Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0017636 (glioblastoma)
 18,345 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

PTEN/MMAC1/TEP1 is a tumor suppressor that possesses intrinsic phosphatase activity. Deletions or mutations of its encoding gene are associated with a variety of human cancers. However, very little is known about the molecular mechanisms by which this important tumor suppressor regulates cell growth. Here, we show that PTEN expression potently suppressed the growth and tumorigenicity of human glioblastoma U87MG cells. The growth suppression activity of PTEN was mediated by its ability to block cell cycle progression in the G1 phase. Such an arrest correlated with a significant increase of the cell cycle kinase inhibitor p27(KIP1) and a concomitant decrease in the activities of the G1 cyclin-dependent kinases. PTEN expression also led to the inhibition of Akt/protein kinase B, a serine-threonine kinase activated by the phosphatidylinositol 3-kinase (PI 3-kinase) signaling pathway. In addition, the effect of PTEN on p27(KIP1) and the cell cycle can be mimicked by treatment of U87MG cells with LY294002, a selective inhibitor of PI 3-kinase. Taken together, our studies suggest that the PTEN tumor suppressor modulates G1 cell cycle progression through negatively regulating the PI 3-kinase/Akt signaling pathway, and one critical target of this signaling process is the cyclin-dependent kinase inhibitor p27(KIP1).
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PMID:PTEN/MMAC1/TEP1 suppresses the tumorigenicity and induces G1 cell cycle arrest in human glioblastoma cells. 986 Sep 81

The tumor suppressor protein PTEN is mutated in glioblastoma multiform brain tumors, resulting in deregulated signaling through the phosphoinositide 3-kinase (PI3K)-protein kinase B (PKB) pathway, which is critical for maintaining proliferation and survival. We have examined the relative roles of the two major phospholipid products of PI3K activity, phosphatidylinositol 3,4-biphosphate [PtdIns(3,4)P2] and phosphatidylinositol 3,4,5-triphosphate [PtdIns(3,4,5)P3], in the regulation of PKB activity in glioblastoma cells containing high levels of both of these lipids due to defective PTEN expression. Reexpression of PTEN or treatment with the PI3K inhibitor LY294002 abolished the levels of both PtdIns(3, 4)P2 and PtdIns(3,4,5)P3, reduced phosphorylation of PKB on Thr308 and Ser473, and inhibited PKB activity. Overexpression of SHIP-2 abolished the levels of PtdIns(3,4,5)P3, whereas PtdIns(3,4)P2 levels remained high. However, PKB phosphorylation and activity were reduced to the same extent as they were with PTEN expression. PTEN and SHIP-2 also significantly decreased the amount of PKB associated with cell membranes. Reduction of SHIP-2 levels using antisense oligonucleotides increased PKB activity. SHIP-2 became tyrosine phosphorylated following stimulation by growth factors, but this did not significantly alter its phosphatase activity or ability to antagonize PKB activation. Finally we found that SHIP-2, like PTEN, caused a potent cell cycle arrest in G(1) in glioblastoma cells, which is associated with an increase in the stability of expression of the cell cycle inhibitor p27(KIP1). Our results suggest that SHIP-2 plays a negative role in regulating the PI3K-PKB pathway.
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PMID:5' phospholipid phosphatase SHIP-2 causes protein kinase B inactivation and cell cycle arrest in glioblastoma cells. 1095 82

The PTEN tumor suppressor acts as a phosphatase for phosphatidylinositol-3,4,5-trisphosphate (PIP3) [1, 2]. We have shown previously that PTEN negatively controls the G1/S cell cycle transition and regulates the levels of p27(KIP1), a CDK inhibitor [3, 4]. Recently, we and others have identified an ubiquitin E3 ligase, the SCF(SKP2) complex, that mediates p27 ubiquitin-dependent proteolysis [5-7]. Here we report that PTEN and the PI 3-kinase pathway regulate p27 protein stability. PTEN-deficiency in mouse embryonic stem (ES) cells causes a decrease of p27 levels with concomitant increase of SKP2, a key component of the SCF(SKP2) complex. Conversely, in human glioblastoma cells, ectopic PTEN expression leads to p27 accumulation, which is accompanied by a reduction of SKP2. We found that ectopic expression of SKP2 alone is sufficient to reverse PTEN-induced p27 accumulation, restore the kinase activity of cyclin E/CDK2, and partially overcome the PTEN-induced G1 cell cycle arrest. Consistently, recombinant SCF(SKP2) complex or SKP2 protein alone can rescue the defect in p27 ubiquitination in extracts prepared from cells treated with a PI 3-kinase inhibitor. Our findings suggest that SKP2 functions as a critical component in the PTEN/PI 3-kinase pathway for the regulation of p27(KIP1) and cell proliferation.
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PMID:PTEN regulates the ubiquitin-dependent degradation of the CDK inhibitor p27(KIP1) through the ubiquitin E3 ligase SCF(SKP2). 1125 Jan 55

Aberrant epidermal growth factor receptor (EGFR) signaling is a typical oncogenic signature in glioblastoma. Here, we show that EGFR inhibition in primary glioma stem cells (GSCs) with oncogenic EGFRvIII and EGFRvIII-transduced glioma stem-like cells promotes invasion by decreasing ID3 levels. ID3 suppresses GSC invasiveness by inhibiting p27(KIP1)-RhoA-dependent migration and MMP3 expression. Xenograft and human glioblastoma specimens show that ID3 localizes within glioblastoma cores, whereas p27(KIP1) and MMP3 are predominantly expressed in glioma cells in invasive fronts. Together, our findings show that EGFR inhibition induces GSC invasiveness by abolishing ID3-mediated inhibition of p27(KIP1) and MMP3 expression.
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PMID:Blockade of EGFR signaling promotes glioma stem-like cell invasiveness by abolishing ID3-mediated inhibition of p27(KIP1) and MMP3 expression. 2302 73

TRIP6 is an adaptor protein that regulates cell motility and antiapoptotic signaling. Although it has been implicated in tumorigenesis, the underlying mechanism remains largely unknown. Here we provide evidence that TRIP6 promotes tumorigenesis by serving as a bridge to promote the recruitment of p27(KIP1) to AKT in the cytosol. TRIP6 regulates the membrane translocation and activation of AKT and facilitates AKT-mediated recognition and phosphorylation of p27(KIP1) specifically at T157, thereby promoting the cytosolic mislocalization of p27(KIP1). This is required for p27(KIP1) to enhance lysophosphatidic acid (LPA)-induced ovarian cancer cell migration. TRIP6 also promotes serum-induced reduction of nuclear p27(KIP1) expression levels through Skp2-dependent and -independent mechanisms. Consequently, knockdown of TRIP6 in glioblastoma or ovarian cancer xenografts restores nuclear p27(KIP1) expression and impairs tumor proliferation. As TRIP6 is upregulated in gliomas and its levels correlate with poor clinical outcomes in a dose-dependent manner, it may represent a novel prognostic marker and therapeutic target in gliomas.
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PMID:TRIP6 regulates p27 KIP1 to promote tumorigenesis. 2333 69

MicroRNAs (miRNAs) control cell cycle progression by targeting the transcripts encoding for cyclins, CDKs and CDK inhibitors, such as p27(KIP1) (p27). p27 expression is controlled by multiple transcriptional and posttranscriptional mechanisms, including translational inhibition by miR-221/222 and posttranslational regulation by the SCF(SKP2) complex. The oncosuppressor activity of miR-340 has been recently characterized in breast, colorectal and osteosarcoma tumor cells. However, the mechanisms underlying miR-340-induced cell growth arrest have not been elucidated. Here, we describe miR-340 as a novel tumor suppressor in non-small cell lung cancer (NSCLC). Starting from the observation that the growth-inhibitory and proapoptotic effects of miR-340 correlate with the accumulation of p27 in lung adenocarcinoma and glioblastoma cells, we have analyzed the functional relationship between miR-340 and p27 expression. miR-340 targets three key negative regulators of p27. The miR-340-mediated inhibition of both Pumilio family RNA-binding proteins (PUM1 and PUM2), required for the miR-221/222 interaction with the p27 3'-UTR, antagonizes the miRNA-dependent downregulation of p27. At the same time, miR-340 induces the stabilization of p27 by targeting SKP2, the key posttranslational regulator of p27. Therefore, miR-340 controls p27 at both translational and posttranslational levels. Accordingly, the inhibition of either PUM1 or SKP2 partially recapitulates the miR-340 effect on cell proliferation and apoptosis. In addition to the effect on tumor cell proliferation, miR-340 also inhibits intercellular adhesion and motility in lung cancer cells. These changes correlate with the miR-340-mediated inhibition of previously validated (MET and ROCK1) and potentially novel (RHOA and CDH1) miR-340 target transcripts. Finally, we show that in a small cohort of NSCLC patients (n=23), representative of all four stages of lung cancer, miR-340 expression inversely correlates with clinical staging, thus suggesting that miR-340 downregulation contributes to the disease progression.
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PMID:miR-340 inhibits tumor cell proliferation and induces apoptosis by targeting multiple negative regulators of p27 in non-small cell lung cancer. 2515 66