Skip to content

Advertisement

You're viewing the new version of our site. Please leave us feedback.

Learn more

Molecular Pain

Open Access

mTOR, a new potential target for chronic pain and opioid-induced tolerance and hyperalgesia

  • Brianna Marie Lutz1, 2,
  • Sam Nia2,
  • Ming Xiong2,
  • Yuan-Xiang Tao2Email author and
  • Alex Bekker2
Molecular Pain201511:32

https://doi.org/10.1186/s12990-015-0030-5

Received: 17 March 2015

Accepted: 21 May 2015

Published: 30 May 2015

Abstract

Chronic pain is a major public health problem with limited treatment options. Opioids remain a routine treatment for chronic pain, but extended exposure to opioid therapy can produce opioid tolerance and hyperalgesia. Although the mechanisms underlying chronic pain, opioid-induced tolerance, and opioid-induced hyperalgesia remain to be uncovered, mammalian target of rapamycin (mTOR) is involved in these disorders. The mTOR complex 1 and its triggered protein translation are required for the initiation and maintenance of chronic pain (including cancer pain) and opioid-induced tolerance/hyperalgesia. Given that mTOR inhibitors are FDA-approved drugs and an mTOR inhibitor is approved for the treatment of several cancers, these findings suggest that mTOR inhibitors will likely have multiple clinical benefits, including anticancer, antinociception/anti-cancer pain, and antitolerance/hyperalgesia. This paper compares the role of mTOR complex 1 in chronic pain, opioid-induced tolerance, and opioid-induced hyperalgesia.

Keywords

PainNMTOROpioidHyperalgesiaTolerance

Introduction

Chronic pain and its related sequelae represent a severe public health challenge affecting nearly 30 % of the population [1]. In addition to its impact on quality of life, chronic pain has an economic impact, costing over $560 billion annually [2]. Opioids have been the mainstay of chronic pain treatment for many decades despite a host of shortcomings including tolerance and hyperalgesia, which ultimately limit the efficacy of these medications [3, 4]. Tolerance is the diminishing response to medication, requiring escalating doses to achieve the same pain relief. Increasing the dose of opioids increases the possibility of adverse side effects including constipation, respiratory depression, and nausea [5, 6]. Conversely, hyperalgesia is hypersensitivity to pain and also can be caused by the administration of opioid medication [6]. The therapeutic limitations of opioid medications in chronic pain management show a clear need to understand the molecular mechanisms which underpin the biologic processes governing chronic pain, tolerance to pharmacologic medicine, and hyperalgesia.

Neuroplasticity in the form of adaptive changes in protein transcription and translation may contribute to the development of chronic pain, opioid tolerance, and its hyperalgesia [7]. Changes in the expression of neuronal nitric oxide synthase (nNOS), protein kinase C (PKC), CaMKIIα, and other proteins are associated with chronic pain conditions and opioid-induced hyperalgesia or tolerance [811]. The mechanisms and signaling pathways are still not fully understood, but mammalian target of rapamycin (mTOR) represents a key player in the mechanism governing neuroplasticity in chronic pain and opioid-induced hyperalgesia/tolerance disorders [1221]. This paper reviews recent evidence regarding the role of mTOR in chronic pain, opioid tolerance, and opioid-induced hyperalgesia and discusses how mTOR participates in the development and maintenance of these disorders. Current evidence suggests that mTOR likely represents an excellent candidate target for novel pharmaceutical intervention in chronic pain, opioid tolerance, and opioid-induced hyperalgesia in patients.

mTORC1 and mRNA translation

Mammalian target of rapamycin (mTOR) is a serine-threonine protein kinase which forms 2 distinct evolutionary preserved protein complexes known as mTOR complex-1 (mTORC1) and mTOR complex-2 (mTORC2) [22, 23]. Active mTOR bound to Raptor protein forms the rapamycin-sensitive mTORC1 complex that is predominantly responsible for regulating protein translation (Fig. 1) [24]. The mTORC1 regulates the activity of at least 4 proteins involved in protein translation via phosphorylation—4E-BP1/2, eIF4B, S6K1, S6—during the following steps. Most mature eukaryotic mRNAs possess a 7-methyl-guanine cap structure at the 5’-end, which controls initiation of translation [23]. During translation initiation, the cap structure is recognized by the eIF4G initiation complex that includes the eIF4E protein [23]. Under basal conditions, eIF4E remains bound to the eukaryotic initiation factor 4E (eIF4E)-binding protein 1/2 (4E-BP1/2), which prevents formation of eIF4G (Fig. 1) [25]. Active mTOR leads to phosphorylation of 4E-BP1/2, which changes its shape and releases eIF4E, allowing the formation of the functional eIF4G complex and initiation of translation (Fig. 1) [23, 25]. In addition, recruitment of the eukaryotic initiation factor 4B (eIF4B) to the initiation complex is mTOR-dependent [26, 27]. The eIF4B needs to be phosphorylated by the p70 ribosomal S6 protein kinase 1/2 (S6K1/2) to associate with the translation initiation complex (Fig. 1) [26, 27] and mTOR activation also induces phosphorylation of S6K1, thereby activating it. S6K1/2 is better known for kinase activity toward ribosomal S6 proteins (S6) [22, 28, 29], which are critical for stimulating the translation rate of mRNAs containing the 5’-oligopyrimidine tract (Fig. 1). This subgroup of mRNAs encodes primarily the proteins involved in the translation process itself, such as all ribosomal proteins and several elongation factors [30]. Thus, mTOR activation leads to an increase in the translation capacity of the cell.
Fig. 1

mTOR signaling pathway. Activated mTOR phosphorylates 4E-BP1/2 and S6K1/2. The phosphorylation of 4E-BP1/2 causes the release of eIF4E which is then free to combine with the translation initiation complex, resulting in increased protein translation. Phosphorylated S6K1 phosphorylates eIF4B and S6 which also lead to increased protein translation. 4E-BP1/2: eIF4E-binding protein1/2. 40S: an eukaryotic small ribosomal subunit. 60S: an eukaryotic large ribosomal subunit. eIF4E/B/G/A: eukaryotic translation initiation factor 4E/4B/4G/4A. mTOR: mammalian target of rapamycin. p: phosphorylated. S6K1/2, p70 ribosomal S6 Kinase 1/2

mTOR inhibitors in clinical use

Rapamycin, a specific inhibitor of mTOR, was discovered at Easter Island (former Rapa Nui) in a bacterial strain named Streptomyces hygroscopius [31]. Rapamycin was first found to inhibit the growth of yeast and was being developed as an antifungal drug [32]. Its anti-fungal use was temporally abandoned after the discovery of its potent immunosuppressive activity, which later proved beneficial for transplant patients [33, 34]. The mTOR inhibitor and some of its derivatives also showed anti-proliferative activity which was found useful in the treatment of certain cancers [31, 3537]. Studies have shown hyperactivity of mTOR in gliomas [38] as well as nonglial brain tumors [39]. The specificity by which rapamycin and its analogues bind to and inhibit mTORC1 activity thereby abrogating the proliferation of these cancers has prompted clinical trials to investigate the efficacy of rapamycin and its analogues “Rapalogs” as novel treatments in cancer therapy and their approval for specific indications [34, 40, 41]. Rapamycin was recently shown to prolong the life of mice [42], whether this effect occurs in humans is unknown and remains to be determined.

mTOR expression in pain-related regions

mTOR is expressed and distributed in pain-related central nervous system regions. Xu et al. used immunofluorescence to analyze the distribution of mTOR, 4E-BP1/2, S6K and their phosphorylated counterparts in dorsal root ganglia (DRG) and spinal cord dorsal horn [43]. mTOR was found in approximately 26.1 % of DRG neurons and S6K was found in about 19.1 % of DRG neurons, with most of small diameter [43]. 4E-BP1 was exclusively found in DRG satellite glial cells, but it co-localized in dorsal horn with mTOR and S6K. 4E-BP1, mTOR, and S6K are highly expressed in the superficial dorsal horn [43]. Interestingly, the activated or phosphorylated forms of these proteins were virtually undetectable or at very low levels under normal conditions in the DRG and dorsal horn [43]. These findings support the behavioral observation that intrathecal administration of the mTOR inhibitor rapamycin does not affect basal pain perception, suggesting that mTOR and its downstream effectors do not play a key role in acute pain.

mTOR in chronic pain

mTOR’s role in cancer treatment is not simply limited to its effects on neoplastic cell survival and proliferation. Studies have shown that activation of mTOR and its downstream effectors in spinal cord (but not in DRG) are implicated in cancer pain [18, 44]. Shih et al. showed that rats injected with prostate cancer cells into the tibia, a model of bone cancer pain, experienced pain hypersensitivity [18]. This hypersensitivity was attenuated following intrathecal injection of rapamycin [18]. Rapamycin’s effect is dose-dependent without affecting locomotor function and without significant systemic side effects such as immunosuppression [18]. Furthermore, they showed that levels of phosphorylated mTOR (p-mTOR) and p-S6K increased in the L4-5 dorsal horn and DRG on the side of the prostate cancer cell injection [18]. This increase in p-mTOR and p-S6K was blocked in the presence of an NMDA receptor antagonist [18]. The authors proposed that the activation of NMDA receptor-mediated spinal cord mTOR pathways contribute to the initiation, establishment, and maintenance of bone cancer-induced pain hypersensitivity [18] (Fig. 2). This conclusion is further supported by the observation that NMDA receptor subunit NR1 co-localized with mTOR and S6K in dorsal horn neurons [18].
Fig. 2

Proposed mechanism of spinal cord NMDA receptor-mediated activation of mTOR signaling in cancer pain. Under normal conditions (a), magnesium blocks NMDAR activity, thus silencing the intracellular kinases including the mTOR signaling pathway. Under cancer conditions (b), cancer-caused noxious insult leads to removal of the magnesium from NMDA receptors, resulting in calcium influx through NMDA receptor activation. The influx of calcium may then activate PI3K and Akt kinases which go on to phosphorylate mTOR. Active mTOR phosphorylates S6K1/2 and 4E-BP1/2 leading to protein translation initiation. 4E-BP1/2: eIF4E-binding protein1/2. Akt: protein kinase B. mTOR: mammalian target of rapamycin. NMDAR: NMDA receptor; NR1: a subunit of NMDA receptors. p: phosphorylated. PI3K: phosphoinositide 3-kinase. S6K1/2, p70 ribosomal S6 Kinase 1/2

Spinal cord mTOR and its downstream pathway also are involved in inflammatory pain. Liang et al. showed that intraplantar injection of complete Freund’s adjuvant (CFA) in a model of chronic inflammatory pain increased the levels of p-mTOR and p-S6K1 in the ipsilateral L4/5 spinal cord and DRG [16]. Behavioral testing demonstrated that CFA-induced mechanical and thermal pain hypersensitivity could be alleviated by intrathecal administered rapamycin [16]. Additionally, Xu et al., used λ-carrageenan to induce persistent peripheral inflammation in rats and found increased levels of not only p-mTOR but also upstream phosphorylated protein kinase B (Akt) in dorsal horn [20]. The downstream targets of mTOR activation, p-S6K and p-4E-BP1 were also elevated in dorsal horn [20]. More importantly, intrathecal administration of rapamycin produced anti-nociceptive effects in this persistent inflammatory pain model [20]. These anti-nociceptive effects of rapamycin were also observed in the second phase of the formalin model [20]. Selective inhibitors of PI3K (upstream of Akt), Akt, or mTORC1 attenuated phase II flinching behavior in rats that were injected with formalin [20]. Phase II of formalin-induced inflammation is known to represent spinal sensitization [45]. These findings demonstrate the potential highly targeted role of mTOR inhibitors in the treatment of inflammatory pain.

Although the mechanism of mTOR-induced inflammatory pain sensitivity is relatively clear, how mTOR is involved in neuropathic pain remains elusive. Rapamycin administration in neuropathic pain models attenuates pain hypersensitivity in several studies in both rats and mice [17, 18, 46]. Géranton et al. reported that spared nerve injury (SNI)-induced mechanical allodynia was attenuated by rapamycin delivered intrathecally 6 days after surgery [47]. However, western blotting analysis of dorsal horn and dorsal roots 7 days after SNI revealed no significant changes in the expression of p-S6K [47]. Additionally, immunostaining showed no change in the percentage of peripherin-labeled fibers expressing p-mTOR [47]. Liang et al. also showed no change in the basal level of p-mTOR in spinal cord and DRG after spinal nerve ligation [16]. Conversely, Zhang et al. used the chronic constriction injury (CCI) model of neuropathic pain to analyze the role of mTOR in neuropathic pain [21]. The phosphorylated counterparts of mTOR, 4E-BP1, and S6K were upregulated in the spinal cord 7 days and 14 days after CCI [21]. Intrathecal rapamycin not only blocked this upregulation but also attenuated CCI-induced mechanical allodynia (but not thermal hyperalgesia) [21]. These data suggest that distinct types of peripheral nerve injury differentially may regulate the activation of mTOR and its downstream effectors in spinal cord and DRG. Further research into the mechanism of rapamycin antinociception in neuropathic pain is required.

mTOR in opioid-induced tolerance and hyperalgesia

Evidence has shown that opiate-induced tolerance and hyperalgesia may be attributed to changes in the transcription and translation of several key tolerance-associated proteins including neuronal NOS, PKCγ, and CaMKIIα in the central nervous system as well as in the peripheral nervous system [3, 4851]. Given that mTOR regulates protein translation, it is reasonable to assume that mTOR participates in the development and maintenance of opioid-induced tolerance and hyperalgesia. Indeed, Xu et al. used an animal model of opioid tolerance/hyperalgesia: twice-daily intrathecal injections of 10 μg of morphine for 6 continuous days produced a time-dependent decrease in morphine’s maximal potential analgesic effect (MPAE) at 3, 5, and 7 days post morphine injection [19]. Reductions in mechanical threshold and thermal latency occurred at 8 days post morphine injection [19]. Rapamycin administered intrathecally before or after morphine treatment blocked a decrease in morphine's MPAE, and attenuated morphine’s effect on mechanical threshold and thermal latency [19]. Similar to the effect of rapamycin, intrathecal administration of siRNA specific for mTOR before morphine attenuated the tolerance and hyperalgesia [19].

Xu et al. further demonstrated that mTOR and its downstream effectors is activated by repeated morphine injections through the μ opioid receptor-triggered P13K/Akt pathway in dorsal horn neurons of the spinal cord [19]. A PI3K or Akt specific inhibitor prevented morphine induced increases in the phosphorylated forms of 4E-BP1, mTOR, and S6K1 in the spinal cord. These inhibitors also attenuated behavioral responses observed in the opioid-induced tolerance and hyperalgesia model [19]. In contrast, basal pain perception and locomotor functioning were left untouched. These findings indicate that PI3K and Akt are involved in mTOR’s effect on opioid-induced tolerance and hyperalgesia but not basal pain perception and locomotor functioning.

To further uncover the mTOR-dependent mechanism (s) of opioid-induced tolerance and hyperalgesia, Xu et al. observed protein translation in their model of morphine-induced tolerance [19]. Repeated morphine injections increased nascent protein synthesis as determined by L-azidohomoalanie. Rapamycin co-administered with morphine diminished morphine’s increase in nascent protein synthesis. The binding of eIF4A to eIF4E, components of the translation initiation complex, increased in dorsal horn after repeated morphine exposure, but this increase was attenuated following rapamycin co-injection. Rapamycin also attenuated the increases of several tolerance-associated proteins including PKCγ, nNOS, and CaMKIIα. These findings provide a mechanism of opioid-induced tolerance and hyperalgesia in which μ opioid receptor activation activates PI3K/Akt which triggers an mTOR-dependent signaling cascade that results in increased protein translation (Fig. 3) [19].
Fig. 3

Proposed model for the involvement of spinal cord mTOR in chronic opioid tolerance and hyperalgesia. Under normal conditions (a), mTOR is inactivated. 4E-BP1/2 binds to eIF4E, preventing its associations with the translation initiation complex, thus silencing protein translation. After repeated morphine exposure (b), activation of μ opioid receptors leads to the phosphorylation of PI3K and Akt, initiating a phosphorylation cascade including mTOR/S6K1/2/4E-BP1/2. eIF4E release, phosphorylated eIF4B, and phosphorylated S6 trigger protein translation. 4E-BP1/2: eIF4E-binding protein1/2. Akt: protein kinase B. eIF4E/eIF4B, eukaryotic translation initiation factor 4E/4B. mTOR: mammalian target of rapamycin. p: phosphorylated. PI3K: phosphoinositide 3-kinase. S6K1/2, p70 ribosomal S6 Kinase 1/2. S6K1, S6 Kinase 1. μ: μ opioid receptor

Conclusion

The significance of mTOR’s function in the grand scheme of pain medicine is undisputed. mTOR is a key puzzle piece which contributes to the understanding of many aspects of the science of chronic pain. Numerous potential therapeutic options exist in rapamycin and its analogues, given mTOR’s versatility in function in many aspects of pain mediation, cancer, and post-transplant immunosuppression. mTOR is involved in cancer pathogenesis, and mTOR inhibitors are currently being used as antineoplastic agents. New data demonstrates that mTOR shows promise as a target for chronic inflammatory pain, neuropathic pain, as well as cancer pain. Recent data also delivers cutting edge science tying the vital role mTOR has in the acquisition and maintenance of opioid tolerance/hyperalgesia. These findings prompt us to investigate the applicability of mTOR-targeting therapies for future treatment of a vast cadre of chronic pain syndromes.

Summary statement

This review highlights recent findings regarding the role of mTOR and its downstream signals in pain-related regions after persistent inflammation, nerve injury, or repeated opioid injections and it discusses how mTOR participates in the development and maintenance of chronic pain and opioid-induced tolerance and hyperalgesia.

Abbreviations

4E-BP1/2: 

Eukaryotic initiation factor 4E (eIF4E)-binding protein 1/2

DRG: 

/Akt, protein kinase B dorsal root ganglia

eIF4A: 

Eukaryotic initiation factor 4A

eIF4B: 

Eukaryotic initiation factor 4B

eIF4G: 

Eukaryotic initiation factor 4G

mTOR: 

Mammalian target of rapamycin

mTORC1: 

MTOR complex-1

mTORC2: 

MTOR complex-2

NMDA: 

N-Methyl-D-aspartate

NMDAR: 

Receptor for N-Methyl-D-aspartate

NNOS: 

Neuronal nitric oxide synthase

NR1: 

A subunit of NMDA receptors

PI3K: 

Phosphoinositide 3-kinase

PKC: 

Protein kinase C

S6K1: 

P70 ribosomal S6 protein kinase 1/2

S6: 

P70 ribosomal protein S6

Declarations

Acknowledgements

The authors would like to thank Dr. K. Molnar-Kimber of Kimnar Group LLC for editing assistance which was fully funded by the authors. This work was supported by grants from the NIH (NS072206, HL117684, and DA033390) and the Rita Allen Foundation.

Authors’ Affiliations

(1)
Rutgers Graduate School of Biomedical Sciences, New Jersey Medical School, Rutgers, The State University of New Jersey
(2)
Department of Anesthesiology, New Jersey Medical School, Rutgers, The State University of New Jersey

References

  1. Johannes CB, Le TK, Zhou X, Johnston JA, Dworkin RH. The prevalence of chronic pain in united states adults: results of an internet-based survey. The Journal of Pain. 2010;11(11):1230–9.PubMedView ArticleGoogle Scholar
  2. Pizzo PA, Clark NM. Alleviating suffering 101–pain releif in the United States. N Engl J Med. 2012;366:197–9.PubMedView ArticleGoogle Scholar
  3. Christie MJ. Cellular neuroadaptations to chronic opioids: tolerance, withdrawal and addiction. Br J Pharmacol. 2008;154(2):384–96.PubMed CentralPubMedView ArticleGoogle Scholar
  4. Dumas EO, Pollack GM. Opioid tolerance development: a pharmacokinetic/pharmacodynamic perspective. AAPS J. 2008;10(4):537–51.PubMed CentralPubMedView ArticleGoogle Scholar
  5. Deyo RA, Von Korff M, Duhrkoop D. Opioids for low back pain. BMJ. 2015;350.Google Scholar
  6. Bekhit MH. Opioid-induced hyperalgesia and tolerance. Am J Ther. 2010;17(5):498–510.PubMedView ArticleGoogle Scholar
  7. Mao J, Mayer DJ. Spinal cord neuroplasticity following repeated opioid exposure and its relation to pathological pain. Ann N Y Acad Sci. 2001;933:175–84.PubMedView ArticleGoogle Scholar
  8. Mayer DJ, Mao J, Holt J, Price DD. Cellular mechanisms of neuropathic pain, morphine tolerance, and their interactions. Proc Natl Acad Sci U S A. 1999;96(14):7731–6.PubMed CentralPubMedView ArticleGoogle Scholar
  9. Zeitz KP, Malmberg AB, Gilbert H, Basbaum AI. Reduced development of tolerance to the analgesic effects of morphine and clonidine in PKC gamma mutant mice. Pain. 2001;94(3):245–53.PubMedView ArticleGoogle Scholar
  10. Granados-Soto V, Kalcheva I, Hua X, Newton A, Yaksh TL. Spinal PKC activity and expression: role in tolerance produced by continuous spinal morphine infusion. Pain. 2000;85(3):395–404.PubMedView ArticleGoogle Scholar
  11. Liang D, Li X, Clark JD. Increased expression of Ca2+/calmodulin-dependent protein kinase II alpha during chronic morphine exposure. Neuroscience. 2004;123(3):769–75.PubMedView ArticleGoogle Scholar
  12. Price TJ, Rashid MH, Millecamps M, Sanoja R, Entrena JM, Cervero F. Decreased nociceptive sensitization in mice lacking the fragile X mental retardation protein: role of mGluR1/5 and mTOR. J Neurosci. 2007;27(51):13958–67.PubMed CentralPubMedView ArticleGoogle Scholar
  13. Norsted GE, Codeluppi S, Gregory JA, Steinauer J, Svensson CI. Mammalian target of rapamycin in spinal cord neurons mediates hypersensitivity induced by peripheral inflammation. Neuroscience. 2010;169(3):1392–402.View ArticleGoogle Scholar
  14. Cui J, He W, Yi B, Zhao H, Lu K, Ruan H, et al. mTOR pathway is involved in ADP-evoked astrocyte activation and ATP release in the spinal dorsal horn in a rat neuropathic pain model. Neuroscience. 2014;275:395–403.PubMedView ArticleGoogle Scholar
  15. Cui Y, Zhang XQ, Cui Y, Xin WJ, Jing J, Liu XG. Activation of phosphatidylinositol 3-kinase/Akt-mammalian target of Rapamycin signaling pathway in the hippocampus is essential for the acquisition of morphine-induced place preference in rats. Neuroscience. 2010;171(1):134–43.PubMedView ArticleGoogle Scholar
  16. Liang L, Tao B, Fan L, Yaster M, Zhang Y, Tao YX. mTOR and its downstream pathway are activated in the dorsal root ganglion and spinal cord after peripheral inflammation, but not after nerve injury. Brain Res. 2013;1513:17–25.PubMed CentralPubMedView ArticleGoogle Scholar
  17. Obara I, Tochiki KK, Geranton SM, Carr FB, Lumb BM, Liu Q, et al. Systemic inhibition of the mammalian target of rapamycin (mTOR) pathway reduces neuropathic pain in mice. Pain. 2011;152(11):2582–95.PubMedView ArticleGoogle Scholar
  18. Shih MH, Kao SC, Wang W, Yaster M, Tao YX. Spinal cord NMDA receptor-mediated activation of mammalian target of rapamycin is required for the development and maintenance of bone cancer-induced pain hypersensitivities in rats. The Journal of Pain. 2012;13(4):338–49.PubMed CentralPubMedView ArticleGoogle Scholar
  19. Xu JT, Zhao JY, Zhao X, Ligons D, Tiwari V, Atianjoh FE, et al. Opioid receptor-triggered spinal mTORC1 activation contributes to morphine tolerance and hyperalgesia. J Clin Invest. 2014;124(2):592–603.PubMed CentralPubMedView ArticleGoogle Scholar
  20. Xu Q, Fitzsimmons B, Steinauer J, Neill AO, Newton AC, Hua XY, et al. Spinal phosphinositide 3-kinase-Akt-mammalian target of rapamycin signaling cascades in inflammation-induced hyperalgesia. The Journal of Neuroscience. 2011;31(6):2113–24.PubMed CentralPubMedView ArticleGoogle Scholar
  21. Zhang W, Sun XF, Bo JH, Zhang J, Liu XJ, Wu LP, et al. Activation of mTOR in the spinal cord is required for pain hypersensitivity induced by chronic constriction injury in mice. Pharmacol Biochem Behav. 2013;111:64–70.PubMedView ArticleGoogle Scholar
  22. Hay N, Sonenberg N. Upstream and downstream of mTOR. Genes Dev. 2004;18(16):1926–45.PubMedView ArticleGoogle Scholar
  23. Proud CG. Signalling to translation: how signal transduction pathways control the protein synthetic machinery. Biochem J. 2007;403(2):217–34.PubMedView ArticleGoogle Scholar
  24. Sarbassov DD, Ali SM, Kim DH, Guertin DA, Latek RR, Erdjument-Bromage H, et al. Rictor, a novel binding partner of mTOR, defines a rapamycin-insensitive and raptor-independent pathway that regulates the cytoskeleton. Curr Biol. 2004;14(14):1296–302.PubMedView ArticleGoogle Scholar
  25. Beretta L, Gingras AC, Svitkin YV, Hall MN, Sonenberg N. Rapamycin blocks the phosphorylation of 4E-BP1 and inhibits cap-dependent initiation of translation. EMBO J. 1996;15(3):658–64.PubMed CentralPubMedGoogle Scholar
  26. Holz MK, Ballif BA, Gygi SP, Blenis J. mTOR and S6K1 mediate assembly of the translation preinitiation complex through dynamic protein interchange and ordered phosphorylation events. Cell. 2005;123(4):569–80.PubMedView ArticleGoogle Scholar
  27. Shahbazian D, Roux PP, Mieulet V, Cohen MS, Raught B, Taunton J, et al. The mTOR/PI3K and MAPK pathways converge on eIF4B to control its phosphorylation and activity. EMBO J. 2006;25(12):2781–91.PubMed CentralPubMedView ArticleGoogle Scholar
  28. Jaworski J, Sheng M. The growing role of mTOR in neuronal development and plasticity. Mol Neurobiol. 2006;34(3):205–19.PubMedView ArticleGoogle Scholar
  29. Swiech L, Perycz M, Malik A, Jaworski J. Role of mTOR in physiology and pathology of the nervous system. Biochim Biophys Acta. 2008;1784(1):116–32.PubMedView ArticleGoogle Scholar
  30. Jefferies HB, Fumagalli S, Dennis PB, Reinhard C, Pearson RB, Thomas G. Rapamycin suppresses 5'TOP mRNA translation through inhibition of p70s6k. EMBO J. 1997;16(12):3693–704.PubMed CentralPubMedView ArticleGoogle Scholar
  31. Gibbons JJ, Abraham RT, Yu K. Mammalian Target of Rapamycin: Discovery of Rapamycin Reveals a Signaling Pathway Important for Normal and Cancer Cell Growth. Seminars in Oncology 2009; 36, Supplement 3(0):S3-S17.Google Scholar
  32. Singh K, Sun S, Vezina C. Rapamycin (AY-22,989), a new antifungal antibiotic. IV Mechanism of action J Antibiot. 1979;32(6):630–45.Google Scholar
  33. Lopez P, Kohler S, Dimri S. Interstitial lung disease associated with mTOR inhibitors in solid organ transplant recipients: results from a large phase III clinical trial program of everolimus and review of the literature. Journal of Transplantation. 2014;2014.Google Scholar
  34. Yee KW, Zeng Z, Konopleva M, Verstovsek S, Ravandi F, Ferrajoli A, et al. Phase I/II study of the mammalian target of rapamycin inhibitor everolimus (RAD001) in patients with relapsed or refractory hematologic malignancies. Clin Cancer Res. 2006;12(17):5165–73.PubMedView ArticleGoogle Scholar
  35. Al-Batran SE, Ducreux M, Ohtsu A. mTOR as a therapeutic target in patients with gastric cancer. Int J Cancer. 2012;130(3):491–6.PubMedView ArticleGoogle Scholar
  36. Ma L, Chen Z, Erdjument-Bromage H, Tempst P, Pandolfi PP. Phosphorylation and functional inactivation of TSC2 by Erk implications for tuberous sclerosis and cancer pathogenesis. Cell. 2005;121(2):179–93.PubMedView ArticleGoogle Scholar
  37. Sabatini DM. mTOR and cancer: insights into a complex relationship. Nat Rev Cancer. 2006;6(9):729–34.PubMedView ArticleGoogle Scholar
  38. Fan QW, Weiss W. Inhibition of PI3K-Akt-mTOR Signaling in Glioblastoma by mTORC1/2 Inhibitors. In: Weichhart T, editor. mTOR. 821 ed. Humana Press; 2012. p. 349–359.Google Scholar
  39. Dasgupta B, Yi Y, Chen DY, Weber JD, Gutmann DH. Proteomic analysis reveals hyperactivation of the mammalian target of rapamycin pathway in neurofibromatosis 1GÇôAssociated human and mouse brain tumors. Cancer Res. 2005;65(7):2755–60.PubMedView ArticleGoogle Scholar
  40. Lisi L, Aceto P, Navarra P, Dello Russo C. mTOR Kinase: A possible Pharmacological Target in the Management of Chronic Pain. BioMed Research International 2015; 2015.Google Scholar
  41. Molina AM, Feldman DR, Voss MH, Ginsberg MS, Baum MS, Brocks DR et al. Phase 1 trial of everolimus plus sunitinib in patients with metastatic renal cell carcinoma. Cancer 2011.Google Scholar
  42. Miller RA, Harrison DE, Astle CM, Baur JA, Boyd AR, de Cabo R, et al. Rapamycin, but Not resveratrol or simvastatin, extends life span of genetically heterogeneous mice. J Gerontol A: Biol Med Sci. 2011;66A(2):191–201.View ArticleGoogle Scholar
  43. Xu JT, Zhao X, Yaster M, Tao YX. Expression and distribution of mTOR, p70S6K, 4E-BP1, and their phosphorylated counterparts in rat dorsal root ganglion and spinal cord dorsal horn. Brain Res. 2010;1336:46–57.PubMedView ArticleGoogle Scholar
  44. Lucas LK, Lipman AG. Recent advances in pharmacotherapy for cancer pain management. Cancer Pract. 2002;10 Suppl 1:S14–20.PubMedView ArticleGoogle Scholar
  45. Puig S, Sorkin L. Formalin-evoked activity in identified primary afferent fibers: systemic lidocaine suppresses phase-2 activity. Pain. 1996;64:345–55.PubMedView ArticleGoogle Scholar
  46. Asante CO, Wallace VC, Dickenson AH. Mammalian target of rapamycin signaling in the spinal cord is required for neuronal plasticity and behavioral hypersensitivity associated with neuropathy in the rat. J Pain. 2010;11(12):1356–67.PubMedView ArticleGoogle Scholar
  47. Geranton SM, Jimenez-Diaz L, Torsney C, Tochiki KK, Stuart SA, Leith JL, et al. A rapamycin-sensitive signaling pathway is essential for the full expression of persistent pain states. J Neurosci. 2009;29(47):15017–27.PubMed CentralPubMedView ArticleGoogle Scholar
  48. Belanger S, Ma W, Chabot JG, Quirion R. Expression of calcitonin gene-related peptide, substance P and protein kinase C in cultured dorsal root ganglion neurons following chronic exposure to mu, delta and kappa opiates. Neuroscience. 2002;115(2):441–53.PubMedView ArticleGoogle Scholar
  49. Chakrabarti S, Regec A, Gintzler AR. Chronic morphine acts via a protein kinase Cgamma-G(beta)-adenylyl cyclase complex to augment phosphorylation of G(beta) and G(betagamma) stimulatory adenylyl cyclase signaling. Brain Res Mol Brain Res. 2005;138(1):94–103.PubMedView ArticleGoogle Scholar
  50. Gintzler AR, Chakrabarti S. Post-opioid receptor adaptations to chronic morphine; altered functionality and associations of signaling molecules. Life Sci. 2006;79(8):717–22.PubMedView ArticleGoogle Scholar
  51. Williams JT, Christie MJ, Manzoni O. Cellular and synaptic adaptations mediating opioid dependence. Physiol Rev. 2001;81(1):299–343.PubMedGoogle Scholar

Copyright

© Lutz et al. 2015

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Advertisement