Src-independent ERK signaling through the rat alpha 3 isoform of Na/K-ATPase

• Published in: American Journal of Physiology: Cell Physiology 2017-03, Vol.312 (3), p.C222-C222
• Main Authors: Madan, Namrata, Xu, Yunhui, Duan, Qiming, Banerjee, Moumita, Larre, Isabel, Pierre, Sandrine V, Xie, Zijian
• Format: Article
• Language: English
• ISSN: 0363-6143
• DOI: 10.1152/ajpcell.00199.2016

The Na/K-ATPase alpha 1 polypeptide supports both ion-pumping and signaling functions. The Na/K-ATPase alpha 3 polypeptide differs from alpha 1 in both its primary structure and its tissue distribution. The expression of alpha 3 seems particularly important in neurons, and recent clinical evidence supports a unique role of this isoform in normal brain function. The nature of this specific role of alpha 3 has remained elusive, because the ubiquitous presence of alpha 1 has hindered efforts to characterize alpha 3-specific functions in mammalian cell systems. Using Na/K-ATPase alpha 1 knockdown pig kidney cells (PY-17), we generated the first stable mammalian cell line expressing a ouabain-resistant form of rat Na/K-ATPase alpha 3 in the absence of endogenous pig alpha 1 detectable by Western blotting. In these cells, Na/K-ATPase alpha 3 formed a functional ion-pumping enzyme and rescued the expression of Na/K-ATPase beta 1 and caveolin-1 to levels comparable with those observed in PY-17 cells rescued with a rat Na/K-ATPase alpha 1 (AAC-19). The alpha 3-containing enzymes had lower Na+ affinity and lower ouabain-sensitive transport activity than their alpha 1-containing counterparts under basal conditions, but showed a greater capacity to be activated when intracellular Na+ was increased. In contrast to Na/K-ATPase alpha 1, alpha 3 could not regulate Src. Upon exposure to ouabain, Src activation did not occur, yet ERK was activated through Src-independent pathways involving PI3K and PKC. Hence, alpha 3 expression confers signaling and pumping properties that are clearly distinct from that of cells expressing Na/K-ATPase alpha 1.