FOXO3a mediates the cytotoxic effects of cisplatin in colon cancer cells

FOXO1A is a target for HER2-overexpressing breast tumors

Trastuzumab treatment has improved the overall survival of HER2-overexpressing breast cancer patients. However, many of these patients will eventually become resistant to treatment. The mechanisms that contribute to resistance to trastuzumab are unknown. In this study, we tested the hypothesis that targeting of the FKHR transcription factor FOXO1A in HER2-overexpressing breast tumor cells can overcome the trastuzumab resistance in vitro. We have shown that overexpression of HER2 leads to activation of phosphatidylinositol 3-kinase (PI3K)/Akt pathway and subsequent inactivation of FOXO1A in HER2-overexpressing breast cancer cells SKBR3, BT474, and MCF7-HER2. In wild-type SKBR3 and BT474 cells, trastuzumab downregulates active Akt and increases FOXO1A expression that leads to increase in p27(kip1) and decrease in cyclin D1 and finally inhibits cell proliferation. In contrast, the effect of trastuzumab was eliminated by the reduction of FOXO1A in HER2-overexpressing cells with constitutively active Akt1 (SKBR3/AA28 and BT474/AA9). The downregulation of FOXO1A resulted in nuclear export of p27(kip1). Blocking the constitutively active Akt by a specific Akt/protein kinase B signaling inhibitor-2 (API-2) significantly increased FOXO1A expression and rendered the cells more responsive to trastuzumab-induced growth inhibition. Reactivation of FOXO1A by stable or transient transfection also restored the growth-inhibitory effects of trastuzumab in SKBR3/AA28, BT474/AA9, and MCF7-HER2 cells. Knocking down FOXO1A by small interfering RNA resulted in reducing trastuzumab-induced growth inhibition. In summary, trastuzumab can inhibit proliferation of HER2-overexpressing breast cancer cells by reactivating FOXO1A through inhibition of the PI3K/Akt pathway. FOXO1A may therefore serve as a target for HER2-overexpressing breast tumors.

p38alpha is required for ovarian cancer cell metabolism and survival

INTRODUCTION

Ovarian cancer is highly sensitive to chemotherapy but also shows a high rate of recurrence and drug resistance. These negative outcomes mostly depend on altered apoptotic pathways, making the design of new therapeutic strategies based on the induction of other types of cell death highly desirable. Several lines of research are now addressing cancer-specific features to specifically target tumor cells, thus reducing adverse effects. In this light, a great deal of attention has been devoted to the metabolic reprogramming occurring in cancer cells, which display increased levels of glycolysis compared with their normal counterparts. We recently showed that inhibition of p38alpha impairs key metabolic functions of colorectal cancer cells, inducing growth arrest, autophagy, and cell death both in vivo and in vitro. These effects are mediated by a switch from hypoxia-inducible factor 1alpha (HIF1alpha) to forkhead transcription factor O (FoxO)-dependent transcription.

METHODS

We first characterized p38 expression in OVCAR-3, A2780, and SKOV-3 ovarian cancer cell lines. Then, we treated these cells with the p38alpha/p38beta-specific inhibitor SB202190 and performed a morphological, proliferation, and survival analyses. Finally, we studied HIF1alpha and FoxO3A expressions and signaling pathways to evaluate their role in SB202190-induced effects.

RESULTS

p38alpha blockade induces the formation of intracellular autophagic vacuoles and reduces growth and viability of ovarian cancer cells. As in colorectal cancer, the underlying molecular mechanism seems to rely on a shift from HIF1alpha- to FoxO3A-dependent transcription, which is promoted by the activation of the adenosine monophosphate-activated protein kinase pathway.

CONCLUSIONS

These data corroborate the hypothesis that pharmacological modulation of genes involved in cancer-specific homeostasis, such as p38alpha, might be exploited to design new therapeutic approaches to cancer treatment.

Foxo3a expression and acetylation regulate cancer cell growth and sensitivity to cisplatin

Many advanced cancers receive cisplatin-based chemotherapy. However, cisplatin resistance is a major obstacle for cancer chemotherapy. Foxo3a is a member of the Foxo transcription factor family, which modulates the expression of genes involved in DNA damage repair, apoptosis, and other cellular processes. In this study, we found that cisplatin-resistant cells were more sensitive to the anticancer agent mithramycin than their parental cells, and had a decreased level of Foxo3a expression. Foxo3a knockdown increased cell proliferation and resistance to cisplatin. On the other hand, mithramycin stimulated Foxo3a expression through reactive oxygen species production and sensitized cells to cisplatin, which was abolished by Foxo3a knockdown, while the acetylation status of Foxo3a was decreased in response to cisplatin treatment and was lower in cisplatin-resistant cells. Knockdown of Foxo3a-associated acetyltransferase p300 promoted cancer-cell growth and cisplatin resistance. In addition, non-acetylation-mimicking Foxo3a overexpression decreased cancer cell growth and sensitized cells to cisplatin less than wild-type Foxo3a overexpression. The current work may contribute to the evaluation of the therapeutic potential of inducing the Foxo3a pathway and acetylating the Foxo3a transcription factor, and lead to the reevaluation of cancer treatments based on mithramycin.

FOXO3A as a key molecule for all-trans retinoic acid-induced granulocytic differentiation and apoptosis in acute promyelocytic leukemia

All-trans retinoic acid (ATRA) induces granulocytic differentiation and apoptosis in acute promyelocytic leukemia (APL) cells, although the detailed mechanisms are not fully understood. We investigated ATRA-induced cellular responses mediated by the transcription factor FOXO3A in APL cells. FOXO3A was constitutively phosphorylated and localized in the cytoplasm in both APL-derived NB4 cells and primary APL cells. Upon treating the cells with ATRA, FOXO3A phosphorylation was reduced and FOXO3A translocated into the nucleus. In addition, the expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a target molecule for FOXO3A, was increased at the transcriptional and protein levels. As expected, transfection of a short hairpin RNA (shRNA) oligonucleotide specific for FOXO3A significantly inhibited ATRA-induced granulocytic differentiation and apoptosis in NB4 cells. In NB4-derived ATRA-resistant NB4/RA cells, neither FOXO3A nuclear localization nor subsequent TRAIL induction was observed after ATRA treatment. Furthermore, forced expression of active FOXO3A in the nucleus induced TRAIL production and apoptosis in NB4/RA cells. We conclude that activation of FOXO3A is an essential event for ATRA-induced cellular responses in NB4 cells. FOXO3A is a promising target for therapeutic approaches to overcome ATRA resistance in APL.

FOXO transcription factors: from cell fate decisions to regulation of human female reproduction

All key reproductive events in the human ovary and uterus, including follicle activation, ovulation, implantation, decidualization, luteolysis and menstruation, are dependent upon profound tissue remodelling, characterised by cyclical waves of cell proliferation, differentiation, apoptosis, tissue breakdown and regeneration. FOXO transcription factors, an evolutionarily conserved subfamily of the forkhead transcription factors, have emerged as master regulators of cell fate decision capable of integrating avariety of stress, growth factor and cytokine signaling pathways with the transcription machinery. The ability of FOXOs to regulate seemingly opposing cellular responses, ranging from cell cycle arrest and oxidative stress responses to differentiation and apoptosis, renders these transcription factors indispensable for cyclic tissue remodelling in female reproduction. Conversely, perturbations in the expression or activity of FOXO transcription factors are increasingly linked to common reproductive disorders, such as pregnancy loss, endometriosis, endometrial cancer and primary ovarian insufficiency.