PKD1 and cyst: The absence or lack of flow, as well as the loss or dysfunction of the cilia, PC1, or PC2, decreases Ca2+ influx and activates intramembrane proteolysis, which allows STAT6 and its coactivator P100, in a complex bound to the PC1 tail, to translocate to the nucleus and stimulate transcription, resulting in uncontrolled cell proliferation and cyst formation 52.