What's lipitor's mechanism for altering protein involved in cholesterol?

Lipitor’s active ingredient is atorvastatin. Its key mechanism is:

• Inhibits HMG‑CoA reductase (the rate‑limiting enzyme in hepatic cholesterol synthesis).
• By lowering intracellular cholesterol in liver cells, it causes the liver to increase LDL (“bad cholesterol”) receptor expression on hepatocytes.
• Those extra LDL receptors pull more LDL cholesterol out of the blood, lowering circulating LDL levels.

So the “protein involved in cholesterol” that Lipitor directly targets is HMG‑CoA reductase (the enzyme driving cholesterol production), and it also indirectly changes the amount of LDL receptors on liver cells to enhance clearance of LDL.