The Forkhead Transcription Factor FOXO3a Increases Phosphoinositide-3 Kinase/Akt Activity in Drug-Resistant Leukemic Cells through Induction of PIK3CA Expression

Abstract

The phosphoinositide-3 kinase (PI3K)/Akt signal pathway plays a key role in the tumorigenesis of many cancers and in the subsequent development of drug resistance. Using the K562 chronic myelogenous leukemia (CML) cell line and the doxorubicin-resistant derivative lines KD30 and KD225 as models, we observed that enhanced PI3K/Akt activity and the acquisition of chemoresistance correlated unexpectedly with the increased expression and nuclear accumulation of FOXO3a. Moreover, we found that the induction of FOXO3a activity in naïve K562 cells was sufficient to enhance PI3K/Akt activity and to confer resistance to the cytotoxic effects of doxorubicin. Conversely, the knockdown of endogenous FOXO3a expression reduced PI3K/Akt activity and sensitized these cells to doxorubicin. Further chromatin immunoprecipitation and promoter mutation analyses demonstrated that FOXO3a regulates the expression of the PI3K catalytic subunit p110␣ through the activation of a promoter region proximal to a novel untranslated exon upstream from the reported transcription start site of the p110␣ gene PIK3CA. As was the case for FOXO3a, the expression or knockdown of p110␣ was sufficient to amplify or reduce PI3K/Akt activity, respectively. Thus, our results suggest that the chronic activation of FOXO3a by doxorubicin in CML cells can enhance survival through a feedback mechanism that involves enhanced p110␣ expression and hyperactivation of the PI3K/Akt pathway.Chemotherapy is widely used for the treatment of leukemia and other advanced or metastatic cancers. However, its efficacy is often hampered by the development of intrinsic or acquired multidrug resistance (MDR), characterized by simultaneous cross-resistance to anticancer drugs that differ in their chemical structures, modes of action, and cellular targets (35). An understanding of the mechanisms of MDR is important for the development of more effective therapies. At the cellular level, three general mechanisms confer MDR in cancer cells, including decreased hydrophilic drug uptake, increased hydrophobic drug efflux, and enhanced cell survival signals or mechanisms. The first one involves a decrease in the expression or activity of transporters that regulate the uptake of hydrophilic chemotherapeutic drugs, such as folate antagonists, nucleoside analogues, and cisplatin. The second mechanism entails an upregulation of transporters, resulting in an increased energy-dependent efflux of a wide variety of hydrophobic chemotherapeutic agents. Finally, cancer cells often counteract the cytotoxic effects of therapeutic agents by amplifying the activity of proliferation and survival signal pathways, by increasing DNA damage repair, or by altering drug metabolism.Phosphoinositide-3 kinases (PI3Ks) are a family of lipid kinases that serve as mediators of signals generated by many different activated growth factor receptors and adhesion molecules. The class IA PI3Ks are heterodimers composed of a p110 catalytic subunit and a p85 regulatory subunit (25). When activated by growth factors, the p...

The forkhead transcription factor FOXO1 mediates cisplatin resistance in gastric cancer cells by activating phosphoinositide 3-kinase/Akt pathway

“…As a recent study showed that Akt overexpression decreases the chemosensitivity of gastric cancer cells to CDDP in vitro and in vivo [12], we investigated whether Akt is related to the FOXO1 regulation of CDDP cytotoxicity in gastric cancer cells. In the present study, constitutive activation and silencing of Our results agree with those of Hui et al [19], which showed FOXO3-induced PI3K/Akt activation in response to doxorubicin treatment of chronic myelogenous leukemia cells. However, our observations contrast with those of Gao et al [10], which demonstrated that FOXO1 enhanced CDDP cytotoxicity in ovarian cancer cells.…”

“…We have previously shown that phosphorylated FOXO1 is overexpressed in gastric cancer specimens and that FOXO1 inactivation is related to better prognosis of gastric cancer patients [18]. Although FOXO proteins, especially FOXO1 and FOXO3, have been reported to be related to chemoresistance in various cancer cells [8][9][10][19][20][21], their involvement in chemoresistance of gastric cancer cells has not been reported. In the present study, we used two gastric cancer cell lines, MKN45 and SNU-601, with constitutive FOXO1 expression and found that CDDP treatment increased the levels of FOXO1 protein expression and activation.…”

The transcriptional induction of PIK3CA in tumor cells is dependent on the oncoprotein Y-box binding protein-1

“…We demonstrated that PIK3CA transcription is repressed by the tumor suppressor protein p53 in ovarian surface epithelial cells, and provided evidence to show that loss of p53 in ovarian cancer is one mechanism that leads to elevated p110a levels (Astanehe et al, 2008). In addition, it has recently been demonstrated that the forkhead transcription factor, FOXO3a, induces PIK3CA by directly binding to its promoter rendering chronic myelogenous leukemia cells resistant to doxorubicin (Hui et al, 2008). However, the induction of PIK3CA by FOXO3a is paradoxical as it is a known tumor suppressor with its activation mediating apoptosis in cancers including those of the breast (Sunters et al, 2003).…”

FOXP1 acts through a negative feedback loop to suppress FOXO-induced apoptosis

“…In line with this, FOXP1 expression is increased in colorectal cancer cells in response to treatment with the chemotherapeutic doxorubicin as well as after specific inhibition of PI3K-PKB signaling. We propose that similar to FOXO-induced HER3 and PIK3CA expression in response to cancer therapy aimed at inhibiting PI3K-PKB signaling, 14,16,47 FOXP1 possibly represents another mode of developing escape from treatment by protecting the cells against FOXO-induced cell death.…”