ASK1/JNK-mediated TAp63 activation controls the cell survival signal of baicalein-treated EBV-transformed B cells

Transcriptionally active p63 (TAp63) promotes cell cycle arrest, senescence, and apoptosis in several cancer cells. Migration inhibitory factor (MIF)/CD74 regulates B-cell survival through nuclear factor (NF)-kappa B-dependent TAp63 expression. In this study, we investigated how the level of TAp63 expression influences the induction of apoptosis in baicalein-treated EBV-transformed B cells. Baicalein induced the expression of TAp63 and apoptosis signal-regulating kinase 1 (ASK1), as well as cytotoxicity, by disrupting the mitochondrial membrane and inhibiting the activation of phosphoinositide 3-kinase (PI3K)/Akt and NF-kappa B. Genetic knockdown of TAp63 or ASK1 by small interfering RNA resulted in protection from apoptosis accompanied by the recovery of CD74, CD44, alpha 4 integrin, Bcl-2, and NF-kappa B activation. Baicalein-induced reactive oxygen species activated the ASK1/JNK pathway with subsequent expression of TAp63. Pre-engagement with MIF/CD74 maintained the expression of CD74, CD44, and alpha 4 integrin, as well as Syk/Src-mediated PI3K/Akt activation, in baicalein-treated EBV-transformed B cells. Meanwhile, ASK1/JNK-dependent TAp63 expression was efficiently suppressed after pre-treatment with MIF. Our results suggest that baicalein-mediated ASK1/JNK activation regulates the mitochondria-dependent apoptosis pathway through the up-regulation of TAp63 and downregulation of NF-kappa B and CD74/CD44 in B-cell malignancies.