Mutations in pkd2 result in the type 2 form of autosomal dominant polycystic kidney disease, which accounts for approximately 15% of all cases of the disease. PKD2, the protein product of pkd2, belongs to the transient receptor potential superfamily of cation channels, and it can function as a mechanosensitive channel in the primary cilium of kidney cells, an intracellular Ca(2+) release channel in the endoplasmic reticulum, and/or a nonselective cation channel in the plasma membrane. We have identified mDia1/Drf1 (mammalian Diaphanous or Diaphanous-related formin 1 protein) as a PKD2-interacting protein by yeast two-hybrid screen. mDia1 is a member of the RhoA GTPase-binding formin homology protein family that participates in cytoskeletal organization, cytokinesis, and signal transduction. We show that mDia1 and PKD2 interact in native and in transfected cells, and binding is mediated by the cytoplasmic C terminus of PKD2 binding to the mDia1 N terminus. The interaction is more prevalent in dividing cells in which endogenous PKD2 and mDia1 co-localize to the mitotic spindles. RNA interference experiments reveal that endogenous mDia1 knockdown in HeLa cells results in the loss of PKD2 from mitotic spindles and alters intracellular Ca(2+) release. Our results suggest that mDia1 facilitates the movement of PKD2 to a centralized position during cell division and has a positive effect on intracellular Ca(2+) release during mitosis. This may be important to ensure equal segregation of PKD2 to the daughter cell to maintain a necessary level of channel activity. Alternatively, PKD2 channel activity may be important in the cell division process or in cell fate decisions after division.