1973
The phorbol ester , PMA , was also a potent inducer of Fos kinase activity in all of the above populations, suggesting that PKC plays a role in the regulation of this enzyme .
 ( protein: Fos kinase, None) , ( protein: enzyme, None) , ( protein: PKC, 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: Fos kinase, None) , ( protein: enzyme, None) , ( protein: PKC, None) 