Na, K-ATPase as signaling transducer
Year: 2007
Type: dissertation
Abstract: It is now generally agreed that Na,K-ATPase (NKA), in addition to its \nrole in the maintenance of Na+ and K+ gradients across the cell membrane, \nis a signal transducer. Our group has identified a novel signaling \npathway where NKA interact with IP3R to form a signaling microdomain. \nOuabain, a specific ligand of NKA, activates this pathway, triggers slow \nCa2+ oscillations and activates NF-κB. In current study, the molecular \nmechanisms and some important downstream effects of NKA signaling are \ndemonstrated. \n \n \n \nThe critical binding motifs in NKA/IP3R signaling microdomain and the \nrole of ankyrin B (Ank- B) were demonstrated. N-terminal tail of the NKA \nα-subunit (αNT-t) binds directly to N terminus of IP3R. Three amino acid \nresidues, LKK, conserved in most species and α-isoforms of NKA, are \nessential for binding. Ank-B expressed in most mammalian cells, plays a \npivotal role for NKA/IP3R signalosome. The N-terminal tails of NKA a \nsubunit and IP3R are novel binding sites for Ank-B. In Ank-B silenced \ncells, the interaction between NKA and IP3R is decreased. \n \n \n \nThe role of NKA/IP3R signaling for activation of NF-κB was elucidated. \nCells overexpressing a peptide corresponding to αNT-t, which binds to IP3R \nand blocks NKA/IP3R binding, suppresses ouabain’s effect. Knockdown of \nAnk-B abolishes the ouabain effect on NF-κB. \n \n \n \nThe downstream effects of this signaling pathway include protection from \napoptosis and stimulation of cell proliferation. Ouabain (nM) completely \nabolishes serum deprivation induced apoptosis. Ouabain protection from \napoptosis is not observed in cells overexpressing a mutant NKA α subunit \nwith deletion of the N-terminal tail or a peptide corresponding to αNT-t. \nBoth of them block the interaction between NKA and IP3R. Inhibition of Ca2+release from intracellular stores via IP3R or inhibition of NF-κB activity \nabolishes the anti-apoptotic effect of ouabain. Ouabain stimulates cell \nproliferation which depends on Ca2+release via IP3R. \n \n \n \nActivation of this signaling pathway rescues nephrogenesis in growth \nfactor deprived embryonic rat kidney. Exposure to ouabain triggers Ca2+oscillations and activates NF-κB in embryonic kidney cells. Growth factor deprivation retards formation of new glomeruli and increases apoptotic index. Ouabain (nM) completely prevents these effects. The protective effects of ouabain are abolished by depletion of intracellular Ca2+ stores and by inhibition \nof NF-κB. The expression of the inductive factors Wt1 and Pax2 activated \nby NF-κB, are increased in ouabain exposed growth factor deprived \nkidneys. Thus we have identified a novel mechanism by which kidney \ndevelopment can be protected under adverse intrauterine circumstances. \n \n \n \nIn conclusion, this thesis demonstrates that NKA directly binds to IP3R \nto form a signaling microdomain and Ank-B tethers this binding. Ouabain \nactivates this signaling pathway that results in NF-κB activation, the \ndownstream effects of which are stimulation of cell proliferation, \nprotection from apoptosis and rescue of growth factor deprivation-induced \ninhibition of embryonic kidney nephrogenesis.
Source: Figshare
Author: Juan Li
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W1601775139