MEK/ERK signaling drives the transdifferentiation of supporting cells into functional hair cells by modulating the Notch pathway

Loss of cochlear hair cells (HCs) leads to permanent hearing loss in mammals, and regenerative medicine is regarded as an ideal strategy for hearing recovery. Limited genetic and pharmaceutical approaches for HC regeneration have been established, and the existing strategies cannot achieve recovery of auditory function. A promising target to promote HC regeneration is MEK/ERK signaling because dynamic shifts in its activity during the critical stages of inner ear development have been observed. Here, we first showed that MEK/ERK signaling is activated specifically in supporting cells (SCs) after aminoglycoside-induced HC injury. We then selected 4 MEK/ERK signaling inhibitors, and PD0325901 (PD03) was found to induce the transdifferentiation of functional supernumerary HCs from SCs in the neonatal mammalian cochlear epithelium. We next found that PD03 facilitated the generation of HCs in inner ear organoids. Through genome-wide high-throughput RNA sequencing and verification, we found that the Notch pathway is the downstream target of MEK/ERK signaling. Importantly, delivery of PD03 into the inner ear induced mild HC regeneration in vivo. Our study thus reveals the importance of MEK/ERK signaling in cell fate determination and suggests that PD03 might serve as a new approach for HC regeneration.

Anti-inflammation of LZTFL1 knockdown in OVA-induced asthmatic mice: Through ERK/GATA3 signaling pathway

Asthma is a common chronic respiratory disease characterized by Th2-type inflammation in the airways. Leucine zip transcription factor-like 1 (LZTFL1) has been implicated in the regulation of Th2-related factors. The knockdown of LZTFL1 resulted in decreased levels of IL-4, IL-5, and IL-13. We hypothesize that LZTFL1 may have an effect on asthma. We established an acute asthmatic mouse model using the Ovalbumin (OVA) sensitization, and we found that LZTFL1 expression was upregulated in OVA-induced CD4 + T cells. Mice challenged with OVA were administered 5 × 107 TU of lentivirus via tail vein injection. LZTFL1 knockdown reversed the frequency of sneezing and nose rubbing in OVA mice. LZTFL1 knockdown reduced inflammatory cell infiltration, reduced goblet cell numbers, and mitigated collagen deposition in lung tissue. LZTFL1 knockdown decreased the levels of OVA-specific IgE, IL-4, IL-5, and IL-13 in alveolar lavage fluid of asthmatic mice. Furthermore, LZTFL1 knockdown inhibited the aberrant activation of MEK/ERK signaling pathway in asthmatic mice. GATA binding protein 3 (GATA3) is an essential transcription factor in Th2 differentiation. Flow cytometry results revealed that LZTFL1 knockdown reduced the number of GATA3 + CD4 + Th2 cells, while it did not affect the stability of GATA3 mRNA. This may be attributed to ERK signaling which stabilized GATA3 by preventing its ubiquitination and subsequent degradation. In conclusion, LZTFL1 knockdown attenuates inflammation and pathological changes in OVA-induced asthmatic mice through ERK/GATA3 signaling pathway.

CircPCNXL2 promotes tumor growth and metastasis by interacting with STRAP to regulate ERK signaling in intrahepatic cholangiocarcinoma

BACKGROUND

circular RNAs (circRNAs) have been reported to exert important effects in the progression of numerous cancers. However, the functions of circRNAs in intrahepatic cholangiocarcinoma (ICC) are still unclear.

METHODS

circPCNXL2 (has_circ_0016956) were identified in paired ICC by circRNA microarray. Then, we assessed the biological functions of circPCNXL2 by CCK8, EdU, clone formation, transwell, wound healing assays, and xenograft models. RNA pull-down, mass spectrometry, and RNA immunoprecipitation (RIP) were applied to explore the interaction between cirrcPCNXL2 and serine-threonine kinase receptor-associated protein (STRAP). RNA pull-down, RIP and luciferase reporter assays were used to investigate the sponge functions of circPCNXL2. In the end, we explore the effects of circPCNXL2 and trametinib (a MEK1/2 inhibitor) in vivo.

RESULTS

circPCNXL2 was upregulated in ICC tissues and cell lines, which promoted the proliferation and metastasis of ICC in vitro and in vivo. In terms of the mechanisms, circPCNXL2 could directly bind to STRAP and induce the interaction between STRAP and MEK1/2, resulting in the tumor promotion in ICC by activation of ERK/MAPK pathways. Besides, circPCNXL2 could regulate the expression of SRSF1 by sponging miR-766-3p and subsequently facilitated the growth of ICC. Finally, circPCNXL2 could partially inhibit the anti-tumor activity of trametinib in vivo.

CONCLUSION

circPCNXL2 played a crucial role in the progression of ICC by interacting with STRAP to activate the ERK signaling pathway, as well as by modulating the miR-766-3p/SRSF1 axis. These findings suggest that circPCNXL2 may be a promising biomarker and therapeutic target for ICC.

A Positive Feedback Loop of lncRNA HOXD-AS2 and SMYD3 Facilitates Hepatocellular Carcinoma Progression via the MEK/ERK Pathway

Purpose

HOX cluster-embedded long noncoding RNAs (HOX-lncRNAs) have been shown to be tightly related to hepatocellular carcinoma (HCC). However, the potential biological roles and underlying molecular mechanism of HOX-lncRNAs in HCC largely remains to be elucidated.

Methods

The expression signature of eighteen HOX-lncRNAs in HCC cell lines were measured by qRT-PCR. HOXD-AS2 expression and its clinical significance in HCC was investigated by bioinformatics analysis utilizing the TCGA data. Subcellular localization of HOXD-AS2 in HCC cells was observed by RNA-FISH. Loss‑of‑function experiments in vitro and in vivo were conducted to probe the roles of HOXD-AS2 in HCC. Potential HOXD-AS2-controlled genes and signaling pathways were revealed by RNA-seq. Rescue experiments were performed to validate that SMYD3 mediates HOXD-AS2 promoting HCC progression. The positive feedback loop of HOXD-AS2 and SMYD3 was identified by luciferase reporter assay and ChIP-qPCR.

Results

HOXD-AS2 was dramatically elevated in HCC, and its up-regulation exhibited a positive association with aggressive clinical features (T stage, pathologic stage, histologic grade, AFP level, and vascular invasion) and unfavorable prognosis of HCC patients. HOXD-AS2 was distributed both in the nucleus and the cytoplasm of HCC cells. Knockdown of HOXD-AS2 restrained the proliferation, migration, invasion of HCC cells in vitro, as well as tumor growth in subcutaneous mouse model. Transcriptome analysis demonstrated that SMYD3 expression and activity of MEK/ERK pathway were impaired by silencing HOXD-AS2 in HCC cells. Rescue experiments revealed that SMYD3 as downstream target mediated oncogenic functions of HOXD-AS2 in HCC cells through altering the expression of cyclin B1, cyclin E1, MMP2 as well as the activity of MEK/ERK pathway. Additionally, HOXD-AS2 was uncovered to be positively regulated at transcriptional level by its downstream gene of SMYD3.

Conclusion

HOXD-AS2, a novel oncogenic HOX-lncRNA, facilitates HCC progression by forming a positive feedback loop with SMYD3 and activating the MEK/ERK pathway.

Hypoxia-Inducible Factor-2alpha Affects the MEK/ERK Signaling Pathway via Primary Cilia in Connection with the Intraflagellar Transport Protein 88 Homolog

The ability of cells to communicate with their surrounding is a prerequisite for essential processes such as proliferation, apoptosis, migration, and differentiation. To this purpose, primary cilia serve as antennae-like structures on the surface of most mammalian cell types. Cilia allow signaling via hedgehog, Wnt or TGF-beta pathways. Their length, in part controlled by the activity of intraflagellar transport (IFT), is a parameter for adequate function of primary cilia. Here we show, in murine neuronal cells, that intraflagellar transport protein 88 homolog (IFT88) directly interacts with the hypoxia-inducible factor-2α (HIF-2α), hitherto known as an oxygen-regulated transcription factor. Furthermore, HIF-2α accumulates in the ciliary axoneme and promotes ciliary elongation under hypoxia. Loss of HIF-2α affected ciliary signaling in neuronal cells by decreasing transcription of Mek1/2 and Erk1/2. Targets of the MEK/ERK signaling pathway, such as Fos and Jun, were significantly decreased. Our results suggest that HIF-2α influences ciliary signaling by interacting with IFT88 under hypoxic conditions. This implies an unexpected and far more extensive function of HIF-2α than described before.

N-Caffeoyltryptophan enhances adipogenic differentiation in preadipocytes and improves glucose tolerance in mice

Coffee consumption has been shown to reduce the risk of developing type 2 diabetes mellitus (T2DM) in humans; however, the exact mechanism is not completely understood. Here, we demonstrate that N-caffeoyltryptophan (CTP), an ingredient of coffee, enhances adipogenic differentiation and promotes glucose uptake into adipocytes. CTP increased lipid accumulation and adipogenic markers (PPARγ, C/EBPα, and FABP4) expression in mouse 3T3-L1 preadipocyte cell lines and primary preadipocytes. In addition, CTP promoted glucose uptake in 3T3-L1 cells. In the oral glucose tolerance test, daily administration of CTP (30 mg/kg/day, i.p.) for a week reduced blood glucose levels in mice. In 3T3-L1 cells, adipogenic differentiation and increased adipogenic markers expression induced by CTP were inhibited by U0126, a selective MEK1/2 inhibitor. Furthermore, mRNA induction of Pparg by CTP was abrogated in SIRT1 siRNA-transfected 3T3-L1 cells. These results suggest the involvement of the MEK/ERK signaling and SIRT1 in the mechanism of adipogenic function of CTP. Taken together, CTP might contribute to the reduction in postprandial glycemia and a subsequent reduction in onset risk for T2DM.

Propofol suppresses cell viability, cell cycle progression and motility and induces cell apoptosis of ovarian cancer cells through suppressing MEK/ERK signaling via targeting circVPS13C/miR-145 axis

Background

Propofol is a kind of common intravenous anaesthetic agent that plays an anti-tumor role in a variety of cancers, including ovarian cancer. However, the working mechanism of Propofol in ovarian cancer needs further exploration.

Methods

The viability and metastasis of ovarian cancer cells were assessed by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and transwell assays. Flow cytometry was used to evaluate the cell cycle and apoptosis. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to examine the abundance of circular RNA vacuolar protein sorting 13 homolog C (circVPS13C) and microRNA-145 (miR-145). The target relationship between miR-145 and circVPS13C was predicted by circinteractome database and verified by dual-luciferase reporter assay, RNA-binding protein immunoprecipitation (RIP) assay and RNA-pull down assay. Western blot assay was used to detect the levels of phosphorylated extracellular regulated MAP kinase (p-ERK), ERK, p-MAP kinse-ERK kinase (p-MEK) and MEK, in ovarian cancer cells.

Results

Propofol treatment suppressed the viability, cell cycle and motility and elevated the apoptosis rate of ovarian cancer cells. Propofol up-regulated miR-145 in a dose-dependent manner. Propofol exerted an anti-tumor role partly through up-regulating miR-145. MiR-145 was a direct target of circVPS13C. Propofol suppressed the progression of ovarian cancer through up-regulating miR-145 via suppressing circVPS13C. Propofol functioned through circVPS13C/miR-145/MEK/ERK signaling in ovarian cancer cells.

Conclusion

Propofol suppressed the proliferation, cell cycle, migration and invasion and induced the apoptosis of ovarian cancer cells through circVPS13C/miR-145/MEK/ERK signaling in vitro.

The Altered Metabolic Molecular Signatures Contribute to the RAD001 Resistance in Gastric Neuroendocrine Tumor

Although the inhibition of mTOR is a promising treatment for neuroendocrine tumors, several questions are still open for cell specificity and resistance. With the newly characterized gastric neuroendocrine tumor mouse model (CEA424-SV40 T antigen transgenic mice), the anti-tumor efficiency of RAD001 (Everolimus) was tested both in vitro and in vivo. Tumor samples were analyzed for the expression of RNA by cDNA microarrays and also signaling pathways to get more details on the local surviving or selected cells. RAD001 treatment dramatically slowed down tumor growth and prolonged the animals' survival. This inhibitory effect has a preference for tumor cells since gastrointestinal hormone and neuroendocrine tumor specific markers were more reduced than the epithelial ones. While phosphorylation of p70S6K was almost completely blocked both in vitro and in vivo, the phosphorylation of 4EBP1 was only partially inhibited in vitro and unaffected in vivo. RAD001 treatment induced feedback activation of metabolism related pathways like PI(3)K–Akt–mTOR and MEK/ERK signalings. An induction of senescence as well as differential expression of genes responsible for metabolism was also observed, which highlighted the contribution of metabolic molecular signatures to the escape of the tumor cells from the treatment. Together, our data revealed efficient anti-tumor ability of RAD001 in a new gastric neuroendocrine tumor mouse model system and offered new insights into the clinical aspects of the incomplete elimination of tumor cells in patients treated.

Effect of bFGF on the growth and matrix turnover of stem cells from human apical papilla: Role of MEK/ERK signaling

BACKGROUND/PURPOSE

Basic fibroblast growth factor (bFGF) exhibits multiple biological functions in various tissues. Stem cells from apical papilla (SCAP) can be isolated from human apical papilla tissues in developmental teeth of children. The purposes of this study were to investigate the expression of FGF receptors (FGFRs) and the effects of bFGF on SCAP and related MEK/ERK signaling.

METHODS

SCAP cells were treated under different concentrations of bFGF with or without U0126 (an inhibitor of MEK/ERK). Expression of FGFR1 and FGFR2 in SCAP was analyzed by RT-PCR. Cell proliferation was measured by MTT assay. The expressions of type I collagen, cdc 2, cyclin B1, TIMP-1 and p-ERK proteins were examined by Western blot.

RESULTS

SCAP cells expressed FGFR1 and FGFR2. Exposure of SCAP to bFGF enhanced cell proliferation, and the expression cyclinB1, cdc 2, and TIMP-1, but not type I collagen. U0126 pretreatment and co-incubation attenuated the bFGF-induced proliferation, cdc2, cyclin B1 and TIMP-1 proteins' expression, but not type I collagen in SCAP.

CONCLUSION

SCAP cells express FGFRs. bFGF may stimulate proliferation and affect the matrix turnover of SCAP cells, possibly via stimulation of FGFRs and MEK/ERK signaling pathway. These results are useful for clinical therapies for apexogenesis and regeneration of pulpo-dentin complex.

TRAF3IP3 at the trans-Golgi network regulates NKT2 maturation via the MEK/ERK signaling pathway

Thymic natural killer T (NKT)2 cells are a subset of invariant NKT cells with PLZF^hiGATA3^hiIL-4⁺. The differentiation of NKT2 cells is not fully understood. In the present study, we report an important role of TRAF3-interacting protein 3 (TRAF3IP3) in the functional maturation and expansion of committed NKT2s in thymic medulla. Mice with T-cell-specific deletion of TRAF3IP3 had decreased thymic NKT2 cells, decreased IL-4-producing peripheral iNKTs, and defects in response to α-galactosylceramide. Positive selection and high PLZF expression in CD24⁺CD44^- and CCR7⁺CD44^- immature iNKTs were not affected. Only CD44^hiNK1.1^- iNKTs in Traf3ip3^-/- mice showed reduced expression of Egr2, PLZF, and IL-17RB, decreased proliferation, and reduced IL-4 production upon stimulation. This Egr2 and IL-4 expression was augmented by MEK1/ERK activation in iNKTs, and TRAF3IP3 at the trans-Golgi network recruited MEK1 and facilitated ERK phosphorylation and nuclear translocation. LTβR-regulated bone marrow-derived nonlymphoid cells in the medullary thymic microenvironment were required for MEK/ERK activation and NKT2 maturation. These data demonstrate an important functional maturation process in NKT2 differentiation that is regulated by MEK/ERK signaling at the trans-Golgi network.

Cecropin A Modulates Tight Junction-Related Protein Expression and Enhances the Barrier Function of Porcine Intestinal Epithelial Cells by Suppressing the MEK/ERK Pathway

Inflammatory bowel disease (IBD) in humans and animals is associated with bacterial infection and intestinal barrier dysfunction. Cecropin A, an antimicrobial peptide, has antibacterial activity against pathogenic bacteria. However, the effect of cecropin A on intestinal barrier function and its related mechanisms is still unclear. Here, we used porcine jejunum epithelial cells (IPEC-J2) as a model to investigate the effect and mechanism of cecropin A on intestinal barrier function. We found that cecropin A reduced Escherichia coli (E. coli) adherence to IPEC-J2 cells and downregulated mRNA expression of tumor necrosis factor α (TNF-α), interleukin-6 (IL-6), and interleukin-8 (IL-8). Furthermore, cecropin A elevated the transepithelial electrical resistance (TER) value while reducing the paracellular permeability of the IPEC-J2 cell monolayer barrier. Finally, by using Western blotting, immunofluorescence and pathway-specific antagonists, we demonstrated that cecropin A increased ZO-1, claudin-1 and occludin protein expression and regulated membrane distribution and F-actin polymerization by increasing CDX2 expression. We conclude that cecropin A enhances porcine intestinal epithelial cell barrier function by downregulating the mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway. We suggest that cecropin A has the potential to replace antibiotics in the treatment of IBD due to its antibacterial activity on gram-negative bacteria and its enhancement effect on intestinal barrier function.

Ascorbic acid induces cardiac differentiation of white adipose tissue-derived stem cells

White adipose tissue (WAT) is the bulk of fatty tissues in humans. Enhancing the potential of WAT-derived stem cells (WATDCs) to generate cardiomyocytes may help supply sufficient number of therapeutically potent cells for heart repair in vivo. Therefore, we investigated whether ascorbic acid (AA) could facilitate the cardiac differentiation of WATDCs and the underlying mechanisms. Our results indicated that AA dose-dependently stimulates the cardiac differentiation of WATDCs, which is supported by the up-regulated expression of cardiac markers and the appearance of myotube-like cell morphologies. Time-course study showed that the front phase (0-4 days) is crucial for the action of AA on cardiac differentiation, which hints that AA may take effect through enhancing the proliferation of cardiac progenitor cells. EdU assay ascertained AA indeed promotes cell growth dose-dependently in the front phase. Further investigation indicated that AA induces the phosphorylation of MEK and ERK, and the synthesis of collagen I (Col I). Interference of MEK/ERK activity or Col I synthesis blocks the cardiomyogenic activity of AA in WATDCs. These findings demonstrated that AA facilitates WATDC cardiogenesis via promoting the proliferation of cardiac progenitor cells through MEK/ERK signaling and collagen synthesis.

Stomatin-like protein 2 inhibits cisplatin-induced apoptosis through MEK/ERK signaling and the mitochondrial apoptosis pathway in cervical cancer cells

Stomatin-like protein 2 (STOML2 or SLP-2) is an oncogenic anti-apoptotic protein that is upregulated in several types of cancer, including cervical cancer. However, the mechanisms responsible for the SLP-2 anti-apoptotic function remain poorly understood. Here, we show that siRNA-mediated SLP-2 suppression decreases growth of human cervical cancer HELA and SIHA cells, and increases cisplatin-induced apoptosis through activation of MEK/ERK signaling and suppression of the mitochondrial pathway. The inhibition of the mitochondrial pathway is mediated by increasing the mitochondrial Ca²⁺ concentration and mitochondrial membrane potential, thereby downregulating p-MEK and p-ERK levels, upregulating the Bax/Bcl-2 ratio, increasing cytochrome C release from mitochondria into the cytosol, and upregulating levels of cleaved-caspase 9, cleaved-caspase 3, and cleaved poly ADP-ribose polymerase (PARP). Overexpression of SLP-2 using adenovirus-STOML2 has the opposite effect: it upregulates p-MEK and p-ERK and downregulates the Bax/Bcl-2 ratio and levels of cleaved-caspase 9 to caspase 9, cleaved-caspase 3 to caspase 3, and cleaved-PARP to PARP in cisplatin-treated cells. These data show that SLP-2 inhibits cisplatin-induced apoptosis by activating the MEK/ERK signaling and inhibiting the mitochondrial apoptosis pathway in cervical cancer cells.

Inhibition of the NEDD8 conjugation pathway induces calcium-dependent compensatory activation of the pro-survival MEK/ERK pathway in acute lymphoblastic leukemia

De novo and acquired drug resistance and subsequent relapse remain major challenges in acute lymphoblastic leukemia (ALL). We previously identified that pevonedistat (TAK-924, MLN4924), a first-in-class inhibitor of NEDD8 activating enzyme (NAE), elicits ER stress and has potent in vitro and in vivo efficacy against ALL. However, in pevonedistat-treated ALL cell lines, we found consistent activation of the pro-survival MEK/ERK pathway, which has been associated with relapse and poor outcome in ALL. We uncovered that inhibition of the MEK/ERK pathway in vitro and in vivo sensitized ALL cells to pevonedistat. The observed synergistic apoptotic effect appears to be mediated by inhibition of the MEK/ERK pro-survival cascade leading to de-repression of the pro-apoptotic BIM protein. Mechanistically, Ca²⁺ influx via the Ca²⁺-release-activated Ca²⁺ (CRAC) channel induced protein kinase C β2 (PKC-β2) was responsible for activation of the MEK/ERK pathway in pevonedistat-treated ALL cells. Sequestration of Ca²⁺ using BAPTA-AM or blockage of store-operated Ca²⁺ entry (SOCE) using BTP-2 both attenuated the compensatory activation of MEK/ERK signaling in pevonedistat-treated ALL cells. Pevonedistat significantly altered the expression of Orai1 and stromal interaction molecule 1 (STIM1), resulting in significantly decreased STIM1 protein levels relative to Orai1. Further, we identified eIF2α as an important post-transcriptional regulator of STIM1, suggesting that pevonedistat-induced eIF2α de-phosphorylation selectively down-regulates translation of STIM1 mRNA. Consequently, our data suggest that pevonedistat potentially activates SOCE and promotes Ca²⁺ influx leading to activation of the MEK/ERK pathway by altering the stoichiometric Orai1:STIM1 ratio and inducing ER stress in ALL cells.

Luteolin exerts pro-apoptotic effect and anti-migration effects on A549 lung adenocarcinoma cells through the activation of MEK/ERK signaling pathway

An increasing amount of evidence suggests that luteolin, a common dietary flavonoid that is widely distributed in plants and foods, has been shown to be protective against cancer. However, the precise underlying mechanisms of its action against lung cancer are still poorly understood. In the present study, we investigated whether luteolin exhibits the anti-cancer effect in lung cancer through the induction of cell apoptosis and inhibition of cell migration, and whether mitogen-activated protein kinases (MAPKs) and Akt signaling pathways are required. Results revealed that luteolin exerted an anti-proliferation effect in a dose- and time-dependent manner in A549 lung adenocarcinoma cells, and induced apoptosis with a concomitant increase in the activation of caspases-3 and -9, diminution of Bcl-2, elevation in Bax expression, and the phosphorylation of MEK and its down-stream kinase ERK, as well as the activation of Akt. Luteolin also dramatically inhibited cell motility and migration in A549 cells. The inhibitor of MEK-ERK pathway protected against luteolin-induced cell death and suppressed the apoptosis-inducing and anti-migratory effects of luteolin, suggesting MEK-ERK signaling pathway plays an important role in mediating the pro-apoptotic effect and anti-migration effects of luteolin. Taken together, this study provides a new insight into the mode of action of luteolin on lung cancer.

Rapamycin Inhibits Cardiac Hypertrophy by Promoting Autophagy via the MEK/ERK/Beclin-1 Pathway

Rapamycin, also known as sirolimus, is an antifungal agent and immunosuppressant drug used to prevent organ rejection in transplantation. However, little is known about the role of rapamycin in cardiac hypertrophy and the signaling pathways involved. Here, the effect of rapamycin was examined using phenylephrine (PE) induced cardiomyocyte hypertrophy in vitro and in a rat model of aortic banding (AB) - induced hypertrophy in vivo. Inhibition of MEK/ERK signaling reversed the effect of rapamycin on the up-regulation of LC3-II, Beclin-1 and Noxa, and the down-regulation of Mcl-1 and p62. Silencing of Noxa or Beclin-1 suppressed rapamycin-induced autophagy, and co-immunoprecipitation experiments showed that Noxa abolishes the inhibitory effect of Mcl-1 on Beclin-1, promoting autophagy. In vivo experiments showed that rapamycin decreased AB-induced cardiac hypertrophy in a MEK/ERK dependent manner. Taken together, our results indicate that rapamycin attenuates cardiac hypertrophy by promoting autophagy through a mechanism involving the modulation of Noxa and Beclin-1 expression by the MEK/ERK signaling pathway.

Inhibition of MEK/ERK activation attenuates autophagy and potentiates pemetrexed-induced activity against HepG2 hepatocellular carcinoma cells

Identification of efficient chemo-therapeutic/chemo-preventive agents for treatment of hepatocellular carcinoma (HCC) is important. In this study, we examined the activity of pemetrexed, an anti-folate chemotherapy drug, against HepG2 human HCC cells. Pemetrexed treatment in vitro exerted weak but significant cytotoxic activity against HepG2 cells. When analyzing the possible pemetrexed-resistance factors, we indentified that pemetrexed treatment in HepG2 cells induced cyto-protective autophagy activation, evidenced by GFP-light chain 3B (LC3B) puncta formation, p62 downregulation and Beclin-1/LC3B-II upregulation. Correspondingly, autophagy inhibitors, including bafliomycin A1, 3-methyladenine and chloroquine, enhanced pemetrexed-induced cytotoxicity against HepG2 cells. Further, RNAi-mediated knockdown of Beclin-1 in HepG2 cells also increased pemetrexed sensitivity. Pemetrexed activated MEK (mitogen-activated protein kinase/ERK kinase)/ERK (extracellular-signal-regulated kinase) signaling in HepG2 cells, which was required for autophagy induction. Pharmacological inhibition of MEK/ERK activation attenuated pemetrexed-induced autophagy, enhanced HepG2 cell death and apoptosis. In summary, pemetrexed activates MEK/ERK-dependent cyto-protective autophagy, and inhibition of this pathway potentiates pemetrexed's activity in HepG2 cells.

Anti-proliferative actions of N'-desmethylsorafenib in human breast cancer cells

The multi-kinase inhibitor sorafenib is used for the treatment of renal and hepatic carcinomas and is undergoing evaluation for treatment of breast cancer in combination with other agents. Cytochrome P450 (CYP) 3A4 converts sorafenib to multiple metabolites that have been detected in patient plasma. However, recent clinical findings suggest that combination therapy may elicit inhibitory pharmacokinetic interactions involving sorafenib that increase toxicity. While sorafenib N-oxide is an active metabolite, information on the anti-tumor actions of other metabolites is unavailable. The present study evaluated the actions of sorafenib and its five major metabolites in human breast cancer cell lines. All agents, with the exception of N'-hydroxymethylsorafenib N-oxide, decreased ATP formation in four breast cancer cell lines (MDA-MB-231, MDA-MB-468, MCF-7 and T-47D). Prolonged treatment of MDA-MB-231 cells with N'-desmethylsorafenib, N'-desmethylsorafenib N-oxide and sorafenib (10 μM, 72 h) produced small increases in caspase-3 activity to 128-139% of control. Sorafenib and its metabolites, again with the exception of N'-hydroxymethylsorafenib N-oxide, impaired MEK/ERK signaling in MDA-MB-231 cells and modulated the expression of cyclin D1 and myeloid cell leukemia sequence-1, which regulate cell viability. When coadministered with doxorubicin (0.5 or 1 μM), sorafenib and N'-desmethylsorafenib (25 μM) produced greater effects on ATP production than either treatment alone. Thus, it emerges that, by targeting the MEK/ERK pathway, multiple sorafenib metabolites may contribute to the actions of sorafenib in breast cancer. Because N'-desmethylsorafenib is not extensively metabolized and does not inhibit major hepatic CYPs, this metabolite may have a lower propensity to precipitate pharmacokinetic drug interactions than sorafenib.