Apigenin-induced-apoptosis is mediated by the activation of PKCdelta and caspases in leukemia cells.

Apigenin, a flavone abundantly found in fruits and vegetables, exhibits antiproliferative, anti-inflammatory, and antimetastatic activities through poorly defined mechanisms. In the present study, the treatment of different cell lines with apigenin resulted in selective antiproliferative and apoptotic effect in monocytic and lymphocytic leukemias. Apigenin-induced-apoptosis was mediated by the activation of caspase-9 and caspase-3. Apigenin was found intracellularly and localized to the mitochondria. Treatment of monocytic cells with apigenin was accompanied by an increase in reactive oxygen species (ROS) and phosphorylation of the MAPKs, p38 and ERK. However, the inhibition of ROS, p38 or ERK failed to block apoptosis, suggesting that these cellular responses induced by apigenin are not essential for the induction of apoptosis. In addition, apigenin induced the activation of PKCdelta. Pharmacological inhibition of PKCdelta, the expression of dominant-negative PKCdelta and silencing of PKCdelta in leukemia cells showed that apigenin-induced-apoptosis requires PKCdelta activity. Together, these results indicate that this flavonoid provides selective activity to promote caspase-dependent-apoptosis of leukemia cells and uncover an essential role of PKCdelta during the induction of apoptosis by apigenin.

A trafficking pathway for anthocyanins overlaps with the endoplasmic reticulum-to-vacuole protein-sorting route in Arabidopsis and contributes to the formation of vacuolar inclusions.

Plants produce a very large number of specialized compounds that must be transported from their site of synthesis to the sites of storage or disposal. Anthocyanin accumulation has provided a powerful system to elucidate the molecular and cellular mechanisms associated with the intracellular trafficking of phytochemicals. Benefiting from the unique fluorescent properties of anthocyanins, we show here that in Arabidopsis (Arabidopsis thaliana), one route for anthocyanin transport to the vacuole involves vesicle-like structures shared with components of the secretory pathway. By colocalizing the red fluorescence of the anthocyanins with green fluorescent protein markers of the endomembrane system in Arabidopsis seedlings, we show that anthocyanins are also sequestered to the endoplasmic reticulum and to endoplasmic reticulum-derived vesicle-like structures targeted directly to the protein storage vacuole in a Golgi-independent manner. Moreover, our results indicate that vacuolar accumulation of anthocyanins does not depend solely on glutathione S-transferase activity or ATP-dependent transport mechanisms. Indeed, we observed a dramatic increase of anthocyanin-filled subvacuolar structures, without a significant effect on total anthocyanin levels, when we inhibited glutathione S-transferase activity, or the ATP-dependent transporters with vanadate, a general ATPase inhibitor. Taken together, these results provide evidence for an alternative novel mechanism of vesicular transport and vacuolar sequestration of anthocyanins in Arabidopsis.