MKP1 repression is required for the chemosensitizing effects of NF-κB and PI3K inhibitors to cisplatin in non-small cell lung cancer

Radiation for Multiple Myeloma in the Era of Novel Agents: Indications, Safety, and Dose Selection

Survival outcomes for multiple myeloma (MM) have drastically improved over the past two decades with the advent of highly effective biologic agents and integration of autologous stem cell transplant (ASCT) for select patients. Despite these advances, MM remains an incurable disease and duration of remission decreases with each relapse. Palliative radiotherapy (RT) for MM, including treatment of pain, relief of compression, and prevention of fracture, is highly effective and generally well tolerated. Though RT can be delivered concurrently with biologic agents, caution should be exercised for potential added hematologic toxicity that may disrupt systemic therapy, especially in heavily pretreated patients, who have limited bone marrow reserve. In this review, we discuss the safety of RT with biologic agents (proteasome inhibitors, immunomodulators, monoclonal antibodies), review indications for palliative RT in MM, and present a framework for how to personalize RT based on goals of treatment, classification of uncomplicated versus complicated lesions, and patient and lesion characteristics. Additionally, we discuss the emerging role of bridging RT prior to chimeric antigen receptor (CAR) T-cell therapy.

MicroRNA-98 as a novel diagnostic marker and therapeutic target in cancer patients

The progress of cancer treatment methods in the last decade has significantly reduced mortality rate among these patients. Nevertheless, cancer is still recognized as one of the main causes of human deaths. One of the main reasons for the high death rate in cancer patients is the late diagnosis in the advanced tumor stages. Therefore, it is necessary to investigate the molecular biology of tumor progressions in order to introduce early diagnostic markers. MicroRNAs (miRNAs) have an important role in regulating cellular processes associated with tumor progression. Due to the high stability of miRNAs in body fluids, they are widely used as non-invasive markers in the early tumor diagnosis. Since, deregulation of miR-98 has been reported in a wide range of cancers, we investigated the molecular mechanisms of miR-98 during tumor progression. It has been reported that miR-98 mainly inhibits the tumor growth by the modulation of transcription factors and signaling pathways. Therefore, miR-98 can be introduced as a tumor marker and therapeutic target among cancer patients.

Circular RNA 0006349 Augments Glycolysis and Malignance of Non-small Cell Lung Cancer Cells Through the microRNA-98/MKP1 Axis

Background: The involvement of dysregulated circular RNAs (circRNAs) in human diseases has been increasingly recognized. In this study, we focused on the function of a newly screened circRNA, circ_0006349, in the progression of non-small-cell lung cancer (NSCLC) and the molecules of action.

Methods: The NSCLC circRNA dataset GSE101684, microRNA (miRNA) dataset GSE29250, and mRNA dataset GSE51852 obtained from the GEO database were used to identify the differentially expressed genes in NSCLC samples. Tumor and normal tissues were collected from 59 patients with NSCLC. The expression of circ_0006349, miR-98, and MAP kinase phosphatase 1 (MKP1) in collected tissue samples and in acquired cells was determined. The binding relationships between miR-98 and circ_0006349/MKP1 were predicted and validated. Altered expression of circ_0006349, miR-98, and MKP1 was introduced in NSCLC cells to examine their roles in cell growth, apoptosis, and glycolysis.

Results: Circ_0006349 and MKP1 were upregulated, and miR-98 was poorly expressed in the collected tumor tissues and the acquired NSCLC cell lines. Circ_0006349 was identified as a sponge for miR-98 to elevate MKP1 expression. Silencing of circ_0006349 suppressed proliferation and increased apoptosis of Calu-3 and H1299 cells, and it reduced glycolysis, glucose uptake, and the production of lactate in cells. Upon circ_0006349 knockdown, further downregulation of miR-98 or upregulation of MKP1 restored the malignant behaviors of cells.

Conclusion: This research demonstrated that circ_0006349 derepressed MKP1 expression by absorbing miR-98, which augmented the proliferation and glycolysis of NSCLC cells and promoted cancer development.

The MAPK/ERK Pathway and the Role of DUSP1 in JCPyV Infection of Primary Astrocytes

JC polyomavirus (JCPyV) is a neuroinvasive pathogen causing a fatal, demyelinating disease of the central nervous system (CNS) known as progressive multifocal leukoencephalopathy (PML). Within the CNS, JCPyV predominately targets two cell types: oligodendrocytes and astrocytes. The underlying mechanisms of astrocytic infection are poorly understood, yet recent findings suggest critical differences in JCPyV infection of primary astrocytes compared to a widely studied immortalized cell model. RNA sequencing was performed in primary normal human astrocytes (NHAs) to analyze the transcriptomic profile that emerges during JCPyV infection. Through a comparative analysis, it was validated that JCPyV requires the mitogen-activated protein kinase, extracellular signal-regulated kinase (MAPK/ERK) pathway, and additionally requires the expression of dual-specificity phosphatases (DUSPs). Specifically, the expression of DUSP1 is needed to establish a successful infection in NHAs, yet this was not observed in an immortalized cell model of JCPyV infection. Additional analyses demonstrated immune activation uniquely observed in NHAs. These results support the hypothesis that DUSPs within the MAPK/ERK pathway impact viral infection and influence potential downstream targets and cellular pathways. Collectively, this research implicates DUSP1 in JCPyV infection of primary human astrocytes, and most importantly, further resolves the signaling events that lead to successful JCPyV infection in the CNS.

Downregulation of microRNA-4295 enhances cisplatin-induced gastric cancer cell apoptosis through the EGFR/PI3K/Akt signaling pathway by targeting LRIG1

Gastric cancer (GC) is one of the leading causes of cancer-associated mortality worldwide. The aim of the present study was to investigate the mechanism of microRNA-4295 (miR-4295), which regulates cisplatin (DDP)-induced apoptosis in GC cells through the leucine-rich repeats and immunoglobulin-like domains 1 (LRIG1)-mediated epidermal growth factor receptor (EGFR)/phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway. Two cell lines were selected, one with the highest expression of miR-4295 and one with the lowest expression of LRIG1, for the experiments. The half maximal inhibitory concentration of DDP in the human GC MKN-28 and MKN-45 cell lines was calculated, and mitochondrial membrane potentials of the GC cells were detected by tetramethylrhodamine, ethyl ester, perchlorate staining. The proliferation and apoptosis of GC cells with or without DDP treatment were assessed by MTT assay and plate colony formation, as well as flow cytometry and TUNEL staining. Western blot analysis and reverse transcription-quantitative polymerase chain reaction were employed to determine the expression of EGFR/PI3K/Akt signaling pathway-related genes and apoptosis-related genes. LRIG1 was identified as a target gene of miR-4295. The expression of miR-4295 was upregulated, and the expression of LRIG1 was downregulated in GC cells. Furthermore, DDP enhanced the decrease in miR-4295 expression and the increase in LRIG1 expression in GC cells. miR-4295 promoted the proliferation and inhibited the DDP-induced apoptosis of GC cells without DDP treatment. In addition, miR-4295 increased the expression levels of EGFR, PI3K, Akt, p-PI3K and p-Akt, suggesting that miR-4295 promotes the activation of the EGFR/PI3K/Akt signaling pathway by targeting LRIG1. miR-4295 targeted and negatively regulated LRIG1 expression to activate the EGFR/PI3K/Akt signaling pathway, thereby promoting the proliferation of the GC cells and inhibiting the apoptosis of the GC cells induced by DDP. Therefore, miR-4295 may be a novel therapeutic target in patients with GC.

DUSP1 enhances the chemoresistance of gallbladder cancer via the modulation of the p38 pathway and DNA damage/repair system

Cisplatin (CDDP) is a commonly used drug for gallbladder cancer (GBC) chemotherapy. However, resistance to CDDP treatment results in relapse. Therefore, there is a need for the development of more effective treatment strategies to overcome chemoresistance. Dual-specificity phosphatase 1 (DUSP1) was reported to be involved in the resistance of a number of chemotherapeutic agents and was revealed to be highly expressed in CDDP-resistant GBC cells and CDDP-treated tumor types compared with normal cells or tissues in the present study. DUSP1 was revealed to inhibit the cytotoxicity of CDDP in two GBC cell lines, SGC996 and GBC-SD. P38 mitogen-activated protein kinases may be involved in the mechanism of chemoresistance. Furthermore, the number of DNA double-strand breaks in SGC996 OE cells was reduced compared with SGC996 vector cells indicating DUSP1 may attenuate the chemotherapeutic efficiency. Due to its potency against CDDP treatment, DUSP1 may be a promising target to overcome chemoresistance in GBC therapy.

Phosphatases and solid tumors: focus on glioblastoma initiation, progression and recurrences

Phosphatases and cancer have been related for many years now, as these enzymes regulate key cellular functions, including cell survival, migration, differentiation and proliferation. Dysfunctions or mutations affecting these enzymes have been demonstrated to be key factors for oncogenesis. The aim of this review is to shed light on the role of four different phosphatases (PTEN, PP2A, CDC25 and DUSP1) in five different solid tumors (breast cancer, lung cancer, pancreatic cancer, prostate cancer and ovarian cancer), in order to better understand the most frequent and aggressive primary cancer of the central nervous system, glioblastoma.

Inhibition of IKK-NFκB pathway sensitizes lung cancer cell lines to radiation

Objective

: Cancer cell radioresistance is a stumbling block in radiation therapy. The activity in the nuclear factor kappa B (NFκB) pathway correlates with anti-apoptotic mechanisms and increased radioresistance. The IKK complex plays a major role in NFκB activation upon numerous signals. In this study, we examined the interaction between ionizing radiation (IR) and different members of the IKK-NFκB pathway, as well as upstream activators, RAF1, ERK, and AKT1.

Methods

: The effect of 4 Gy of IR on the expression of the RAF1-ERK-IKK-NFκB pathway was examined in A549 and H1299 lung cancer cell lines using Western blot analysis and confocal microscopy. We examined changes in radiation sensitivity using gene silencing or pharmacological inhibitors of ERK and IKKβ.

Results

: IKKα, IKKγ, and IκBα increased upon exposure to IR, thereby affecting nuclear levels of NFκB (phospho-p65). ERK inhibition or siRNA-mediated down-regulation of RAF1 suppressed the post-irradiation survival of the examined lung cancer cell lines. A similar effect was detected on survival upon silencing IKKα/IKKγ or inhibiting IKKβ.

Conclusions

: Exposure of lung cancer cells to IR results in NFκB activation via IKK. The genetic or pharmacological blockage of the RAF1-ERK-IKK-NFκB pathway sensitizes cells to therapeutic doses of radiation. Therefore, the IKK pathway is a promising target for therapeutic intervention in combination with radiotherapy.

Role of DUSP1/MKP1 in tumorigenesis, tumor progression and therapy

Dual‐specificity phosphatase‐1 (DUSP1/MKP1), as a member of the threonine‐tyrosine dual‐specificity phosphatase family, was first found in cultured murine cells. The molecular mechanisms of DUSP1‐mediated extracellular signal‐regulated protein kinases (ERKs) dephosphorylation have been subsequently identified by studies using gene knockout mice and gene silencing technology. As a protein phosphatase, DUSP1 also downregulates p38 MAPKs and JNKs signaling through directly dephosphorylating threonine and tyrosine. It has been detected that DUSP1 is involved in various functions, including proliferation, differentiation, and apoptosis in normal cells. In various human cancers, abnormal expression of DUSP1 was observed which was associated with prognosis of tumor patients. Further studies have revealed its role in tumorigenesis and tumor progression. Besides, DUSP1 has been found to play a role in tumor chemotherapy, immunotherapy, and biotherapy. In this review, we will focus on the function and mechanism of DUSP1 in tumor cells and tumor treatment.

RNA interference-mediated knockdown of Aurora-B alters the metastatic behavior of A549 cells via modulation of the phosphoinositide 3-kinase/Akt signaling pathway

Accumulating evidence has revealed that an elevated expression level of Aurora-B is associated with metastasis in various types of malignant tumor. However, it is currently unclear whether this molecule is involved in non-small lung cancer (NSCLC) metastasis, and the molecular mechanisms associated with Aurora-B and metastasis remain unknown. In the present study, in order to investigate whether Aurora-B is involved in the development and metastasis of NSCLC, the Aurora-B protein expression in NSCLC tissues was detected by immunohistochemistry and its association with metastasis was analyzed. The results revealed that the expression levels of the Aurora-B protein in tissues obtained from NSCLC patients with lymph node metastasis were significantly higher than those without metastatic disease. Furthermore, the effect of Aurora-B inhibition on A549 cell migration and invasion, as well as the activity of the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway was evaluated. Aurora-B was inhibited in the A549 cells using short hairpin RNA, and the cell migration and invasion rates were investigated using wound healing and Transwell invasion assays. In addition, the expression of the main proteins in the PI3K/Akt/nuclear factor-κB (NF-κB) signaling pathway, and matrix metalloproteinase (MMP)-2 and -9 were measured by western blot analysis. The results demonstrated that cell migration and invasion were decreased as a result of silencing Aurora-B. Furthermore, the activity of the PI3K/Akt/NF-κB signaling pathway and the expression of MMP-2 and -9 protein were suppressed by silencing Aurora-B. The results of the present study indicate that the knockdown of Aurora-B suppresses A549 cell invasion and migration via the inhibition of the PI3K/Akt signaling pathway in vitro and thus, targeting Aurora-B may present a potential treatment strategy for NSCLC.

Accelerated repair and reduced mutagenicity of DNA damage induced by cigarette smoke in human bronchial cells transfected with E.coli formamidopyrimidine DNA glycosylase

Cigarette smoke (CS) is associated to a number of pathologies including lung cancer. Its mutagenic and carcinogenic effects are partially linked to the presence of reactive oxygen species and polycyclic aromatic hydrocarbons (PAH) inducing DNA damage. The bacterial DNA repair enzyme formamidopyrimidine DNA glycosylase (FPG) repairs both oxidized bases and different types of bulky DNA adducts. We investigated in vitro whether FPG expression may enhance DNA repair of CS-damaged DNA and counteract the mutagenic effects of CS in human lung cells. NCI-H727 non small cell lung carcinoma cells were transfected with a plasmid vector expressing FPG fused to the Enhanced Green Fluorescent Protein (EGFP). Cells expressing the fusion protein EGFP-FPG displayed accelerated repair of adducts and DNA breaks induced by CS condensate. The mutant frequencies induced by low concentrations of CS condensate to the Na(+)K(+)-ATPase locus (oua(r)) were significantly reduced in cells expressing EGFP-FPG. Hence, expression of the bacterial DNA repair protein FPG stably protects human lung cells from the mutagenic effects of CS by improving cells' capacity to repair damaged DNA.

Involvement of the cellular phosphatase DUSP1 in vaccinia virus infection

Poxviruses encode a large variety of proteins that mimic, block or enhance host cell signaling pathways on their own benefit. It has been reported that mitogen-activated protein kinases (MAPKs) are specifically upregulated during vaccinia virus (VACV) infection. Here, we have evaluated the role of the MAPK negative regulator dual specificity phosphatase 1 (DUSP1) in the infection of VACV. We demonstrated that DUSP1 expression is enhanced upon infection with the replicative WR virus and with the attenuated VACV viruses MVA and NYVAC. This upregulation is dependent on early viral gene expression. In the absence of DUSP1 in cultured cells, there is an increased activation of its molecular targets JNK and ERK and an enhanced WR replication. Moreover, DUSP1 knock-out (KO) mice are more susceptible to WR infection as a result of enhanced virus replication in the lungs. Significantly, MVA, which is known to produce non-permissive infections in most mammalian cell lines, is able to grow in DUSP1 KO immortalized murine embryo fibroblasts (MEFs). By confocal and electron microscopy assays, we showed that in the absence of DUSP1 MVA morphogenesis is similar as in permissive cell lines and demonstrated that DUSP1 is involved at the stage of transition between IVN and MV in VACV morphogenesis. In addition, we have observed that the secretion of pro-inflammatory cytokines at early times post-infection in KO mice infected with MVA and NYVAC is increased and that the adaptive immune response is enhanced in comparison with WT-infected mice. Altogether, these findings reveal that DUSP1 is involved in the replication and host range of VACV and in the regulation of host immune responses through the modulation of MAPKs. Thus, in this study we demonstrate that DUSP1 is actively involved in the antiviral host defense mechanism against a poxvirus infection.

Phosphorylation is a post-translational modification that is highly conserved throughout the animal kingdom. Viruses have evolved to acquire their own kinases and phosphatases and to be able to modulate host phosphorylation mechanisms on their benefit. DUSP1 is an early induced gene that belongs to the superfamily of Dual-specificity phosphatases and provides an essential negative feedback regulation of MAPKs. DUSP1 is involved in innate and adaptive immune responses against different bacteria and parasites infections. The use of Knock-out technology has allowed us to understand the role of DUSP1 in the context of VACV infection both in cultured cells and in the in vivo mouse model. Here, we have showed that DUSP1 expression is upregulated during VACV infection and that DUSP1 plays an important role in VACV replication. Interestingly, we have demonstrated that the VACV attenuated virus MVA is able to grow in immortalized murine embryo fibroblasts in the absence of DUSP1. In vivo results showed that VACV replication-competent WR pathogenesis is enhanced in the absence of DUSP1. Furthermore, we have demonstrated that DUSP1 is involved in the host innate and adaptive responses against VACV. Altogether, we have presented a novel role for DUSP1 in VACV replication and anti-VACV host immune response.

Downregulation of insulin-like growth factor-binding protein 7 in cisplatin-resistant non-small cell lung cancer

Cisplatin is an effective anticancer drug used to treat many types of cancer, including non-small cell lung carcinoma (NSCLCs), but development of resistance is the primary impediment in cancer treatment. Insulin-like growth factor-binding protein 7 (IGFBP7) is a secreted tumor suppressor that is inactivated in human lung cancer. IGFBP7 is known to alter sensitivity to interferon-based anticancer therapy, and here, we examined loss of IGFBP7 as a potential contributor to chemo-resistance to cisplatin. The transcriptional level of IGFBP7 was decreased in cisplatin-resistant human cancer cell lines and NSCLC xenografts. IGFBP7 knock-down increased cellular resistance to cisplatin and increased the level of mitogen-activated protein kinase phosphatases (MKP) 3 levels. The expression of MKP3 increased in a cisplatin-resistant NSCLC cell line and lung xenografts. MKP3 knock-down increased IGFBP7 level, indicating that MKP3 regulates IGFBP7. These findings suggest a novel molecular mechanism responsible for the tumor suppressive function of IGFBP7 in cisplatin-resistant human lung cancer and could lead to the development of IGFBP7 as a cisplatin-sensitizing agent.

Roles of AKT1 and AKT2 in non-small cell lung cancer cell survival, growth, and migration

Although AKT ⁄ protein kinase B is constitutively active in nonsmall cell lung cancer (NSCLC) cells and is an attractive target for enhancing the cytotoxicity of therapeutic agents, the distinct roles of the AKT isoforms in NSCLC are largely unknown. In the present study, we investigated the roles of AKT1 and AKT2 in NSCLC cells using RNAi. The siRNA targeting of AKT1 or AKT2 effectively decreased protein levels of AKT1 and AKT2, respectively, in A549 and H460 cells. Cisplatin treatment of these cells increased apoptotic cell death compared with control. The siRNA-induced knockdown of AKT1 in H460 cells significantly decreased basal MEK⁄ ERK1 ⁄ 2 activity, resulting in nuclear factor-κB activation, whereas knockdown of AKT2 resulted in anti-apoptotic Bcl-2 family protein MCL-1 (MCL-1) cleavage, the collapse of mitochondrial membrane potential, cytochrome c release, and activation of the caspase cascade. Consequently, both siRNA treatments enhanced the chemosensitivity of H460 cells to cisplatin. However, neither AKT1 nor AKT2 siRNA treatment had any effect of p27 expression, and although both treatments tended to induced G₂ ⁄M phase arrest, the effect was not statistically significant. Treatment with AKT1 siRNA markedly decreased colony formation growth and migration, but AKT2 siRNA had no significant effects on these parameters. These data suggest that AKT1 and AKT2 both contribute to cell survival, albeit via different mechanisms, and that the effects on cell growth and migration are predominantly regulated by AKT1. These findings may aid in refining targeted strategies for the inhibition of AKT isoforms towards the sensitization of NSCLC cells to therapeutic agents.

Cell signaling molecules as drug targets in lung cancer: an overview

PURPOSE OF REVIEW

Lung being one of the vital and essential organs in the body, lung cancer is a major cause of mortality in the modern human society. Lung cancer can be broadly subdivided into nonsmall cell lung cancer (NSCLC) and small cell lung cancer (SCLC). Although NSCLC is sometimes treated with surgery, the advanced and metastatic NSCLC and SCLC usually respond better to chemotherapy and radiation. The most important targets of these chemotherapeutic agents are various intracellular signaling molecules. The primary focus of this review article is to summarize the description of various cell signaling molecules involved in lung cancer development and their regulation by chemotherapeutic agents.

RECENT FINDINGS

Extensive research work in recent years has identified several cellular signaling molecules that may be intricately involved in the complexity of lung cancer. Some of these cell signaling molecules are epidermal growth factor receptors, vascular endothelial growth factor receptors, mammalian target of rapamycin, mitogen-activated protein kinase phosphatase-1, peroxisome proliferator-activated receptor-gamma, matrix metalloproteinases and receptor for advanced glycation end-products.

SUMMARY

The present review will strengthen our current knowledge regarding the efficacy of the above-mentioned cell signaling molecules as potential beneficial drug targets against lung cancer.

The dual-specificity protein phosphatase MkpB, homologous to mammalian MKP phosphatases, is required for D. discoideum post-aggregative development and cisplatin response

Dual-specificity protein phosphatases participate in signal transduction pathways inactivating mitogen-activated protein kinases (MAP kinases). These signaling pathways are of critical importance in the regulation of numerous biological processes, including cell proliferation, differentiation and development. The social ameba Dictyostelium discoideum harbors 14 genes coding for proteins containing regions very similar to the dual-specificity protein phosphatase domain. One of these genes, mkpB, additionally codes for a region similar to the Rhodanase domain, characteristic of animal MAP kinase-phosphatases, in its N-terminal region. Cells that over-express this gene show increased protein phosphatase activity. mkpB is expressed in D. discoideum ameba at growth but it is greatly induced at 12h of multicellular development. Although it is expressed in all the cells of developmental structures, mkpB mRNA is enriched in cells with a distribution typical of anterior-like cells. Cells that express a catalytically inactive mutant of MkpB grow and aggregate like wild-type cells but show a greatly impaired post-aggregative development. In addition, the expression of cell-type specific genes is very delayed, indicating that this protein plays an important role in cell differentiation and development. Cells expressing the MkpB catalytically inactive mutant show increased sensitivity to cisplatin, while cells over-expressing wild type MkpB, or MkpA, proteins or mutated in the MAP kinase erkB gene are more resistant to this chemotherapeutic drug, as also shown in human tumor cells.

Expression and functional role of negative signalling regulators in tumour development and progression

Alterations in intracellular signalling pathways such as the mitogen-activated protein kinases (MAPKs) are key common mechanisms of tumour development and progression. As such, there has been intense research into developing drugs that can inhibit or attenuate intracellular signalling. In recent years, there has been increasing recognition that the cell already has innate negative regulatory proteins that achieve this in normal homeostasis. These regulators provide a feedback inhibitory mechanism that controls the intensity and duration of activated signalling by exogenous stimuli. Members of this group include Raf kinase inhibitor protein 1, the MAPK phosphatases, the SPROUTY and SPRED families and similar expression to FGF. A number of studies have now demonstrated significant alterations in expression of negative regulators in malignant tissue in different cancer types. In functional studies, manipulated expression of these regulators has been shown to significantly influence tumour cell behaviour and phenotype. Here, we summarise the evidence for the functional expression of negative signalling regulators in tumour growth and progression and discuss their potential role as cancer biomarkers and targets for novel drug therapy.

Induction of MKP-1 prevents the cytotoxic effects of PI3K inhibition in hilar cholangiocarcinoma cells

PURPOSE

Hilar cholangiocarcinoma (Klatskin tumor) is one of the most difficult cancers to treat. We demonstrate activation of phosphoinositide-3-kinase (PI3K)/Akt signaling, which is a critical pathway for cell survival, in hilar cholangiocarcinoma cells. However, inhibition of PI3K has little effect on hilar cholangiocarcinoma cell survival. In this study, we investigated the mechanism by which hilar cholangiocarcinoma cells resist PI3K inhibitors.

METHODS

Human hilar cholangiocarcinoma cells KKU-100 were treated with PI3K inhibitors, and cell viability and apoptosis assays were performed. The expression of a MAPK phosphatase (MKP-1) that contributes to cancer cell survival in response to multiple stress stimuli was assayed by quantitative real-time RT-PCR and western blotting. In addition, the effects of the MKP-1 inhibitor were studied in KKU-100 cells treated with PI3K inhibitors.

RESULTS

Incubation of KKU-100 cells with PI3K inhibitors resulted in increased expression of MKP-1. Furthermore, we found that inhibition of MKP-1 using siRNA silencing sensitized KKU-100 cells to PI3K inhibitor-induced apoptosis via increased phosphorylation of p38 MAPK.

CONCLUSIONS

These results indicate that concurrent inhibition of PI3K and MKP-1 induces apoptosis in KKU-100 cells. Simultaneous targeting of the PI3K pathway and MKP-1 may be a useful approach to improve therapies directed against hilar cholangiocarcinoma.

The dual-specificity MAP kinase phosphatases: critical roles in development and cancer

Intracellular signaling by mitogen-activated protein (MAP) kinases (MAPK) is involved in many cellular responses and in the regulation of various physiological and pathological conditions. Tight control of the localization and duration of extracellular-regulated kinase (ERK), c-Jun NH(2)-terminal kinase (JNK), or p38 MAPK activity is thus a fundamental aspect of cell biology. Several members of the dual-specificity phosphatase (DUSPs) family are able to dephosphorylate MAPK isoforms with different specificity, cellular, and tissue localization. Understanding how these phosphatases are themselves regulated during development or in physiological and pathological conditions is therefore fundamental. Over the years, gene deletion and knockdown studies have completed initial in vitro studies and shed a new light on the global and specific roles of DUSPs in vivo. Whereas DUSP1, DUSP2, and DUSP10 appear as crucial players in the regulation of immune responses, other members of the family, like the ERK-specific DUSP6, were shown to play a major role in development. Recent findings on the involvement of DUSPs in cancer progression and resistance will also be discussed.