Threonine 32 (Thr32) of FoxO3 is critical for TGF-β-induced apoptosis via Bim in hepatocarcinoma cells

Transforming growth factor-β (TGF-β) exerts apoptotic effects on various types of malignant cells, including liver cancer cells. However, the precise mechanisms by which TGF-β induces apoptosis remain poorly known. In the present study, we have showed that threonine 32 (Thr32) residue of FoxO3 is critical for TGF-β to induce apoptosis via Bim in hepatocarcinoma Hep3B cells. Our data demonstrated that TGF-β induced FoxO3 activation through specific de-phosphorylation at Thr32. TGF-β-activated FoxO3 cooperated with Smad2/3 to mediate Bim up-regulation and apoptosis. FoxO3 (de)phosphorylation at Thr32 was regulated by casein kinase I-ε (CKI-ε). CKI inhibition by small molecule D4476 could abrogate TGF-β-induced FoxO/Smad activation, reverse Bim up-regulation, and block the sequential apoptosis. More importantly, the deregulated levels of CKI-ε and p32FoxO3 were found in human malignant liver tissues. Taken together, our findings suggest that there might be a CKI-FoxO/Smad-Bim engine in which Thr32 of FoxO3 is pivotal for TGF-β-induced apoptosis, making it a potential therapeutic target for liver cancer treatment.

The Unscheduled Expression of Cyclin B1/CDK1 Contributes to the Transition of Cell Cycle of Lymphocytes in vivo from G_0 to G_1 Phase / 华中科技大学学报(医学版)

Objective To study the mechanism of unscheduled Cyclin B1 expression at G_1 phase which is usually at G_2/M phase.Methods Human peripheral blood lymphocytes(PBL) from healthy volunteers were firstly activated by PHA and then went into cell cycle.The cells were collected at 0,36,48 and 60 h after activation and divided into two parts:one for Cyclins/DNA muhiparameter assay,and another for Post-sorting Western blot.Results After activation by PHA,Cyclin B1 and CDK1 of lymphocytes were expressed at G_1 phase.Conclusion Unscheduled Cyclin B1/CDKl probably contributes to lymphocytes in vivo into cell cycle.