Paclitaxel-Induced Nuclear Translocation of FOXO3a in Breast Cancer Cells Is Mediated by c-Jun NH2-Terminal Kinase and Akt

Abstract

The microtubule-targeting compound paclitaxel is often used in the treatment of endocrine-resistant or metastatic breast cancer. We have previously shown that apoptosis of breast cancer cells in response to paclitaxel is mediated by induction of FOXO3a expression, a transcription factor downstream of the phosphatidylinositol-3-kinase/Akt signaling pathway. To further investigate its mechanism of action, we treated MCF-7 cells with paclitaxel and showed a dose-dependent increase in nuclear localization of FOXO3a, which coincided with decreased Akt signaling but increased c-Jun NH 2 -terminal kinase 1/2 (JNK1/2), p38, and extracellular signal-regulated kinase 1/2 (ERK1/2) activity. Flow cytometry revealed that paclitaxel-induced apoptosis of MCF-7 cells and of other paclitaxel-sensitive breast cancer cell lines was maintained in the presence of inhibitors of p38 (SB203580) or mitogenactivated protein/ERK kinase 1 signaling (PD98059) but abrogated when cells were treated with the JNK1/2 inhibitor SP600125. SP600125 reversed Akt inhibition and abolished FOXO3a nuclear accumulation in response to paclitaxel. Moreover, conditional activation of JNK mimicked paclitaxel activity and led to dephosphorylation of Akt and FOXO3a. Furthermore, mouse embryonic fibroblasts (MEF) derived from JNK1/2 knockout mice displayed very high levels of active Akt, and in contrast to wild-type MEFs, paclitaxel treatment did not alter Akt activity or elicit FOXO3a nuclear translocation. Taken together, the data show that cell death of breast cancer cells in response to paclitaxel is dependent upon JNK activation, resulting in Akt inhibition and increased FOXO3a activity.

PARP-1 inhibition-induced activation of PI-3-kinase-Akt pathway promotes resistance to taxol

“…We checked what kinase signaling pathways were activated by the paclitaxel treatment when applied alone or in combination with PJ-34. In agreement with the literature [17], paclitaxel treatment induced the activation of JNK, but it was not significantly affected by PJ-34 (Fig. 5).…”

“…In addition, paclitaxel can induce cytosolic calcium oscillations [15] and mitochondrial permeability transition, as well as elevated generation of reactive oxygen species predominantly at cytochrome oxidase in tumour cells [16]. In the paclitaxel-induced cell death process, activation of c-Jun N-terminal kinase (JNK) plays a critical role by suppressing Akt activation and promoting the nuclear accumulation of forkhead-related transcription factor-3a (Foxo3a; [17]). Nuclear translocation of Foxo3a can facilitate apoptosis by inducing the expression of Bim, a BH3-only proapoptotic bcl-2 homolog protein [18].…”

p38 MAP kinase mediates arsenite-induced apoptosis through FOXO3a activation and induction of Bim transcription

“…ERK5, another member of the MAP kinases that is often pro-survival [39,40], is also a negative regulator of FOXO3a and fibroblasts from ERK5 and MEK5 null mice display increased FOXO3a activity [28]. JNK regulates FOXO3a nuclear translocation in breast cancer cells after paclitaxel treatment [29]. We discovered that arsenite-induced FOXO3a nuclear translocation is blocked by p38 inhibition, identifying p38 as a novel upstream regulator for FOXO3a.…”

“…Furthermore, other members of the MAP kinase family, such as JNK and ERK5, have been reported to directly or indirectly regulate FOXO3a expression [28,29]. To determine if FOXO3a plays a role in arsenite induction of Bim EL expression, we examined if FOXO3a is activated upon arsenite treatment.…”

Many forks in the path: cycling with FoxO

“…Indeed, recent evidence indicates that FoxO transcription factors play a key role in mediating the cytostatic and cytotoxic effects of various chemotherapeutic drugs. For example, paclitaxel (Taxol), an anticancer drug that targets the spindle checkpoint, activates FoxO3a in breast cancer cells to induce G2/M arrest and apoptosis (Sunters et al, 2003(Sunters et al, , 2006. Moreover, in paclitaxelresistant breast cancer cells the G2/M cell cycle checkpoint and apoptosis are uncoupled in the resistant cells, possibly through a loss of FoxO3a activation ( Sunters et al, 2003).…”