Some cancers are caused by the overexpression of receptor tyrosine kinases (RTKs). It is known that RTK-signaling pathways commonly stimulate cell division. Why would the overexpression of receptor tyrosine kinases lead to cancer development?
A. If there are too many RTKs on the cell surface, this will promote the inhibition of autophosphorylation. In the absence of autophosphorylation, it is more likely that the RTK downstream signaling pathway will be active.
B. RTKs are activated by dimerization, caused by ligand binding. If there are too many receptors on the cell surface, it is possible that these receptors dimerize in the absence of ligand binding, thus stimulating cell division at inappropriate times.
C. If there are too many RTKs on the cell surface, this will tend to allow cells to adhere to each other. Once they adhere, RTKs from one cell can bind to RTKs from another cell, and they can activate each other leading to activation of downstream signaling pathways in both cells.
D. If there are too many RTKs on the cell surface, it is less likely that inhibitors will bind to all of the available RTKs and block their ability to enter the nucleus. As a result, some of the RTKs will be able to enter the nucleus to stimulate transcription.
Answer: B
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