Insulin-like growth factor-I induces the phosphorylation and nuclear exclusion of forkhead transcription factors in human neuroblastoma cells

Abstract

Akt-mediated phosphorylation of forkhead transcription factors is linked to growth factor-stimulated cell survival. We investigated whether the survival activity of insulin-like growth factor-I (IGF-I) in SH-SY5Y human neuroblastoma (NBL) cells is associated with phosphorylation and/or localization changes in forkhead proteins. IGF-I induced phosphorylation of Erks (p42/p44), FKHR (FOXO1a) (Ser 253), FKHRL1 (FOXO3a) (Ser 256), and Akt (Ser 473). PI3-K inhibitor, LY294002, reduced IGF-I-stimulated phosphorylation of FKHR, FKHRL1, and Akt, but did not affect Erk phosphorylation. Using a GFP-FKHR construct, FKHR imported into the nucleus during growth factor withdrawal-induced apoptosis. In addition, IGF-I rescue from serum withdrawal-induced apoptosis is associated with a rapid export of GFP-FKHR into the cytoplasm. Leptomycin B, an inhibitor of Crm1-mediated nuclear export, decreased the level of FKHRL1 phosphorylation in the presence of IGF-I in vector and FKHR overexpressing cells, but had no effect on the phosphorylation status of FKHR. In addition, leptomycin B prevented IGF-I stimulated nuclear export of GFP-FKHR. These studies show IGF-I phosphorylation of FKHR and FKHRL1 via a PI3-K-dependent pathway in NBL cells.

Remote neurotrophic support of epidermal nerve fibres in experimental diabetes

“…In vitro studies of DRG neurons from insulin-treated diabetic rats have demonstrated correction of diabetesrelated depolarisation of the mitochondrial inner membrane [22] involving activation of the PI 3-K pathway, and subsequent downstream activation of Akt and CREB [27,34]. In vitro, IGF-1 induces Akt phosphorylation via a PI 3-K dependent pathway, and ERK (p42/p44) phosphorylation via a PI 3-K independent pathway [35]. IGF-I may also have an anti-apoptotic effect, as the phosphorylation of forkhead proteins, important mediators of growth factorstimulated cellular survival, also depends upon PI 3-K and Akt [35].…”

“…In vitro, IGF-1 induces Akt phosphorylation via a PI 3-K dependent pathway, and ERK (p42/p44) phosphorylation via a PI 3-K independent pathway [35]. IGF-I may also have an anti-apoptotic effect, as the phosphorylation of forkhead proteins, important mediators of growth factorstimulated cellular survival, also depends upon PI 3-K and Akt [35]. It is clear now that activation of Akt and MAPK also correlates with sensory neurite elongation and branching [36].…”

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

“…Activation of these pathways can directly result in phosphorylation of FOXOs and their subsequent cytoplasmic sequestration and/or degradation via the ubiquitin-proteasome pathway. In neuroblastoma, AKT-mediated phosphorylation of FOXO has previously been correlated with neuroblastoma cell survival in response to growth factor stimulation (16,17). When FOXO is activated by inhibition of the PI3K/AKT pathway, FOXOs can promote a wide range of effects including cell-cycle arrest, cell differentiation, autophagy, and apoptosis via various mechanisms (18,19).…”

FKHRL1-mediated expression of Noxa and Bim induces apoptosis via the mitochondria in neuroblastoma cells

“…[8][9][10][11] Activation of the PI3K pathway by nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4 (NT-4) and IGF-1 causes inactivation of FKHRL1 and provides neuronal survival. 1,11,12 Neuroblastoma tumors with high BDNF and TrkB expression show an unfavorable prognosis and in such tumors PKB is one of the key mediators of BDNF/TrkB survival signaling that protects neuroblastoma cells from chemotherapy-induced cell death. 13 Although BDNF has been shown to induce phosphorylation of FKHRL1 in human SH-SY5Y neuroblastoma cells, it is unclear whether this results in reduced cell death sensitivity in neuroblastoma cells.…”