Impaired glycosylation blocks DPP10 cell surface expression and alters the electrophysiology of Ito channel complex.

DPP10 is a transmembrane glycosylated protein belonging to the family of dipeptidyl aminopeptidase-like proteins (DPPLs). DPPLs are auxiliary subunits involved in the regulation of voltage-gated Kv4 channels, key determinants of cardiac and neuronal excitability. Although it is known that DPPLs are needed to generate native-like currents in heterologous expression systems, the molecular basis of this involvement are still poorly defined. In this study, we investigated the functional relevance of DPP10 glycosylation in modulating Kv4.3 channel activities. Using transfected Chinese hamster ovary (CHO) cells to reconstitute Kv4 complex, we show that the pharmacological inhibition of DPP10 glycosylation by tunicamycin and neuraminidase affects transient outward potassium current (I (to)) kinetics. Tunicamycin completely blocked DPP10 glycosylation and reduced DPP10 cell surface expression. The accelerating effects of DPP10 on Kv4.3 current kinetics, i.e. on inactivation and recovery from inactivation, were abolished. Neuraminidase produced different effects on current kinetics than tunicamycin, i.e., shifted the voltage dependence to more negative potentials. The effects of tunicamycin on the native I (to) currents of human atrial myocytes expressing DPP10 were similar to those of the KV4.3/KChIP2/DPP10 complex in CHO cells. Our results suggest that N-linked glycosylation of DPP10 plays an important role in modulating Kv4 channel activities.