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In contrast, stat1 proteins were not tyrosine phosphorylated after IL-2 ligation , whereas tyrosine -phosphorylated stat1 proteins ( 91 and 84 kDa proteins ) were translocated to the nucleus following interferon-gamma treatment of HeLa cells .
 interferon-gamma, HeLa cells, tyrosine -phosphorylated stat1 proteins, IL-2
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:
 interferon-gamma, HeLa cells, tyrosine -phosphorylated stat1 proteins, IL-2