8500
To further explore the ramifications of CD19 signaling, the current study examined whether phosphorylation of Elk-1 , activation of activator protein-1 ( AP-1 ), or activation of nuclear factor-kappaB ( NF-kappaB ) transcription factors occurred following CD19 cross-linking .
 ( protein: CD19, None) , ( protein: transcription factors, None) , ( protein: CD19, None) , ( protein: NF-kappaB, None) , ( protein: activator protein-1, None) , ( protein: Elk-1, None) , ( protein: AP-1, 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:
 ( protein: CD19, None) , ( protein: transcription factors, None) , ( protein: CD19, None) , ( protein: NF-kappaB, None) , ( protein: activator protein-1, None) , ( protein: Elk-1, None) , ( protein: AP-1, None) 