IGF Binding proteins such as IGFBP3 make IGF-1 bind much better to IGF-1 receptors that expressed in muscle and adipose tissue. True False
The correct answer and explanation is:
Correct Answer: False
Explanation:
Insulin-like Growth Factor Binding Proteins (IGFBPs), such as IGFBP-3, do not enhance the binding of IGF-1 to its receptor. Instead, they regulate the availability and activity of IGF-1 in the bloodstream and extracellular fluids. IGFBP-3 is the most abundant binding protein for IGF-1 and forms a ternary complex with IGF-1 and an acid-labile subunit (ALS). This complex helps extend the half-life of IGF-1 in circulation and prevents its rapid degradation. However, when IGF-1 is bound to IGFBP-3, it is generally not free to interact with the IGF-1 receptor.
For IGF-1 to activate the IGF-1 receptor, it must be in its free or unbound form. The IGF-1 receptor is a transmembrane tyrosine kinase receptor found on the surface of cells, especially in tissues like muscle and adipose. When free IGF-1 binds to this receptor, it triggers a cascade of intracellular signals that promote cell growth, differentiation, and survival. This is especially important in muscle development and metabolic regulation.
IGFBPs, including IGFBP-3, play a modulatory role by sequestering IGF-1 and controlling how much of it is available for receptor binding. In some cases, proteases may cleave IGFBP-3 to release IGF-1 near target tissues, indirectly supporting receptor interaction. But this is a regulated process and does not mean IGFBP-3 directly improves receptor binding.
In summary, IGFBP-3 binds IGF-1 and extends its stability but inhibits immediate binding to the IGF-1 receptor. Only when IGF-1 is released from IGFBP-3 can it effectively activate its receptor in muscle or adipose tissue. Therefore, the statement is false.