| Breast cancer is one of the malignant tumors with the highest incidencerate in women. In the biogenesis of breast cancer, estrogen and estrogenreceptor p1ay a very important role. Human estrogen receptor related receptorl (hERRl ), an orphan nuclear recePtor, is a member of the nuclearsuPerfamily. The cDNA encoding this protein was initially isolated by areduced-stringency screening of cDNA libraries fusing probes correspondingto the DNA binding domain(DBD) of the human estrogen receptor Q (hER Q ).Nucleotide and protein sequence aligrunent of hERR1 shows a closerelationship to hER, and they may affect the activities of similar target genes.ERRl has been shown to enhance expression of a number ofestrogen-mediated genes by directly interacting with ER and/or comPetingwith ER for DNA binding. ERRl was found to express in embryo breast tissue,indicating that ERRl may play a role in the biogenesis of breast. ERRl wasalso found to express in normal and malignant breast tissues, and theexpression level ofhERRl in breast cancer tissue was found to be higher thanthat in normal breast tissues. These results suggest that hERRl may play arole in breast cancer development, and it may be an additiona1 receptor, inaddition to hER Q and hER6, for breast cancer cell proliferation.To test this hypothesis, in this study, we (l) collected more than 30c1inical specimens, analysed the expression pattern of hERRl in carcinomaand corresponding normal mammary tissues by RT-PCR; (2) appliedtransient transfection to examine the effects ofhERRl overexpression on thetranscriptiona1 activity of the human aromatase gene promotef, Whoseproduct is responsib1e for estrogen biosynthesis; (3) constructed a MCP-7cell line, MCF-7/ERRl, which stab1ely overexpresses hERR1; (4) examinedthe growth rate of hERRl transfected breast cancer cel1s by MTT assays; (5)performed co-transfection experiments to examine the effects of ERRl.overexpression on ER's transactivation function.Results: (1) The results from RT-PCR analysis of hERR1 mRNA inpaired breast tissue revealed that hERR1 expressed in both normal andmalignan breast tissues, with higher levels in carcinoma tissues than in pairnormal tissues in the most of samples examined (positive rate: 6l.5%); (2)The transient transfection assays showed that hERR1 increased CATtranscription under the control of promoter l .3 of the human aromatase genein a dose-dependent manner. (3) hERR1 eukaryote expression plasmid, pH 6-neo-hBRRl, was correctly constructed, and the levels of both ERRl mRNAand ERR1 protein in the ERRl -transfected ce1ls are much higher than that ofin the cells transfected with empty vector. (4) Preliminary data from MTTassays showed that the hERR1 transfected MCF-7 cells grew slightly slowerthan MCF-7 cel1s transfected with empty vector in the presellt culturecondition. (5) Further transfection analysis showed that the CAT activities incells co-transfected with hERR1, ER and reporter were 1ower than that ofcel1s co-transfected with ER and reporter only. -Conclusions: ERRl level in carcinoma tissues is higher than that ofnormal breast tissues; ERR1 upregulated the transcription of promoter l .3 ofthe human aromatase gene, indicating the relevance of ERRl to breast cancer;ERRl stable expression breast cancer cell line was successfully established toexamine ERR1 's biological function; preliminary data showed that hERRlcould compete with hER for ERE binding site in target gene promoter region,and therefOre, reduced the estrogen response of cell growth. This could be oneof the mechanisms by which overexpression of ERRl slightly reduces thegrowth rate of ERR1-transfected MCF-7 cells. More carefully defineexperiments are needed to further explore the role ofhERRl in breast cance]developmeni. |
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