Surface biotinylation revealed that heterologously expressed CNIH-2 could only be found on the cell surface when GluA subunits were co-expressed (Fig. 6A). In the absence of GluA subunits, even high expression levels of CNIH-2 were not sufficient to drive detectable amounts of CNIH-2 to the plasma membrane. Thus, only upon interaction with AMPARs, CNIH-2 leaves the ER-to-Golgi cycle and is rendered a surface membrane protein. In line with this result, both endogenous and exogenously over-expressed CNIH-2 was detected on the cell surface of dissociated hippocampal neurons, which express endogenous GluAs (Fig. 6B).
