9518
In this study, therefore, the human monoblastic leukemia cell line U937 has been used as a model system to investigate the role of one of the RXRs , RXR-alpha , in monoblast differentiation .
 ( cell line: human monoblastic leukemia cell line U937, None) , ( protein: RXRs, None) , ( protein: RXR-alpha, 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: human monoblastic leukemia cell line U937, None) , ( protein: RXRs, None) , ( protein: RXR-alpha, None) 