1. ¹The State Key Lab of Pharmaceutical Biotechnology, College of Life Science, Nanjing University, Nanjing, People's Republic of China
2. ²Pulmonary Critical Care Medicine Branch, National Institute of Health, Bethesda, MD, USA

Correspondence: Dr Z-C Hua, The State Key Lab of Pharmaceutical Biotechnology, College of Life Science, Nanjing University, Nanjing 210093, People's Republic of China. E-mail: zchua@nju.edu.cn

Received 26 November 2006; Revised 29 April 2007; Accepted 9 May 2007; Published online 7 June 2007.

Abstract

Human T-cell leukemia is a malignant disease that needs various regimens of cytotoxic chemotherapy to overcome drug resistance. Recently, Na⁺,K⁺-ATPase has emerged as a potential target for cancer therapy. However, its exact signaling pathway in human T-cell leukemia cell death has not been well defined. In the current study, we found CD95(APO-1) was able to trigger the internalization of plasma membrane Na⁺,K⁺-ATPase in Jurkat cells or primary T cells as a mechanism to suppress its activity. This internalization was closely relevant to intracellular glutathione (GSH) depletion in Jurkat cells downstream of Fas-associated death domain protein (FADD) and caspase 8. GSH depletion in Fas L-treated Jurkat cells induced the generation of hydrogen peroxide (H₂O₂), which subsequently increased the serine phosphorylation of Na⁺,K⁺-ATPase 1 subunit. Exogenous H₂O₂ even mimicked the effect of Fas L to upregulate the serine phosphorylation of Na⁺,K⁺-ATPase 1 subunit and suppress Na⁺,K⁺-ATPase activity. Overall, our results indicate that CD95(APO-1) induces the FADD- and caspase 8-dependent internalization of Na⁺,K⁺-ATPase through intracellular GSH loss, and the subsequent generation of H₂O₂-mediated serine phosphorylation of Na⁺,K⁺-ATPase 1 subunit. Taken together, this study presents a novel regulatory mechanism of Na⁺,K⁺-ATPase in CD95(APO-1)-mediated human T-leukemia cell apoptosis.