6140
Recent studies suggest that one or more cytoplasmic serine kinases also phosphorylate STAT3 and are necessary for maximal gene activation .
 cytoplasmic serine kinases, STAT3
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
Answer:
 cytoplasmic serine kinases, STAT3