This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General Physiology, Subject name: Physiology
True about caveolin: 
Select and explain. 
A. Involved in transcytosis, B. Involved in cholesterol regulation, C. Signal transduction, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Caveolins are proteins that interact with cholesterol and polymerize to form the caveolae (flask-shaped membrane depressions). These are prominent in endothelial cells, where they help in the uptake of nutrients from the blood. These are involved in cholesterol regulation and transcytosis. Transcytosis across capillary endothelium