11380
The activity of the transcription factor CREB is regulated by extracellular stimuli that result in its phosphorylation at a critical serine residue , Ser133 .
 transcription factor CREB
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 transcription factor CREB