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This technique was successfully applied to evaluate differences in glucocorticoid receptor expression in U937 cells before and after the addition of potent differentiation inducers : 12-O-tetradecanoylphorbol 13-acetate ( TPA ) and a combination of all-trans retinoic acid ( RA ) and 1,25-dihydroxyvitamin D2 ( VD ).
 U937 cells, glucocorticoid receptor
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:
 U937 cells, glucocorticoid receptor