Question

What are the consequences of LDL uptake by liver cells?

a. cholesterol is degraded

b. the cell content of cholesterol increases

c. SREBP is activated

d. B and C

e. A and C

Answer 1

D

LDL receptors are mostly expressed in the liver, where its regulation is mediated by sterol regulatory element-binding proteins (SREBPs). SREBPs are found in inactive forms in the endoplasmic reticulum (ER). When cellular cholesterol levels rise after the delivery of cholesterol by the LDL receptor, increased ER sterol content causes cholesterol to bind to Scap, a protein that promotes the migration of SREBPs from the ER to the Golgi. In the Golgi, SREBPs undergo proteolytic conversion to active forms that move to the nucleus and stimulate the expression of genes involved in cholesterol synthesis. The binding of cholesterol to Scap induces a conformational change that causes it to bind to Insigs, ER anchor proteins