kv1.3 into the IS; the fraction of cells showing polarized Kv1.3 expression upon engagement in an IS was significantly lower than in control cells expressing the full-length Kv1.3, and the rearrangement of Kv1.3 did not show time dependence. In contrast, Jurkat cells expressing the full-length channel showed marked time dependence in the recruitment into the IS peaking at 1 min after the conjugation of the cells. These results demonstrate that PSD-95 participates in the targeting of Kv1.3 into the IS, implying its important role in human T-cell activation.