Role of Rap1B and tumor suppressor PTEN in the negative regulation of lysophosphatidic acid--induced migration by isoproterenol in glioma cells

MicroRNAs as the pivotal regulators of Temozolomide resistance in glioblastoma

Glioblastoma (GBM) is an aggressive nervous system tumor with a poor prognosis. Although, surgery, radiation therapy, and chemotherapy are the current standard protocol for GBM patients, there is still a poor prognosis in these patients. Temozolomide (TMZ) as a first-line therapeutic agent in GBM can easily cross from the blood-brain barrier to inhibit tumor cell proliferation. However, there is a high rate of TMZ resistance in GBM patients. Since, there are limited therapeutic choices for GBM patients who develop TMZ resistance; it is required to clarify the molecular mechanisms of chemo resistance to introduce the novel therapeutic targets. MicroRNAs (miRNAs) regulate chemo resistance through regulation of drug metabolism, absorption, DNA repair, apoptosis, and cell cycle. In the present review we discussed the role of miRNAs in TMZ response of GBM cells. It has been reported that miRNAs mainly induced TMZ sensitivity by regulation of signaling pathways and autophagy in GBM cells. Therefore, miRNAs can be used as the reliable diagnostic/prognostic markers in GBM patients. They can also be used as the therapeutic targets to improve the TMZ response in GBM cells.

Synthesis and Significance of Arachidonic Acid, a Substrate for Cyclooxygenases, Lipoxygenases, and Cytochrome P450 Pathways in the Tumorigenesis of Glioblastoma Multiforme, Including a Pan-Cancer Comparative Analysis

Glioblastoma multiforme (GBM) is one of the most aggressive gliomas. New and more effective therapeutic approaches are being sought based on studies of the various mechanisms of GBM tumorigenesis, including the synthesis and metabolism of arachidonic acid (ARA), an omega-6 polyunsaturated fatty acid (PUFA). PubMed, GEPIA, and the transcriptomics analysis carried out by Seifert et al. were used in writing this paper. In this paper, we discuss in detail the biosynthesis of this acid in GBM tumors, with a special focus on certain enzymes: fatty acid desaturase (FADS)1, FADS2, and elongation of long-chain fatty acids family member 5 (ELOVL5). We also discuss ARA metabolism, particularly its release from cell membrane phospholipids by phospholipase A₂ (cPLA₂, iPLA₂, and sPLA₂) and its processing by cyclooxygenases (COX-1 and COX-2), lipoxygenases (5-LOX, 12-LOX, 15-LOX-1, and 15-LOX-2), and cytochrome P450. Next, we discuss the significance of lipid mediators synthesized from ARA in GBM cancer processes, including prostaglandins (PGE₂, PGD₂, and 15-deoxy-Δ^12,14-PGJ₂ (15d-PGJ₂)), thromboxane A₂ (TxA₂), oxo-eicosatetraenoic acids, leukotrienes (LTB₄, LTC₄, LTD₄, and LTE₄), lipoxins, and many others. These lipid mediators can increase the proliferation of GBM cancer cells, cause angiogenesis, inhibit the anti-tumor response of the immune system, and be responsible for resistance to treatment.

C3G Protein, a New Player in Glioblastoma

C3G (RAPGEF1) is a guanine nucleotide exchange factor (GEF) for GTPases from the Ras superfamily, mainly Rap1, although it also acts through GEF-independent mechanisms. C3G regulates several cellular functions. It is expressed at relatively high levels in specific brain areas, playing important roles during embryonic development. Recent studies have uncovered different roles for C3G in cancer that are likely to depend on cell context, tumour type, and stage. However, its role in brain tumours remained unknown until very recently. We found that C3G expression is downregulated in GBM, which promotes the acquisition of a more mesenchymal phenotype, enhancing migration and invasion, but not proliferation. ERKs hyperactivation, likely induced by FGFR1, is responsible for this pro-invasive effect detected in C3G silenced cells. Other RTKs (Receptor Tyrosine Kinases) are also dysregulated and could also contribute to C3G effects. However, it remains undetermined whether Rap1 is a mediator of C3G actions in GBM. Various Rap1 isoforms can promote proliferation and invasion in GBM cells, while C3G inhibits migration/invasion. Therefore, other RapGEFs could play a major role regulating Rap1 activity in these tumours. Based on the information available, C3G could represent a new biomarker for GBM diagnosis, prognosis, and personalised treatment of patients in combination with other GBM molecular markers. The quantification of C3G levels in circulating tumour cells (CTCs) in the cerebrospinal liquid and/or circulating fluids might be a useful tool to improve GBM patient treatment and survival.

M2 macrophage-derived exosomal microRNAs inhibit cell migration and invasion in gliomas through PI3K/AKT/mTOR signaling pathway

Background

Glioma, the most common primary brain tumor, account Preparing figures for 30 to 40% of all intracranial tumors. Herein, we aimed to study the effects of M2 macrophage-derived exosomal microRNAs (miRNAs) on glioma cells.

Methods

First, we identified seven differentially expressed miRNAs in infiltrating macrophages and detected the expression of these seven miRNAs in M2 macrophages. We then selected hsa-miR-15a-5p (miR-15a) and hsa-miR-92a-3p (miR-92a) for follow-up studies, and confirmed that miR-15a and miR-92a were under-expressed in M2 macrophage exosomes. Subsequently, we demonstrated that M2 macrophage-derived exosomes promoted migration and invasion of glioma cells, while exosomal miR-15a and miR-92a had the opposite effects on glioma cells. Next, we performed the target gene prediction in four databases and conducted target gene validation by qRT-PCR, western blot and dual luciferase reporter gene assays.

Results

The results revealed that miR-15a and miR-92a were bound to CCND1 and RAP1B, respectively. Western blot assays demonstrated that interference with the expression of CCND1 or RAP1B reduced the phosphorylation level of AKT and mTOR, indicating that both CCND1 and RAP1B can activate the PI3K/AKT/mTOR signaling pathway.

Conclusion

Collectively, these findings indicate that M2 macrophage-derived exosomal miR-15a and miR-92a inhibit cell migration and invasion of glioma cells through PI3K/AKT/mTOR signaling pathway.

Supplementary information

The online version contains supplementary material available at 10.1186/s12967-021-02766-w.

miR-200b/c-RAP1B axis represses tumorigenesis and malignant progression of papillary thyroid carcinoma through inhibiting the NF-κB/Twist1 pathway

Papillary thyroid carcinoma (PTC) is a common endocrine malignancy with an increasing occurrence and recurrence. MicroRNAs (miRNAs) have been widely acknowledged to be participated in human cancers. However, how these miRNAs exert roles and potential mechanisms in PTC regulatory networks is still lacking. The purpose of our study lies in discovering the regulatory basis of miR-200b/c and Rap1b for PTC tumorigenesis and malignant progression, as well as the underlying molecular mechanisms. Herein, miR-200b/c expression was sharply dropped and Rap1b expression was up-regulated in PTC cells and tissues samples when compared to normal thyroid epithelial cells and normal tissues. miR-200b/c targeted Rap1 directly and negatively regulated its expression. miR-200b/c overexpression suppressed proliferative, colony forming, migratory and invasive capabilities and EMT as well as elevated apoptosis of PTC cells through inhibiting Rap1b. Furthermore, xenograft experiments showed miR-200b/c overexpression constrained growth of PTC xenograft and EMT. miR-200b/c inhibited NF-κB/Twist1 signals via regulating the Rap1b expression in cells and animal models. Taken together, our study suggested that upregulation of miR-200b/c-RAP1B axis constrained PTC cell proliferation, invasion, migration and EMT. Also, the upregulation of miR-200b/c-RAP1B leaded to elevated apoptosis through inhibiting the NF-κB/Twist1 pathway, thus inhibiting PTC tumorigenesis and malignant progression.

TRPM7 Induces Mechanistic Target of Rap1b Through the Downregulation of miR-28-5p in Glioma Proliferation and Invasion

Objectives: Our previous findings demonstrate that channel-kinase transient receptor potential (TRP) ion channel subfamily M, member 7 (TRPM7) is critical in regulating human glioma cell migration and invasion. Since microRNAs (miRNAs) participate in complex regulatory networks that may affect almost every cellular and molecular process during glioma formation and progression, we explored the role of miRNAs in human glioma progression by comparing miRNA expression profiles due to differentially expressed TRPM7. Methods: First, we performed miRNA microarray analysis to determine TRPM7's miRNA targets upon TRPM7 silencing in A172 cells and validated the miRNA microarray data using A172, U87MG, U373MG, and SNB19 cell lines by stem-loop RT-qPCRs. We next determined whether TRPM7 regulates glioma cell proliferation and migration/invasion through different functional domains by overexpressing wild-type human TRPM7 (wtTRPM7), two mutants with TRPM7's α-kinase domain deleted (Δkinase-DK), or a point mutation in the ATP binding site of the α-kinase domain (K1648R-KR). In addition, we determined the roles of miR-28-5p in glioma cell proliferation and invasion by overexpressing or under expressing miR-28-5p in vitro. Lastly, we determined whether a Ras-related small GTP-binding protein (Rap1b) is a target of miR-28-5p in glioma tumorigenesis. Results: The miRNA microarray data revealed a list of 16 downregulated and 10 upregulated miRNAs whose transcripts are significantly changed by TRPM7 knock-down. Cell invasion was significantly reduced in two TRPM7 mutants with inactive kinase domain, Δkinase, and K1648R transfected glioma cells. miR-28-5p overexpression suppressed glioma cells' proliferation and invasion, and miR-28-5p under expression led to a significant increase in glioma cell proliferation and migration/invasion compared to that of the controls. miR-28-5p suppressed glioma cell proliferation and migration by targeting Rap1b. Co-transfection of siRap1b with miR28-5p inhibitor reduced the glioma cell proliferation and invasion, caused by the latter. Conclusions: These results indicate that TRPM7's channel activity is required for glioma cell growth while the kinase domain is required for cell migration/invasion. TRPM7 regulates miR-28-5p expression, which suppresses cell proliferation and invasion in glioma cells by targeting Rap1b signaling.

Overexpression of EPAC2 reduces the invasion of glioma cells via MMP-2

Exchange proteins directly activated by cAMP (EPACs) are crucial cyclic adenosine 3′,5′-monophosphate- determined signaling pathway intercessors, which are associated with the pathogenesis of neurological disorders and numerous human diseases. To the best of our knowledge, the role of EPAC2 signaling via matrix metalloproteinase 2 (MMP-2) in the pathogenesis of glioma has not been studied. Therefore, the present study focused on the role of EPAC2 in glioma, and assessed the invasiveness of human glioma cell lines following EPAC2 overexpression. Expression levels of EPAC2 in normal brain tissues and clinical glioma specimens were detected by western blotting. An EPAC2 overexpression vector was transfected into U251 and U87 cell lines to increase the expression levels of EPAC2. Expression levels of MMP-2 were detected by western blotting, and the invasive abilities of glioma cells were detected by a Transwell assay. EPAC2 was relatively highly expressed in normal brain tissue, while EPAC2 expression was significantly decreased in clinical glioma specimens (P<0.01). In vitro transfection of EPAC2 overexpression vector significantly reduced the MMP-2 protein levels of glioma cells, and, at the same time, the invasive cell number was significantly decreased in a Transwell assay. The present study demonstrated that MMP-2 regulation via EPAC2 overexpression is a novel promising therapeutic route in malignant types of glioma.

An in vivo RNAi mini-screen in Drosophila cancer models reveals novel potential Wnt targets in liver cancer

BACKGROUND/AIMS

Aberrant activation of the Wnt/β-catenin signaling, which arises from the accumulation of mutant β-catenin in the cell, is one of the most common driving forces in hepatocellular carcinoma (HCC). We previously identified several genes that are regulated on the overexpression of β-catenin in the HCC cell line that are suggested to be novel Wnt/β-catenin targets playing effective roles in cancer. The aim of the present study was to elucidate the roles of these putative target genes in tumorigenesis with an in vivo analysis in Drosophila.

MATERIALS AND METHODS

We selected 15 genes downregulated in two Drosophila cancer models.

RESULTS

The results from the RNAi mini-screen revealed novel roles for the analyzed putative Wnt/β-catenin target genes in tumorigenesis. The downregulation of the analyzed nine genes led to tumor formation as well as metastasis in Drosophila, suggesting a tumor suppressor function. On the other hand, the knockdown of the other two genes suppressed tumor and metastasis formations and disturbed the development of the analyzed eye tissues, indicating an oncogenic or developmental role for these genes.

CONCLUSION

These findings could serve to identify novel subjects for cancer research in order to provide insight into the diagnostic and therapeutic processes of several cancer types.

Rap1b enhances the invasion and migration of hepatocellular carcinoma cells by up-regulating Twist 1

Rap1b was found be dysregulated in several types of cancers. Previously, we have demonstrated that Rap1b affects proliferation, migration and invasion of hepatocellular carcinoma (HCC) cells. However, the definite function of Rap1b in HCC remains unknown. Here, we reported that Rap1b was significantly up-regulated in HCC tissues compared with the non-tumoral liver tissues. Overexpression of Rap1b promoted tumor growth and migration in vitro and tumor formation in vivo. Oppositely, inhibition of Rap1b suppressed the proliferation and migration of HCC cells. Mechanism study revealed that Rap1b could up-regulate Twist 1 expression by enhancing its promoter activity. We concluded that Rap1b increased Twist 1 expression by targeting its promoter activity to induce proliferation and migration of HCC cells.

miR-28-5p acts as a tumor suppressor in renal cell carcinoma for multiple antitumor effects by targeting RAP1B

The incidence and mortality rate of renal cell carcinoma (RCC) have been significantly increasing; however, the mechanisms involved in RCC development and progression are unclear. In this study, we found that miR-28-5p was decreased in RCC tumor specimens and several renal carcinoma cell lines. By using a combination of luciferase reporter assays and western blotting, we identified RAP1B, a Ras-related small GTP-binding oncoprotein implicated in a variety of tumors, as a direct target of miR-28-5p in RCC. The RAP1B protein level was increased in RCC tumor specimens and renal carcinoma cell lines, and this was inversely correlated with miR-28-5p expression. In vitro gain-of-function and loss-of-function studies in human renal carcinoma cell lines, demonstrated that miR-28-5p suppressed cell proliferation and migration by directly inhibiting RAP1B, and this effect was reversed by co-transfection with RAP1B. In addition, the stable overexpression of miR-28-5p inhibited tumor cell proliferation in vivo. This newly identified miR-28-5p/RAP1B axis provides a novel mechanism for the pathogenesis of RCC, and molecules in this axis may serve as potential biomarkers and therapeutic targets for RCC.

Insights into exchange factor directly activated by cAMP (EPAC) as potential target for cancer treatment

Cancer remains a global health problem and approximately 1.7 million new cancer cases are diagnosed every year worldwide. Although diverse molecules are currently being explored as targets for cancer therapy the tumor treatment and therapy is highly tricky. Secondary messengers are important for hormone-mediated signaling pathway. Cyclic AMP (cAMP), a secondary messenger responsible for various physiological processes regulates cell metabolism by activating Protein kinase A (PKA) and by targeting exchange protein directly activated by cAMP (EPAC). EPAC is present in two isoforms EPAC1 and EPAC2, which exhibit different tissue distribution and is involved in GDP/GTP exchange along with activating Rap1- and Rap2-mediated signaling pathways. EPAC is also known for its dual role in cancer as pro- and anti-proliferative in addition to metastasis. Results after perturbing EPAC activity suggests its involvement in cancer cell migration, proliferation, and cytoskeleton remodeling which makes it a potential therapeutic target for cancer treatments.

LncRNA MT1JP functions as a tumor suppressor by interacting with TIAR to modulate the p53 pathway

Accumulating evidence suggests that long noncoding RNAs (lncRNAs) play important roles in transcriptional regulation, whereas the extent to which the lncRNAs also function at the posttranscriptional level is less known. In the present study, we report a lncRNA named MT1JP which acts as a tumor suppressor through a posttranscriptional mechanism. We found that MT1JP is differentially expressed in tumor tissues by analyzing data from a customized microarray applied to 76 pairs of matched normal and cancer tissue samples. By associating with the RNA-binding protein TIAR, MT1JP enhanced the translation of the master transcription factor p53, thereby regulating a series of pathways involving p53, such as the cell cycle, apoptosis and proliferation. When MT1JP was down-regulated, the protein level of p53 declined, which in turn accelerated cell deterioration and tumor formation. Moreover, differential expression of MT1JP in cancerous and normal tissues suggests that it may be a promising prognostic marker and a therapeutic target. Taken together, we identified MT1JP as a critical factor in restraining cell transformation by modulating p53 translation through interactions with TIAR, and this finding is likely to shed new light on future investigations about posttranscriptional or translational effects of lncRNAs during cell transformation.

Loss of SH3GL2 promotes the migration and invasion behaviours of glioblastoma cells through activating the STAT3/MMP2 signalling

SH3GL2 (Src homology 3 (SH3) domain GRB2‐like 2) is mainly expressed in the central nervous system and regarded as a tumour suppressor in human glioma. However, the molecular mechanism of the SH3GL2 protein involved in malignant behaviours of human glioma has not been elucidated. In this study, we tried to investigate the role of SH3GL2 in glioma cell migration and invasion and explore its underlined molecular mechanism. Firstly, we discovered that the protein level of SH3GL2 was widely decreased in the human glioma patients, especially in high‐grade glioma tissues. Then, we determined the role of SH3GL2 in migration and invasion of glioma cells upon SH3GL2 knocking down and overexpressing. It was showed that knocking down of SH3GL2 promoted the migration and invasion of glioma cells, whereas overexpression of SH3GL2 inhibited them. Further study on molecular mechanism disclosed that silencing of SH3GL2 obviously activated the STAT3 (signal transducer and activator of transcription 3) signalling thereby promoting the expression and secretion of MMP2. On the contrary, overexpression of SH3GL2 had opposite effect. Taken together, the above results suggest that SH3GL2 suppresses migration and invasion behaviours of glioma cells through negatively regulating STAT3/MMP2 signalling and that loss of SH3GL2 may intensify the STAT3/MMP2 signalling thereby contributing to the migration and invasion of glioma cells.

Roles of Rap1 signaling in tumor cell migration and invasion

Ras-associated protein-1 (Rap1), a small GTPase in the Ras-related protein family, is an important regulator of basic cellular functions (e.g., formation and control of cell adhesions and junctions), cellular migration, and polarization. Through its interaction with other proteins, Rap1 plays many roles during cell invasion and metastasis in different cancers. The basic function of Rap1 is straightforward; it acts as a switch during cellular signaling transduction and regulated by its binding to either guanosine triphosphate (GTP) or guanosine diphosphate (GDP). However, its remarkably diverse function is rendered by its interplay with a large number of distinct Rap guanine nucleotide exchange factors and Rap GTPase activating proteins. This review summarizes the mechanisms by which Rap1 signaling can regulate cell invasion and metastasis, focusing on its roles in integrin and cadherin regulation, Rho GTPase control, and matrix metalloproteinase expression.

High constitutive Akt2 activity in U937 promonocytes: effective reduction of Akt2 phosphorylation by the histamine H2-receptor and the β2-adrenergic receptor

Histamine (HA) is approved for the treatment of acute myeloid leukemia (AML). Its antileukemic activity is related to histamine H2-receptor (H2R)-mediated inhibition of reactive oxygen species (ROS) production in myeloid cells facilitating survival of antineoplastic lymphocytes. The phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway, which plays a crucial role in cell survival and proliferation, is constitutively activated in leukemic cells of most AML patients resulting in poor survival prognosis. In a proof-of-principle experiment using a human phosphorylated mitogen-activated protein kinase (MAPK) array, we found high phosphorylation levels of Akt2 in U937 promonocytes that was abrogated by HA or selective H2R agonists. The H2R and the β2-adrenergic receptor (β2AR) are Gs-protein-coupled receptors. Stimulation results in adenylyl cyclase activation followed by generation of the second messenger adenosine 3′,5′-cyclic monophosphate (cAMP). In our present study, we evaluated the pharmacological profile of the H2R and the β2AR regarding Akt2 phosphorylation at Ser474 via western blot analysis and ELISA and cAMP accumulation via HPLC-MS/MS in U937 promonocytes. H2R and β2AR agonists concentration-dependently decreased Akt2 phosphorylation at Ser474. Deviations of potencies and efficacies of agonists in Akt2 phosphorylation and cAMP accumulation assays indicated participation of cAMP-independent signaling in GPCR-induced reduction of Akt2 phosphorylation. Accordingly, our study supports the concept of functional selectivity of the H2R and the β2AR in U937 promonocytes. In summary, we extended the antileukemic mechanism of HA via H2R and revealed the potential of β2AR agonists, which are already approved in the treatment of bronchial asthma and chronic obstructive pulmonary disease, as antileukemic drugs.

Membrane proteome analysis of glioblastoma cell invasion

Glioblastoma multiforme (GBM) tumor invasion is facilitated by cell migration and degradation of the extracellular matrix. Invadopodia are actin-rich structures that protrude from the plasma membrane in direct contact with the extracellular matrix and are proposed to participate in epithelial-mesenchymal transition. We characterized the invasiveness of 9 established GBM cell lines using an invadopodia assay and performed quantitative mass spectrometry-based proteomic analyses on enriched membrane fractions. All GBM cells produced invadopodia, with a 65% difference between the most invasive cell line (U87MG) and the least invasive cell line (LN229) (p = 0.0001). Overall, 1,141 proteins were identified in the GBM membrane proteome; the levels of 49 proteins correlated with cell invasiveness. Ingenuity Pathway Analysis predicted activation "cell movement" (z-score = 2.608, p = 3.94E(-04)) in more invasive cells and generated a network of invasion-associated proteins with direct links to key regulators of invadopodia formation. Gene expression data relating to the invasion-associated proteins ITGA5 (integrin α5), CD97, and ANXA1 (annexin A1) showed prognostic significance in independent GBM cohorts. Fluorescence microscopy demonstrated ITGA5, CD97, and ANXA1 localization in invadopodia assays, and small interfering RNA knockdown of ITGA5 reduced invadopodia formation in U87MG cells. Thus, invasion-associated proteins, including ITGA5, may prove to be useful anti-invasive targets; volociximab, a therapeutic antibody against integrin α5β1, may be useful for treatment of patients with GBM.

G protein-coupled receptors as oncogenic signals in glioma: emerging therapeutic avenues

Gliomas are the most common malignant intracranial tumors. Newly developed targeted therapies for these cancers aim to inhibit oncogenic signals, many of which emanate from receptor tyrosine kinases, including the epidermal growth factor receptor (EGFR) and the vascular endothelial growth factor receptor (VEGFR). Unfortunately, the first-generation treatments targeting these oncogenic signals provide little survival benefit in both mouse xenograft models and human patients. The search for new treatment options has uncovered several G protein-coupled receptor (GPCR) candidates and generated a growing interest in this class of proteins as alternative therapeutic targets for the treatment of various cancers, including glioblastoma multiforme (GBM). GPCRs constitute a large family of membrane receptors that influence oncogenic pathways through canonical and non-canonical signaling. Accordingly, evidence indicates that GPCRs display a unique ability to crosstalk with receptor tyrosine kinases, making them important molecular components controlling tumorigenesis. This review summarizes the current research on GPCR functionality in gliomas and explores the potential of modulating these receptors to treat this devastating disease.

miR-128 and miR-149 enhance the chemosensitivity of temozolomide by Rap1B-mediated cytoskeletal remodeling in glioblastoma

Glioblastoma multiforme (GBM) is one of the most deadly diseases affecting humans, and is often characterized by poor survival and by high resistance to chemotherapy and radiotherapy. Temozolomide (TMZ) is an oral alkylating agent which is widely used in the treatment of GBM following surgery. Although TMZ may restrain GBM growth, TMZ resistance is also common and accounts for numerous cases of treatment failure. Studies indicate that aberrant miRNA expression is associated with hallmark malignant properties of GBM. Thus, miRNA-based anticancer therapeutic approaches have been exploited, either alone or in combination with standard targeted therapies to enhance the efficacy of chemotherapy agents. In the present study, we demonstrated that the expression of miR-128 and miR-149 was downregulated in glioblastoma, and their overexpression inhibited the invasion of glioblastoma cells by targeting Rap1B-mediated cytoskeletal and related molecular alterations. Moreover, miR-128 and miR-149 enhanced the chemosensitivity of glioblastoma cells to TMZ.

miR-181 subunits enhance the chemosensitivity of temozolomide by Rap1B-mediated cytoskeleton remodeling in glioblastoma cells

Glioblastoma multiforme (GBM) is the most malignant and frequent brain tumor, with an aggressive growth pattern and poor prognosis despite best treatment modalities. Although chemotherapy with temozolomide (TMZ) may restrain tumor growth for some months, TMZ resistance is also common and accounts for many treatment failures. Research into microRNA's role in GBM has shown that microRNAs play a key regulatory role in the GBM, making it a potential therapeutic target. In this study, we demonstrated that the lower expression of miR-181a/b/c/d subunits contributes to astrocytoma tumorigenesis, and their overexpression could inhibit the invasive proliferation of glioblastoma cells by targeting Rap1B-mediated cytoskeleton remodeling and related molecular (Cdc42, RhoA and N-cadherin) changes, suggesting that miR-181 was a critical regulator and might be an important target for glioblastoma treatment. TMZ as a standard chemotherapeutic agent for GBM inhibited the Rap1B expression and actin cytoskeleton remodeling to exert its cell killing by upregulating miR-181a/b/c/d subunits; conversely, each miR-181a/b/c/d subunit enhanced the chemosensitivity of TMZ in glioblastoma cells.

Inhibition of interleukin-1β production by extracellular acidification through the TDAG8/cAMP pathway in mouse microglia

Interleukin-1β (IL-1β) is released from activated microglia and involved in the neurodegeneration of acute and chronic brain disorders, such as stroke and Alzheimer's disease, in which extracellular acidification has been shown to occur. Here, we examined the extracellular acidic pH regulation of IL-1β production, especially focusing on TDAG8, a major proton-sensing G-protein-coupled receptor, in mouse microglia. Extracellular acidification inhibited lipopolysaccharide -induced IL-1β production, which was associated with the inhibition of IL-1β cytoplasmic precursor and mRNA expression. The IL-1β mRNA and protein responses were significantly, though not completely, attenuated in microglia derived from TDAG8-deficient mice compared with those from wild-type mice. The acidic pH also stimulated cellular cAMP accumulation, which was completely inhibited by TDAG8 deficiency. Forskolin and a cAMP derivative, which specifically stimulates protein kinase A (PKA), mimicked the proton actions, and PKA inhibitors reversed the acidic pH-induced IL-1β mRNA expression. The acidic pH-induced inhibitory IL-1β responses were accompanied by the inhibition of extracellular signal-related kinase and c-Jun N-terminal kinase activities. The inhibitory enzyme activities in response to acidic pH were reversed by the PKA inhibitor and TDAG8 deficiency. We conclude that extracellular acidic pH inhibits lipopolysaccharide-induced IL-1β production, at least partly, through the TDAG8/cAMP/PKA pathway, by inhibiting extracellular signal-related kinase and c-Jun N-terminal kinase activities, in mouse microglia.

Regulation of RAP1B by miR-139 suppresses human colorectal carcinoma cell proliferation

BACKGROUND

MicroRNAs (miRNAs) are strongly implicated in carcinogenesis, but their specific roles in the major cancers have yet to be fully elucidated.

METHODS

The expression levels of miR-139 in colorectal carcinoma and paired normal tissues were examined using real-time PCR assays. Potential functions of miR-139 were evaluated in colorectal carcinoma cell lines (SW480, SW620, LS174 T, and HCT116) using miR-139 mimics, anti-miR-139, and siRNA RAP1B.

RESULTS

In this study, we determined that miR-139 is down-regulated in colorectal carcinoma (CRC) tissues. Lower miR-139 expression correlates with more advanced CRC and lower overall survival of patients with CRC. The ectopic expression of miR-139 in human CRC cells decreased cell growth and tumorigenicity, whereas the silencing of miR-139 promoted cell growth. Mechanistic studies revealed that miR-139 repressed the activity of a reporter gene fused to the 3'-untranslated region of RAP1B, whereas miR-139 silencing up-regulated the expression of the reporter gene. RNAi-mediated knockdown of RAP1B phenocopied the antiproliferative effect of miR-139, whereas the overexpression of RAP1B blocked miR-139-mediated antiproliferative effects in CRC cells.

CONCLUSIONS

Taken together, these results demonstrated that miR-139 decreases proliferation by directly targeting RAP1B, defining miR-139 as a new putative tumour suppressor miRNA in CRC.

Rho GTPases in primary brain tumor malignancy and invasion

Gliomas are the most common type of malignant primary brain tumor in humans, accounting for 80 % of malignant cases. Expression and activity of Rho GTPases, which coordinate several cellular processes including cell-cycle progression and cell migration, are commonly altered in many types of primary brain tumor. Here we review the suggested effects of deregulated Rho GTPase signaling on brain tumor malignancy, highlighting the controversy in the field. For instance, whereas expression of RhoA and RhoB has been found to be significantly reduced in astrocytic tumors, other studies have reported Rho-dependent LPA-induced migration in glioma cells. Moreover, whereas the Rac1 expression level has been found to be reduced in astrocytic tumor, it was overexpressed and induced invasion in medulloblastoma tumors. In addition to the Rho GTPases themselves, several of their downstream effectors (including ROCK, mDia, and N-WASP) and upstream regulators (including GEFs, GAPs, PI3K, and PTEN) have also been implicated in primary brain tumors.

Acute activation of β2-adrenergic receptor regulates focal adhesions through βArrestin2- and p115RhoGEF protein-mediated activation of RhoA

β(2)-Adrenergic receptors (β(2)ARs) regulate cellular functions through G protein-transduced and βArrestin-transduced signals. β(2)ARs have been shown to regulate cancer cell migration, but the underlying mechanisms are not well understood. Here, we report that β(2)AR regulates formation of focal adhesions, whose dynamic remodeling is critical for directed cell migration. β(2)ARs induce activation of RhoA, which is dependent on βArrestin2 but not G(s). βArrestin2 forms a complex with p115RhoGEF, a guanine nucleotide exchange factor for RhoA that is well known to be activated by G(12/13)-coupled receptors. Our results show that βArrestin2 forms a complex with p115RhoGEF in the cytosol in resting cells. Upon β(2)AR activation, both βArrestin2 and p115RhoGEF translocate to the plasma membrane, with concomitant activation of RhoA and formation of focal adhesions and stress fibers. Activation of RhoA and focal adhesion remodeling may explain, at least in part, the role of β(2)ARs in cell migration. These results suggest that βArrestin2 may serve as a convergence point for non-G(12/13) and non-G(q) protein-coupled receptors to activate RhoA.

Activation of tumor suppressor protein PTEN and induction of apoptosis are involved in cAMP-mediated inhibition of cell number in B92 glial cells

During brain development, cAMP induces morphological changes and inhibits growth effects in several cell types. However, the molecular mechanisms underlying the growth inhibition remain unknown. Tumor suppressor protein phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a lipid phosphatase that inhibits the phosphoinositide 3-kinase (PI3K) pathway. The phosphorylation of Akt, which is one of the key molecules downstream of PI3K, inhibits apoptosis. In this study, we investigated the role of PTEN in cAMP-mediated growth inhibition. B92 rat glial cells were treated with 2 different cAMP stimulatory agents, a phosphodiesterase (PDE) inhibitor and a β-adrenoceptor agonist. Both cAMP stimulatory agents induced marked morphological changes in the cells, decreased cell number, decreased Akt phosphorylation, activated PTEN, cleaved caspase-3, and induced the condensation and fragmentation of nuclei. These results indicate that the cAMP stimulatory agents induced apoptosis. Protein phosphatase inhibitor prevented cAMP-induced dephosphorylation of PTEN and Akt. In addition, cAMP analogs and Epac-selective agonists affected PTEN and Akt activities. These results suggested that cAMP-induced apoptosis may be mediated by PTEN activation and Akt inhibition through protein phosphatase in B92 cells. Our results provide new insight into the role of PTEN in cAMP-induced apoptosis in glial cells.