Regulation of Na+/H+ exchanger in dendritic cells by Akt2

Abstract

Dendritic cells (DCs) are antigen-presenting cells decisive in primary immune responses and establishment of immunological memory. They are activated by bacterial lipopolysaccharides (LPS), which lead to activation of Na(+)/H(+) exchanger activity, cell swelling, reactive oxygen species (ROS) formation, and migration. The effects require functional phosphoinositide 3 kinase and are paralleled by Akt phosphorylation. The present study explored the putative involvement of the Akt isoform Akt2. To this end, experiments were performed in DCs isolated from bone marrow of mice lacking functional Akt2/PKBß (akt2 (-/-)) and respective wild-type animals (akt2 (+/+)). Based on BCECF fluorescence, cytosolic pH (pH(i)) was significantly lower in akt2 (-/-) than in akt2 (+/+) DCs. Transient exposure to NH(4)Cl was followed by profound cytosolic acidification in both genotypes. Subsequent re-alkalinization was largely dependent on Na(+) thus reflecting Na(+)/H(+) exchanger activity and was significantly lower in akt2 (-/-) than in akt2 (+/+) DCs. According to forward scatter in FACS analysis, cell volume was significantly lower in akt2 (-/-) than in akt2 (+/+) DCs. Exposure of DCs to LPS led within 4 h to significant increases of Na(+)/H(+) exchanger activity, cell volume, ROS production, and migration in akt2 (+/+) mice, and its effects were significantly blunted in akt2 (-/-) DCs. The present observations disclose a role of Akt2 in the regulation of pH(i), cell volume, ROS production, and migration in dendritic cells.

Up-Regulation of Amino Acid Transporter SLC6A19 Activity and Surface Protein Abundance by PKB/Akt and PIKfyve

“…Accordingly, the upregulation of Na + -coupled amino acid transport by PKB/Akt may represent a challenge for cell volume regulation. PKB/Akt activation has indeed been shown to increase cell size [44], an effect, which may not only be based on the stimulation of amino acid uptake, but as well on activation of further carriers resulting in cellular ion accumulation, such as the Na + /H + exchanger [45]. Cellular uptake of amino acids may foster survival of proliferating cells [46,47].…”

Lumen LPS inhibits HCO3−absorption in the medullary thick ascending limb through TLR4-PI3K-Akt-mTOR-dependent inhibition of basolateral Na+/H+exchange

“…Thus it is conceivable that lumen LPS inhibits MTAL HCO 3 Ϫ absorption through PI3K-mTOR-mediated inhibition of NHE1. LPS has been shown to modulate NHE1 in other cell systems, including immune cells, endothelial cells, and intestinal epithelial cells (5,8,14,58,65). Whether NHE1 is regulated by LPS or is a downstream target of TLR4 signaling in renal tubules has not been determined.…”

Up-Regulation of Voltage Gated K+ Channels Kv1.3 and Kv1.5 by Protein Kinase PKB/Akt

“…PKB/Akt activation has, however, been shown to increase cell size [50] and T-cells overexpressing active Akt1 are enlarged [51]. The swelling effect of PKB/Akt may result from cellular ion accumulation by the Na + /H + exchanger [52]. Arithmetic means ± SEM (n = 94 -98) of normalized Kv1.5-HA chemiluminescence in Xenopus oocytes injected with water (dotted bar), expressing Kv1.5-HA alone (white bar) or expressing Kv1.5-HA together with wild-type PKB/Akt (black bar).…”