Ell cycle progression, and the mice develop a myeloproliferative disease which leads to leukemic transformation [346]. In T-acute lymphoblastic leukemia (T-ALL), PTEN-downregulation is also closely correlated with Akt-activation [347,348]. To discern the role of PTEN for Akt-activation, it may be useful to exclude concomitant causes for Akt-activation such as mutant upstream targets and to include the investigation of regulators of PTEN such as c-Myc and Notch/Hes1 [347,348]. PTEN promoter methylation leads to low PTEN expression [349]. In one study, 26 of primary breast cancers had low PTEN levels that correlated with lymph node metastases and poor prognoses [350]. Other mechanisms important in the regulation of PTEN are miRNAs. Certain miRNAs have been shown to regulate PTEN protein expression. mi-214 induces cell survival and may contribute to oncogenesis and drugwww.impactjournals.com/oncotargetresistance (see below) by binding the 3’untranslated region (3’UTR) of PTEN which prevents PTEN mRNA translation and leads of overexpression of downstream Akt [351]. In some cancer settings, PTEN and BRAF mutations appear to interact. Two studies papers have highlighted the hypothesis of mutant BRAF- and PTEN-loss-driven carcinogenesis in mouse models [352,353]. In a study by Dhomen et al., inducible expression of B-RafV600E was sufficient to induce multiple melanocytic lesions including skin hyperpigmentation, dysplastic nevi and melanoma [352]. Tumor cells from these B-RafV600E mice displayed both melanoma growth and melanocyte senescence in this system. Approximately 70 of these mice developed melanomas that exhibited histological and molecular characteristics similar to that of human melanoma and were able to colonize the lungs in nude mice [352]. In contrast, another group of researchers generated mice that conditionally-expressed melanocyte-specific BRAF V600E that were only able to induce benign melanocytic hyperplasias and were unable to progress any further over a 15-20 month period [353]. However, BRAF V600E expression in a PTEN RG7800MedChemExpress RG7800 gene-silenced background led to the production of melanomas with 100 establishment, short latency and metastasis to lymph nodes and lungs. This development was prevented by the treatment of mice with either the mTOR inhibitor rapamycin or the MEK1/2 inhibitor (PD0325901). Moreover, while combination treatment with rapamycin or PD0325901 led to the reduction of established tumors, upon termination of drug treatment the melanomas reappeared most likely due to the presence of drug ��-AmatoxinMedChemExpress alpha-Amanitin resistant melanoma-initiating cells in these mice. Overall, these two papers further validated the mutated B-Raf/MEK/ERK and the PI3K/Akt/mTOR pathways, as promising therapeutic targets in melanoma.Mutations at SHIP Phosphatase in Human CancerThe SHIP-1 phosphatase has been implicated as a suppressor of hematopoietic transformation as it basically can prevent Akt-activation [354]. SHIP-1-deficient mice develop a myeloproliferative disease [355] and an inactivating point mutation (SHIP1 V684E) has been observed in approximately one of thirty AML cases [354]. Also another mutation, SHIP1 Q1154L, has been observed in AML, but was even less frequent (1 of 192 cases) [355]. Though some studies confirmed, that SHIP-1 is a leukemia suppressor [354,355] it is unlikely that SHIP1 mutations are a frequent cause of Akt-activation in AML. Disruption of PTEN or SHIP activity by various genetic mechanisms could have vast effects on different pro.Ell cycle progression, and the mice develop a myeloproliferative disease which leads to leukemic transformation [346]. In T-acute lymphoblastic leukemia (T-ALL), PTEN-downregulation is also closely correlated with Akt-activation [347,348]. To discern the role of PTEN for Akt-activation, it may be useful to exclude concomitant causes for Akt-activation such as mutant upstream targets and to include the investigation of regulators of PTEN such as c-Myc and Notch/Hes1 [347,348]. PTEN promoter methylation leads to low PTEN expression [349]. In one study, 26 of primary breast cancers had low PTEN levels that correlated with lymph node metastases and poor prognoses [350]. Other mechanisms important in the regulation of PTEN are miRNAs. Certain miRNAs have been shown to regulate PTEN protein expression. mi-214 induces cell survival and may contribute to oncogenesis and drugwww.impactjournals.com/oncotargetresistance (see below) by binding the 3’untranslated region (3’UTR) of PTEN which prevents PTEN mRNA translation and leads of overexpression of downstream Akt [351]. In some cancer settings, PTEN and BRAF mutations appear to interact. Two studies papers have highlighted the hypothesis of mutant BRAF- and PTEN-loss-driven carcinogenesis in mouse models [352,353]. In a study by Dhomen et al., inducible expression of B-RafV600E was sufficient to induce multiple melanocytic lesions including skin hyperpigmentation, dysplastic nevi and melanoma [352]. Tumor cells from these B-RafV600E mice displayed both melanoma growth and melanocyte senescence in this system. Approximately 70 of these mice developed melanomas that exhibited histological and molecular characteristics similar to that of human melanoma and were able to colonize the lungs in nude mice [352]. In contrast, another group of researchers generated mice that conditionally-expressed melanocyte-specific BRAF V600E that were only able to induce benign melanocytic hyperplasias and were unable to progress any further over a 15-20 month period [353]. However, BRAF V600E expression in a PTEN gene-silenced background led to the production of melanomas with 100 establishment, short latency and metastasis to lymph nodes and lungs. This development was prevented by the treatment of mice with either the mTOR inhibitor rapamycin or the MEK1/2 inhibitor (PD0325901). Moreover, while combination treatment with rapamycin or PD0325901 led to the reduction of established tumors, upon termination of drug treatment the melanomas reappeared most likely due to the presence of drug resistant melanoma-initiating cells in these mice. Overall, these two papers further validated the mutated B-Raf/MEK/ERK and the PI3K/Akt/mTOR pathways, as promising therapeutic targets in melanoma.Mutations at SHIP Phosphatase in Human CancerThe SHIP-1 phosphatase has been implicated as a suppressor of hematopoietic transformation as it basically can prevent Akt-activation [354]. SHIP-1-deficient mice develop a myeloproliferative disease [355] and an inactivating point mutation (SHIP1 V684E) has been observed in approximately one of thirty AML cases [354]. Also another mutation, SHIP1 Q1154L, has been observed in AML, but was even less frequent (1 of 192 cases) [355]. Though some studies confirmed, that SHIP-1 is a leukemia suppressor [354,355] it is unlikely that SHIP1 mutations are a frequent cause of Akt-activation in AML. Disruption of PTEN or SHIP activity by various genetic mechanisms could have vast effects on different pro.
