May act as a mediator of stress-activated signals. Mediates the inhibition of SLC4A4, SLC26A6 as well as CFTR activities by the WNK scaffolds, probably through phosphorylation (PubMed:21317537, PubMed:23542070). Phosphorylates RELT (PubMed:16530727). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] The phosphorylated form forms a complex with WNK2 (PubMed:21733846). Interacts with RELT (PubMed:16530727). Interacts with SORL1 (via cytosolic C-terminus) (By similarity). Nucleus when caspase-cleaved. Expressed in the kidney, including in epithelial cells of the thick ascending limb of Henle's loop and in the distal convoluted tubule (at protein level). PAPA box (proline-alanine repeats) may target the kinase to a specific subcellular location by facilitating interaction with intracellular proteins such as actin or actin-like proteins. Phosphorylated at Ser-321 by PRKCQ (PubMed:21733846). Autophosphorylation at Thr-243 positively regulates its activity (PubMed:16530727). Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. STE20 subfamily.