Aquaporin 1 expression during the cell cycle in A5 cells.

Aquaporin 1 is an integral membrane protein which functions as a water channel. It is reportedly (Lanahan et al., 1992) encoded by a delayed early response gene. We asked if the expression of aquaporin 1 varied during the cell cycle in an epithelial cell line (A5) in which its is constitutively expressed. A5 cells were synchronized by double thymidine block and cell cycle stages defined by flow cytometric analysis. AQP1 mRNA and protein levels were highest when most cells were in G0/G1, then decreased approximately 40-60% when the cells moved into the S and G2/M phases. These results provide the first demonstration that constitutive aquaporin 1 expression can fluctuate during the cell cycle.