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We have cloned and sequenced a portion of the ER upstream regulatory region from the ER -positive MCF-7 and the ER -negative MDA-MB-231 breast cancer cell lines to determine if sequence alterations in this region account for the ER -negative phenotype of some tumors .
 ( DNA: upstream regulatory region, None) , ( protein: ER, None) , ( protein: ER, None) , ( cell line: ER -positive MCF-7, None) , ( protein: ER, None) , ( cell line: ER -negative MDA-MB-231 breast cancer cell lines, None) , ( protein: ER, None) 
Locate the role in the text that participated in the event based on the event type and return it in the event list. 
 Option: Event type: RNA,cell type,protein,cell line,DNA, Arguments type: . 
Text: {0} 
Answer:
 ( DNA: upstream regulatory region, None) , ( protein: ER, None) , ( protein: ER, None) , ( cell line: ER -positive MCF-7, None) , ( protein: ER, None) , ( cell line: ER -negative MDA-MB-231 breast cancer cell lines, None) , ( protein: ER, None) 