Apoptosis and epithelial-to-mesenchymal transition (EMT) have been implicated in a variety of biological processes, such as embryonic development, fibrosis and tumor progression. Transforming growth factor-b (TGFb) can induce simultaneously both EMT and apoptotic response of epithelial cells. However, the underlying mechanism of these biological events remains not well understood. In the present study, we show that TGF-b1 induces apoptosis and EMT in AML-12 cells in a cell cycle-related manner, in which apoptosis and EMT took place at G2/M and G1/S phases, respectively. TGF-b1-induced apoptosis was correlated with different extent of caspase activation at different cell cycle phases. Interestingly, increased phosphorylation of protein kinase D (PKD) can be observed in G1/S phase in response to TGFb1, and inhibition of PKD by inhibitor or by small interference RNA blocked EMT but not apoptosis. Our data suggest a previously unrecognized role of cell cycle state in the regulation of TGF-b-induced EMT and apoptosis, and demonstrate that PKD is involved in the TGF-b1-induced EMT.

Bystander effects induced by cytoplasmic irradiation have been reported recently. However, the mechanism(s) underlying, such as the functional role of mitochondria, is not clear. In the present study, we used either mtDNA-depleted (r 0 ) A L or normal (r þ ) A L cells as irradiated donor cells and normal human skin fibroblasts as receptor cells in a series of medium transfer experiments to investigate the mitochondria-related signal process. Our results indicated that mtDNA-depleted cells or normal A L cells treated with mitochondrial respiratory chain function inhibitors had an attenuated g-H2AX induction, which indicates that mitochondria play a functional role in bystander effects. Moreover, it was found that treatment of normal A L donor cells with specific inhibitors of NOS, or inhibitor of mitochondrial calcium uptake (ruthenium red) significantly decreased g-H2AX induction and that radiation could stimulate cellular NO and O 2 KÀ production in irradiated r þ A L cells, but not in r 0 A L cells. These observations, together with the findings that ruthenium red treatment significantly reduced the NO and O 2 KÀ levels in irradiated r þ A L cells, suggest that radiationinduced NO derived from mitochondria might be an intracellular bystander factor and calcium-dependent mitochondrial NOS might play an essential role in the process.