Effects of downregulation of HDAC6 expression on cell cycle, proliferation and migration of laryngeal squamous cell carcinoma / 中华肿瘤杂志

<p><b>OBJECTIVE</b>To detect the expression of histone deacetylase 6 (HDAC6) in laryngeal squamous cell carcinoma, and to analyze the effects of downregulation of HDAC6 expression on cell cycle, proliferation and migration of laryngeal squamous cell carcinoma cell line Hep-2 cells, and to explore their possible molecular mechanisms.</p><p><b>METHODS</b>Immunohistochemistry was used to detect the expression of HDAC6 protein in 55 cases of laryngeal squamous cell carcinoma and 20 cases of normal laryngeal mucosa. HDAC6 siRNA and control siRNA were transfected into Hep-2 cells via lipofectamine 2000, and the interfering effect was analyzed using Western blotting. The effects of downregulation of HDAC6 expression on cell cycle, proliferation and migration were determined by cell counting kit-8 (CCK-8), flow cytometry and Boyden chamber, respectively. Finally, Western blotting was used to detect the expressions of cell cycle, proliferation and migration related proteins.</p><p><b>RESULTS</b>There was a high level expression of HDAC6 protein in laryngeal squamous cell carcinoma, and its expression was not related to age and sex of the patients (P > 0.05), but closely associated with the degree of histological differentiation, TNM staging and lymph node metastasis (P < 0.05). HDAC6 siRNA effectively down-regulated the expression of HDAC6 protein in laryngeal squamous cell carcinoma cell line Hep-2 cells, and downregulation of its expression obviously inhibited cell proliferation, arrested cell cycle at G(0)/G(1) phase and decreased cell migration ability in Hep-2 cells. Additionally, the downregulation of HDAC6 protein expression markedly decreased the expressions of cyclin D1, cyclin E, cdk2 and MMP-9 proteins, but increased the expressions of p21 and E-cadherin proteins.</p><p><b>CONCLUSIONS</b>HDAC6 may play a pivotal role in the carcinogenesis and development of laryngeal squamous cell carcinoma. The downregulation of HDAC6 expression-mediated cell proliferation inhibition, cell cycle arrest and decreased cell migration ability may be closely associated with the decrease of cyclin D1, cyclin E, cdk2 and MMP-9 proteins and increase of p21 and E-cadherin proteins.</p>

Arsenic trioxide restores ERα expression in ERα-negative human breast cancer cells and its treatment efficacy in combination with tamoxifen in xenografts in nude mice / 中华肿瘤杂志

<p><b>OBJECTIVE</b>To study the demethylation effect of arsenic trioxide (As2O3) on ERα-negative human breast cancer MDA-MB-435s cells and its possible mechanisms, and to observe its treatment efficacy in combination with tamoxifen (TAM) after ERα re-expression.</p><p><b>METHODS</b>MTT assay was used to examine the inhibitory effect of As2O3 treatment alone or in combination with TAM on cell proliferation. A nude mouse xenograft model was used to further examine the treatment efficacy in vivo. MSP was used to detect the methylation status of ERα gene after treated with As2O3 in MDA-MB-435s cells and the transplanted tumor tissues. RT-PCR was used to detect the mRNA expression of DNMT1 and Erα. Western bolt was used to detect the DNMT1 and ERα protein expression. The diameter of xenograft tumors was measured weekly, and the tumor growth curve was drawn.</p><p><b>RESULTS</b>The level of proliferation of the MDA-MB-435s cells was significantly suppressed after treatment with different concentration of As2O3 alone or As2O3 combined with TAM, and the 4 µmol/L As2O3 + TAM treatment for 72 h showed the highest inhibition rate (62.6%). 1, 2, 4 µmol/L As2O3 had demethylation effect on MDA-MB-435s cells, and the DNMT1 mRNA and protein expression was inhibited and accompanied by ERα mRNA and protein re-expression. The unmethylation specific bands of ERα gene were enhanced after treated by As2O3 alone or As2O3 combined with TAM in the xenograft tumors. The expression of DNMT1 mRNA and protein was inhibited, and accompanied by ERα mRNA and protein re-expression. An significant decrease of volume and weight of the xenograft tumors in the As2O3 treated alone or combined with TAM groups was observed compared with those of the normal saline group or TAM alone group (P < 0.05), and the 4 mg/kg As2O3 + TAM group had the highest inhibition rate of tumor weight (79.5%) and volume (76.4%).</p><p><b>CONCLUSIONS</b>ERα can be re-expressed in ERα-negative breast cancer MDA-MB-435s cells after treated with As2O3 by inhibiting the DNMT1 activity. MDA-MB-435s cells are re-sensitized to endocrine therapy after ERα re-expression. As2O3 combined with TAM may provide a new therapeutic approach for patients with ERα-negative breast cancer in the clinic.</p>

Expression and significance of matrix metalloproteinase and tissue inhibitor of matrix metalloproteinase in non-melanoma skin cancer / 中华肿瘤杂志

<p><b>OBJECTIVE</b>To investigate the expression and significance of matrix metalloproteinases (MMP-2, MMP-9) and tissue inhibitor of matrix metalloproteinase (TIMP-2, TIMP-1) in non-melanoma skin cancer (NMSC).</p><p><b>METHODS</b>Thirty six patients with squamous cell carcinoma (SCC) and 32 patients with basal cell carcinoma (BCC), confirmed by pathology, were selected, and 30 cases of normal skin were selected as control. The expression of MMP-2, MMP-9, TIMP-1 and TIMP-2 in all samples were examined by immunohistochemistry and reverse transcription polymerase chain reaction (RT-PCR). The expression rate, expression intensity and expression level of each factor were recorded. The results were compared between the groups.</p><p><b>RESULTS</b>The expression rates of MMP-2 and MMP-9 in the control group were 30.0% and 36.7%, the expression levels of MMP-2 and MMP-9 in the control group were 57.216 ± 12.785 and 59.318 ± 13.262, all significantly lower than those in the tumor edge and center of the SCC and BCC groups (P < 0.01). The expression rates of TIMP-1 and TIMP-2 in the control group were 96.7% and 100%, their expression levels were 121.738 ± 25.516 and 122.612 ± 25.964, all significantly higher than those in the SCC and BCC groups (P < 0.01). The expression levels of MMP-2 and MMP-9 in the tumor center and edge of SCC group were significantly higher than those in the corresponding parts of the BCC group, while the expression levels of TIMP-1 and TIMP-2 were significantly lower than those in the BCC group (P < 0.01). The expression levels of MMP-2 and MMP-9 in the tumor edge of the SCC and BCC groups were significantly higher than those in the tumor centers (P < 0.01), while the expression levels of TIMP-1and TIMP-2 were significantly lower than those in the tumor centers (P < 0.01).</p><p><b>CONCLUSION</b>MMP-2, MMP-9 and TIMP-2, TIMP-1 may play an important role in the development, progression, invasion and metastasis of non-melanoma skin cancer.</p>

Correlation of TOP2A gene expression and survival of breast cancer patients / 中华肿瘤杂志

<p><b>OBJECTIVE</b>The aim of this study was to assess the TOP2A RNA expression and the relationship of TOP2A protein expression with metastasis-free interval in breast cancer patients.</p><p><b>METHODS</b>TOP2A expression was analyzed prior to surgery in 86 patients. The level of TOP2A gene amplification was analyzed by fluorescence in situ hybridization (FISH), its RNA expression level with RT-PCR, and their correlation with TOP2A protein expression was assessed by immunohistochemistry (IHC). The correlation between RNA expression level and metastasis-free interval in breast cancer patients was also analyzed.</p><p><b>RESULTS</b>Aberrations (amplification or deletion) of TOP2A copy number was observed in 25.6% (22/86) of the cases. TOP2A protein expression was detected in 66.3% (57/86) of the samples. There was a significant correlation between the TOP2A RNA expression and protein expression (P < 0.001). TOP2A gene expression was significantly associated with the metastasis-free interval in the breast cancer patients (P = 0.001). There was no significant correlation between TOP2A gene amplification and TOP2A protein expression (P = 0.211).</p><p><b>CONCLUSIONS</b>TOP2A RNA level is an objective and reliable prognostic indicator in breast cancer.</p>

Expression of IGF-1R in esophageal squamous cell carcinoma and the effect of its silencing by siRNA on the proliferation of esophageal cancer EC9706 cells in vitro / 中华肿瘤杂志

<p><b>OBJECTIVE</b>To explore the correlation of IGF-1R expression with clinical features of esophageal squamous cell carcinoma (ESCC) and to investigate the effect of silencing IGF-1R by siRNA on the proliferation of esophageal cancer cell line EC9706 cells.</p><p><b>METHODS</b>Immunohistochemistry was used to detect the expresion of IGF-1R in 80 specimens of ESCC and 18 specimens of normal esophageal mucosa. IGF-1R siRNA was transfected into esophageal squamous cell carcinoma EC9706 cells, and the effect of RNAi was assessed by Western blot. The proliferation of EC9706 cells was determined by drawing growth curve, MTT assay and plate colony-forming assay.</p><p><b>RESULTS</b>The total and strong positive rates of IGF-1R expression were 86.3% and 51.3% in ESCC, and 61.1% and 11.1% in normal esophageal epithelium, respectively. The total and strong positive rates of IGF-1R expression in patients with lymph node metastasis were 94.4% and 74.1%, significantly higher than 69.2% and 3.9%, respectively, in those without lymph node metastasis (P<0.01). A significantly higher IGF-1R expression was associated with lower histological grade (P<0.05). The total and strong rates of IGF-1R expression in 39 patients of stages III and IV were 97.4% and 71.8% , significantly higher than the 75.6% and 31.7%, respectively, in 41 cases of stages I and II (P<0.01). IGF-1R RNAi significantly inhibited IGF-1R expression and the growth of EC9706 cells. The clone formation rate of RNAi-IGF-1R transfected cells was 19.1%, significantly lower than that of 52.3% in non-transfected cells and 49.0% in empty vector-transfected EC9706 cells (P<0.05).</p><p><b>CONCLUSIONS</b>The overexpression of IGF-1R is colerated with lymph node metastasis, differentiation and clinical stage. Down-regulation of IGF-1R can inhibit the proliferation of esophageal cancer EC9706 cells in vitro.</p>

Inhibition effects of all trans-retinoic acid on the growth and angiogenesis of esophageal squamous cell carcinoma in nude mice / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>The potential application of retinoic acid receptor activators, such as all trans-retinoic acid (ATRA), for treating various cancers have been studied both pre-clinically and clinically. Whether ATRA has an anticancer effect on human esophageal squamous cancer cell (ESCC) is still unknown. We have explored the anticancer effect of ATRA in ESCC, and in this study, the effects of ATRA on levels and patterns of expression of the vascular endothelial growth factor (VEGF) signal transduction pathway in transplantable tumor growth of the human ESCC cell line, EC9706, in nude mice.</p><p><b>METHODS</b>The animal model of the ESCC xenograft was made by subcutaneous implantation of tumor cells into nude mice. Reverse transcription-polymerase chain reaction (RT-PCR), Western blotting and immunohistochemical assays were used to detect the expression of the VEGF signal transduction pathway in ESCC xenograft tissues.</p><p><b>RESULTS</b>Compared to the control group, the tumor inhibition rates in the low dose ATRA, high dose ATRA, and 5-FU groups were 83.21%, 88.32%, 91.02%, respectively. The protein and mRNA levels of VEGF were down-regulated after being treated with ATRA and 5-FU compared to the control group (P < 0.05). The study also revealed that ATRA specifically down-regulated VEGF and the component of the VEGF signal transduction pathway of CD31, CD34, and CD105 (component of the TGF-β receptor) in ESCC xenograft tissues (P < 0.05).</p><p><b>CONCLUSIONS</b>ATRA can significantly inhibit tumor growth and has anticancer effects on transplantable tumor growth of human ESCC cell line EC9706 in nude mice. These findings indicate that ATRA specifically down regulated VEGF and the components of VEGF signal transduction, which may be an important mechanism responsible for the neoangiogenesis inhibition of ESCC cells.</p>

Insulin induces anticancer cytotoxicity of 5-Fu to two human colon cancer cell lines / 中华肿瘤杂志

<p><b>OBJECTIVE</b>To explore the possibility of use of insulin as a potentiator of 5-Fu to human colon cancer cell lines HCT-8 and HT-29 and study its mechanism.</p><p><b>METHODS</b>MTT assay was used to examine the inhibition rate of cell growth after treatment with 5-Fu and insulin. Cell cycle was determined by flow cytometry.</p><p><b>RESULTS</b>Insulin showed an enhancing effect on the chemotherapeutic response of 5-Fu when insulin was applied at a dose of exceeding 0.8 mU/ml 0 approximately 8 h before 5-Fu. Within the range of from 0.8 mU/ml to 8 mU/ml, a higher concentration of insulin gave a higher proportion of inhibited cells. But when the insulin concentration exceeds 8 mU/ml, the proportion became stable as that of 8 mU/ml. Insulin increased the percentage of S phase cells and decreased the percentage of G(1) phase cells (P < 0.01). The percentage of S phase cells reached a peak when the cells were treated with insulin for 6 hours.</p><p><b>CONCLUSION</b>Insulin can enhance the anticancer toxicity of 5-Fu to human colon cancer cell lines HCT-8 and HT-29 cells. Insulin increases the percentage of S phase cells, which may be one of the main mechanisms of insulin-induced enhancement of anticancer response of cancer cells to 5-Fu chemotherapy.</p>

Promoting effect of all-trans retinoic acid on the chemosensitivity of esophageal cancer EC9706 cells / 中华肿瘤杂志

<p><b>OBJECTIVE</b>To investigate the impact of all-trans retinoic acid (ATRA) on chemosensitivity to esophageal squamous cell carcinoma EC9706 cells in vitro and its mechanism.</p><p><b>METHODS</b>EC9706 cells were routinely cultured as the control group. The experimental group was divided into three groups. The ATRA group with ATRA in final concentration of 1 µmol/L; the 5-Fu group with 5-Fu in final concentration of 50 mg/L; the combined treatment group with ATRA in final concentration of 1 µmol/L and 5-Fu 50 mg/L. The cell apoptosis was detected by terminal deoxynucleotidy transferase mediated dUTP nick end labelling (TUNEL). The cell cycle and apoptosis were detected by flow cytometry.</p><p><b>RESULTS</b>The results of TUNEL showed that in the combined treatment group appeared a large number of apoptotic cells, and their nuclei were stained brown, with a positive rate of 89.7%. There was a significant difference in the comparison with the ATRA group (38.3%) and 5-Fu group (40.3%) (P < 0.05). The flow cytometry showed that the ATRA + 5-Fu group had a significantly higher apoptosis rate (76.9% ± 2.7%) than that in the ATRA group (38.2% ± 2.6%) and 5-Fu group (45.2% ± 2.3%) (P < 0.05). The ratio of cells in G(1) phase increased in the ATRA + 5-Fu group (83.4% ± 3.0%), significantly higher than (48.2% ± 2.5%) in the ATRA group and (53.2% ± 2.6%) in the 5-Fu group (P < 0.05). The ratio of cells in S + G(2)/M phase was decreased in the ATRA + 5-Fu group, with a significant difference (P < 0.05) when compared with other groups. There was no significant difference between the ATRA group and 5-Fu group (P > 0.05) in the apoptosis rate and the proportion of cells at different phases.</p><p><b>CONCLUSION</b>ATRA can induce apoptosis of esophageal carcinoma EC9706 cells in vitro. The combination of ATRA and 5-Fu may enhance the chemotherapeutic efficacy.</p>

Mechanism of apoptosis of esophageal cancer EC9706 in nude mice induced by all-trans retinoic acid / 中华肿瘤杂志

<p><b>OBJECTIVE</b>To investigate the mechanism of apoptosis of EC9706 tumor-bearing nude mice induced by all-trans retinoic acid (ATRA).</p><p><b>METHODS</b>Human esophageal carcinoma cell line EC9706 cells were inoculated into nude mice to establish the solid tumor model. The tumor models were divided into the following groups: ATRA group, fluorouracil group, the two-drugs combination group, and with an equal volume fraction of solvent as the control group. The nude mice were sacrificed after 10 days of medication. TUNEL staining was used to detect cell apoptosis. RT-PCR was used to detect the expression level of mRNA and immunohistochemistry was used to detect the expression level of protein of caspase-3 and survivin, the apoptosis-related genes in the tumor tissue.</p><p><b>RESULTS</b>The apoptosis rates of the ATRA group, 5-Fu group and ATRA + 5-Fu group were 44.3%, 39.7% and 91.0%, respectively. There was a significant difference in comparison with the control group (0.7%), and the ATRA group had no significant difference compared with that of the fluorouracil group (P > 0.05), but the apoptosis rate of the two-drugs combination group was significantly higher than that in the two single-drug groups (P < 0.05). The average gray value of caspase-3 protein expressed in the control group was 46.12 ± 0.33 and the relative expression of caspase-3 mRNA was 0.14 ± 0.03, both were significantly lower than that in the ATRA group, 5-Fu group and the two-drugs combination group (P < 0.05). The average gray value of survivin protein expressed in the control group was 96.07 ± 0.13 and the relative expression of survivin mRNA was 0.84 ± 0.04, both were significantly higher than those of other groups (P < 0.05). The ATRA group had no significant difference compared with the fluorouracil group (P > 0.05), but the two-drugs combination group was significantly different compared with the single-drug groups (P < 0.05).</p><p><b>CONCLUSION</b>Apoptosis in the EC9706 tumor cells in nude mice can be induced by ATRA. The mechanism may be related with down-regulation of the level of survivin gene expression and up-regulation of the level of caspase-3 gene expression.</p>

Expression of stathmin in esophageal squamous cell carcinoma and its biological significance / 南方医科大学学报

<p><b>OBJECTIVE</b>To explore the expression of stathmin gene in esophageal squamous cell carcinoma (ESCC) and its correlation to oncogenesis of ESCC.</p><p><b>METHODS</b>Three ESCC cell lines, 75 ESCC samples, 25 tumor-adjacent samples and 30 normal esophageal mucosa samples were examined for the expression of stathmin mRNA and protein by in situ hybridization and immunohistochemistry, respectively. The correlations of stathmin expression to the clinicopathological features of the patients were analyzed.</p><p><b>RESULTS</b>Overexpression of stathmin mRNA and protein was found in 3 ESCC cell lines EC9706, Eca109 and EC-1, with the positive expression rates exceeding 80%. The positive rates of stathmin mRNA and protein in ESCC samples were 82.7% and 81.3%, respectively. There were significant differences in the relative contents of stathmin mRNA and protein among normal mucosa tissue, tumor-adjacent tissue and cancer tissue (chi2=19.204 and 25.03, respectively, P<0.01). In addition, a positive correlation was noted between stathmin mRNA and protein expressions in ESCC (r=0.413, P=0.000). The relative contents of stathmin mRNA and protein were significantly correlated to the differentiation degree, lymph node metastasis, invasive depth and TNM stage of ESCC (P<0.05).</p><p><b>CONCLUSIONS</b>The expression of stathmin mRNA and protein is upregulated in ESCC with correlation to the differentiation degree, lymph node metastasis, invasive depth and TNM stage of ESCC, suggesting the possible involvement of stathmin in the oncogenesis of ESCC. Combined detection of stathmin mRNA and protein may prove valuable for early diagnosis and prognosis of ESCC, and stathmin may serve as a potential molecular target for biotherapy of the tumor.</p>

Construction and expression of human stathmin gene eukaryotic expression vector and its effect on esophageal cancer cells / 中华肿瘤杂志

<p><b>OBJECTIVE</b>To construct an eukaryotic expression vector of human stathmin gene and to assess its effect on esophageal cancer EC9706 cells.</p><p><b>METHODS</b>Stathmin cDNA coding sequence was amplified by RT-PCR from Eca109 cells and was cloned into pMD18-T vector. After identifying and sequencing, the correct inserting stathmin gene was sub-cloned into eukaryotic expression vector pEGFP-C2. EC9706 cells were transfected with this recombinant plasmid and control plasmid using Lipofectamine 2000, and the stable intergrant was selected with G418 medium. The expression of enhanced green fluorescent protein (EGFP) protein was detected by fluorescence microscopy and EGFP/stathmin fusion protein by Western blot assay in transfected EC9706 cells. The growth curve of the two stably transfected cells was protracted with cell counting. FACS was used to detect the cell cycle. The clone formation rate in plate and in nude mice was tested to investigate the tumorigenic characteristics of the two stably transfected cells in vitro and vivo.</p><p><b>RESULTS</b>A 450 bp coding sequence of stathmin cDNA was amplified by RT-PCR, which was cloned into pMD18-T vector. After identified with restriction enzyme the recombinant plasmid pMD18-T-stathmin containing reverse inserting sequence was constructed successfully. Then, the sub-clone pEGFP-stathmin was sequenced, confirming that the recombinant vector was right. The recombinant plasmid pEGFP-stathmin and pEGFP-C2 vector were transfected separately into EC9706 cells. After selecting with G418, the cells were transfected steadily. EGFP in EC9706 cells was observed after transfection by fluorescence microscopy. The expressed product was proved to be 46,000 EGFP/stathmin fusion protein by Western blot. Compared with those transfected with pEGFP-C2, the growth of cells transfected with pEGFP-stathmin became slow, the cells were swelled, the cell cycle was blocked at G2/M phase, the average clone formation rate decreased in vitro, and the tumorigenicity of inoculated cells in nude mice was decreased.</p><p><b>CONCLUSION</b>The recombinant eukaryotic expression vector pEGFP-stathmin has been constructed successfully. It expresses steadily in esophageal cancer cells and inhibits the proliferation and tumorigenicity of transfected cells.</p>

Apoptosis in esophageal cancer cells induced by all-trans retinoic acid / 中华肿瘤杂志

<p><b>OBJECTIVE</b>To study the anti-tumor effects of all-trans retinoic acid (ATRA) and mechanisms of its action.</p><p><b>METHODS</b>Human esophageal carcinoma cell line EC9706 cells were treated with ATRA at different concentration. The proliferation inhibition was examined by MTT assay. Morphological examination, TUNEL method and flow cytometry were used to detect the apoptosis and changes of cell cycle. Immunohistochemical method was used to detect the expression of apoptosis-related genes caspase-3 and bcl-2. The semi-quantification of protein expression was analyzed by pathological image analysis.</p><p><b>RESULTS</b>ATRA inhibited the proliferation of EC9706 cells moderately. Apoptosis in EC9706 cells was induced by ATRA treatment. The morphology of EC9706 cells showed changes such as nuclear chromatin condensation and fragmentation. Sub-G1 peak was found by flow cytometry. The maximal apoptosis rate was 32.6%. The expression of caspase-3 gene was enhanced. The expression of bcl-2 gene was decreased. All these effects were presented in a dose-dependent and time-depend manner.</p><p><b>CONCLUSION</b>Apoptosis is one of the key mechanisms of ATRA action on EC9706 cells.</p>

Bcl-XL antisense oligodeoxynucleotide sensitizes human esophageal cancer cell line to 5-fluorouracil / 中华肿瘤杂志

<p><b>OBJECTIVE</b>To investigate the effects of the Bcl-XL antisense oligodeoxynucleotides (ASODN) in suppressing the Bcl-XL expression and increasing the sensitivity of esophageal cancer cell line EC9706 to 5-fluorouracil (5-Fu).</p><p><b>METHODS</b>The proliferation inhibitory rate of EC9706 was assessed by MTT, the expression of Bcl-XL was detected by RT-PCR and Western blot, and the apoptotic changes were examined by acridine orange (AO) fluorescent staining and flow cytometry, respectively.</p><p><b>RESULTS</b>In the group of ASODN combined with 5-Fu, the proliferation inhibitory rate of esophageal cancer cells was 71.58%, the expression inhibitory rate of Bcl-XL mRNA was 81.25%, the expression of Bcl-XL protein was decreased significantly. The apoptosis rates detected by AO fluorescent staining and flow cytometry were 69.5% and (63.32 +/- 9.23)%, respectively. There were significant differences as compared with the cell control group, the vacuity control group, the N-ODN group, the ASODN group and the 5-Fu group, respectively (P < 0.05).</p><p><b>CONCLUSION</b>Bcl-XL ASODN combined with 5-Fu can effectively inhibit the proliferation of esophageal cancer cells in vitro. Bcl-XL ASODN can significantly increase the sensitivity of esophageal cancer cells to 5-Fu through suppressing the expression of Bcl-XL.</p>

Demethylation of estrogen receptor gene and its re-expression in estrogen receptor-negative breast / 中华肿瘤杂志

<p><b>OBJECTIVE</b>To investigate the correlation between the lack of estrogen receptor (ER) gene expression and hypermethylation of ER gene, and detect whether re-expressed ER protein is activated.</p><p><b>METHODS</b>The methylation status of ER gene promoter in the ER-negative breast cancer cells was evaluated by methylation specific PCR (MSP) and genomic sequencing. The expression of ER and progesterone receptor (PR) mRNA as well as the production of ER protein were detected by RT-PCR and Western blot method, respectively. MTI assay was used to examine the function of re-expressed ER protein.</p><p><b>RESULTS</b>The ER gene promoter was highly methylated, while ER mRNA and ER protein were not expressed in the ER-negative breast cell line MDA-MB-231. The ER-negative breast cells treated with demethylating agent 5 -aza-2'-deoxycytidine (5-AZA-2'-deoxyC) restored the expression of ER mRNA and ER protein. Expression of the endogenous ER-responsive PR gene was activated and the methylation of ER gene was simultaneously decreased. After MDA-MB-231 was treated with 5-AZA-2'-deoxyC, the protein of ER was re-expressed and the growth of cells treated with tamoxifen were inhibited significantly (P < 0.05).</p><p><b>CONCLUSION</b>inactivation of ER gene has a close relationship with the abnormal methylation of ER gene promoter. 5-AZA-2'-deoxyC may effectively cause demethylation and restore functional expression of ER silenced by aberrant hypermethylation. The result may offer a new measure and theory for breast cancer patients with ER-negative expression to receive endocrine therapies.</p>