P70 Ribosomal Protein S6 Kinase Research Articles

Immunohistochemical analysis of the mTOR pathway in intrahepatic cholangiocarcinoma

The aim of the study was to evaluate the expression of activated mammalian rapamycin (mTOR) and its downstream effectors, phosphorylated p70 ribosomal protein S6 kinase (p70S6K) and eukaryotic initiation factor 4E-binding protein 1 (4EBP1), in intrahepatic cholangiocarcinomas (ICC), in order to strengthen the rationale for targeted therapy using mTOR inhibitors in patients with ICC. p-mTOR (Ser 2448), p-4EBP1 (Thr 70) and p-p70S6K (Thr 389) were detected in 77 primary ICC tumors by immunohistochemistry. High levels of p-mTOR, p-4EBP1 and p-p70S6K expression were defined in 48.1% (37/77), 50.6% (39/77) and 51.9% (40/77) of all tumors, respectively. No significant correlation was observed between mTOR pathway proteins overexpression with clinicopathological characteristics and patient's prognosis, except that high p-p70S6K expression correlated with the poorly differentiated subtype, and high expression of p-4EBP1 predicted poor prognosis in ICC patients and retained an independent prognostic factor in multivariate analysis. In conclusion, our results showed high prevalence of activation of mTOR pathway in ICC tumors, suggesting that a high proportion of ICC patients might benefit from mTOR pathway targeted therapies. In addition, p-4EBP1 phosphorylation at Thr 70 could be a useful prognostic biomarker for ICC patients.

TOR signaling is involved in PTTH-stimulated ecdysteroidogenesis by prothoracic glands in the silkworm, Bombyx mori

The prothoracicotropic hormone (PTTH) is a stimulator of ecdysteroidogenesis in prothoracic gland of larval insects. Our recent studies showed that phosphoinositide 3-kinase (PI3K)/Akt signaling was involved in PTTH-stimulated ecdysteroidogenesis by Bombyx mori prothoracic glands. In the present study, downstream signaling of PI3K/Akt was further investigated. Results showed that PTTH rapidly enhanced the phosphorylation of translational repressor 4E-binding protein (4E-BP) and p70 ribosomal protein S6 kinase (S6K), two known downstream signaling targets of the target of rapamycin complex 1 (TORC1). PTTH stimulated 4E-BP phosphorylation in time- and dose-dependent manners. Injection of PTTH into day-6 last instar larvae greatly increased 4E-BP phosphorylation, verifying the in vitro effect. PTTH-stimulated 4E-BP phosphorylation was blocked by both LY294002 and wortmannin, indicating the involvement of PI3K. Mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitors (PD 98059 and U0126), did not inhibit PTTH-stimulated 4E-BP phosphorylation, implying that ERK signaling is not related to PTTH-stimulated 4E-BP phosphorylation. The phosphorylation of S6K was also stimulated by PTTH both in vitro and in vivo. PI3K signaling appears to be involved in PTTH-stimulated phosphorylation of S6K. Rapamycin, a specific inhibitor of mammalian TOR signaling attenuated PTTH-stimulated phosphorylation of 4E-BP and S6K of the glands, and greatly inhibited PTTH-stimulated ecdysteroidogenesis. Examination of gene expression levels of 4E-BP and S6K showed that PTTH inhibited mRNA levels of both 4E-BP and S6K, indicating that PTTH may exert its action at both the transcriptional and phosphorylation levels. These results suggest that PTTH/PI3K/TOR/4E-BP (S6K) signaling is involved in PTTH-stimulated ecdysteroidogenesis by prothoracic glands in B. mori.

Type I Keratin 17 Protein Is Phosphorylated on Serine 44 by p90 Ribosomal Protein S6 Kinase 1 (RSK1) in a Growth- and Stress-dependent Fashion

Keratin 17 (K17) is a type I intermediate filament protein that is constitutively expressed in ectoderm-derived epithelial appendages and robustly induced in epidermis following injury, during inflammation, and in chronic diseases such as psoriasis and cancer. Mutations within K17 are responsible for two rare diseases related to ectodermal dysplasias. Studies in K17-null mice uncovered several roles for K17, including structural support, resistance to TNFα-induced apoptosis, regulation of protein synthesis, and modulation of cytokine expression. Yet, little is known about the regulation of K17 protein via post-translational modification. Here, we report that serine 44 in the N-terminal head domain of K17 (K17-Ser(44)) is phosphorylated in response to extracellular stimuli (serum, EGF, and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate) that alter skin keratinocyte growth, and to cellular stresses (sorbitol-induced hyperosmotic shock, UV irradiation, and hydrogen peroxide-induced oxidative stress). It also occurs in basaloid skin tumors in situ. Upon its stimulation in skin keratinocytes, K17-Ser(44) phosphorylation is induced rapidly but stays on transiently. The majority of the phosphorylated K17-Ser(44) pool is polymer-bound and is not obviously related to a change in filament organization. The amino acid sequence surrounding K17-Ser(44) matches the consensus for the AGC family of basophilic kinases. We show that p90 RSK1, an AGC kinase involved in the regulation of cell survival and proliferation, phosphorylates K17-Ser(44) in skin keratinocytes. These findings confirm and expand the tight link that has emerged between K17 up-regulation and growth and stress responses in the skin epithelium.

Glycogen synthase kinase (GSK)-3 promotes p70 ribosomal protein S6 kinase (p70S6K) activity and cell proliferation

The p70 ribosomal protein S6 kinase 1 (S6K1) plays a key role in cell growth and proliferation by regulating insulin sensitivity, metabolism, protein synthesis, and cell cycle. Thus, deregulation of S6K contributes to the progression of type 2 diabetes, obesity, aging, and cancer. Considering the biological and clinical importance of S6K1, a complete understanding of its regulation is critical. One of the key motifs in the activation of S6K1 is a turn motif, but its regulation is not well understood. Here we provide evidence for two mechanisms of modulating turn motif phosphorylation and S6K1 activity. First, mammalian target of rapamycin regulates turn motif phosphorylation by inhibiting its dephosphorylation. Second, we unexpectedly found that glycogen synthase kinase (GSK)-3 promotes turn motif phosphorylation. Our studies show that mammalian target of rapamycin and GSK-3 cooperate to control the activity of S6K1, an important regulator of cell proliferation and growth. Our unexpected results provide a clear rationale for the development and use of drugs targeting GSK-3 to treat diseases such as diabetes, cancer, and age-related diseases that are linked to improper regulation of S6K1.

Tetrahydrocurcumin, a major metabolite of curcumin, induced autophagic cell death through coordinative modulation of PI3K/Akt‐mTOR and MAPK signaling pathways in human leukemia HL‐60 cells

Autophagy (type II programmed cell death) is crucial for maintaining cellular homeostasis. Several autophagy-deficient or knockout studies indicate that autophagy is a tumor suppressor. Tetrahydrocurcumin (THC), a major metabolite of curcumin, has been demonstrated with anti-colon carcinogenesis and antioxidation in vivo. In the present study, we found that treatment with THC induced autophagic cell death in human HL-60 promyelocytic leukemia cells by increasing autophage marker acidic vascular organelle (AVO) formation. Flow cytometry also confirmed that THC treatment did not increase sub-G1 cell population whereas curcumin did with strong apoptosis-inducing activity. At the molecular levels, the results from Western blot analysis showed that THC significantly down-regulated phosphatidylinositol 3-kinase/protein kinase B and mitogen-activated protein kinase signalings including decreasing the phosphorylation of mammalian target of rapamycin, glycogen synthase kinase 3β and p70 ribosomal protein S6 kinase. Further molecular analysis exhibited that the pretreatment of 3-methyladenine (an autophagy inhibitor) also significantly reduced acidic vascular organelle production in THC-treated cells. Taken together, these results demonstrated the anticancer efficacy of THC by inducing autophagy as well as provided a potential application for the prevention of human leukemia.

Down-regulation of JAK1 by RNA interference inhibits growth of the lung cancer cell line A549 and interferes with the PI3K/mTOR pathway

The mammalian Janus kinase (JAK) family plays a critical role in cytokine/growth factor signalling pathways and is associated with human cancers. In this study, we explored the role of JAK1 in the non-small cell lung cancer (NSCLC) cell line A549 and its molecular crosstalk with the phosphatidyl inositol-3-kinase (PI3K)/mammalian target of the rapamycin (mTOR) pathway. One hundred and two NSCLC and 50 normal lung specimens were collected after surgical resection. JAK1 expression and phosphorylation were determined via immunohistochemical staining (IHC) assay. A stable knockdown of JAK1 was performed in A549 cells by RNA interference. Stable cell proliferation, cell cycle, apoptosis, and invasion were characterised in vitro. Tumourigenicity was analysed in vivo. The NSCLC xenograft protein expression of PI3K/mTOR pathway molecules was determined by Western blot assay. JAK1 expression was higher in NSCLC tissues than in normal lung tissues (P < 0.01). JAK1 knockdown in A549 cells significantly inhibited cell proliferation and invasion while promoting cell arrest at G0/G1 phase (all P < 0.05). The xenograft model showed that JAK1 suppression inhibited tumour growth compared with normal control (P < 0.05). Moreover, JAK1 knockdown inhibited mTOR or P70 ribosomal protein S6 kinase (P70S6K) phosphorylation, but increased glycogen synthase kinase-3α (GSK-3α) and B-cell lymphoma-extra large (Bcl-xl) phosphorylation. Total protein expression and Akt1/2 phosphorylated status remained unchanged. Our study suggests that JAK1 expression and phosphorylation is abnormal in NSCLC tissues. The knockdown of JAK1 significantly inhibits tumourigenicity of the A549 cell line and demonstrates that crosstalk between the JAK1 and PI3K/mTOR pathways is involved.

Gene program-specific regulation of PGC-1α activity

Peroxisome proliferator-activated receptor γ (PPARγ) coactivator 1 α (PGC-1α) activation coordinates induction of the hepatic fasting response through coactivation of numerous transcription factors and gene programs. In the June 15, 2011, issue of Genes & Development, Lustig and colleagues (pp. 1232-1244) demonstrated that phosphorylation of PGC-1α by the p70 ribosomal protein S6 kinase 1 (S6K1) specifically interfered with the interaction between PGC-1α and HNF4α in liver and blocked the coactivation of the gluconeogenic target genes. This demonstrates how independent fine-tuning of gene programs coregulated by the same coactivator can be obtained.

Hydrophobic Motif Phosphorylation Is Not Required for Activation Loop Phosphorylation of p70 Ribosomal Protein S6 Kinase 1 (S6K1)

p70 ribosomal protein S6 kinase 1 (S6K1) is regulated by multiple phosphorylation events. Three of these sites are highly conserved among AGC kinases (cAMP dependent Protein Kinase, cGMP dependent Protein Kinase, and Protein Kinase C subfamily): the activation loop in the kinase domain, and two C-terminal sites, the turn motif and the hydrophobic motif. The common dogma has been that phosphorylation of the hydrophobic motif primes S6K1 for the phosphorylation at the activation loop by phosphoinositide-dependent protein kinase 1 (PDK1). Here, we show that the turn motif is, in fact, phosphorylated first, the activation loop second, and the hydrophobic motif is third. Specifically, biochemical analyses of a construct of S6K1 lacking the C-terminal autoinhibitory domain as well as full-length S6K1, reveals that S6K1 is constitutively phosphorylated at the turn motif when expressed in insect cells and becomes phosphorylated in vitro by purified PDK1 at the activation loop. Only the species phosphorylated at the activation loop by PDK1 gets phosphorylated at the hydrophobic motif by mammalian target of rapamycin (mTOR) in vitro. These data are consistent with a previous model in which constitutive phosphorylation of the turn motif provides the key priming step in the phosphorylation of S6K1. The data provide evidence for regulation of S6K1, where hydrophobic motif phosphorylation is not required for PDK1 to phosphorylate S6K1 at the activation loop, but instead activation loop phosphorylation of S6K1 is required for mTOR to phosphorylate the hydrophobic motif of S6K1.

SHAFTS: A Hybrid Approach for 3D Molecular Similarity Calculation. 2. Prospective Case Study in the Discovery of Diverse p90 Ribosomal S6 Protein Kinase 2 Inhibitors To Suppress Cell Migration

We described a prospective application of ligand-based virtual screening program SHAFTS to discover novel inhibitors for p90 ribosomal S6 protein kinase 2 (RSK2). Taking the putative 3D conformations of two weakly binding RSK2 NTKD inhibitors as query templates, SHAFTS was used to perform 3D similarity based virtual screening because of a lack of crystal structure of RSK2 protein, thus leading to the identification of several novel scaffolds that would have been missed by conventional 2D fingerprint methods. The most potent hit compounds show low micromolar inhibitory activities against RSK2. In particular, one of the hit compounds exhibits potent antimigration activity against the MDA-MB-231 tumor cell. The results exemplified SHAFTS' application in active enrichment and scaffold hopping, which is of general interest for lead identification in drug discovery endeavors and also provides novel scaffolds that lay the foundation for uncovering new RSK2 regulatory mechanisms.

Activation of mammalian target of rapamycin pathway confers adverse outcome in nonsmall cell lung carcinoma

Dysregulation of the mammalian target of rapamycin (mTOR) pathway has been shown to contribute to tumorigenesis. This study explored protein expression profiles of mTOR pathway and the relationship with prognosis in patients with nonsmall cell lung carcinoma (NSCLC). The protein expression profiles of mTOR/phosphorylated (p-)mTOR, phosphoinositide-dependent kinase 1 (PDK1)/p-PDK1, p-Akt1, and P70 ribosomal protein S6 kinase (P70S6K)/p-P70S6K were determined via immunohistochemical staining assay. The clinical prognostic values of both single and combined protein expression were investigated with univariate and multivariate survival analysis. Compared with normal lung tissues, the protein levels of mTOR/p-mTOR, p-Akt1 Ser473/Thr308, and P70S6K/p-P70S6K were higher (all P < .05), whereas p-PDK1 was lower (P < .05) in tumor tissues. p-mTOR expression was associated with histological differentiation, histological type, lymph node invasion, and stage (all P < .05). Overall survival in NSCLC patients was significantly shorter in cases with positive phenotype for p-mTOR, p-PDK1, and p-P70S6K (all P < .05). Subjects with coexpression of any 2 of p-mTOR, p-PDK1, p-Akt1 Ser473, and p-P70S6K demonstrated worse prognosis than those expressing no biomarker or any 1 biomarker alone (all P < .05). Multivariate analysis showed that the combination of p-mTOR/p-P70S6K is an independent prognostic factor in addition to tumor stage. This study provides clinical evidence that activated components of mTOR pathway, not total protein, are predictors of poor prognosis in NSCLC. Moreover, evaluating protein-expression profiles of these molecules might be a new strategy for individual therapy in subjects with NSCLC.

α-Mangostin, a Dietary Xanthone, Induces Autophagic Cell Death by Activating the AMP-Activated Protein Kinase Pathway in Glioblastoma Cells

This study is the first to investigate the anticancer effects of α-mangostin in human glioblastoma cells. α-Mangostin decreases cell viability by inducing autophagic cell death but not apoptosis. Pretreatment of cells with the autophagy inhibitors 3-methyladenine (3-MA) and bafilomycin or knockdown beclin-1, resulted in the suppression of α-mangostin-mediated cell death. We also found that liver kinase B1 (LKB1)/AMP-activated protein kinase (AMPK) signaling is a critical mediator of α-mangostin-induced inhibition of cell growth. Activation of AMPK induces α-mangostin-mediated phosphorylation of raptor, which subsequently associates with 14-3-3γ and results in the loss of mTORC1 activity. The phosphorylation of both downstream targets of mTORC1, p70 ribosomal protein S6 kinase (p70S6 kinase) and 4E-BP1, is also diminished by activation of AMPK. Furthermore, the inhibition of AMPK expression with shRNAs or an inhibitor of AMPK reduced α-mangostin-induced autophagy and raptor phosphorylation, supporting the theory that activation of AMPK is beneficial to autophagy. A further investigation revealed that α-mangostin also induced autophagic cell death in transplanted glioblastoma in nude mice. Together, these results suggest a critical role for AMPK activation in the α-mangostin-induced autophagy of human glioblastoma cells.

Caffeine induces apoptosis by enhancement of autophagy via PI3K/Akt/mTOR/p70S6K inhibition

Caffeine is one of the most frequently ingested neuroactive compounds. All known mechanisms of apoptosis induced by caffeine act through cell cycle modulation or p53 induction. It is currently unknown whether caffeine-induced apoptosis is associated with other cell death mechanisms, such as autophagy. Herein we show that caffeine increases both the levels of microtubule-associated protein 1 light chain 3-II and the number of autophagosomes, through the use of western blotting, electron microscopy and immunocytochemistry techniques. Phosphorylated p70 ribosomal protein S6 kinase (Thr389), S6 ribosomal protein (Ser235/236), 4E-BP1 (Thr37/46) and Akt (Ser473) were significantly decreased by caffeine. In contrast, ERK1/2 (Thr202/204) was increased by caffeine, suggesting an inhibition of the Akt/mTOR/p70S6K pathway and activation of the ERK1/2 pathway. Although insulin treatment phosphorylated Akt (Ser473) and led to autophagy suppression, the effect of insulin treatment was completely abolished by caffeine addition. Caffeine-induced autophagy was not completely blocked by inhibition of ERK1/2 by U0126. Caffeine induced reduction of mitochondrial membrane potentials and apoptosis in a dose-dependent manner, which was further attenuated by the inhibition of autophagy with 3-methyladenine or Atg7 siRNA knockdown. Furthermore, there was a reduced number of early apoptotic cells (annexin V positive, propidium iodide negative) among autophagy-deficient mouse embryonic fibroblasts treated with caffeine than their wild-type counterparts. These results support previous studies on the use of caffeine in the treatment of human tumors and indicate a potential new target in the regulation of apoptosis.

Regulatory Effects of Ribosomal S6 Kinase 1 (RSK1) in IFNλ Signaling

Although the mechanisms of generation of signals that control transcriptional activation of Type III IFN (IFNλ)-regulated genes have been identified, very little is known about the mechanisms by which the IFNλ receptor generates signals for mRNA translation of IFNλ-activated genes. We provide evidence that IFNλ activates the p90 ribosomal protein S6 kinase 1 (RSK1) and its downstream effector, initiation factor eIF4B. Prior to its engagement by the IFNλ receptor, the non-active form of RSK1 is present in a complex with the translational repressor 4E-BP1 in IFNλ-sensitive cells. IFNλ-inducible phosphorylation/activation of RSK1 results in its dissociation from 4E-BP1 at the same time that 4E-BP1 dissociates from eIF4E to allow formation of eIF4F and initiation of cap-dependent translation. Our studies demonstrate that such IFNλ-dependent engagement of RSK1 is essential for up-regulation of p21(WAF1/CIP1) expression, suggesting a mechanism for generation of growth-inhibitory responses. Altogether, our data provide evidence for a critical role for the activated RSK1 in IFNλ signaling.

Resistance exercise enhances mTOR and MAPK signalling in human muscle over that seen at rest after bolus protein ingestion

Feeding protein after resistance exercise enhances the magnitude and duration of myofibrillar protein synthesis (MPS) over that induced by feeding alone. We hypothesized that the underlying mechanism for this would be a greater and prolonged phosphorylation of signalling involved in protein translation. Seven healthy young males performed unilateral resistance exercise followed immediately by the ingestion of 25 g of whey protein to maximally stimulate MPS in a rested and exercised leg. Phosphorylation of p70 ribosomal protein S6 kinase (p70S6K) was elevated (P<0.05) above fasted at 1 h at rest whereas it was elevated at 1, 3 and 5 h after exercise with protein ingestion and displayed a similar post-exercise time course to that shown by MPS. Extracellular regulated kinase1/2 (ERK1/2) and p90 ribosomal S6 kinase (p90RSK) phosphorylation were unaltered after protein ingestion at rest but were elevated (P < 0.05) above fasted early in recovery (1 h) and were greater for the exercised-fed leg than feeding alone (main effect; P < 0.01). Eukaryotic elongation factor 2 (eEF2) phosphorylation was also less (main effect; P<0.05) in the exercised-fed leg than in the rested leg suggesting greater activity after exercise. Eukaryotic initiation 4E binding protein-1 (4EBP-1) phosphorylation was increased (P<0.05) above fasted to the same extent in both conditions. Our data suggest that resistance exercise followed by protein feeding stimulates MPS over that induced by feeding alone in part by enhancing the phosphorylation of select proteins within the mammalian target of rapamycin (p70S6K, eEF2) and by activating proteins within the mitogen-activated protein kinase (ERK1/2, p90RSK) signalling.

Arginine-induced stimulation of protein synthesis and survival in IPEC-J2 cells is mediated by mTOR but not nitric oxide

Arginine is an indispensable amino acid in neonates and is required for growth. Neonatal intestinal epithelial cells (IEC) are capable of arginine transport, catabolism, and synthesis and express nitric oxide (NO) synthase to produce NO from arginine. Our aim was to determine whether arginine directly stimulates IEC growth and protein synthesis and whether this effect is mediated via mammalian target of rapamycin (mTOR) and is NO-dependent. We studied neonatal porcine IEC (IPEC-J2) cultured in serum- and arginine-free medium with increasing arginine concentrations for 4 or 48 h. Our results show that arginine enhances IPEC-J2 cell survival and protein synthesis, with a maximal response at a physiological concentration (0.1-0.5 mM). Addition of arginine increased the activation of mTOR, p70 ribosomal protein S6 (p70 S6) kinase, and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) in a time- and dose-dependent manner. The arginine-induced protein synthesis response was not inhibited by the NO inhibitors nitro-l-arginine methyl ester (l-NAME) and aminoguanidine, despite inducible NO synthase expression in IPEC-J2 cells. Moreover, protein synthesis was not increased or decreased in some cases by addition of an NO donor (S-nitroso-N-acetylpenicillamine), arginine precursors (proline and citrulline) in the absence of arginine, or insulin; S-nitroso-N-acetylpenicillamine suppressed phosphorylation of mTOR, p70 S6 kinase, and 4E-BP1. We found a markedly higher arginase activity in IPEC-J2 cells than in primary pig IEC. Furthermore, mTOR inhibition by rapamycin partially (42%) reduced the arginine-induced protein synthesis response and phosphorylation of mTOR and 4E-BP1. We conclude that arginine-dependent cell survival and protein synthesis signaling in IPEC-J2 cells are mediated by mTOR, but not by NO.

Immunohistochemical examination of the mTORC1 pathway in high grade prostatic intraepithelial neoplasia (HGPIN) and prostatic adenocarcinomas (PCa): A tissue microarray study (TMA)

The mammalian target of rapamycin (mTOR) is a serine/threonine protein kinase and a key regulator of protein synthesis and growth and is upregulated in many cancers. mTOR is activated by AKT phosphorylation (p-mTOR). p-mTOR associates with regulatory-associated protein of TOR (RAPTOR), forming the mTORC1 complex. mTORC1 promotes the activation of p70 ribosomal protein s6 kinase 1 (p70(S6K1)) and ribosomal protein s6 (RPS6). Upregulation of this pathway can lead to an aberrant increase in cell growth and metabolism characteristic of malignant transformation. This study presents the immunohistochemical (IHC) expression of the mTORC1 pathway in prostate neoplasia. The expression of p-mTOR and RAPTOR and p-p70(S6K1) and p-RPS6 were examined in HGPIN and PCa using tissue microarrays (TMA). Since each case in our TMAs was represented by three tissue cores, we quantified the IHC intratumoral heterogeneity of mTOR expression. This extensive analysis is the first detailed assessment documenting the IHC heterogeneity of mTOR expression in HGPIN and prostate cancer and represents the first IHC description of the mTORC1 pathway in HGPIN and PCa. A Cochran-Armitage analysis demonstrated decreasing p-mTOR activity progressing from PIN through GL6 and GL7 to HG PCa. There was considerable intratumoral IHC heterogeneity within an individual patient. However, a statistically significant correlation was observed between p-mTOR, p-p70(S6K1), and p-RPS6 in each representative core. mTOR inhibitors may be an effective treatment for HGPIN and PCa. The extent of mTOR expression in an individual patient would determine the effective use of mTOR inhibitors as a potential therapeutic strategy.

ATP-mediated protein kinase B Akt/mammalian target of rapamycin mTOR/p70 ribosomal S6 protein p70S6 kinase signaling pathway activation promotes improvement of locomotor function after spinal cord injury in rats

The protein kinase B (Akt)/mammalian target of rapamycin (mTOR)/p70 ribosomal S6 protein kinase (p70S6K) signaling pathway, as a central controller of cell growth, proliferation, survival, and differentiation in response to extracellular signals, growth factors, nutrient availability, energy status of the cell, and stress, has recently gained attention in neuroscience. The effects of this signaling pathway on repair of spinal cord injury (SCI), however, have not been well elucidated. ATP is increasingly recognized as an important regulator of signal transduction pathways, and plays important roles in functional recovery after nervous system injury. In the present study, we examined the ATP-induced changes of the Akt/mTOR/p70S6K signaling pathway in injured spinal cord of adult rats and potential therapeutic effects of this pathway on SCI-induced locomotor dysfunction. SCI was produced by extradural weight-drop using modified Allen's stall with damage energy of 50 g-cm force. The rats were divided into four groups: SCI plus ATP, SCI plus saline, SCI plus ATP and rapamycin, and sham-operated. Using immunostaining studies, Western blot analyses and real-time qualitative RT-PCR analyses, we demonstrated that the Akt/mTOR/p70S6K signaling pathway is present in the injured spinal cord and the expression of its components at the protein and mRNA levels is significantly elevated by exogenous administration of ATP following SCI. We observed the effectiveness of the activated Akt/mTOR/p70S6K signaling pathway in improving locomotor recovery, significantly increasing the expression of nestin, neuronal nuclei (NeuN), neuron specific enolase (NSE), and neurofilament 200 (NF200), and relatively inhibiting excessive reactive astrogliosis after SCI in a rapamycin-sensitive manner. We concluded that ATP injection produced a significant activation of the Akt/mTOR/p70S6K signaling pathway in the injured spinal cord and that enhancement of rapamycin-sensitive signaling produces beneficial effects on SCI-induced motor function defects and repair potential. We suggest that modulation of this protein kinase signaling pathway activity should be considered as a potential therapeutic strategy for SCI.

845 The RYBP apoptosis pathway is deactivated in cervical cancer patients with 3p-loss

The mammalian target of rapamycin complex 1 (mTORC1) is a critical regulator of cap-dependent translation through its direct activation of ribosomal protein p70 S6 kinase (S6 kinase) and indirect activation of eukaryotic initiation factor 4E (eIF4E). We recently reported that inhibition of eIF4E expression caused apoptosis in cancer cells in the absence of serum. This was indicated by treatment with the mTORC1 inhibitor rapamycin, which suppressed both S6 kinase and 4E-BP1 phosphorylation (dephosphorylated 4E-BP1 binds and inactivates eIF4E), or by knockdown of eIF4E. We report here that knockdown of eIF4E also causes apoptosis in the presence of serum. This was unexpected because rapamycin induces G1 cell cycle arrest in the presence of serum. Upon investigation, we have found that inactivated S6 kinase prevents the apoptotic effect observed by singular knockdown of eIF4E and results in G1 cell cycle arrest. This effect is dependent on TGF-β (transforming growth factor-β) signaling which contributes to G1 cell cycle arrest. Suppression of S6 kinase phosphorylation alone is insufficient to mediate cell cycle arrest, indicating that complete G1 cell cycle arrest is due to suppression of both S6 kinase and eIF4E. These data indicate that the cytostatic effect of rapamycin is suppression of both S6 kinase and eIF4E, while the cytotoxic effects are due suppression of eIF4E in the absence of S6 kinase-dependent activation of TGF-β signals. Our findings place an importance on the evaluating the activity/expression level of S6 kinase and eIF4E as readouts for rapamycin/rapalog efficacy.

The Early Mtor Signaling Responses To Resistance Exercise Stimuli In Skeletal Muscle In Well-trained Athletes

INTRODUCTION: Muscle contractile activity associated with physical exercise stimulates multiple signaling pathways and induces transient changes in gene transcription. The bulk of skeletal muscle is regulated by the control of hypertrophy (anabolic) and atrophy (catabolic) processes. Muscle protein synthesis (MPS) is stimulated, while a small suppression of muscle protein breakdown (MPB) occurs, such that protein balance becomes positive (MPS > MPB). Recently several line of studies has been focused on the role played by the mammalian target of rapamycin (mTOR) signal pathway, i.e., activation of mTOR and its downstream signaling proteins p70 ribosomal protein S6 kinase (p70S6k) and eukaryotic initiation factor (eIF) 4E-binding protein (4E-BP1), in regulating translation initiation to syntheses of muscle protein. Furthermore, more recent work has shown that artificial activation of AMPK suppresses muscle protein synthesis by inhibiting the mTOR signaling pathway. Therefore, we hypothesized that the cellular mechanism for the decrease in muscle protein synthesis during an acute bout of resistance exercise in humans would be associated with an activation of AMPK in addition to an inhibition of the downstream components of the mTOR signaling pathway (4E-BP1 Thr37/46 and S6K1 Thr421/Ser424). METHODS: Eight healthy elite male (n=4) and female (n=4) athletes (22.8±1yrs) performed 10 sets of 10 leg extensions at 60°deg/sec. Muscle biopsies were taken from the vastus lateralis at rest, and 30 s after stopping the exercise. Western blotting with phosphospecific and pan antibodies was used to determine the phosphorylation status of AMPK, 4E-BP1, mTOR, and p70S6k. Blood samples were analysed for serum estradiol(E2), testosterone, insulin, GH and IGF- 1. RESULTS: The phosphorylation states of p70S6k on Thr421/Ser424 and AMPK on Thr172 were increased by 137% and 27% (p<.05). However, high intensity of resistance exercise did not induce any significant changes in mTOR and 4E-BP1 phosphorylations after acute exercise. In addition, estradiol(E2) and growth hormone were increased by 21% (p<.05) and 1784% (p<.001), whereas insulin was decreased by 112% (p<.05) after exercise. CONCLUSION: The present study demonstrates that resistance exercise increases AMPK activity and inhibit mTOR, 4E-BP1 phosphorylation and protein synthesis in human skeletal muscle. Thus, we postulated that one session of resistance exercise activates rather p70S6k in human muscle via an Akt-independent pathway as reported in the previous studies. KEY WORDS: resistance exercise, mTOR, AMPK, 4E-BP1, p70S6K and Western blotting *[email protected]

Expression and distribution of mTOR, p70S6K, 4E-BP1, and their phosphorylated counterparts in rat dorsal root ganglion and spinal cord dorsal horn

Mammalian target of rapamycin (mTOR) controls protein translation and has an important role in the mechanism of pain hypersensitivity under persistent pain conditions. However, its expression and localization in pain-related regions of the nervous system is not completely understood. Here, we examined the expression and distribution of mTOR, eukaryotic initiation factor 4E-binding protein1/2 (4E-BP1/2), p70 ribosomal S6 protein kinase (p70S6K), and their phosphorylated (active) counterparts in two major pain-related regions, the dorsal root ganglion (DRG) and spinal cord dorsal horn. Reverse transcriptase-polymerase chain reaction showed that mTOR, 4E-BP1, and p70S6K mRNA are expressed in the DRG and dorsal horn. Western blot analysis further confirmed the existence of their protein products in these two regions, but expression of their phosphorylated counterparts was very low in dorsal horn and was not detected in the DRG. Immunohistochemistry revealed mTOR and p70S6K in the DRG neurons. Quantitative analysis showed that approximately 26.1% (± 3.2%) of DRG neurons were positive for mTOR and 19.1% (± 1.9%) were positive for p70S6K. Most of these neurons were small—less than 600 µm 2 in cross-sectional area—and some co-labeled with substance P or isolectin B4. Surprisingly, 4E-BP1 was observed only in the DRG satellite glial cells. In the dorsal horn, mTOR, p70S6K, and 4E-BP1 were detected in neurons, but not in astrocytes or microglia. They were distributed in the whole dorsal horn, especially in the superficial dorsal horn. Immunostaining for their phosphorylated counterparts was very low or undetectable in DRG and dorsal horn. Behavioral study showed that intrathecal mTOR inhibitor, rapamycin, did not affect acute nocicepetive transmission. The results indicate that although mTOR, p70S6K, and 4E-BP1 are highly expressed in the DRG and dorsal horn, their activate forms are very low in both regions under normal conditions. Our findings support the view that mTOR and its downstream effectors do not play a key role in acute pain.