8144
Furthermore, CoCl2 also caused time-dependent tyrosine phosphorylation of mitogen-activated protein (MAP) kinase isoform ERK2 without significantly affecting ERK1 , indicating ERK2 is the preferred substrate for upstream kinase of the MAPK pathway .
 ERK2, ERK2, upstream kinase, ERK1, MAPK, mitogen-activated protein (MAP) kinase
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:
 ERK2, ERK2, upstream kinase, ERK1, MAPK, mitogen-activated protein (MAP) kinase