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Magazine Chapter 9: Q. 1 (page 250)
HER2 is a receptor tyrosine kinase. In 30 percent of human breast cancers, HER2 is permanently activated, resulting in unregulated cell division. Lapatinib, a drug used to treat breast cancer, inhibits HER2 receptor tyrosine kinase autophosphorylation (the process by which the receptor adds phosphates onto itself), thus reducing tumor growth by 50 percent. Besides autophosphorylation, which of the following steps would be inhibited by Lapatinib?
a. Signaling molecule binding, dimerization, and the downstream cellular response.
b. Dimerization, and the downstream cellular response.
c. The downstream cellular response.
d. Phosphatase activity, dimerization, and the downsteam cellular response.
Short Answer
The correct answer is option (c).
Step by step solution
Introduction
Tyrosine Kinase receptor is an enzyme-linked receptor. Enzyme-linked receptors are the cell surface receptors with an enzyme associated with its intracellular domains. HER2 belongs to the family of human epidermal growth factor receptors that play crucial role in the pathogenesis of breast cancer.
Explanation for the correct answer
HER2 receptor is a tyrosine kinase receptor that undergoes dimerization upon binding of signalling ligand to its extracellular domain. As a result, autophosphorylation of the tyrosine residue takes place in its intracellular domain which initiates a downstream signalling response.
Lapitinib is a drug that inhibits the autophosphorylation of tyrosine residues of HER2. Thus, the downstream cellular response also gets inhibited by its action.
Hence, Option (c) is the correct answer.
Explanation for the incorrect options
The binding of a signalling molecule to the extracellular domain of the HER2 receptor causes dimerization. Lapatinib can't prevent the binding of the ligand and the dimerization process.
Hence, Option (a) is incorrect.
Lapatinib inhibits autophosphorylation that occurs after the dimerization of the receptor. So, the dimerization process is independent of lapatinib action.
Hence, option (b) is incorrect.
Lapatinib exhibits phosphatase activity by removing phosphates.
Hence, option (d) is incorrect.
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