Creatine kinase is a central regulatory enzyme of ATP generation,which catalyzes the reversible transfer of the N-phosphoryl group from phosphocreatine to ADP to regenerate ATP,plays a key role in highly energy-demanding processes.While its roles in other ATP-consuming events,such as signal transduction and consequential cell fate decisions,remain largely unknown.Here we reported that the expression level of creatine kinase B (CKB) was significantly upregulated during the differentiation of DP thymocytes into mature CD4+CD8 and CD4CD8+ single-positive (SP) cells,which is concurrent with the specific loss of CpG methylation from the proximal promoter region of CKB.Ectopic expression of CKB resulted in increased intercellular level of ATP and enhanced TCR-induced phosphorylation of Zap-70,LAT,the kinase Erk and P38.