Glucagon Binding to Liver Cells Induces an Increase in Intracellular

Glucagon binding to liver cells induces an increase in intracellular cAMP concentration. The rate-limiting step in cholesterol biosynthesis is regulated as a consequence of this glucagon-mediated rise in cAMP. The effect of increased cAMP on the rate of cholesterol biosynthesis occurs because of which of the following?

A) AMP-regulated kinase (AMPK) is activated and directly phosphorylates human HMG-CoA reductase (HMGR) , leading to an increase in the activity of the latter enzyme
B) cAMP-dependent protein kinase (PKA) is activated and directly phosphorylates HMGR, reducing the activity of the latter enzyme
C) PKA is activated and phosphorylates AMPK, which then phosphorylates and activates HMGR
D) PKA activation results in a reduced level of phosphate removal from HMG-CoA reductase so that the latter enzyme is kept less active.
E) the increased cAMP directly inhibits HMGR via allosteric interaction