Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PTEN”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources
PubMed2003

PTEN reverses MDM2-mediated chemotherapy resistance by interacting with p53 in acute lymphoblastic leukemia cells.

The tumor suppressor PTEN has been associated with the cellular localization of MDM2 in regulation of apoptosis through inhibiting PI3k/Akt signaling. To investigate whether expression of PTEN is involved in MDM2-mediated chemoresistance, we examined a set of acute lymphoblastic leukemia (ALL) cell lines for the expression of PTEN and sensitivity to doxorubicin. Testing 9 ALL cell lines selected for wild-type p53 phenotype and uniformly high levels of MDM2 expression, we initially demonstrated that cell lines with high levels of PTEN expression were sensitive to doxorubicin, whereas lines lacking PTEN expression were generally resistant. Forced expression of PTEN in a PTEN-negative and doxorubicin-resistant ALL line (EU-1) resulted in decreased cell growth and enhanced sensitivity to doxorubicin. Examining the cellular localization of MDM2, we confirmed that the majority of MDM2 is localized in the nucleus in PTEN-negative doxorubicin-sensitive ALL cells, whereas MDM2 is expressed predominantly in the cytoplasm in either PTEN-positive or PTEN-transfected cells. Furthermore, by coimmunoprecipitaton and cotransfection assays, we found that PTEN physically binds p53 in vitro as well as in vivo. Binding of PTEN to p53 attenuated MDM2-mediated p53 inhibition. These results suggest that PTEN inhibits MDM2 and protects p53 through both p13k/Akt-dependent and -independent pathways. Furthermore, loss of PTEN can result in resistance to apoptosis by activating MDM2-mediated antiapoptotic mechanism.

Antibiotics, Antineoplastic↗
PubMed2004

[PTEN and p27Kip1 have a cooperative role on inhibition proliferation, modulation of cell cycle and inducing apoptosis in prostate cancer PC-3 cell].

OBJECTIVES: To investigate whether the human PC-3 cell infected with recombinant Ad-PTEN and Ad-p27Kip1 can steadily produce PTEN and p27Kip1 protein and change the biologic behaviors such as cell proliferation, cell cycle and apoptosis. The synergistic effect of PTEN and p27Kip1 on the therapy for prostate cancer has also been investigated. METHODS: We constructed recombinant adenovirus vector of human tumor suppressor gene PTEN and p27Kip1. The viral titer was examined by plaque assay and the mRNA and protein expressions of PTEN and p27Kip1 in human prostate cancer cell line PC-3 infected with Ad-PTEN and Ad-p27Kip1 were determined by RT-PCR and Western blot respectively. MTT assay was used to determine the effect of PTEN and p27Kip1 on growth and proliferation of PC-3 cell; the change of cell cycle and apoptosis was examined by flow cytometry, and to compare between the combined therapy group and single gene therapy group. RESULTS: The viral titers of Ad-PTEN and Ad-p27Kip1 were 1.8 x 10(7) pfu/ml and 1.2 x 10(9) pfu/ml respectively. After infected by adenovirus, it had been verified that the mRNA and protein expression of PTEN and p27Kip1 were steady in human PC-3 cell. Ad-PTEN and Ad-p27 Kip1 inhibited the growth and proliferation of PC-3 cells. The progression of cell cycle of PC-3 cell was arrested in G(0)-G(1) phase, meanwhile the apoptosis rate of PC-3 was also affected after Ad-PTEN or/and Ad-p27 Kip1 infected. There was significant difference between combined therapy group and single gene therapy group. CONCLUSION: The recombinant Ad-PTEN and Ad-p27Kip1 vector were constructed successfully and the expression of specific PTEN and p27Kip1 was high, steadily in PC-3 cell line. These results suggested that combination of PTEN with p27Kip1 has an application value in treatment of prostate cancer in future.

Adenoviridae↗
PubMed2006

[The relationship between hypermethylation of the PTEN promoter and laryngeal squamous cell carcinoma].

OBJECTIVE: To explore the relationship between hypermethylation of the PTEN gene promoter and laryngeal squamous cell carcinoma (LSCC). METHOD: Promoter hypermethylation and mRNA expression were detected by methylation specific PCR and RT-PCR in LSCC and normal laryngeal tissue. RESULT: Among the 40 patients with LSCC, hypermethylation of PTEN gene promoter was detected in 16 cases (40.0%). Among the nine normal laryngeal tissues, hypermethylation of PTEN gene promoter was detected in no case. The high and moderate expression rates of PTEN gene mRNA in nine normal laryngeal tissues were 77.8% (7/9) and 22.2% (2/9), respectively; The high, moderate, low and negative expression rates of PTEN mRNA in 15 laryngeal cancers with lymph node metastasis were 26.7% (4/15), 33.3% (5/15), 26.7% (4/15) and 13.3% (2/15), respectively. The PTEN mRNA expression in normal laryngeal tissues was higher than that in the laryngeal cancers with lymph node metastasis (P < 0.05). The high, moderate and low expression rates of PTEN mRNA in 10 highly differentiated laryngeal cancers were 60.0% (6/10), 30.0% (3/10) and 10.0% (1/10), respectively; The high, moderate, low and negative expression rates of PTEN mRNA in 12 low differentiated laryngeal cancers were 16.7% (2/12), 25.0% (3/12), 41.7% (5/12) and 16.7% (2/12), respectively. The differences of PTEN mRNA expression between high and low differentiation laryngeal cancers were statistically significant (P < 0.05). The hypermethylation rate of PTEN gene promoter in the low mRNA expression laryngeal cancers was 70.0% (7/10), the hypermethylation rate of PTEN gene promoter in the high mRNA expression laryngeal cancers was 23.5% (4/17). The hypermethylation rate of PTEN gene promoter in the low mRNA expression laryngeal cancers was higher than that in the high mRNA expression laryngeal cancers (P < 0.05). CONCLUSION: Hypermethylation of PTEN gene promoter is associated with loss of its transcription in laryngeal squamous cell carcinoma, the decreasing of PTEN mRNA expression may be related to lymph node metastasis and low differentiation of laryngeal squamous cell carcinoma.

Adult↗
PubMed2002

Expression and prognostic significance of PTEN product protein in patients with esophageal squamous cell carcinoma.

BACKGROUND: PTEN is a candidate tumor-suppressor gene in a variety of malignant tumors. The prognostic importance of PTEN product protein (PTEN) and its correlation with clinicopathologic characteristics have yet to be delineated in patients with esophageal carcinoma. METHODS: Specimens from 97 patients with esophageal squamous cell carcinoma were used for the immunohistochemical evaluation of PTEN expression. RESULTS: PTEN expression was detected in the nucleus in 48 specimens (49.5%). There were statistically significant correlations between nuclear PTEN expression and macroscopic tumor classification, T stage, and American Joint Committee on Cancer (AJCC) stage (P < 0.01), indicating that PTEN expression was down-regulated by advancement of the disease process. There were no statistically significant correlations between nuclear PTEN expression and the intensity and extent of cytoplasmic PTEN expression. The 10-year overall survival rate was significantly better in patients with positive nuclear PTEN expression (n = 48 patients) compared with the rate in patients with negative nuclear PTEN expression (n = 49 patients; P < 0.01). The results of a multivariate analysis of factors that were prognostic for survival showed that AJCC stage (P < 0.05; relative risk, 2.038) and negative nuclear PTEN expression (P < 0.05; relative risk, 1.825) were significant factors indicative of poor survival. CONCLUSIONS: Nuclear PTEN expression may be a favorable biologic marker and a useful prognostic indicator in patients with esophageal squamous cell carcinoma.

Aged↗
PubMed2006

The PTEN gene in locally progressive prostate cancer is preferentially inactivated by bi-allelic gene deletion.

PTEN is frequently inactivated during the development of many cancers, including prostate cancer, and both bi-allelic and mono-allelic PTEN inactivation may contribute to tumorigenesis. PTEN mutations in clinical cancer specimens can easily be recorded but mono- or bi-allelic gene deletions are often difficult to assess. We performed a comprehensive study to detect PTEN inactivation in 40 locally progressive clinical prostate cancer specimens obtained by transurethral resection of the prostate, utilizing a variety of complementary technical approaches. The methods to detect PTEN deletion included allelotype analysis, dual-colour FISH and array-based CGH. We also applied a novel semi-quantitative approach, assessing the PTEN-WT (wild-type): PTEN-Psi (pseudogene) ratio (WPR). Structural analysis of PTEN was performed by single-strand conformational polymorphism (PCR-SSCP) and sequencing. PTEN protein expression was assessed by immunohistochemistry. Our data predict complete PTEN inactivation in 12 samples (30%), nine of these by bi-allelic deletion. Loss of one PTEN copy was also detected by several methodologies but the number could not be accurately assessed. Immunohistochemistry indicated the absence of PTEN protein in 15 samples, and heterogeneous expression of the protein in eight tumours. Taken together, these data show that bi-allelic deletion is a major mechanism of PTEN inactivation in locally progressive prostate cancer.

Chromosomes, Human, Pair 10↗
PubMed2003

The coexistence of ERBB2, INT2, and CMYC oncogene amplifications and PTEN gene mutations in endometrial carcinoma.

PURPOSE: To evaluate the frequency of ERBB2, INT2 and CMYC oncogene amplifications and their coexistence with PTEN gene mutations in endometrial carcinomas. METHODS: In 54 endometrial carcinomas amplification of ERBB2, INT2 and CMYC was determined using differential polymerase chain reaction (dPCR), and mutations in all exons of PTEN were investigated by PCR-SSCP and direct sequencing methods. Results were correlated with clinicopathological features of tumors. RESULTS: In 31 out of 54 endometrial carcinomas (57.4%) genetic defects were found within the examined genes. Of all identified defects, mutations in PTEN and the amplification of CMYC were most frequent (26/54-48.1% and 10/54-18.5%, respectively). INT2 was amplified in 5.6% (3/54) of cases. In no case did we find ERBB2 amplification. In 77.4% (24/31) of cases only one gene was damaged. Of these, 20 cases showed only PTEN mutations, three cases only CMYC, and one case only INT2 amplification. In another seven out of 31 tumors (22.5%) defects in two or three genes coexisted simultaneously: PTEN and CMYC in five cases, CMYC and INT2 in one case, and PTEN, CMYC, and INT2 in one case. We found a number of interesting relations between the location of mutations within the PTEN sequence and the presence (+) or lack (-) of CMYC amplification. In the PTEN+CMYC- tumors the PTEN mutations were most frequent in exons 1-5, and less frequent in exons 7-8 (66.7% and 33.3%, respectively). In contrast, in the PTEN+CMYC+ carcinomas the PTEN mutations were found mainly in exons 7-8 (85.7%). PTEN mutations were equally frequent in both early and more advanced endometrial carcinomas. The CMYC amplification, however, was more frequent in advanced as compared to early tumors, although this difference did not reach statistical significance. CONCLUSIONS: Our data suggest that differences in the presence of genetic defects may reflect the different molecular pathways of endometrial carcinogenesis. These data also suggest that location of intragenic PTEN mutations and their coexistence with the CMYC amplification may play a crucial part in the development of various subtypes of endometrial carcinoma, but this preliminary suggestion requires further research.

Carcinoma, Endometrioid↗
PubMed2005

PTEN expression in non-small-cell lung cancer: evaluating its relation to tumor characteristics, allelic loss, and epigenetic alteration.

The tumor suppressor PTEN encodes a lipid phosphatase that negatively regulates the phosphatidylinositol 3-kinase/AKT cell survival pathway. Mutations of this gene are common in brain, prostate, endometrial, and gastric cancers but occur rarely in non-small-cell lung cancer (NSCLC), although the PTEN protein is often lost in lung tumors. We have studied hypermethylation of the PTEN promoter, loss of heterozygosity (LOH) at microsatellites in chromosome 10q23 (surrounding and intragenic to the PTEN locus), and hypermethylation of PTEN's highly homologous pseudogene, PTENP1, and their association with PTEN protein loss in a surgical case series study of primary NSCLC. PTEN protein expression was reduced or lost in 74% (86/117) of tumors, with loss occurring more often in well to moderately differentiated tumors. In squamous cell carcinomas, PTEN loss occurred significantly more often in early-stage (stage I or II) disease. PTEN protein loss also occurred more frequently in tumors with low to no aberrant TP53 staining. Methylation of PTEN occurred in 26% (39/151) of tumors, and LOH at 10q23 was rare, occurring in only 19% (17/90) of informative tumors. Neither methylation nor LOH was a significant predictor of PTEN protein expression, although LOH occurred exclusively in early-stage disease. In NSCLC, loss of PTEN protein expression occurs frequently, although the mechanism responsible for loss is not clearly attributable to deletion or epigenetic silencing. PTEN loss may also be a favorable prognostic marker, although further studies are needed to confirm this finding.

Aged↗
PubMed2006

PTEN mutation, expression and LOH at its locus in ovarian carcinomas. Relation to TP53, K-RAS and BRCA1 mutations.

OBJECTIVE: We aimed to evaluate frequency of PTEN mutation, LOH and expression in ovarian tumors. In search for a molecular pathway, we confronted PTEN gene mutations with TP53, K-RAS and BRCA1 gene status in the same tumors. We also evaluated clinical significance of PTEN expression in a subgroup of patients uniformly treated with platinum-based regimens. METHODS: Molecular analysis was performed on 105 ovarian tumors (100 carcinomas) with the use of the SSCP and sequencing. Seventy-six tumors were analyzed for LOH at 10q23 locus with the use of six polymorphic markers. Immunohistochemical PTEN expression was done on paraffin-embedded material. Multivariate and univariate analysis was performed with the STATA program. RESULTS: PTEN mutations occurred in 5/100 (5%) of all carcinomas and in 3/15 (20%) of endometrioid carcinomas (EC). Low-grade EC that developed in borderline tumors had PTEN and/or K-RAS mutation (4/5, 80%), while high-grade EC had TP53 mutations only. There was a reverse association between PTEN and TP53 mutations (P = 0.005). LOH at PTEN locus was found in 60% of endometrioid and in 28% of serous and clear cell carcinomas. PTEN expression did not associate with PTEN mutations or LOH. Strong PTEN expression diminished risk of death in a TP53 positive group only (HR = 0.35, P = 0.029). CONCLUSION: Our results suggest that PTEN mutations may play a role in a development of low-grade endometrioid tumors. PTEN haploinsufficiency caused by LOH or epigenetic events may possibly contribute to development of other histological types and may be an adverse prognostic factor.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2005

Immunohistochemical analysis of PTEN in endometrial carcinoma: a tissue microarray study with a comparison of four commercial antibodies in correlation with molecular abnormalities.

The tumor suppressor gene PTEN/MMAC1 is located on chromosome 10q23.3. Inactivation of PTEN, either by mutations, deletions, or promoter hypermethylation, has been identified in a wide variety of tumors. Inactivation of the two alleles of PTEN is required, because it is a tumor suppressor gene. Immunohistochemical staining may be an effective screening method to demonstrate the absence of the protein in tumors exhibiting PTEN inactivation. We studied a tissue microarray, constructed from paraffin-embedded blocks of 95 endometrial carcinomas, 38 of them previously evaluated for alterations in PTEN. We also studied cell blocks obtained from one PTEN-defective endometrial cancer cell line, after transfection with either a plasmid encoding wild-type PTEN or the empty vector. The tumor samples were tested with four different anti-PTEN commercial antibodies: a polyclonal antibody, the monoclonal antibody 28H6, the monoclonal antibody 10P03, and the monoclonal antibody 6.H2.1. Results were correlated with the presence of abnormalities in PTEN, as well as with the immunohistochemical expression of phosphorylated AKT. Antibody 28H6 produced a predominant nuclear staining, while the other three antibodies produced a predominant cytoplasmic staining. There was no significant correlation between the results obtained with the four antibodies. The monoclonal antibody 6.H2.1 was the only one that exhibited a correlation with the presence of molecular alterations in PTEN, and a statistically significant association with immunostaining for phosphorylated AKT (r=-0.249, P=0.037). The monoclonal antibody 10P03 exhibited an association with phospho-AKT that did not have statistical significance. Both 6.H2.1 and 10P03 antibodies stained PTEN-transfected cells, and were negative in the PTEN-deficient cell line blocks. The polyclonal antibody and the monoclonal antibody 28H6 produced positive staining in PTEN-deficient cell line blocks, suggesting nonspecific staining. The results indicate that monoclonal antibody 6.H2.1 may be a suitable alternative for tumors with inactivation of PTEN.

Antibodies, Monoclonal↗
PubMed2003

Adenovirus-mediated transfer of the PTEN gene inhibits human colorectal cancer growth in vitro and in vivo.

The tumor-suppressor gene PTEN encodes a multifunctional phosphatase that is mutated in a variety of human cancers. PTEN inhibits the phosphatidylinositol 3-kinase pathway and downstream functions, including activation of Akt/protein kinase B (PKB), cell survival, and cell proliferation in tumor cells carrying mutant- or deletion-type PTEN. In such tumor cells, enforced expression of PTEN decreases cell proliferation through cell-cycle arrest at G1 phase accompanied, in some cases, by induction of apoptosis. More recently, the tumor-suppressive effect of PTEN has been reported in ovarian and thyroid tumors that are wild type for PTEN. In the present study, we examined the tumor-suppressive effect of PTEN in human colorectal cancer cells that are wild type for PTEN. Adenoviral-mediated transfer of PTEN (Ad-PTEN) suppressed cell growth and induced apoptosis significantly in colorectal cancer cells (DLD-1, HT29, and SW480) carrying wtPTEN than in normal colon fibroblast cells (CCD-18Co) carrying wtPTEN. This suppression was induced through downregulation of the Akt/PKB pathway, dephosphorylation of focal adhesion kinase (FAK) and mitogen-activated protein kinase (MAPK) and cell-cycle arrest at the G2/M phase, but not the G1 phase. Furthermore, treatment of human colorectal tumor xenografts (HT-29, and SW480) with Ad-PTEN resulted in significant (P=0.01) suppression of tumor growth. These results indicate that Ad-PTEN exerts its tumor-suppressive effect on colorectal cancer cells through inhibition of cell-cycle progression and induction of cell death. Thus Ad-PTEN may be a potential therapeutic for treatment of colorectal cancers.

Adenoviridae↗
PubMed2003

Preferential killing of PTEN-null myelomas by PI3K inhibitors through Akt pathway.

We recently reported that internal deletion of PTEN tumor suppressor gene in OPM2 and Delta47 myeloma lines led to high Akt activation. Re-expression of PTEN induced strong apoptosis and growth inhibition. To understand the biologic importance of the phosphatidylinositol 3 kinase (PI3K)/Akt activation affected by PTEN deletion, we analysed apoptosis and growth inhibition by applying PI3K inhibitors to myeloma lines and by expressing Akt constructs. The PI3K inhibitors preferentially suppressed PTEN-null myeloma growth to those expressing PTEN, indicating that PI3K activation is more critical for growth and survival of those lines with PTEN mutations than others expressing a functional PTEN gene. Since PTEN-null myeloma lines exhibited much stronger Akt activation than PTEN-expressing cells in response to insulin-like growth factor I stimulation, we determined whether Akt could be responsible for PI3K-mediated cell survival and growth of PTEN-null myeloma lines. Expression of an active Akt, but not its kinase dead mutant, reversed wortmannin- and dexamethasone-induced apoptosis and growth inhibition in PTEN-null myeloma lines, suggesting that Akt lies downstream of PI3K for PTEN-null myeloma survival and dexamethasone resistance. In summary, we have provided evidence that PTEN-null myeloma cells are stringently dependent on the PI3K/Akt activation for cell survival. These results may provide a basis to treat myeloma patients with PI3K and Akt inhibitors.

Androstadienes↗
PubMed2004

Regulation of c-Met-dependent gene expression by PTEN.

Receptor tyrosine kinases (RTK) and the tumor suppressor PTEN co-regulate oncogenic cell signaling pathways. How these interactions influence gene transcription is inadequately understood. We used expression microarrays to investigate the effects of PTEN on gene expression changes caused by activating c-Met in human glioblastoma cells. c-Met activation by scatter factor/hepatocyte growth factor (SF/HGF) altered the expression of 27-fold more genes in PTEN-null U-373MG cells than in PTEN homozygous primary normal human astrocytes (523 vs 19 genes). Restoring wt-PTEN in U-373MG cells dramatically altered patterns of c-Met regulated gene expression. This effect was varied depending on the specific gene in question. PTEN reduced the number of c-Met regulated transcripts from 931 to 502, decreased the relative number of genes upregulated by c-Met from 46 to 25%, and increased the relative number of downregulated genes from 54 to 75%. PTEN and c-Met co-regulated many genes involved in cell growth regulation such as oncogenes, growth factors, transcription factors, and constituents of the ubiquitin pathway. c-Met activation in PTEN-null (but not PTEN reconstituted) cells led to upregulation of the EGFR agonist TGFalpha and subsequently to EGFR activation. Using PTEN mutants, we found that PTEN's transcriptional effects were either lipid-phosphatase dependent, protein-phosphatase dependent, or phosphatase-independent. These results show that PTEN has critical and mechanistically complex effects on RTK-regulated gene transcription. These findings expand our understanding of tumor promoter/suppressor inter-relationships and downstream transcriptional effects of PTEN loss and c-Met overexpression in malignant gliomas.

Blotting, Northern↗
PubMed2003

Zinc-induced PTEN protein degradation through the proteasome pathway in human airway epithelial cells.

The tumor suppressor PTEN is a putative negative regulator of the phosphatidylinositol 3-kinase/Akt pathway. Exposure to Zn2+ ions induces Akt activation, suggesting that PTEN may be modulated in this process. Therefore, the effects of Zn2+ on PTEN were studied in human airway epithelial cells and rat lungs. Treatment with Zn2+ resulted in a significant reduction in levels of PTEN protein in a dose- and time-dependent fashion in a human airway epithelial cell line. This effect of Zn2+was also observed in normal human airway epithelial cells in primary culture and in rat airway epithelium in vivo. Concomitantly, levels of PTEN mRNA were also significantly reduced by Zn2+ exposure. PTEN phosphatase activity evaluated by measuring Akt phosphorylation decreased after Zn2+ treatment. Pretreatment of the cells with a proteasome inhibitor significantly blocked zinc-induced reduction of PTEN protein as well as the increase in Akt phosphorylation, implicating the involvement of proteasome-mediated PTEN degradation. Further study revealed that Zn2+-induced ubiquitination of PTEN protein may mediate this process. A phosphatidylinositol 3-kinase inhibitor blocked PTEN degradation induced by Zn2+, suggesting that phosphatidylinositol 3-kinase may participate in the regulation of PTEN. However, both the proteasome inhibitor and phosphatidylinositol 3-kinase inhibitor failed to prevent significant down-regulation of PTEN mRNA expression in response to Zn2+. In summary, exposure to Zn2+ ions causes PTEN degradation and loss of function, which is mediated by an ubiquitin-associated proteolytic process in the airway epithelium.

Animals↗
PubMed2005

Genetic analysis of Pten and Tsc2 functional interactions in the mouse reveals asymmetrical haploinsufficiency in tumor suppression.

The role of tumor suppressor haploinsufficiency in oncogenesis is still poorly understood. The PTEN and TSC2 tumor suppressors function to antagonize mTOR (mammalian target of rapamycin) activation by Akt; hence, compound heterozygous inactivation of Pten and Tsc2 in the mouse may in principle exacerbate the tumor phenotypes observed in the single mutants in a reciprocal manner. In contrast, we found that while Tsc2 heterozygosity unmasks Pten haploinsufficiency in growth and tumor suppression, tumorigenesis in Tsc2+/- mutants is surprisingly not accelerated by Pten heterozygosity, even though mTOR activation is cooperatively enhanced by compound Pten/Tsc2 heterozygosity. We show that the wild-type alleles of both Pten and Tsc2 are retained in prostate tumors from both Pten+/- and Pten+/-Tsc2+/- mice, whereas TSC-related tumor lesions are invariably associated with Tsc2 loss of heterozygosity (LOH) in both Tsc2+/- and Pten+/-Tsc2+/- mice. These findings demonstrate that inactivation of TSC2 is epistatic to PTEN in the control of tumor initiation and progression and, importantly, that both Pten and Tsc2 are haploinsufficient for suppression of tumorigenesis initiated by Pten heterozygosity, while neither Pten nor Tsc2 is haploinsufficient for repression of carcinogenesis arising from Tsc2 heterozygosity, providing a rationale for the differential cancer susceptibility of the two human conditions associated with PTEN or TSC2 heterozygous mutations.

Animals↗
PubMed2005

PTEN represses RNA Polymerase I transcription by disrupting the SL1 complex.

PTEN is a tumor suppressor whose function is frequently lost in human cancer. It possesses a lipid phosphatase activity that represses the activation of PI3 kinase/Akt signaling, leading to decreased cell growth, proliferation, and survival. The potential for PTEN to regulate transcription of the large rRNAs by RNA polymerase I (RNA Pol I) was investigated. As increased synthesis of rRNAs is a hallmark of neoplastic transformation, the ability of PTEN to control the transcription of rRNAs might be crucial for its tumor suppressor function. The expression of PTEN in PTEN-deficient cells represses RNA Pol I transcription, while decreasing PTEN expression enhances transcription. PTEN-mediated repression requires its lipid phosphatase activity and is independent of the p53 status of the cell. This event can be uncoupled from PTEN's ability to regulate the cell cycle. RNA Pol I is regulated through PI3 kinase/Akt/mammalian target of rapamycin/S6 kinase, and the expression of constitutively activated S6 kinase is able to abrogate transcription repression by PTEN. No change in the expression of the RNA Pol I transcription components, upstream binding factor or SL1, was observed upon PTEN expression. However, chromatin immunoprecipitation assays demonstrate that PTEN differentially reduces the occupancy of the SL1 subunits on the rRNA gene promoter. Furthermore, PTEN induces dissociation of the SL1 subunits. Together, these results demonstrate that PTEN represses RNA Pol I transcription through a novel mechanism that involves disruption of the SL1 complex.

Cell Line, Tumor↗
PubMed2004

Control of phosphatase and tensin homolog (PTEN) gene expression in normal and neoplastic thyroid cells.

The lipid phosphatase, phosphatase and tensin homolog (PTEN), is a key element in controlling cell growth and survival and has a well established role as tumor suppressor protein in many neoplasia. Several data indicate that silencing of PTEN gene expression may be relevant in follicular thyroid cell transformation. Thus, in the present study regulation of PTEN gene expression in thyroid cells was investigated. Cotransfection experiments indicated that in normal FRTL-5 rat thyroid cells, PTEN promoter activity was increased by overexpression of the transcription factor early growth response protein-1 (Egr-1). Moreover, Western blot experiments indicated that when Egr-1 expression was up-regulated by treating FRTL-5 cells with H2O2, an increase in PTEN expression was also observed. TSH induced opposite modifications on PTEN and Egr-1 protein levels. Moreover, acute or chronic TSH stimulation determined distinct effects. In fact, acute TSH stimulation (30 and 60 min) induced a decrease in PTEN, but an increase in Egr-1 protein levels. These effects were cAMP dependent; in fact, they were mimicked by forskolin. A chronic TSH treatment (5 d) stimulated PTEN protein expression, whereas Egr-1 protein was down-regulated. In contrast to normal thyroid cells, when the thyroid tumor cell lines ARO and BCPAP were exposed to H2O2, neither Egr-1 nor PTEN protein levels were increased. Acute stimulation of ARO and BCPAP cells with forskolin increased Egr-1, but not PTEN, protein levels. Therefore, thyroid tumor cell lines show alteration of PTEN gene expression regulation. RT-PCR experiments performed on human thyroid tumors showed that the absence of Egr-1 mRNA is always paralleled by the absence of PTEN mRNA. Thus, modification of the Egr-1-dependent mechanisms may play a role in the silencing of PTEN gene expression occurring during thyroid cell transformation.

Animals↗
PubMed2001

Regulation of phosphoinositide metabolism, Akt phosphorylation, and glucose transport by PTEN (phosphatase and tensin homolog deleted on chromosome 10) in 3T3-L1 adipocytes.

To investigate the roles of PTEN (phosphatase and tensin homolog deleted on chromosome 10) in the regulation of 3-position phosphorylated phosphoinositide metabolism as well as insulin-induced Akt phosphorylation and glucose metabolism, wild-type PTEN and its phosphatase-dead mutant (C124S) with or without an N-terminal myristoylation tag were overexpressed in Sf-9 cells and 3T3-L1 adipocytes using baculovirus and adenovirus systems, respectively. When expressed in Sf-9 cells together with the p110alpha catalytic subunit of phosphoinositide 3-kinase, myristoylated PTEN markedly reduced the accumulations of both phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate induced by p110alpha. In contrast, overexpression of the C124S mutants apparently increased these accumulations. In 3T3-L1 adipocytes, insulin-induced accumulations of phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate were markedly suppressed by overexpression of wild-type PTEN with the N-terminal myristoylation tag, but not by that without the tag. On the contrary, the C124S mutants of PTEN enhanced insulin-induced accumulations of phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate. Interestingly, the phosphorylation level of Akt at Thr308 (Akt2 at Thr309), but not at Ser473 (Akt2 at Ser474), was revealed to correlate well with the accumulation of phosphatidylinositol 3,4,5-trisphosphate modified by overexpression of these PTEN proteins. Finally, insulin-induced increases in glucose transport activity were significantly inhibited by the overexpression of myristoylated wild-type PTEN, but were not enhanced by expression of the C124S mutant of PTEN. Therefore, in conclusion, 1) PTEN dephosphorylates both phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate in vivo, and the C124S mutants interrupt endogenous PTEN activity in a dominant-negative manner. 2) The membrane targeting process of PTEN may be important for exerting its function. 3) Phosphorylations of Thr309 and Ser474 of Akt2 are regulated differently, and the former is regulated very sensitively by the function of PTEN. 4) The phosphorylation level of Ser474, but not that of Thr309, in Akt2 correlates well with insulin-stimulated glucose transport activity in 3T3-L1 adipocytes. 5) The activity of endogenous PTEN may not play a major role in the regulation of glucose transport activity in 3T3-L1 adipocytes.

3T3 Cells↗
PubMed1999

Cell cycle arrest and astrocytic differentiation resulting from PTEN expression in glioma cells.

OBJECT: Genetic alterations of the PTEN gene (also known as MMAC1 or TEP1) have frequently been identified in high-grade gliomas, indicating that inactivation of PTEN plays a crucial role in human glioma progression. The aim of this study was to assess the biological significance of PTEN inactivation in the development of glioma. METHODS: The authors introduced wild-type PTEN complementary DNA into four human glioma cell lines (T98G, U-251MG, U-87MG, and A172) containing endogenous aberrant PTEN alleles. The number of colonies transfected with the wild-type PTEN was reduced to 15 to 32% of those found after transfection of a control vector, suggesting growth suppression by the exogenous PTEN. To analyze phenotypic alterations produced by PTEN expression, T98G-derived clones with inducible PTEN expression were further established using a tetracycline-regulated inducible gene expression system. Induction of PTEN expression suppressed the in vitro growth of T98G cells with accumulation of G1 phase cells. Furthermore, when cells were cultured in the presence of the extracellular matrix (ECM), PTEN expression caused distinct morphological changes, with multiple and elongated cytoplasmic processes similar to those of normal astrocytes. The level of glial fibrillary acidic protein, an intermediate protein specifically expressed in differentiated astrocytes, was upregulated concomitantly. CONCLUSIONS: These findings strongly indicate that exogenous PTEN expression inhibits the proliferation of glioma cells by inducing G1 arrest and elicits astrocytic differentiation in the presence of the ECM. Inactivation of PTEN would play an important role in the enhancement of unregulated growth of undifferentiated glioma cells.

Astrocytes↗