REGULATION OF ENAC BY CASEIN KINASE 2
Hypertension affects millions of people in the United States and worldwide. Improved understanding of themolecular and cellular origins of hypertension will improve the efficacy of treatment and diagnosis. TheEpithelial Na+ Channel, ENaC, is the final arbiter of Na+ excretion in the kidneys. As such, discretionary controlof ENaC fine-tunes renal excretion. Appropriate renal excretion is a key factor in the normal regulation ofarterial blood pressure. Consequently, dysfunction of ENaC and its upstream modulators cause dysregulationof blood pressure due to abnormal excretion. Casein kinase 2 (CK2) is known to phosphorylate ENaC. Thephysiological importance of this, though, is obscure. Our preliminary results demonstrate that phosphorylationby CK2 is necessary for normal ENaC activity and renal Na+ excretion. The CK2 phosphorylation site withinENaC resides within a canonical ?anchor? ankyrin binding motif. This site in ENaC shares similarity to CK2phosphorylation sites in the unrelated NaV and KCNQ channels, which also lie within ?anchor? motifs.Phosphorylation of NaV and KCNQ channels by CK2 acts as a molecular ?switch? favoring the binding ofankyrin-3 (Ank-3). The binding of Ank-3 facilitates the proper membrane localization of these channelsincreasing their activity. The targeted deletion of Ank-3 in principal cells (PC) significantly decreased ENaCactivity in our PC-Ank-3 KO mouse. In consideration of our strong preliminary results and the possibleconvergent evolution shaping regulation of ENaC, NaV and KCNQ by CK2, we propose testing the premise thatphosphorylation of ENaC by CK2 within ?anchor? motifs is necessary and sufficient for Ank-3 binding to thechannel, which is required for normal channel locale and function, and the proper regulation of renal Na+excretion. We will test these ideas using a multidisciplinary approach that includes novel thinking and tools,including PC-specific CK2 and Ank-3 KO mice, and a high degree of rigor in conjunction with a researchdesign that is broad in scope asking questions about molecular and cellular mechanisms as well as wholeanimal physiological consequences. The following specific aims will be used to test our ideas: 1) To determinethe cellular and molecular mechanisms of CK2 regulation of ENaC activity; 2) To quantify thephysiological function of CK2 regulation of ENaC; and 3) To determine if CK2 regulation of ENaC isconserved in humans. If CK2 regulation of ENaC is to be of clinic and physiological importance suchregulation must be conserved across phyla particularly in humans. Our pioneering efforts to quantify ENaCactivity in tubules from healthy donor human kidneys allows us to test our ideas in the most relevant settingpossible: the human principal cell within the native collecting duct. After accomplishing these aims, we willknow if, how and when CK2 phosphorylation of ENaC functions as a ?switch? to favor Ank-3 binding to increasechannel activity to include having a detailed understanding of the mechanisms mediating this regulation, and arich appreciation of the physiological consequences of such regulation.