Cardiac glycoside ouabain induces activation of ATF-1 and StAR expression by interacting with the ??4 isoform of the sodium pump in Sertoli cells

摘要

Sertoli cells express ??1 and ??4 isoforms of the catalytic subunit of Na+,K+-ATPase (sodium pump). Our recent findings demonstrated that interactions of the ??4 isoform with cardiotonic steroids (CTS) like ouabain induce signaling cascades that resemble the so-called non-classical testosterone pathway characterized by activation of the c-Src/c-Raf/Erk1/2/CREB signaling cascade. Here we investigate a possible physiological significance of the activated cascade. The results obtained in the current investigation show that the ouabain-induced signaling cascade also leads to the activation of the CREB-related activating transcription factor 1 (ATF-1) in the Sertoli cell line 93RS2 in a concentration- and time-dependent manner, as demonstrated by detection of ATF-1 phosphorylated on Ser63 in western blots. The ouabain-activated ATF-1 protein was found to localize to the cell nuclei. The sodium pump ??4 isoform mediates this activation, as it is ablated when cells are incubated with siRNA to the ??4 isoform. Ouabain also leads to increased expression of steroidogenic acute regulator (StAR) protein, which has been shown to be a downstream consequence of CREB/ATF-1 activation. Taking into consideration that CTS are most likely produced endogenously, the demonstrated induction of StAR expression by ouabain establishes a link between CTS, the ??4 isoform of the sodium pump, and steroidogenesis crucial for male fertility and reproduction. ? 2012 Elsevier B.V.