Involved in maintenance of high-frequency synaptic transmission at hippocampal CA3-CA1 synapses. Regulates AMPA-type glutamate receptor (AMPAR) immobilization at postsynaptic density keeping the channels in an activated state in the presence of glutamate and preventing synaptic depression. May play a role in self-renewal and differentiation of spermatogonial stem cells by inhibiting canonical Wnt signaling pathway. Component of the postsynaptic hippocampal AMPA-type glutamate receptor (AMPAR) complex, at least composed of pore forming AMPAR subunits GRIA1, GRIA2 and GRIA3 and AMPAR auxiliary proteins SHISA6 and SHISA7. Interacts (via PDZ-binding motif) with DLG4/PSD-95 (via PDZ domain); the interaction is direct. Expressed in the developing ventral mesencephalon. The PDZ-binding motif interacts with PDZ-domain of scaffolding protein DLG4. Belongs to the shisa family. Truncated N-terminus. Truncated N-terminus.