Rapamycin inhibition of the G1 to S transition is mediated by effects on cyclin D1 mRNA and protein stability

Rapamycin vs TORin-1 or Gleevec vs Nilotinib: Simple chemical evolution that converts PAK1-blockers to TOR-blockers or vice versa?

Both PAK1 (RAC/CDC42-activating kinase 1) and TOR (Target of Rapamycin) are among the major oncogenic/ageing kinases. However, they play the opposite role in our immune system, namely immune system is suppressed by PAK1, while it requires TOR. Thus, PAK1-blockers, would be more effective for therapy of cancers, than TOR-blockers. Since 2015 when we discovered genetically that PDGF-induced melanogenesis depends on "PAK1", we are able to screening a series of PAK1-blockers as melanogenesis-inhibitors which could eventually promote longevity. Interestingly, rapamycin, the first TOR-inhibitor, promotes melanogenesis, clearly indicating that TOR suppresses melanogenesis. However, a new TOR-inhibitor called TORin-1 no longer suppresses immune system, and blocks melanogenesis in cell culture. These observations strongly indicate that TORin-1 acts as PAK1-blockers, instead of TOR-blockers, in vivo. Thus, it is most likely that melanogenesis in cell culture could enable us to discriminate PAK1-blockers from TORblockers.

Sugar signals pedal the cell cycle!

Cell cycle involves the sequential and reiterative progression of important events leading to cell division. Progression through a specific phase of the cell cycle is under the control of various factors. Since the cell cycle in multicellular eukaryotes responds to multiple extracellular mitogenic cues, its study in higher forms of life becomes all the more important. One such factor regulating cell cycle progression in plants is sugar signalling. Because the growth of organs depends on both cell growth and proliferation, sugars sensing and signalling are key control points linking sugar perception to regulation of downstream factors which facilitate these key developmental transitions. However, the basis of cell cycle control via sugars is intricate and demands exploration. This review deals with the information on sugar and TOR-SnRK1 signalling and how they manoeuvre various events of the cell cycle to ensure proper growth and development.

Effect of Rice Protein Meal Replacement of Fish Meal on Growth, Anti-Oxidation Capacity, and Non-Specific Immunity for Juvenile Shrimp Litopenaeus vannamei

This study assessed the effect of rice protein meal replacement for fish meal on the growth, nonspecific immunity, and disease resistance on juvenile shrimp Litopenaeus vannamei. Six groups of iso-nitrogenous and iso-lipid feeds named FM, R10, R20, R40, R60, and R80 were prepared by replacing 0%, 10%, 20%, 40%, 60%, and 80% in FM protein with RPM, respectively, and then fed to the shrimps (0.54 ± 0.01 g). An amount of 720 healthy and evenly sized shrimps were allocated to six groups (three replicates per group) and fed four times a day (7:00, 11:00, 17:00 and 21:00) for eight weeks. Results revealed no significant differences in WG, FCR, and SGR of shrimps after replacing FM with 10% RPM (p > 0.05). In the R10 and R20 groups, SOD and T-AOC activities were significantly higher than those in the FM group, whereas the opposite was observed for MDA content (p < 0.05). CAT, ACP, and LZM were all significantly higher in the R10, R20, and R40 groups than in the FM group (p < 0.05). GSH-Px activity in the R10 group was significantly higher than the activity in the FM group (p < 0.05). AKP, PO, TYS, GPT, and GOT activities were significantly higher in the R10 group than in the FM group (p < 0.05). Compared to the FM group, the eukaryotic translation initiation factor 3K (eif3k) gene was significantly up-regulated in the R10 group, whereas the penaiedin 3a (pen 3a) and anti-lipopolysaccharide factor (alf) genes were significantly up-regulated in the R10 and R20 groups (p < 0.05). The crustin a (cru a), immune deficiency (imd), and lysozyme (lzm) mRNA levels were significantly higher in the R10, R20, and R40 groups than in the other groups (p < 0.05). The prophenoloxidase (PO) mRNA levels in the R20 group were significantly higher than those in the FM group (p < 0.05). The replacement of 10−40% of FM with RPM improved the gut flora composition of shrimps, increasing beneficial bacteria (Bacteroidetes) abundance and reducing harmful bacteria (Aspergillus and Vibrio) abundance. After the challenge test of Vibrio parahaemolyticus (7 days), the cumulative mortality in the R10 group significantly decreased (p < 0.05). In conclusion, replacement of 10% FM by RPM significantly improved digestibility, protein synthesis, antioxidant capacity, and disease resistance in L. vannamei.

Rapamycin inhibits oral cancer cell growth by promoting oxidative stress and suppressing ERK1/2, NF-κB and beta-catenin pathways

Treatment of oral cancer is based exclusively on surgery combined with or without chemotherapy. However, it has several side effects. Targeting a new, more effective therapy has become an urgent matter. The purpose of this study was to evaluate the anti-tumor activity of rapamycin in oral cancer and its mechanism of action. Human gingival carcinoma cells were stimulated with different concentrations of rapamycin to assess proliferation, colony formation, cell migration, as well as apoptosis, and autophagy. The expression of proteins involved in the cell cycle (cyclin D1, p15, p21, p27) and autophagy, as well as that of oncogenes and tumor suppressor genes, were determined by quantitative PCR. The signaling pathways were evaluated by Western blotting. Our results show that rapamycin has a selective effect at a low dose on cancer cell growth/survival. This was confirmed by low colony formation and the inhibition of cell migration, while increasing cell apoptosis by activating caspase-9 and -3. Rapamycin promoted cell autophagy and increased mitochondrial oxidative stress by being involved in DNA damage in the exposed cells. Finally, rapamycin exhibits potent anti-oral cancer properties through inhibition of several cancer-promoting pathways (MAPK, NF-κB, and Wnt/beta-catenin). These results indicate that rapamycin could be a potential agent for the treatment of oral cancer and for a prevention strategy.

Oncolytic Avian Reovirus p17-Modulated Inhibition of mTORC1 by Enhancement of Endogenous mTORC1 Inhibitors Binding to mTORC1 To Disrupt Its Assembly and Accumulation on Lysosomes

The mechanism by which avian reovirus (ARV)-modulated suppression of mTORC1 triggers autophagy remains largely unknown. In this work, we determined that p17 functions as a negative regulator of mTORC1. This study suggest novel mechanisms whereby p17-modulated inhibition of mTORC1 occurs via upregulation of p53, inactivation of Akt, and enhancement of binding of the endogenous mTORC1 inhibitors (PRAS40, FKBP38, and FKPP12) to mTORC1 to disrupt its assembly and accumulation on lysosomes. p17-modulated inhibition of Akt leads to activation of the downstream targets PRAS40 and TSC2, which results in mTORC1 inhibition, thereby triggering autophagy and translation shutoff, which is favorable for virus replication. p17 impairs the interaction of mTORC1 with its activator Rheb, which promotes FKBP38 interaction with mTORC1. It is worth noting that p17 activates ULK1 and Beclin1 and increases the formation of the Beclin 1/class III PI3K complex. These effects could be reversed in the presence of insulin or depletion of p53. Furthermore, we found that p17 induces autophagy in cancer cell lines by upregulating the p53/PTEN pathway, which inactivates Akt and mTORC1. This study highlights p17-modulated inhibition of Akt and mTORC1, which triggers autophagy and translation shutoff by positively modulating the tumor suppressors p53 and TSC2 and endogenous mTORC1 inhibitors. IMPORTANCE The mechanisms by which p17-modulated inhibition of mTORC1 induces autophagy and translation shutoff is elucidated. In this work, we determined that p17 serves as a negative regulator of mTORC1. This study provides several lines of conclusive evidence demonstrating that p17-modulated inhibition of mTORC1 occurs via upregulation of the p53/PTEN pathway, downregulation of the Akt/Rheb/mTORC1 pathway, enhancement of binding of the endogenous mTORC1 inhibitors to mTORC1 to disrupt its assembly, and suppression of mTORC1 accumulation on lysosomes. This work provides valuable information for better insights into p17-modulated inhibition of mTORC1, which induces autophagy and translation shutoff to benefit virus replication.

Functional impact and targetability of PI3KCA, GNAS, and PTEN mutations in a spindle cell rhabdomyosarcoma with MYOD1 L122R mutation

Spindle cell/sclerosing rhabdomyosarcoma (ssRMS) is a rare subtype of rhabdomyosarcoma, commonly harboring a gain-of-function L122R mutation in the muscle-specific master transcription factor MYOD1. MYOD1-mutated ssRMS is almost invariably fatal, and development of novel therapeutic approaches based on the biology of the disease is urgently needed. MYOD1 L122R affects the DNA-binding domain and is believed to confer MYC-like properties to MYOD1, driving oncogenesis. Moreover, the majority of the MYOD1-mutated ssRMS harbor additional alterations activating the PI3K/AKT pathway. It is postulated that the PI3K/AKT pathway cooperates with MYOD1 L122R. To address this biological entity, we established and characterized a new patient-derived ssRMS cell line OHSU-SARC001, harboring MYOD1 L122R as well as alterations in PTEN, PIK3CA, and GNAS. We explored the functional impact of these aberrations on oncogenic signaling with gain-of-function experiments in C2C12 murine muscle lineage cells. These data reveal that PIK3CA^I459_T462del, the novel PIK3CA variant discovered in this patient specimen, is a constitutively active kinase, albeit to a lesser extent than PI3KCA^E545K, a hotspot oncogenic mutation. Furthermore, we examined the effectiveness of molecularly targeted PI3K/AKT/mTOR and RAS/MAPK inhibitors to block oncogenic signaling and suppress the growth of OHSU-SARC001 cells. Dual PI3K/mTOR (LY3023414, bimiralisib) and AKT inhibitors (ipatasertib, afuresertib) induced dose-dependent reductions in cell growth. However, mTOR-selective inhibitors (everolimus, rapamycin) alone did not exert cytotoxic effects. The MEK1/2 inhibitor trametinib did not impact proliferation even at the highest doses tested. Our data suggest that molecularly targeted strategies may be effective in PI3K/AKT/mTOR-activated ssRMS. Taken together, these data highlight the importance of utilizing patient-derived models to assess molecularly targetable treatments and their potential as future treatment options.

Everolimus Reduces Cancer Incidence and Improves Patient and Graft Survival Rates after Kidney Transplantation: A Multi-Center Study

Kidney transplantation can prevent renal failure and associated complications in patients with end-stage renal disease. Despite the good quality of life, de novo cancers after kidney transplantation are a major complication impacting survival and there is an urgent need to establish immunosuppressive protocols to prevent de novo cancers. We conducted a multi-center retrospective study of 2002 patients who underwent kidney transplantation between 1965 and 2020 to examine patient and graft survival rates and cumulative cancer incidence in the following groups categorized based on specific induction immunosuppressive therapies: group 1, antiproliferative agents and steroids; group 2, calcineurin inhibitors (CNIs), antiproliferative agents and steroids; group 3, CNIs, mycophenolate mofetil, and steroids; and group 4, mammalian target of rapamycin inhibitors including everolimus, CNIs, mycophenolate mofetil, and steroids. The patient and graft survival rates were significantly higher in groups 3 and 4. The cumulative cancer incidence rate significantly increased with the use of more potent immunosuppressants, and the time to develop cancer was shorter. Only one patient in group 4 developed de novo cancer. Potent immunosuppressants might improve graft survival rate while inducing de novo cancer after kidney transplantation. Our data also suggest that everolimus might suppress cancer development after kidney transplantation.

The Intricate Interplay between Cell Cycle Regulators and Autophagy in Cancer

Simple Summary

Autophagy is an intracellular catabolic program regulated by multiple external and internal cues. A large amount of evidence unraveled that cell-cycle regulators are crucial in its control. This review highlights the interplay between cell-cycle regulators, including cyclin-dependent kinase inhibitors, cyclin-dependent kinases, and E2F factors, in the control of autophagy all along the cell cycle. Beyond the intimate link between cell cycle and autophagy, this review opens therapeutic perspectives in modulating together these two aspects to block cancer progression.

Abstract

In the past decade, cell cycle regulators have extended their canonical role in cell cycle progression to the regulation of various cellular processes, including cellular metabolism. The regulation of metabolism is intimately connected with the function of autophagy, a catabolic process that promotes the efficient recycling of endogenous components from both extrinsic stress, e.g., nutrient deprivation, and intrinsic sub-lethal damage. Mediating cellular homeostasis and cytoprotection, autophagy is found to be dysregulated in numerous pathophysiological contexts, such as cancer. As an adaptative advantage, the upregulation of autophagy allows tumor cells to integrate stress signals, escaping multiple cell death mechanisms. Nevertheless, the precise role of autophagy during tumor development and progression remains highly context-dependent. Recently, multiple articles has suggested the importance of various cell cycle regulators in the modulation of autophagic processes. Here, we review the current clues indicating that cell-cycle regulators, including cyclin-dependent kinase inhibitors (CKIs), cyclin-dependent kinases (CDKs), and E2F transcription factors, are intrinsically linked to the regulation of autophagy. As an increasing number of studies highlight the importance of autophagy in cancer progression, we finally evoke new perspectives in therapeutic avenues that may include both cell cycle inhibitors and autophagy modulators to synergize antitumor efficacy.

Translation Inhibitors Activate Autophagy Master Regulators TFEB and TFE3

The autophagy-lysosome pathway is a major protein degradation pathway stimulated by multiple cellular stresses, including nutrient or growth factor deprivation, hypoxia, misfolded proteins, damaged organelles, and intracellular pathogens. Recent studies have revealed that transcription factor EB (TFEB) and transcription factor E3 (TFE3) play a pivotal role in the biogenesis and functions of autophagosome and lysosome. Here we report that three translation inhibitors (cycloheximide, lactimidomycin, and rocaglamide A) can facilitate the nuclear translocation of TFEB/TFE3 via dephosphorylation and 14-3-3 dissociation. In addition, the inhibitor-mediated TFEB/TFE3 nuclear translocation significantly increases the transcriptional expression of their downstream genes involved in the biogenesis and function of autophagosome and lysosome. Furthermore, we demonstrated that translation inhibition increased autophagosome biogenesis but impaired the degradative autolysosome formation because of lysosomal dysfunction. These results highlight the previously unrecognized function of the translation inhibitors as activators of TFEB/TFE3, suggesting a novel biological role of translation inhibition in autophagy regulation.

Loss of Tsc1 in cerebellar Purkinje cells induces transcriptional and translation changes in FMRP target transcripts

Tuberous sclerosis complex (TSC) is a genetic disorder that is associated with multiple neurological manifestations. Previously, we demonstrated that Tsc1 loss in cerebellar Purkinje cells (PCs) can cause altered social behavior in mice. Here, we performed detailed transcriptional and translational analyses of Tsc1-deficient PCs to understand the molecular alterations in these cells. We found that target transcripts of the Fragile X Mental Retardation Protein (FMRP) are reduced in mutant PCs with evidence of increased degradation. Surprisingly, we observed unchanged ribosomal binding for many of these genes using translating ribosome affinity purification. Finally, we found that multiple FMRP targets, including SHANK2, were reduced, suggesting that compensatory increases in ribosomal binding efficiency may be unable to overcome reduced transcript levels. These data further implicate dysfunction of FMRP and its targets in TSC and suggest that treatments aimed at restoring the function of these pathways may be beneficial.

Combinatorial Therapies to Overcome BRAF/MEK Inhibitors Resistance in Melanoma Cells: An in vitro Study

BACKGROUND

Melanoma accounts for only 1% of all skin malignant tumors; however, it is the deadliest form of skin cancer. Since 2011, FDA (Food and Drug Administration) approved several novel therapeutic strategies, such as MAPK pathway targeted therapies, to treat cutaneous melanoma patients. However, their improvements in overall survival were limited, due to the development of resistance.

METHODS

In this work, several combinations of therapies, including the metabolic modulator DCA, were tested in melanoma cell lines, considering that MAPK and PI3K/AKT/mTOR pathways are deregulated and interconnected in melanoma and that the presence of the Warburg effect in melanoma cells may influence the response to therapy. The effect of the treatments was assessed in the proliferation and survival of melanoma cell lines with different genetic profiles. Also, the possibility to overcome resistance to the treatment with vemurafenib was tested.

RESULTS

In general, higher decrease in cell viability and cell proliferation and increase in apoptosis were obtained after the combination treatments, comparing with single treatments, in all the studied cell lines. The combination of cobimetinib and everolimus appear to be the best treatment option. The BRAFV600E -vemurafenib resistant melanoma cell line showed to retain sensitivity to both everolimus and DCA.

DISCUSSION AND CONCLUSION

Our results suggest that the combination of MAPK pathway inhibitors with mTOR pathway inhibitors and DCA should be considered as therapeutic options to treat melanoma patients, as the combinations potentiated the effects of each drug alone. In a cell line resistant to vemurafenib, we verified that combined MAPK inhibitors with inhibition of mTOR pathway and/or DCA metabolism modulation might constitute possible strategies in order to overcome resistance to MAPK inhibition.

The Contribution of Lysosomes to DNA Replication

Lysosomes, acidic, membrane-bound organelles, are not only the core of the cellular recycling machinery, but they also serve as signaling hubs regulating various metabolic pathways. Lysosomes maintain energy homeostasis and provide pivotal substrates for anabolic processes, such as DNA replication. Every time the cell divides, its genome needs to be correctly duplicated; therefore, DNA replication requires rigorous regulation. Challenges that negatively affect DNA synthesis, such as nucleotide imbalance, result in replication stress with severe consequences for genome integrity. The lysosomal complex mTORC1 is directly involved in the synthesis of purines and pyrimidines to support DNA replication. Numerous drugs have been shown to target lysosomal function, opening an attractive avenue for new treatment strategies against various pathologies, including cancer. In this review, we focus on the interplay between lysosomal function and DNA replication through nucleic acid degradation and nucleotide biosynthesis and how these could be exploited for therapeutic purposes.

mTOR Inhibitors as Radiosensitizers in Neuroendocrine Neoplasms

Peptide receptor radioligand therapy (PRRT) has evolved as an important second-line treatment option in the management of inoperable and metastatic neuroendocrine neoplasms (NEN). Though high radiation doses can be delivered to the tumors, complete remission is still rare. Radiosensitization prior to PRRT is therefore considered to be a promising strategy to improve the treatment effect. In this study, effect and mechanism of mTOR inhibitors were investigated in a comprehensive panel of five NEN cell lines (BON, QGP-1, LCC-18, H727, UMC-11), employing assays for cellular proliferation, clonogenic survival, cell cycle modification and signaling. mTOR inhibition lead to growth arrest with a biphasic concentration-response pattern: a partial response at approximately 1 nM and full response at micromolar concentrations (8-48 µM). All cell lines demonstrated elevated p70S6K phosphorylation yet also increased phosphorylation of counterregulatory Akt. The pulmonary NEN cell line UMC-11 showed the lowest induction of phospho-Akt and strongest growth arrest by mTOR inhibitors. Radiation sensitivity of the cells (50% reduction versus control) was found to range between 4 and 8 Gy. Further, mTOR inhibition was employed together with irradiation to evaluate radiosensitizing effects of this combination treatment. mTOR inhibition was found to radiosensitize all five NEN cells in an additive manner with a moderate overall effect. The radiation-induced G2/M arrest was diminished under combination treatment, leading to an increased G1 arrest. Further investigation involving a suitable animal model as well as radioligand application such as ¹⁷⁷Lu-DOTATATE or ¹⁷⁷Lu-DOTATOC will have to demonstrate the full potential of this strategy for radiosensitization in NEN.

Regulation of T Helper Cell Fate by TCR Signal Strength

T cells are critical in orchestrating protective immune responses to cancer and an array of pathogens. The interaction between a peptide MHC (pMHC) complex on antigen presenting cells (APCs) and T cell receptors (TCRs) on T cells initiates T cell activation, division, and clonal expansion in secondary lymphoid organs. T cells must also integrate multiple T cell-intrinsic and extrinsic signals to acquire the effector functions essential for the defense against invading microbes. In the case of T helper cell differentiation, while innate cytokines have been demonstrated to shape effector CD4⁺ T lymphocyte function, the contribution of TCR signaling strength to T helper cell differentiation is less understood. In this review, we summarize the signaling cascades regulated by the strength of TCR stimulation. Various mechanisms in which TCR signal strength controls T helper cell expansion and differentiation are also discussed.

Potential new therapy of Rapalink-1, a new generation mammalian target of rapamycin inhibitor, against sunitinib-resistant renal cell carcinoma

Sunitinib, a multitargeted receptor tyrosine kinase inhibitor including vascular endothelial growth factor, has been widely used as a first-line treatment against metastatic renal cell carcinoma (mRCC). However, mRCC often acquires resistance to sunitinib, rendering it difficult to treat with this agent. Recently, Rapalink-1, a drug that links rapamycin and the mTOR kinase inhibitor MLN0128, has been developed with excellent therapeutic effects against breast cancer cells carrying mTOR resistance mutations. The aim of the present study was to evaluate the in vitro and in vivo therapeutic efficacy of Rapalink-1 against renal cell carcinoma (RCC) compared to temsirolimus, which is commonly used as a small molecule inhibitor of mTOR and is a derivative of rapamycin. In comparison with temsirolimus, Rapalink-1 showed significantly greater effects against proliferation, migration, invasion and cFolony formation in sunitinib-naïve RCC cells. Inhibition was achieved through suppression of the phosphorylation of substrates in the mTOR signal pathway, such as p70S6K, eukaryotic translation initiation factor 4E-binding protein 1 (4EBP1) and AKT. In addition, Rapalink-1 had greater tumor suppressive effects than temsirolimus against the sunitinib-resistant 786-o cell line (SU-R 786-o), which we had previously established, as well as 3 additional SU-R cell lines established here. RNA sequencing showed that Rapalink-1 suppressed not only the mTOR signaling pathway but also a part of the MAPK signaling pathway, the ErbB signaling pathway and ABC transporters that were associated with resistance to several drugs. Our study suggests the possibility of a new treatment option for patients with RCC that is either sunitinib-sensitive or sunitinib-resistant.

Everolimus induces G1 cell cycle arrest through autophagy-mediated protein degradation of cyclin D1 in breast cancer cells

Everolimus inhibits mammalian target of rapamycin complex 1 (mTORC1) and is known to cause induction of autophagy and G1 cell cycle arrest. However, it remains unknown whether everolimus-induced autophagy plays a critical role in its regulation of the cell cycle. We, for the first time, suggested that everolimus could stimulate autophagy-mediated cyclin D1 degradation in breast cancer cells. Everolimus-induced cyclin D1 degradation through the autophagy pathway was investigated in MCF-10DCIS.COM and MCF-7 cell lines upon autophagy inhibitor treatment using Western blot assay. Everolimus-stimulated autophagy and decrease in cyclin D1 were also tested in explant human breast tissue. Inhibiting mTORC1 with everolimus rapidly increased cyclin D1 degradation, whereas 3-methyladenine, chloroquine, and bafilomycin A1, the classic autophagy inhibitors, could attenuate everolimus-induced cyclin D1 degradation. Similarly, knockdown of autophagy-related 7 (Atg-7) also repressed everolimus-triggered cyclin D1 degradation. In addition, everolimus-induced autophagy occurred earlier than everolimus-induced G1 arrest, and blockade of autophagy attenuated everolimus-induced G1 arrest. We also found that everolimus stimulated autophagy and decreased cyclin D1 levels in explant human breast tissue. These data support the conclusion that the autophagy induced by everolimus in human mammary epithelial cells appears to cause cyclin D1 degradation resulting in G1 cell cycle arrest. Our findings contribute to our knowledge of the interplay between autophagy and cell cycle regulation mediated by mTORC1 signaling and cyclin D1 regulation.

TOR as a Regulatory Target in Rhipicephalus microplus Embryogenesis

Embryogenesis is a metabolically intensive process carried out under tightly controlled conditions. The insulin signaling pathway regulates glucose homeostasis and is essential for reproduction in metazoan model species. Three key targets are part of this signaling pathway: protein kinase B (PKB, or AKT), glycogen synthase kinase 3 (GSK-3), and target of rapamycin (TOR). While the role of AKT and GSK-3 has been investigated during tick embryonic development, the role of TOR remains unknown. In this study, TOR and two other downstream effectors, namely S6 kinase (S6K) and eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1), were investigated in in vitro studies using the tick embryonic cell line BME26. First, we show that exogenous insulin can stimulate TOR transcription. Second, TOR chemical inhibition led to a decrease in BME26 cell viability, loss of membrane integrity, and downregulation of S6K and 4E-BP1 transcription. Conversely, treating BME26 cells with chemical inhibitors of AKT or GSK-3 did not affect S6K and 4E-BP1 transcription, showing that TOR is specifically required to activate its downstream targets. To address the role of TOR in tick reproduction, in vivo studies were performed. Analysis of relative transcription during different stages of tick embryonic development showed different levels of transcription for TOR, and a maternal deposition of S6K and 4E-BP1 transcripts. Injection of TOR double-stranded RNA (dsRNA) into partially fed females led to a slight delay in oviposition, an atypical egg external morphology, decreased vitellin content in eggs, and decreased larval hatching. Taken together, our data show that the TOR signaling pathway is important for tick reproduction, that TOR acts as a regulatory target in Rhipicephalus microplus embryogenesis and represents a promising target for the development of compounds for tick control.

Cell size sensing in animal cells coordinates anabolic growth rates and cell cycle progression to maintain cell size uniformity

Cell size uniformity in healthy tissues suggests that control mechanisms might coordinate cell growth and division. We derived a method to assay whether cellular growth rates depend on cell size, by monitoring how variance in size changes as cells grow. Our data revealed that, twice during the cell cycle, growth rates are selectively increased in small cells and reduced in large cells, ensuring cell size uniformity. This regulation was also observed directly by monitoring nuclear growth in live cells. We also detected cell-size-dependent adjustments of G1 length, which further reduce variability. Combining our assays with chemical/genetic perturbations confirmed that cells employ two strategies, adjusting both cell cycle length and growth rate, to maintain the appropriate size. Additionally, although Rb signaling is not required for these regulatory behaviors, perturbing Cdk4 activity still influences cell size, suggesting that the Cdk4 pathway may play a role in designating the cell’s target size.

Animal cells come in many different sizes. In humans, for example, egg cells are thousands of times larger than sperm cells. Yet cells of any given type are often strikingly similar in size. The cells that line the surface of organs including the skin and kidneys are especially uniform; in fact a loss of size uniformity in certain tumors is a sign of malignancy. What kind of regulation could enable separate cells within a tissue to have the same size?

One possibility is that each type of cell is programmed with a specific target size, and that a cell can sense if it strays from its target and take steps to compensate. Animal cells sensing their own size was first reported in the 1960s, and now Ginzberg et al. confirm that human cells grown in the laboratory do indeed monitor their size and correct deviations from their target. It turns out that two separate and independent processes help to keep all the cells in the population roughly uniform in size. Firstly, proliferating human cells that are smaller than their target size spend longer growing before they divide. Secondly, at two time points between cell divisions, large cells adjust their growth rate such that they grow slower than small cells.

To show these processes in action, Ginzberg et al. introduced mutations or chemicals that perturbed the length of time between cell divisions or the rate of a cell’s growth. As expected, most of these perturbations had only a modest influence on cell size, due to the cell’s compensatory strategies. Cells that had less time to grow compensated by more quickly making new protein molecules, meaning that they still had enough material to build two new cells by the time they had to divide. In contrast, if a cell’s division was artificially delayed, it reduced its growth rate to stop it from becoming too large. Similarly, cells grown in conditions that slow the production of proteins extended the time between their cell divisions to give them enough time to accumulate the material required for two new cells.

In a recent related study, Liu, Ginzberg et al. identified some of the molecules that a human cell uses to sense its own size. Together these two studies now pave the road to answering a fundamental question in cell biology: what is the elusive cell size sensor? Understanding how cells sense their size will open a window onto how quantitative information is programmed, sensed and communicated within living cells. These findings will shed also new light onto how cells specialize into cell types of different sizes, and what happens when cells lose the ability to sense or regulate their size in diseases like cancers.

Discovery and Roles of 2',3'-cAMP in Biological Systems

In 2009, investigators using ultra-performance liquid chromatography-tandem mass spectrometry to measure, by selected reaction monitoring, 3',5'-cAMP in the renal venous perfusate from isolated, perfused kidneys detected a large signal at the same m/z transition (330 → 136) as 3',5'-cAMP but at a different retention time. Follow-up experiments demonstrated that this signal was due to a positional isomer of 3',5'-cAMP, namely, 2',3'-cAMP. Soon thereafter, investigative teams reported the detection of 2',3'-cAMP and other 2',3'-cNMPs (2',3'-cGMP, 2',3'-cCMP, and 2',3'-cUMP) in biological systems ranging from bacteria to plants to animals to humans. Injury appears to be the major stimulus for the release of these unique noncanonical cNMPs, which likely are formed by the breakdown of RNA. In mammalian cells in culture, in intact rat and mouse kidneys, and in mouse brains in vivo, 2',3'-cAMP is metabolized to 2'-AMP and 3'-AMP; and these AMPs are subsequently converted to adenosine. In rat and mouse kidneys and mouse brains, injury releases 2',3'-cAMP, 2'-AMP, and 3'-AMP into the extracellular compartment; and in humans, traumatic brain injury is associated with large increases in 2',3'-cAMP, 2'-AMP, 3'-AMP, and adenosine in the cerebrospinal fluid. These findings motivate the extracellular 2',3'-cAMP-adenosine pathway hypothesis: intracellular production of 2',3'-cAMP → export of 2',3'-cAMP → extracellular metabolism of 2',3'-cAMP to 2'-AMP and 3'-AMP → extracellular metabolism of 2'-AMP and 3'-AMP to adenosine. Since 2',3'-cAMP has been shown to activate mitochondrial permeability transition pores (mPTPs) leading to apoptosis and necrosis and since adenosine is generally tissue protective, the extracellular 2',3'-cAMP-adenosine pathway may be a protective mechanism [i.e., removes 2',3'-cAMP (an intracellular toxin) and forms adenosine (a tissue protectant)]. This appears to be the case in the brain where deficiency in CNPase (the enzyme that metabolizes 2',3'-cAMP to 2-AMP) leads to increased susceptibility to brain injury and neurological diseases. Surprisingly, CNPase deficiency in the kidney actually protects against acute kidney injury, perhaps by preventing the formation of 2'-AMP (which turns out to be a renal vasoconstrictor) and by augmenting the mitophagy of damaged mitochondria. With regard to 2',3'-cNMPs and their downstream metabolites, there is no doubt much more to be discovered.

Knockdown of anion exchanger 2 suppressed the growth of ovarian cancer cells via mTOR/p70S6K1 signaling

Anion exchanger 2 (AE2, encoded by SLC4A2) is a sodium-independent chloride/bicarbonate transporter and implicated in the regulation of intracellular pH and membrane potential. Previous studies have linked AE2 to the tumorigenesis of various cancers. Here, AE2 was identified as an up-regulated protein in ovarian cancer tissues compared to adjacent non-tumor lesions based on quantitative proteomics analysis. AE2 mRNA was also overexpressed in human ovarian cancer samples, and that AE2 overexpression correlated with the shortened survival time of ovarian cancer patients. Short-hairpin RNA-mediated knockdown of AE2 in A2780 and SK-OV-R3 cells inhibited cell growth and induced cell cycle G1 phase arrest. In nude mice, its stable knockdown inhibited the tumorigenicity of A2780 cells. Gene set enrichment analysis on The Cancer Genome Atlas dataset identified that the cell cycle process and mTOR pathway were correlatively with the AE2 expression. Expression of key regulators of G1/S transition (Cyclin D1 and CDK4), and phosphorylation levels of p70S6K were notably reduced in AE2 knockdown cells. Moreover, experiments with mTOR inhibitor suggested that AE2 may promote cell cycle progression through mTOR/p70S6K1 pathway. Together, our results suggest up-regulated AE2 promotes ovarian cancer tumorigenesis by activating mTOR/p70S6K1 pathway and implicate the potential application of AE2 in cancer therapy.

Esculetin induces apoptosis of SMMC-7721 cells through IGF-1/PI3K/Akt-mediated mitochondrial pathways

Esculetin (6,7-dihydroxycoumarin) is a coumarin derivative extracted from natural plants and has been reported to have anticancer activity. However, the mechanism by which esculetin prevents human hepatic cancer cell growth is still largely unknown. In this study, we investigated the effect of esculetin on human hepatocellular carcinoma (HCC) SMMC-7721 cells and explored the cell signal mechanism. Our data indicated that esculetin induced apoptosis in SMMC-7721 cells, which were supported by DAPI staining and Annexin V/PI staining. Meanwhile, esculetin increased the activities of caspase-3 and caspase-9, promoted bax expression, decreased bcl-2 expression, and triggered collapse of mitochondrial membrane potential, and increased cytochrome c release from mitochondria. In addition, the inactivation of IGF-1, PI3K, and Akt was observed after esculetin administration. Furthermore, pretreatment with IGF-1 before esculetin administration abrogated the pro-apoptotic effects of esculetin, while PI3K inhibitor increased the pro-apoptotic effects of esculetin. These results indicated that esculetin induced the apoptosis of SMMC-7721 cells through IGF-1/PI3K/Akt-regulated mitochondrial dysfunction.

Enantiomerically pure β-dipeptide derivative induces anticancer activity against human hormone-refractory prostate cancer through both PI3K/Akt-dependent and -independent pathways

The use of peptides that target cancer cells and induce anticancer activities through various mechanisms is developing as a potential anticancer strategy. KUD983, an enantiomerically pure β-dipeptide derivative, displays potent activity against hormone-refractory prostate cancer (HRPC) PC-3 and DU145 cells with submicromolar IC₅₀. KUD983 induced G1 arrest of the cell cycle and subsequent apoptosis associated with down-regulation of several related proteins including cyclin D1, cyclin E and Cdk4, and the de-phosphorylation of RB. The levels of nuclear and total c-Myc protein, which could increase the expression of both cyclin D1 and cyclin E, were profoundly inhibited by KUD983. Furthermore, it inhibited PI3K/Akt and mTOR/p70S6K/4E-BP1 pathways, the key signaling in multiple cellular functions. The transient transfection of constitutively active myristylated Akt (myr-Akt) cDNA significantly rescued KUD983-induced caspase activation but did not blunt the inhibition of mTOR/p70S6K/4E-BP1 signaling cascade suggesting the presence of both Akt-dependent and -independent pathways. Moreover, KUD983-induced effect was enhanced with the down-regulation of anti-apoptotic Bcl-2 members (e.g., Bcl-2, and Mcl-1) and IAP family members (e.g., survivin). Notably, KUD983 induced autophagic cell death using confocal microscopic examination, tracking the level of conversion of LC3-I to LC3-II and flow cytometric detection of acidic vesicular organelles-positive cells. In conclusion, the data suggest that KUD983 is an anticancer β-dipeptide against HRPCs through the inhibition of cell proliferation and induction of apoptotic and autophagic cell death. The suppression of signaling pathways regulated by c-Myc, PI3K/Akt and mTOR/p70S6K/4E-BP1 and the collaboration with down-regulation of Mcl-1 and survivin may explain KUD983-induced anti-HRPC mechanism.

Down-regulation of long non-coding RNA RP11-708H21.4 is associated with poor prognosis for colorectal cancer and promotes tumorigenesis through regulating AKT/mTOR pathway

Long non-coding RNAs (lncRNAs) serve critical roles in cancer development and progression. Herein, through next generation RNA sequencing and experimental validations, we determined the expression status of RP11-708H21.4 in colorectal cancer (CRC) and explored its clinical significance and biological functions in CRC. Differentially expressed lncRNAs from CRC samples and corresponding normal mucosa tissues was screened through RNA sequencing, and RP11-708H21.4 was selected for further experimental validation. The expression levels of RP11-708H21.4 in CRC tissues and cell lines were determined using qRT-PCR. Also, the relationship between the clinicopathological features and RP11-708H21.4 expression was analyzed. Cell viability was examined by CCK-8 and colony assays; cell migration and invasion were detected by transwell assays; cell cycle and cell apoptosis were analyzed by flow cytometry. The chemosensitivity of CRC cells to 5-Fluorouracil (5-FU) was also determined using CCK-8 assay. CRC xenograft tumor models were established to determine the biological functions of RP11-708H21.4 in vivo. Levels of cell cycle-related proteins and AKT/mTOR pathway-related proteins were detected by western blot assay. RP11-708H21.4 expression was aberrantly decreased in CRC, and its expression was closely associated with aggressive clinicopathologic features and unfavorable prognosis of CRC patients. Overexpressed RP11-708H21.4 suppresses CRC cell proliferation through inducing G1 arrest. Moreover, up-regulation of RP11-708H21.4 inhibits cell migration and invasion, causes cell apoptosis, and enhances 5-FU sensitivity of CRC cells. Finally, increased RP11-708H21.4 expression blocked AKT/mTOR pathway, and repressed in vivo CRC xenograft tumor growth. The results indicated that RP11-708H21.4 might have potential roles as a biomarker and a therapeutic target for CRC.

Nudix-type motif 2 contributes to cancer proliferation through the regulation of Rag GTPase-mediated mammalian target of rapamycin complex 1 localization

Lysosomal localization of mammalian target of rapamycin complex 1 (mTORC1) is a critical step for activation of the molecule. Rag GTPases are essential for this translocation. Here, we demonstrate that Nudix-type motif 2 (NUDT2) is a novel positive regulator of mTORC1 activation. Activation of mTORC1 is impaired in NUDT2-silenced cells. Mechanistically, NUDT2 binds to Rag GTPase and controls mTORC1 translocation to the lysosomal membrane. Furthermore, NUDT2-dependent mTORC1 regulation is critical for proliferation of breast cancer cells, as NUDT2-silenced cells arrest in G0/G1 phases. Taken together, these results show that NUDT2 is a novel complex formation enhancing factor regulating mTORC1-Rag GTPase signaling that is crucial for cell growth control.

Function of Translationally Controlled Tumor Protein in Organ Growth: Lessons from Drosophila Studies

Regulation of cell growth and proliferation is crucial for development and function of organs in all animals. Genetic defects in growth control can lead to developmental disorders and cancers. Translationally controlled tumor protein (TCTP) is a family of evolutionarily conserved proteins implicated in cancer. Recent studies have revealed multiple roles of TCTP in diverse cellular events, but TCTP functions in vivo are poorly understood in vertebrate systems. We have used Drosophila melanogaster, the fruit fly, as a model organism for genetic dissection of Tctp function. Our studies have shown that Tctp is essential for organ development by regulating growth signaling. Furthermore, it is required for genome stability by promoting DNA repair and chromatin remodeling in the nucleus. Thus, Tctp acts as a multifaceted cytosolic and nuclear factor for regulating organ growth and genome stability. In this chapter, we describe an overview of our findings on Tctp functions in Drosophila and discuss their implications in cancer.

Everolimus in the management of metastatic neuroendocrine tumours

Neuroendocrine tumours are increasing in incidence and cause a variety of symptoms. The mammalian target of rapamycin (mTOR) pathway plays a key role in neuroendocrine tumour (NET) pathogenesis, leading to increased lipid synthesis, protein synthesis and cellular growth. Upregulation of this pathway is noted in both hereditary and sporadic NETs. This understanding has led to investigations of mTOR inhibitors as therapy for metastatic NETs. After promising preclinical findings, everolimus, an mTOR inhibitor, was trialled in the RADIANT-1-4 studies on patients with advanced, well differentiated NETs. RADIANT-3 and RADIANT-4 established the efficacy of everolimus in improving progression-free survival (PFS) for metastatic NET of pancreatic, lung and gastrointestinal origin, leading to the US Food and Drug Administration (FDA) approval for its use in tumour control in those settings. Everolimus treatment is generally well tolerated; common adverse events include stomatitis, diarrhoea, rash and hyperglycaemia. Although discontinuation rates are low, many patients may require dose modification to successfully continue therapy. The combination of everolimus with somatostatin analogues (SSAs) (such as octreotide or pasireotide) or other targeted agents such as bevacizumab has not produced additional incremental benefit, and dual biologic therapy is not used widely. Ongoing trials are investigating everolimus compared with chemotherapy, optimal sequencing of therapy and combination of everolimus with radiotherapy. Future research should concentrate on identification of predictive biomarkers for benefit from mTOR therapy and include quality of life as a measure.

Upregulation of MiR-196a promotes cell proliferation by downregulating p27kip1 in laryngeal cancer

Background

Accumulating evidence has confirmed that miR-196a plays a critical role in tumorigenesis and tumor progression in a variety of cancers. It has been demonstrated that miR-196a is highly up-regulated in laryngeal cancer by miRNA profiling analysis. However, the functional mechanism of miR-196a in laryngeal cancer remains unclear. This study aims to explore the mechanism of miR-196a in laryngeal cancer.

Methods

In the present study, we conducted qPCR analysis of miR-196a expression in human laryngeal cancer and showed that miR-196a was overexpressed in tumor-derived samples and laryngeal cancer cell lines compared with matched normal controls. Further functional analysis of miR-196a demonstrated that the inhibition of miR-196a could inhibit laryngeal cell-cycle progression and proliferation in vitro. Luciferase reporter assay and western blot confirmed that miR-196a directly targeted p27kip1. Moreover, in order to investigate whether miR-196a regulated cell growth in laryngeal cancer cells by targeting p27kip1, rescue studies were performed in laryngeal cancer cells.

Results

Results showed that overexpression of p27kip1 rescue decreased cell proliferation caused by miR-196a inhibitors. A negative relation between miR-196a and p27kip1 expression in laryngeal cancer tissues were also noted by further analyses.

Conclusions

The present study showed that miR-196a was upregulated in laryngeal cancer and promoted cell proliferation by downregulating p27kip1 in laryngeal cancer. However, further studies are needed to verify this finding.

Growth inhibitory effect of rapamycin in Hodgkin-lymphoma cell lines characterized by constitutive NOTCH1 activation

Growing evidence suggests that deregulation of signalling elements of Notch and mammalian target of rapamycin (mTOR) pathways contribute to tumorigenesis. These signals play important roles in cellular functions and malignancies. Their tumorigenic role in T-cell acute lymphoblastic leukaemia (T-ALL) is well known; however, their potential interactions and functions are poorly characterized in Hodgkin lymphoma (HL). The aim of our study was to characterize mTOR and Notch signalling elements in HL cell lines (DEV, L1236, KMH2) and human biopsies and to investigate their cross-talk in the tumorous process. High mTOR activity and constitutive NOTCH1 activation was confirmed in HL cell lines, without any known oncogenic mutations in key elements, including those common to both pathways. The anti-tumour effect of Notch inhibitors are well known from several preclinical models but resistance and side effects occur in many cases. Here, we tested mTOR and Notch inhibitors and their combinations in gamma-secretase inhibitor (GSI) resistant HL cells in vitro and in vivo. mTOR inhibitor alone or in combination was able to reduce tumour growth; furthermore, it was more effective in xenograft models in vivo. Based on these results, we suggest that constitutively activated NOTCH1 may be a potential target in HL therapy; furthermore, mTOR inhibitors may be effective for decreasing tumour growth if resistance to Notch inhibitors develop.

Ciclopirox olamine inhibits mTORC1 signaling by activation of AMPK

Ciclopirox olamine (CPX), an off-patent antifungal agent, has recently been identified as a potential anticancer agent. The mammalian target of rapamycin (mTOR) is a central controller of cell growth, proliferation and survival. Little is known about whether and how CPX executes its anticancer action by inhibiting mTOR. Here we show that CPX inhibited the phosphorylation of p70 S6 kinase 1 (S6K1) and eukaryotic initiation factor 4E binding protein 1 (4E-BP1), two downstream effector molecules of mTOR complex 1 (mTORC1), in a spectrum of human tumor cells, indicating that CPX inhibits mTORC1 signaling. Using rhabdomyosarcoma cells as an experimental model, we found that expression of constitutively active mTOR (E2419K) conferred resistance to CPX inhibition of cell proliferation, suggesting that CPX inhibition of mTORC1 contributed to its anticancer effect. In line with this, treatment with CPX inhibited tumor growth and concurrently suppressed mTORC1 signaling in RD xenografts. Mechanistically, CPX inhibition of mTORC1 was neither via inhibition of IGF-I receptor or phosphoinositide 3-kinase (PI3K), nor by activation of phosphatase and tensin homolog (PTEN). Instead, CPX inhibition of mTORC1 was attributed to activation of AMP-activated protein kinase (AMPK)-tuberous sclerosis complexes (TSC)/raptor pathways. This is supported by the findings that CPX activated AMPK; inhibition of AMPK with Compound C or ectopic expression of dominant negative AMPKα partially prevented CPX from inhibiting mTORC1; silencing TSC2 attenuated CPX inhibition of mTORC1; and CPX also increased AMPK-mediated phosphorylation of raptor (S792). Therefore, the results indicate that CPX exerts the anticancer effect by activating AMPK, resulting in inhibition of mTORC1 signaling.

Effects of rapamycin on cell apoptosis in MCF-7 human breast cancer cells

BACKGROUND

Rapamycin is an effective anti-angiogenic drug. However, the mode of its action remains unclear. Therefore, in this study, we aimed to elucidate the antitumor mechanism of rapamycin, hypothetically via apoptotic promotion, using MCF-7 breast cancer cells.

MATERIALS AND METHODS

MCF-7 cells were plated at a density of 15105 cells/well in 6-well plates. After 24h, cells were treated with a series of concentrations of rapamycin while only adding DMEM medium with PEG for the control regiment and grown at 37oC, 5% CO2 and 95% air for 72h. Trypan blue was used to determine the cell viability and proliferation. Untreated and rapamycin-treated MCF-7 cells were also examined for morphological changes with an inverted-phase contrast microscope. Alteration in cell morphology was ascertained, along with a stage in the cell cycle and proliferation. In addition, cytotoxicity testing was performed using normal mouse breast mammary pads.

RESULTS

Our results clearly showed that rapamycin exhibited inhibitory activity on MCF-7 cell lines. The IC50 value of rapamycin on the MCF-7 cells was determined as 0.4μg/ml (p<0.05). Direct observation by inverted microscopy demonstrated that the MCF-7 cells treated with rapamycin showed characteristic features of apoptosis including cell shrinkage, vascularization and autophagy. Cells underwent early apoptosis up to 24% after 72h. Analysis of the cell cycle showed an increase in the G0G1 phase cell population and a corresponding decrease in the S and G2M phase populations, from 81.5% to 91.3% and 17.3% to 7.9%, respectively.

CONCLUSIONS

This study demonstrated that rapamycin may potentially act as an anti-cancer agent via the inhibition of growth with some morphological changes of the MCF-7 cancer cells, arrest cell cycle progression at G0/G1 phase and induction of apoptosis in late stage of apoptosis. Further studies are needed to further characterize the mode of action of rapamycin as an anti-cancer agent.

Insulin Protects Cardiac Myocytes from Doxorubicin Toxicity by Sp1-Mediated Transactivation of Survivin

Insulin inhibits ischemia/reperfusion-induced myocardial apoptosis through the PI3K/Akt/mTOR pathway. Survivin is a key regulator of anti-apoptosis against doxorubicin-induced cardiotoxicity. Insulin increases survivin expression in cardiac myocytes to mediate cytoprotection. However, the mechanism by which survivin mediates the protective effect of insulin against doxorubicin-associated injury remains to be determined. In this study, we demonstrated that pretreatment of H9c2 cardiac myocytes with insulin resulted in a significant decrease in doxorubicin-induced apoptotic cell death by reducing cytochrome c release and caspase-3 activation. Doxorubicin-induced reduction of survivin mRNA and protein levels was also significantly perturbed by insulin pretreatment. Reducing survivin expression with survivin siRNA abrogated insulin-mediated inhibition of caspase-3 activation, suggesting that insulin signals to survivin inhibited caspase-3 activation. Interestingly, pretreatment of H9c2 cells with insulin or MG132, a proteasome inhibitor, inhibited doxorubicin-induced degradation of the transcription factor Sp1. ChIP assay showed that pretreatment with insulin inhibited doxorubicin-stimulated Sp1 dissociation from the survivin promoter. Finally using pharmacological inhibitors of the PI3K pathway, we showed that insulin-mediated activation of the PI3K/Akt/mTORC1 pathway prevented doxorubicin-induced proteasome-mediated degradation of Sp1. Taken together, insulin pretreatment confers a protective effect against doxorubicin-induced cardiotoxicity by promoting Sp1-mediated transactivation of survivin to inhibit apoptosis. Our study is the first to define a role for survivin in cellular protection by insulin against doxorubicin-associated injury and show that Sp1 is a critical factor in the transcriptional regulation of survivin.

CCL8 and the Immune Control of Cytomegalovirus in Organ Transplant Recipients

Monitoring of cytomegalovirus cell-mediated immunity is a promising tool for the refinement of preventative and therapeutic strategies posttransplantation. Typically, the interferon-γ response to T cell stimulation is measured. We evaluated a broad range of cytokine and chemokines to better characterize the ex vivo host-response to CMV peptide stimulation. In a cohort of CMV viremic organ transplant recipients, chemokine expression-specifically CCL8 (AUC 0.849 95% CI 0.721-0.978; p = 0.003) and CXCL10 (AUC 0.841, 95% CI 0.707-0.974; p = 0.004)-was associated with control of viral replication. In a second cohort of transplant recipients at high-risk for CMV, the presence of a polymorphism in the CCL8 promoter conferred an increased risk of viral replication after discontinuation of antiviral prophylaxis (logrank hazard ratio 3.6; 95% CI 2.077-51.88). Using cell-sorting experiments, we determined that the primary cell type producing CCL8 in response to CMV peptide stimulation was the monocyte fraction. Finally, in vitro experiments using standard immunosuppressive agents demonstrated a dose-dependent reduction in CCL8 production. Chemokines appear to be important elements of the cell-mediated response to CMV infection posttransplant, as here suggested for CCL8, and translation of this knowledge may allow for the tailoring and improvement of preventative strategies.

Translational Upregulation of an Individual p21Cip1 Transcript Variant by GCN2 Regulates Cell Proliferation and Survival under Nutrient Stress

Multiple transcripts encode for the cell cycle inhibitor p21^Cip1. These transcripts produce identical proteins but differ in their 5’ untranslated regions (UTRs). Although several stresses that induce p21 have been characterized, the mechanisms regulating the individual transcript variants and their functional significance are unknown. Here we demonstrate through ³⁵S labeling, luciferase reporter assays, and polysome transcript profiling that activation of the Integrated Stress Response (ISR) kinase GCN2 selectively upregulates the translation of a p21 transcript variant containing 5’ upstream open reading frames (uORFs) through phosphorylation of the eukaryotic translation initiation factor eIF2α. Mutational analysis reveals that the uORFs suppress translation under basal conditions, but promote translation under stress. Functionally, ablation of p21 ameliorates G₁/S arrest and reduces cell survival in response to GCN2 activation. These findings uncover a novel mechanism of p21 post-transcriptional regulation, offer functional significance for the existence of multiple p21 transcripts, and support a key role for GCN2 in regulating the cell cycle under stress.

Cells sense nutrient levels in their environment in order to determine if conditions are favorable to divide. GCN2 is a protein that senses amino acids and responds to amino acid deficiency by suppressing protein synthesis and increasing the expression of genes involved in recovery from nutrient stress. Although GCN2’s role in amino acid sensing is well-characterized, it is not known how it links nutrient availability with the cell cycle. Here, we show that GCN2 induces the cell cycle inhibitor p21^Cip1 at the level of protein translation. The induction of p21 is limited to a specific messenger RNA variant that contains upstream open reading frames, and these upstream open reading frames are required for its enhanced translation under stress. Previously, the functional significance of these different p21 variants was unknown. Upregulation of p21 allows cells to halt division and survive under conditions of nutrient stress. Collectively, this work demonstrates a new mechanism of p21 regulation and the connection between GCN2 and the cell cycle.

FKBP51 employs both scaffold and isomerase functions to promote NF-κB activation in melanoma

Melanoma is the most aggressive skin cancer; its prognosis, particularly in advanced stages, is disappointing largely due to the resistance to conventional anticancer treatments and high metastatic potential. NF-κB constitutive activation is a major factor for the apoptosis resistance of melanoma. Several studies suggest a role for the immunophilin FKBP51 in NF-κB activation, but the underlying mechanism is still unknown. In the present study, we demonstrate that FKBP51 physically interacts with IKK subunits, and facilitates IKK complex assembly. FKBP51-knockdown inhibits the binding of IKKγ to the IKK catalytic subunits, IKK-α and -β, and attenuates the IKK catalytic activity. Using FK506, an inhibitor of the FKBP51 isomerase activity, we found that the IKK-regulatory role of FKBP51 involves both its scaffold function and its isomerase activity. Moreover, FKBP51 also interacts with TRAF2, an upstream mediator of IKK activation. Interestingly, both FKBP51 TPR and PPIase domains are required for its interaction with TRAF2 and IKKγ, whereas only the TPR domain is involved in interactions with IKKα and β. Collectively, these results suggest that FKBP51 promotes NF-κB activation by serving as an IKK scaffold as well as an isomerase. Our findings have profound implications for designing novel melanoma therapies based on modulation of FKBP51.

Daintain/AIF-1 accelerates the activation of insulin-like growth factor-1 receptor signaling pathway in HepG2 cells

Daintain/allograft inflammatory factor-1 (AIF-1), as a novel inflammatory factor, has been reported to accelerate the proliferation and migration of breast cancer cells. However, the effect of daintain/AIF-1 on hepatocarcinogenesis remains unclear. In order to explore the effect of daintain/AIF-1 on the progression of hepatocellular carcinoma (HCC), enzyme-linked immunosorbent assay (ELISA) and reverse transcription polymerase chain reaction (RT-PCR) were performed to examine the secretion and gene expression of (IGF)-1, IGF-2 and IGFBP-3. The expression of IGF-1R and its downstream targets was evaluated by western blotting. In addition, the proliferation and cell-cycle progression of HepG2 cells was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenylterazolium bromide (MTT) and flow cytometric analysis. The results showed that HepG2 cells subjected to daintain/AIF-1 treatment revealed an obvious increase in the secretion of IGF-1 and IGF-2, and a reduction in the secretion of IGFBP-3. Moreover, daintain/AIF-1 accelerated the activation of IGF-1-induced IGF-1R and its downstream AKT signaling pathway, and subsequently promoted the activation of cyclin D1 pathway, thus accelerating the progression of the cell cycle and eventually promoting the proliferation of HepG2 cells. In conclusion, daintain/AIF-1 promoted the proliferation of HepG2 cells by accelerating the activation of IGF-1R and its downstream signaling pathway, which confirms that daintain/AIF-1 plays a crucial role in the development of HCC.

Acemannan accelerates cell proliferation and skin wound healing through AKT/mTOR signaling pathway

BACKGROUND

Acemannan is a bioactive polysaccharides promoting tissue repair. However, the roles of acemannan in skin wound healing and the underlying molecular mechanisms are largely unclear.

OBJECTIVE

The goal of this study is to investigate the positive role of acemannan in cutaneous wound healing and its mechanism.

METHODS

Mouse skin wound model and skin primary fibroblasts were used to demonstrate the positive effect of acemannan on cutaneous wound healing. The expressions of cell proliferation nuclear antigen ki-67, cyclin D1 and activity of AKT/mTOR signaling were analyzed in acemannan-treated fibroblasts and mice. Rapamycin and AKT inhibitor VIII were used to determine the key role of AKT/mTOR signaling in acemannan-promoting cutaneous wound healing.

RESULTS

We found that acemannan significantly accelerated skin wound closure and cell proliferation. Acemannan promoted the expression of cyclin D1 in cultured fibroblasts, which was mediated by AKT/mTOR signal pathway leading to enhanced activity of the eukaryotic translation initiation factor-4F (eIF4F) and increased translation of cyclin D1. In contrast, pharmaceutical blockade of AKT/mTOR signaling by mTOR inhibitor rapamycin or AKT inhibitor VIII abolished acemannan-induced cyclin D1 translation and cell proliferation. In vivo studies confirmed that the activation of AKT/mTOR by acemannan played a key role in wound healing, which could be reversed by rapamycin.

CONCLUSION

Acemannan promoted skin wound healing partly through activating AKT/mTOR-mediated protein translation mechanism, which may represent an alternative therapy approach for cutaneous wound.

Biological activities of fusarochromanone: a potent anti-cancer agent

Background

Fusarochromanone (FC101) is a small molecule fungal metabolite with a host of interesting biological functions, including very potent anti-angiogenic and direct anti-cancer activity.

Results

Herein, we report that FC101 exhibits very potent in-vitro growth inhibitory effects (IC₅₀ ranging from 10nM-2.5 μM) against HaCat (pre-malignant skin), P9-WT (malignant skin), MCF-7 (low malignant breast), MDA-231 (malignant breast), SV-HUC (premalignant bladder), UM-UC14 (malignant bladder), and PC3 (malignant prostate) in a time-course and dose-dependent manner, with the UM-UC14 cells being the most sensitive. FC101 induces apoptosis and an increase in proportion of cells in the sub-G1 phase in both HaCat and P9-WT cell lines as evidenced by cell cycle profile analysis. In a mouse xenograft SCC tumor model, FC101 was well tolerated, non-toxic, and achieved a 30% reduction in tumor size at a dose of 8 mg/kg/day. FC101 is also a potent anti-angiogenenic agent. At nanomolar doses, FC101 inhibits the vascular endothelial growth factor-A (VEGF-A)-mediated proliferation of endothelial cells.

Conclusions

Our data presented here indicates that FC101 is an excellent lead candidate for a small molecule anti-cancer agent that simultaneously affects angiogenesis signaling, cancer signal transduction, and apoptosis. Further understanding of the underlying FC101’s molecular mechanism may lead to the design of novel targeted and selective therapeutics, both of which are pursued targets in cancer drug discovery.

Interferon-α enhances the susceptibility of renal cell carcinoma to rapamycin by suppressing mTOR activity

The aim of the present study was to investigate the antiproliferative effects of interferon (IFN)-α and rapamycin (RPM) on renal cell carcinoma (RCC) cells and examine the synergistic growth suppression conferred by IFN-α and RPM. The effects of IFN-α and/or RPM on RCC cells were determined using a WST-1 assay and the synergy of IFN-α and RPM against three RCC cell lines was analyzed with isobolographic analysis. The expression of mammalian target of rapamycin (mTOR) was downregulated by RNAi, and the expression and phosphorylation of proteins in the mTOR pathway following treatment with IFN-α and/or RPM was examined by western blot analysis. The observations indicated that IFN-α significantly increased the susceptibility of RCC cells to RPM and the synergistic effect of IFN-α and RPM against RCC cells was confirmed in all three RCC cell lines. The mTOR pathway was shown to be associated with the synergistic effect of IFN-α and RPM against RCC. IFN-α and RPM alone decreased the phosphorylation of mTOR, p70 S6 kinase, S6 and 4E binding protein 1, and IFN-α significantly enhanced the RPM-induced suppression of the mTOR pathway. However, in RCC cells with low mTOR activity, the synergy of IFN-α and RPM was eliminated. Therefore, the results of the present study indicate that the mTOR pathway plays an important role in the synergistic effect of IFN-α and RPM against RCC cells. Thus, mTOR may serve as an effective therapeutic target in the treatment of advanced RCC.

Idiopathic pulmonary fibrosis is strongly associated with productive infection by herpesvirus saimiri

Idiopathic pulmonary fibrosis is a fatal disease without effective therapy or diagnostic test. To investigate a potential role for γ-herpesviruses in this disease, 21 paraffin-embedded lung biopsies from patients diagnosed with idiopathic pulmonary fibrosis and 21 lung biopsies from age-matched controls with pulmonary fibrosis of known etiology were examined for a series of γ-herpesviruses' DNA/RNA and related proteins using in situ hybridization and reverse transcriptase-polymerase chain reaction (RT-PCR)-based methods. We detected four proteins known to be in the genome of several γ-herpesviruses (cyclin D, thymidylate synthase, dihydrofolate reductase, and interleukin-17) that were strongly co-expressed in the regenerating epithelial cells of each of the 21 idiopathic pulmonary fibrosis cases and not in the benign epithelia of the controls. Among the γ-herpesviruses, only herpesvirus saimiri expresses all four of these 'pirated' mammalian proteins. We found herpesvirus saimiri DNA in the regenerating epithelial cells of 21/21 idiopathic pulmonary fibrosis cases using four separate probe sets but not in the 21 controls. RT-PCR showed that the source of the cyclin D RNA in active idiopathic pulmonary fibrosis was herpesvirus saimiri and not human. We cloned and sequenced part of genome corresponding to the DNA polymerase herpesvirus saimiri gene from an idiopathic pulmonary fibrosis sample and it matched 100% with the published viral sequence. These data are consistent with idiopathic pulmonary fibrosis representing herpesvirus saimiri-induced pulmonary fibrosis. Thus, treatment directed against viral proliferation and/or viral-associated proteins may halt disease progression. Further, demonstration of the viral nucleic acids or proteins may help diagnose the disease.

The antimalarial drug artesunate inhibits primary human cultured airway smooth muscle cell proliferation

Airway smooth muscle (ASM) cell hyperplasia contributes to airway wall remodeling (AWR) in asthma. Glucocorticoids, which are used as first-line therapy for the treatment of inflammation in asthma, have limited impact on AWR, and protracted usage of high doses of glucocorticoids is associated with an increased risk of side effects. Moreover, patients with severe asthma often show reduced sensitivity to glucocorticoids. Artesunate, a semisynthetic artemisinin derivative used to treat malaria with minimal toxicity, attenuates allergic airway inflammation in mice, but its impact on AWR is not known. We examined the effects of artesunate on ASM proliferation in vitro and in vivo. Primary human ASM cells derived from nonasthmatic donors were treated with artesunate before mitogen stimulation. Artesunate reduced mitogen-stimulated increases in cell number and cyclin D1 protein abundance but had no significant effect on ERK1/2 phosphorylation. Artesunate, but not dexamethasone, inhibited phospho-Akt and phospho-p70(S6K) protein abundance. Artesunate, but not dexamethasone, inhibited mitogen-stimulated increases in cell number, cyclin D1, and phospho-Akt protein abundance on ASM cells derived from asthmatic donors. In a murine model of allergic asthma, artesunate reduced the area of α-smooth muscle actin-positive cells and decreased cyclin D1 protein abundance. Our study provides a basis for the future development of artesunate as a novel anti-AWR agent that targets ASM hyperplasia via the PI3K/Akt/p70(S6K) pathway and suggests that artesunate may be used as combination therapy with glucocorticoids.

Molecular evidence of cryptotanshinone for treatment and prevention of human cancer

Cryptotanshinone is one of the major tanshinones isolated from the roots of the plant Salvia miltiorrhiza Bunge (Danshen). Danshen has been widely used in traditional Chinese medicine for treatment of a variety of diseases, including coronary artery disease, acute ischemic stroke, hyperlipidemia, chronic renal failure, chronic hepatitis, and Alzheimer's disease, showing no serious adverse effects. Recent studies have shown that cryptotanshinone not only possesses the potential for treatment and prevention of the above-mentioned diseases, but also is a potent anticancer agent. Here we briefly summarize the physical and chemical properties and the pharmacokinetic profiles of cryptotanshinone, and then comprehensively review its anticancer activities as well as the underlying mechanisms.

Dihydroartemisinin inhibits the mammalian target of rapamycin-mediated signaling pathways in tumor cells

Dihydroartemisinin (DHA), an antimalarial drug, has previously unrecognized anticancer activity, and is in clinical trials as a new anticancer agent for skin, lung, colon and breast cancer treatment. However, the anticancer mechanism is not well understood. Here, we show that DHA inhibited proliferation and induced apoptosis in rhabdomyosarcoma (Rh30 and RD) cells, and concurrently inhibited the signaling pathways mediated by the mammalian target of rapamycin (mTOR), a central controller for cell proliferation and survival, at concentrations (<3 μM) that are pharmacologically achievable. Of interest, in contrast to the effects of conventional mTOR inhibitors (rapalogs), DHA potently inhibited mTORC1-mediated phosphorylation of p70 S6 kinase 1 and eukaryotic initiation factor 4E binding protein 1 but did not obviously affect mTORC2-mediated phosphorylation of Akt. The results suggest that DHA may represent a novel class of mTORC1 inhibitor and may execute its anticancer activity primarily by blocking mTORC1-mediated signaling pathways in the tumor cells.

Sex determining region Y-box 2 inhibits the proliferation of colorectal adenocarcinoma cells through the mTOR signaling pathway

Sex determining region Y-box 2 (SOX2), is a high mobility group box transcription factor involved in the maintenance of pluripotency and the self-renewal of embryonic and neuronal stem cells, which also plays differential roles in the cell proliferation of several tumors. However, its role in colorectal adenocarcinoma cell proliferation and the underlying mechanisms remain unclear. The mammalian target of rapamycin (mTOR) signaling pathway has recently emerged as an important regulator of cell proliferation in many types of cancer. In this study, we examined the effect of SOX2 on the proliferation of colorectal adenocarcinoma cells and evaluated the role of the mTOR pathway in this process. Our results indicated that the overexpression of SOX2 significantly inhibited the proliferation of colorectal adenocarcinoma cells. Of note, mechanistic investigations revealed that SOX2 inhibited the activation of the mTOR pathway in HT-29 cells. We then examined the effect of SOX2 on the cell cycle, and the results revealed that SOX2 downregulated cyclin D1 expression and induced G0/G1 arrest in the HT-29 cells. Moreover, we also analyzed the correlation between SOX2 expression and patient clinicopathological characteristics in colorectal adenocarcinoma tissues, as well as the level of phospho-S6 (S235/236), phospho-Akt (S473) and cyclin D1. The results revealed a significant negative correlation between SOX2 expression and tumor size and the levels of phospho-S6 (S235/236), phospho-Akt (S473) and cyclin D1. Taken together, to our knowledge, our findings suggest for the first time that SOX2 suppresses colorectal adenocarcinoma cell proliferation through the inhibition of the mTOR pathway.

Folliculin regulates cyclin D1 expression through cis-acting elements in the 3' untranslated region of cyclin D1 mRNA

Birt-Hogg-Dubé syndrome (BHDS) is an autosomal dominantly inherited disease characterized by spontaneous pneumothorax, hair folliculomas and renal tumors. The responsible gene, BHD, is a tumor suppressor and encodes folliculin. Folliculin is an evolutionarily conserved protein (~67 kDa) with no apparent functional motif and its role has not yet been fully elucidated. In this study, we found that knockdown of BHD increased the levels of cyclin D1 in HeLa cells. A reporter assay with the cyclin D1 gene (CCND1) promoter region indicated that this increase was not caused by activation of transcription through known cis-acting elements. We examined the possibility of post-transcriptional mechanism using reporter constructs containing fragments of the cyclin D1 3' untranslated region (3'UTR). Transfection of control cells with a construct carrying a medial 1.3 kb 3'UTR fragment resulted in a significant reduction in luciferase activity. This effect was largely prevented by knockdown of BHD. Our results suggest that the post-transcriptional regulation of the CCND1 expression by BHD may be associated with microRNA(s) or RNA binding protein(s) that bind to the 3'UTR.

Small‑molecule COH-SR4 inhibits adipocyte differentiation via AMPK activation

Obesity is a chronic metabolic disorder caused by an imbalance between energy intake and expenditure. It is one of the principal causative factors involved in the development of metabolic syndrome and cancer. Inhibition of adipocyte differentiation has often been a target of anti-obesity strategies since obesity is caused not only by hypertrophy but also by adipocyte hyperplasia. In this study, we investigated the effects of COH-SR4, a novel compound with anticancer properties, on the adipogenesis in 3T3-L1 cells. Treatment with COH-SR4 significantly inhibited adipocyte differentiation in a dose-dependent manner. This inhibitory effect mainly occurred at the early phase of differentiation through inhibition of mitotic clonal expansion and cell cycle arrest at the G1/S phase transition. In differentiating adipocytes, COH-SR4 significantly reduced intracellular lipid accumulation and downregulated the expression of key adipogenesis-related transcription factors and lipogenic proteins. COH-SR4 exhibited no cytotoxic effects in 3T3-L1 cells, but indirectly activated AMP-activated protein kinase (AMPK). AMPK activation by COH-SR4 also resulted in the phosphorylation of raptor and tuberous sclerosis protein 2 (TSC2), two proteins involved in the mammalian target of rapamycin (mTOR) signaling pathways. Additionally, COH-SR4 decreased the phosphorylation of p70 kDa ribosomal protein S6 kinase (S6K) and initiation factor 4E (eIF4E) binding protein 1 (4EB‑P1), two downstream effectors of mTOR that regulate protein synthesis. Interestingly, knockdown of AMPKα1/α2 prevented the ability of COH-SR4 to inhibit cell cycle arrest and overall adipogenesis and lipid accumulation in the differentiating 3T3-L1 cells. Taken together, these results suggest that COH-SR4 inhibits 3T3-L1 adipogenesis via AMPK activation. COH-SR4 may be a promising compound for the treatment of obesity and related metabolic disorders.

Inactivation of the enzyme GSK3α by the kinase IKKi promotes AKT-mTOR signaling pathway that mediates interleukin-1-induced Th17 cell maintenance

Interleukin-1 (IL-1)-induced activation of the mTOR kinase pathway has major influences on Th17 cell survival, proliferation, and effector function. Via biochemical and genetic approaches, the kinases IKKi and GSK3α were identified as the critical intermediate signaling components for IL-1-induced AKT activation, which in turn activated mTOR. Although insulin-induced AKT activation is known to phosphorylate and inactivate GSK3α and GSK3β, we found that GSK3α but not GSK3β formed a constitutive complex to phosphorylate and suppress AKT activation, showing that a reverse action from GSK to AKT can take place. Upon IL-1 stimulation, IKKi was activated to mediate GSK3α phosphorylation at S21, thereby inactivating GSK3α to promote IL-1-induced AKT-mTOR activation. Thus, IKKi has a critical role in Th17 cell maintenance and/or proliferation through the GSK-AKT-mTOR pathway, implicating the potential of IKKi as a therapeutic target.