13020
In this study, we present evidence indicating that signal transduction pathways induced by PGE2 necessitate the participation of cyclic AMP , protein kinase A , and Ca2+ .
 protein kinase A
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:
 protein kinase A