5154
We demonstrate that loss of p16 causes upregulation of this DNA precursor pathway enzyme via activation of E2F by a mechanism involving retinoblastoma protein .
 enzyme, p16, E2F, retinoblastoma protein
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:
 enzyme, p16, E2F, retinoblastoma protein