One subtype of breast cancer involves the human epidermal growth factor receptor 2 gene (EGF receptor). One in every five breast cancers has a mutation in this gene. Understanding that this is a growth factor receptor gene, which of the answer choices best describes how this type of cancer develops? Choose one:
a. Mutations in the intracellular domain of the receptor will cause Akt to bind without further signaling and regulation of cell apoptotic processes.
b. Mutations that activate the kinase portion of the receptor result in a receptor that is constantly phosphorylated.
This causes constitutive activation of downstream signaling and the resulting cell growth and proliferation.
c. Interactions of the mutated receptor, which activates protein kinases, will not impact tumor growth because the ligand cannot bind to the receptor.
d. Mutations that block the receptor from functioning will block cell growth, indicating that this is a loss-of- function gene.

Mutations that activate the kinase portion of the receptor result in a receptor that is constantly phosphorylated. This causes constitutive activation of downstream signaling and the resulting cell growth and proliferation

Explanation:

The epidermal growth factor receptor (EGF receptor) is a type of receptor tyrosine kinase that recognizes and binds different ligands (including the Epidermal growth factor), which triggers its dimerization through the interaction of the extracellular domains. In humans, several mutations in genes encoding receptor tyrosine kinases have been associated with cancers. It is for that reason that mutated receptor tyrosine kinase genes are well-known oncogenes. Moreover, mutations in several receptor tyrosine kinase genes that lead to constitutive activation by phosphorylation have also been identified. In this case, it is expected that a mutation in the EGF receptor leads to constitutive phosphorylation of the mutant protein, constitutively activating downstream signaling.