57182
Caspases are activated in apoptotic cells and cleave intracellular protein substrate s. K18 is one such substrate , expressed by many epithelial cells ( e.g. hepatocytes , intestinal cells ) .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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