The scaffold protein PDZK1 governs diurnal localization of CNT2 on the plasma membrane in mouse intestinal epithelial cells.

Diurnal oscillations in the expression of several types of cell surface transporters have been demonstrated in the intestinal epithelial cells, which are mainly generated at transcriptional or degradation processes. Concentrative nucleoside transpoter-2 (CNT2) is expressed at the apical site of intestinal epithelial cells and contributes to the uptake of nucleosides and their analogs from the intestinal lumen into the epithelial cells. In this study, we demonstrated that the localization of CNT2 protein in the plasma membrane of mouse intestinal epithelial cells exhibited a diurnal oscillation without changing its protein level in whole cell. The scaffold protein PDZK1 interacted with CNT2 and stabilized its plasmalemmal localization. The expression of PDZK1 was under the control of molecular components of the circadian clock. Temporal accumulation of PDZK1 protein in intestinal epithelial cells enhanced the plasmalemmal localization of CNT2 at certain times of the day. The temporal increase in CNT2 protein levels at the plasma membrane also facilitated the uptake of adenosine into the intestinal epithelial cells. These results suggest a novel molecular mechanism for the diurnal localization of cell surface transporters and extend our understanding of the biological clock system that generates apparent physiological rhythms.