[Effect of Bmi-1 Expression on Chemotherapy Sensitivity in THP-1 Cells].

OBJECTIVE: To investigate the effect of Bmi-1 expression on the chemosensitivity of THP-1 cells and its relative mechanism. METHODS: The pGenesil-2-Bmi-1 1 siRNA, p-MSCV-Bmi-1 plasmid was transfected into THP-1 cells to reduce or increase the expression of Bmi-1. The expression of Bmi-1 mRNA and protein was verified by PCR and Western blot. The effect of camptothecin (CPT) on the proliferation and chemosensitivity of THP-1 cells affected by Bmi-1 gene were detected by MTT assay. The expression of DNA double-strand breaks marker-γ-H2AX was detected by immunofluorescence assay. Mitochondrial membrane potential and apoptosis were observed by flow cytometry. The expression of Cytochrome C, Caspase 3, Bax and BCL-2 was detected by Western blot. RESULTS: Silencing Bmi-1 could inhibit proliferation and enhance the sensitivity of THP-1 cells to CPT, while overexpressed Bmi-1 could promote the cell proliferation and attenucate sensitivity of THP-1 cells to CPT. Silencing Bmi-1 could enhance CPT-induced DNA double-strand breaks, decrease mitochondrial membrane potential and promote CPT-induced apoptosis. While increasing Bmi-1 gene expression could attenuate CPT-induced DNA double-strand breaks, enhamce mitochondrial membrane potential and significantly reduce CPT-induced apoptosis of cells. CONCLUSION: Bmi-1 expression could influence the sensitivity of THP-1 cells to CPT, and its relative mechanism may relate to DNA double-strand breaks and endogenous apoptotic pathways.

[Effect of Bmi-1 on Multidrug Resistance in K562/ADR Cells and Its Mechanisms].

OBJECTIVE: To investigate the effect of Bmi-1 gene silencing on drug resistance of leukemia cell K562/ADR and to explore its possible mechanism. METHODS: After two sequences of Bmi-1-siRNA were transfected into drug-resistant K562/ADR cells, the mRNA and protein expressions of Bmi-1 gene were detected. After Bmi-1 gene silencing the expression of P-gp and MDR1 were detected and the accumulation of doxorubicin in K562/ADR cells were detected by flow cytometry to determine the effect of Bmi-1 gene silencing on drug resistance of K562/ADR cells. The protein expression of NF-κB was analyzed after Bmi-1 gene silencing. Then after K562/ADR cells were treated with NF-κB inhibitor PDTC, the protein expression of P-gp and its functional changes were analyzed to determine the effect of NF-κB on drug resistance of leukemia cells. The protein expressions of PTEN, AKT and p-AKT after Bmi-1 gene silencing were detected and the effect of Bmi-1 gene silencing on PTEN/PI3K/AKT signaling pathway in drug-resistant cells was determined. After K562/ADR cells were treated with PI3K/AKT pathway inhibitor LY294002, the protein expressions of NF-κB and P-gp were analyzed to determine the regulation of AKT on the expression of NF-κB and P-gp. The protein expressions of AKT, p-AKT, NF-κB and P-gp were detected after the Bmi-1-siRNA transfected cells were treated by PTEN inhibitor BPV. Above-mentioned expression of mRNA was detected by RT-PCR, and the protein expression was detected by Western blot. RESULTS: The expression of Bmi-1 gene in K562/ADR cells decreased at both mRNA and protein levels and the doxorubicin accumulation increased after Bmi-1 gene silencing. The expression of MDR1/P-gp in Bmi-1-siRNA transfected cells was lower than that in K562/ADR cells (P＜0.05). After Bmi-1 gene silencing, the activity of NF-κB decreased. The activity of NF-κB and P-gp expression was inhibited and the function of P-gp in K562/ADR cells was reduced by using NF-κB inhibitor (PDTC). The protein expression of PTEN increased while the protein expression of p-AKT decreased after Bmi-1 gene silencing (P＜0.05). The protein expressions of p-AKT, P-gp and the activity of NF-κB were inhibited significantly by using PI3K/AKT inhibitor LY294002 (P＜0.05). After the Bmi-1-siRNA transfected cells were treated by PTEN inhibitor BPV, the activity of NF-κB and the protein expressions of P-gp were restored. CONCLUSION: Bmi-1 plays a key role in MDR-mediated multidrug resistance in K562/ADR cells, which may be mediated by activating PTEN/AKT pathway to regulate NF-κB.

[Effect of Bmi-1 Silencing on the Proliferation of K562/ADM Cells in vitro and in vivo].

OBJECTIVE: To investigate the effect of Bmi-1 gene silencing on the proliferation of K562/ADM cells in vitro and in vivo and to explore its possible molecular mechanism. METHODS: The small interference RNA (siRNA) sequences of Bmi-1 were transfected into K562/ADM cells for decreasing the expression of Bmi-1. The effect of Bmi-1 silencing on the proliferation of K562/ADM cells in vitro and in vivo was detected by using MTT method, cell colony-forming test and tumoriganicity of nude mice; the expression of Bmi-1, PTEN and PAKT proteins was detected by Wertern blot. The immunohistochemistry assay was used to analyze the expression of Bmi-1 and Ki-67. RESULTS: The Bmi-1 silencing could significantly inhibit the proliferation activity of K562/ADM cells, the cell colony-forming ability and tumorigenicity were reduced. LY294002 decreased p-AKT expression, cell colony-forming ability and tumorigenicity. Bpv reduced the PTEN expression but increased p-AKT expression and restored the colony-forming ability and tumorigenesis of K562/ADM-S1-Bpv cells. Bmi-1-siRNA dramatically suppressed the Bmi-1 and Ki-67 protein levels in xenograft tumor tissue. CONCLUSION: Bmi-1 can mediate the proliferation of K562/ADM cell, the PTEN/p-AKT might be involved in this pathway.

[Bmi-1-siRNA Regulates the Proliferation of K562 Leukemia Cells in vitro and in vivo by PTEN/pAKT Pathway].

OBJECTIVE: To investigate the effect of Bmi-1 gene silence on the proliferation ability of K562 cells in vitro and in vivo, and to explore the relation of molecular mechanism between proliferation ability of K562 cells in vitro and in vivo with PTEN/pAKT signaling pathway. METHODS: The Bmi-1 small interference RNA (siRNA) sequences were transfected into K562 cells for decreasing Bmi-1 expression. The effect of Bmi-1 siRNA on the proliferation of K562 cells in vitro and in vivo was detected by MTT method and colony-forming test, the effect of Bmi-1 siRNA on the tumorogenicity of K562 cells was observed by subcutaneous inoculation of K562 cells, LY294002 and Bpv treated K562 cells in nude mice, the expression of Bmi-1, PTEN and pAKT proteins were detected by Western blot. RESULTS: The Bmi-1 siRNA could inhibit the proliferation activity, colony-forming and tumor-forming abilities of K562 cells. After the silence of Bmi-1 gene, the PTEN expression in Bmi-1 gene-silenced group was significantly enhanced. While the pAKT expression in Bmi-1 gene-silenced group was significantly reduced; after the K562 cells were treated with LY294002 (an inhibitor of pAKT), the pAKT expression colony-forming and tumor forming abilities were reduced in comparison with untreated K562 cells; after the K562-S1 cells were treated with Bpv (an inhibitor of PTEN), the PTEN expression decreased, while the pAKT expression, colony forming and tumor-forming abilities were restored. CONCLUSION: The Bmi-1 gene possibly involves in regulation of K562 proliferation in vivo and in vitro, the effect of PTEN/pAKT signaling pathway maybe one of molecular mechanisms mediating this regulation.

Establishment and biological characteristics of acquired gefitinib resistance in cell line NCI-H1975/gefinitib-resistant with epidermal growth factor receptor T790M mutation.

Non­small cell lung cancer (NSCLC) cells harboring mutations in the epidermal growth factor receptor (EGFR) gene initially respond well to EGFR tyrosine kinase inhibitors (TKI), including gefitinib. However the tumor cells will invariably develop acquired resistance to the drug. The EGFR T790M mutation is generally considered to be the molecular genetic basis of acquired TKI resistance. The present study aimed to explore how the T790M mutation induces tumor cells to escape inhibition by TKI treatment. An acquired gefitinib­resistant cell line (NCI­H1975/GR) was generated from the NCI­H1975 human NSCLC cell line, which harbors the sensitive L858R and resistant T790M mutations of EGFR. The resistant cell line was established by exposing the cells intermittently to increasing concentrations of gefitinib. The mechanisms by which NSCLC acquires resistance to TKIs based on the T790M mutation, were investigated by detecting the protein expression levels of the EGFR/Kirsten rat sarcoma viral oncogene homolog (KRAS)/v­Raf murine sarcoma viral oncogene homolog B (BRAF) transduction pathway, and epithelial­mesenchymal transition (EMT) with immunocytochemistry. The resistance of the NCI­H1975/GR cells to gefitinib was 2.009­fold, as compared with the parent cells; however, the protein expression levels of EGFR, KRAS and BRAF were lower in the resistant cells. Some mesenchymal morphology was observed in the NCI­H1975/GR cells, alongside a decreasing E­cadherin expression and increasing vimentin expression. These results suggest that the reactivation of the EGFR/KRAS/BRAF transduction pathway was not detected in the NCI­H1975/GR cells. EMT may have an important role in the development of acquired resistance to EGFR­TKIs in NSCLC cells with sensitivity and resistance mutations.