FOXO3a Is a Major Target of Inactivation by PI3K/AKT Signaling in Aggressive Neuroblastoma

Abstract

Neuroblastoma is a pediatric tumor of the peripheral sympathetic nervous system with a highly variable prognosis. Activation of the phosphoinositide 3-kinase (PI3K)/AKT pathway in neuroblastoma is correlated with poor patient prognosis, but the precise downstream effectors mediating this effect have not been determined. Here we identify the forkhead transcription factor FOXO3a as a key target of the PI3K/AKT pathway in neuroblastoma. FOXO3a expression was elevated in low-stage neuroblastoma tumors and normal embryonal neuroblasts, but reduced in late-stage neuroblastoma. Inactivation of FOXO3a by AKT was essential for neuroblastoma cell survival. Treatment of neuroblastoma cells with the dual PI3K/mTOR inhibitor PI-103 activated FOXO3a and triggered apoptosis. This effect was rescued by FOXO3a silencing. Conversely, apoptosis induced by PI-103 or the AKT inhibitor MK-2206 was potentiated by FOXO3a overexpression. Furthermore, levels of total or phosphorylated FOXO3a correlated closely with apoptotic sensitivity to MK-2206. In clinical specimens, there was an inverse relationship between gene expression signatures regulated by PI3K signaling and FOXO3a transcriptional activity. Moreover, high PI3K activity and low FOXO3a activity were each associated with an extremely poor prognosis. Our work indicates that expression of FOXO3a and its targets offer useful prognostic markers as well as biomarkers for PI3K/AKT inhibitor efficacy in neuroblastoma. Cancer Res; 73(7); 2189-98. Ó2013 AACR.

Prolyl hydroxylation by EglN2 destabilizes FOXO3a by blocking its interaction with the USP9x deubiquitinase

“…Somatic deletion of all three FOXOs (FOXO1, FOXO3, and FOXO4) engenders a cancer-prone condition in mice, further strengthening its tumor suppressor role in vivo (Paik et al 2007). Consistent with this, decreased expression of FOXO3a associated with poor outcomes in breast cancer and neuroblastoma (Sunayama et al 2011;Jiang et al 2013;Santo et al 2013). Conversely, FOXO3a nuclear localization is associated with good prognosis in luminal-like breast cancer (Habashy et al 2011).…”

Upregulation of MAPK Negative Feedback Regulators and RET in Mutant ALK Neuroblastoma: Implications for Targeted Treatment

“…Further evidence was provided for this regulation, including the finding that mutant ALK likely controls RET expression levels through FOXO3a signaling. The FOXO3a forkhead transcription factor was previously shown as a key target of the PI3K/AKT pathway in neuroblastoma and essential for their survival (26). Here, we showed that mutant ALK signaling blocks FOXO3a phosphorylation through PI3K/AKT and that FOXO3a regulates RET expression, thus strongly indicating the existence of a mutant ALK-PI3K/ AKT-FOXO3a-RET signaling axis in neuroblastoma cells.…”

“…Given the previously described regulation of FOXO3a by PI3K/ AKT signaling (26) and the observation that the related FOXO1 controls RET expression in mouse spermatogonial stem cells (39), we tested the possibility that FOXO3a could regulate RET under the control of mutant ALK. Pharmacologic inhibition of mutant ALK using LDK-378 clearly leads to the expected loss of FOXO3a phosphorylation (leading to activation of FOXO3a; Supplementary Figure S15B).…”

“…Pharmacologic inhibition of mutant ALK using LDK-378 clearly leads to the expected loss of FOXO3a phosphorylation (leading to activation of FOXO3a; Supplementary Figure S15B). Next, we investigated published data on overexpression of FOXO3a in neuroblastoma cells (26) and observed strong repression of RET mRNA expression following activation of FOXO3a in combination with PI3K/AKT inhibition (Supplementary Figure S15A). Taken together, these data convincingly show that RET expression is under direct control of mutant ALK.…”

Post-translational modifications of FOXO family proteins

“…The E3 ligase, S-phase kinase associated protein 2 (Skp2), suppresses FOXO1 transactivation, and eliminates its effect on inhibition of cell proliferation. The normal function of Skp2 phosphorylates the Ser256 site of FOXO1, and subsequently, causes degradation of FOXO1 via the proteasomal pathway (29).…”