You Have Been Studying the Pathway of Cholesterol Biosynthesis Using

You have been studying the pathway of cholesterol biosynthesis using a cell line derived from a human hepatoma. You discover that, unlike in nontransformed liver cells, the addition of oxysterols, such as 25-hydroxycholesterol, does not lead to reduced measurements of newly synthesized cholesterol. These observations indicate that normal regulation of an enzyme in cholesterol biosynthesis is defective in these cancer cells. Which of the following enzymes is the most likely candidate for this loss of regulation?

A) acetoacetyl-CoA thiolase (ACAT2)
B) 7-dehydrocholesterol reductase (DHCR7)
C) HMG-CoA reductase (HMGR)
D) HMG-CoA synthase
E) mevalonate kinase