6551
Although erythroid progenitors appear to be the principal EPO -responsive cell type in vivo due to the restricted expression of the EPOR , many growth factor-dependent cell lines expressing the EPOR can respond to EPO by activating many or all of these pathways.
 ( cell line: growth factor-dependent cell lines, None) , ( protein: EPOR, None) , ( protein: EPOR, None) , ( cell type: EPO -responsive cell type, None) , ( protein: EPO, None) , ( cell type: erythroid progenitors, None) , ( protein: EPO, 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:
 ( cell line: growth factor-dependent cell lines, None) , ( protein: EPOR, None) , ( protein: EPOR, None) , ( cell type: EPO -responsive cell type, None) , ( protein: EPO, None) , ( cell type: erythroid progenitors, None) , ( protein: EPO, None) 