Kinase regulation of Na⁺-K⁺-2Cl⁻cotransport in primary afferent neurons

Abstract

The Na + -K + -2Cl − cotransporter NKCC1 is expressed in sensory neurons where it accumulates intracellular Cl − and facilitates primary afferent depolarization. Depolarization of primary afferent fibre terminals interferes with the gating of incoming sensory signals to the spinal cord. The cotransporter belongs to a family of ion transporters which are sensitive to changes in cell volume. Cell shrinkage, through mechanisms that are still unknown, leads to the phosphorylation and activation of NKCC1. Similarly, axotomy results in increased NKCC1 phosphorylation in dorsal root ganglion (DRG) neurons. This review summarizes the work on the kinases that directly mediate NKCC1 activation. These are the sterile-20-like kinases SPAK and OSR1. Upon their activation through phosphorylation by upstream kinases, SPAK and OSR1 bind to specific peptides located in the cytosolic N-terminal tail of NKCC1, phosphorylate, and stimulate cotransport activity. Expression of SPAK and OSR1 varies from tissue to tissue, but in DRG neurons and in spinal cord, SPAK and OSR1 expression levels are similar. In DRG neurons, both kinases participate in the modulation of NKCC1, as the knockdown of one kinase only results in a partial decrease of NKCC1 function, while the knockdown of both kinases is additive. The identity of the kinases (e.g. WNK kinases) that possibly act upstream of SPAK and OSR1 is also discussed.

Direct control of Na+-K+-2Cl−-cotransport protein (NKCC1) expression with aldosterone

“…Previous studies implicate posttranslational phosphorylation associated with NKCC1 expression changes (1,9,23,25,29,44,50). In contrast, the present investigation is the first report that ALD exerts its effects on NKCC1 expression via prevention of posttranslational ubiquitination, e.g., reduces proteasome-dependent degradation of the NKCC1 protein.…”

“…To measure NKCC1 activity, we used a fluorescence assay to assess cotransporter activity in single isolated HT-29 cells (9,21,59). HT-29 cells were incubated at 37°C/5% CO2 for 24 h before use.…”

“…The human gene locus for NKCC1 has been identified as 5q23. 3 and is encoded by Slc12a2 in mouse (9). NKCC1 also plays key roles in renal physiology and fluid ionic regulation.…”

An Autocrine Neuronal Interleukin-6 Loop Mediates Chloride Accumulation and NKCC1 Phosphorylation in Axotomized Sensory Neurons

“…events leading to NKCC1 phosphorylation involves numerous kinases (Flatman, 2002). In particular the osmosensors Ste-20 related proline-alanine-rich kinase (SPAK) and the oxidative-stress response 1 kinase (OSR1) are involved (Delpire and Austin, 2010). Both of these kinases are under the control of upstream kinases such as the kinases with no lysine (WNK) (Kahle et al, 2010 (Vitari et al, 2006).…”

OSR1-sensitive regulation of Na+/H+ exchanger activity in dendritic cells

“…To this end, total RNA was isolated using the Trifast Reagent (Peqlab, Erlangen, Germany). RNA (2 g) was reverse-transcribed using oligo(dT) [12][13][14][15][16][17][18] primers and SuperScript II Reverse Transcriptase (Invitrogen, Karlsruhe, Germany). Then, quantitative real-time PCR with the Bio-Rad iCycler iQ Real-Time PCR Detection System (Bio-Rad, Munich, Germany) was applied using the TaqMan Gene Expression Assay (Hs00362901 m1, Applied Biosystems) to determine OSR1 transcript levels.…”