Question 1

What is the Meaning of GPCR Downregulation?

Accepted Answer

GPCR Downregulation is a fundamental cellular mechanism where the number or responsiveness of G Protein-Coupled Receptors (GPCRs) on the cell surface is reduced, primarily in response to prolonged or excessive exposure to their specific ligand or hormone. This process serves as a crucial negative feedback loop, preventing overstimulation of the cell and protecting against potential cellular toxicity or exhaustion. It is a key factor in the development of pharmacologic tolerance, where the effectiveness of a drug that targets a GPCR, such as certain peptide hormones, diminishes over time. Understanding this phenomenon is vital for designing effective, long-term therapeutic regimens in endocrinology and pharmacology.

Question 2

What is the Origin of GPCR Downregulation?

Accepted Answer

The concept of receptor downregulation arose from decades of research into cell signaling and the mechanisms by which cells maintain homeostasis in the face of varying external stimuli. GPCRs themselves are one of the largest and most important families of cell surface receptors, mediating responses to a vast array of hormones, neurotransmitters, and sensory stimuli. The identification of downregulation as a protective, adaptive response clarified how cells manage signal intensity and duration.

Question 3

What is the Mechanism of GPCR Downregulation?

Accepted Answer

The process begins with the hyper-stimulation of the GPCR by its ligand, which triggers the phosphorylation of the receptor by specific kinases, such as GPCR kinases (GRKs). This phosphorylation event facilitates the binding of arrestin proteins to the receptor, which physically blocks the G protein from coupling, a process known as desensitization. The receptor-arrestin complex is then internalized into the cell via endocytosis, effectively removing the receptor from the cell surface and marking it for either degradation or recycling back to the membrane. This internalization and subsequent degradation constitute the physical downregulation of the receptor population.

GPCR Downregulation

Meaning

Origin

Mechanism

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