Deck 9: Cell Communication

Question 1

A researcher is working to generate a new cancer drug. Thus far, he has identified a compound that can reduce the size of tumors in the lung. However, in order for the drug to work, the lung tumor has to be small. In addition, the tumor cannot have metastasized (spread to other areas of the body). Furthermore, he knows that the drug acts to prohibit the signaling from one tumor cell to another tumor cell. Given the above information, this new drug prohibits:

A) autocrine signaling between tumor cells.
B) synaptic signaling between tumor cells.
C) paracrine signaling between tumor cells.
D) endocrine signaling between tumor cells.

Answer 1

paracrine signaling between tumor cells.

Question 2

Leptin is a circulating hormone that is produced by fat cells and plays a role in body metabolism and obesity. It normally binds to receptors in the brain and inhibits appetite. Studies have demonstrated that when obese mice that are leptin deficient are injected with leptin they quickly lose their excess weight. Interestingly, however, many overweight people have high levels of leptin in their bloodstream. Why do you think that the high levels of leptin in obese individuals are insufficient to curb their appetite?

A) Obese people who have high levels of leptin may have a leptin receptor with decreased sensitivity.
B) In obese people with high levels of leptin, the leptin is a non-functional second messenger.
C) Paracrine signaling may be disrupted in obese people with high levels of leptin.
D) The form of leptin released by obese people may lack protein kinase activity.

Answer 2

Obese people who have high levels of leptin may have a leptin receptor with decreased sensitivity.

Question 3

Vasopressin is a hormone that is primarily released when the body is low on water. Release of vasopressin causes the kidneys to conserve water by concentrating urine and decreasing urine output. However, vasopressin also has additional functions in other tissues such as the brain and blood vessels, which are not directly involved in urine production. How could it be possible for vasopressin to trigger different responses in different tissues?

A) Vasopressin can bind to, and act on, different receptor subtypes, leading to different cellular responses in different tissues.
B) The kidneys have a receptor for vasopressin, but cells in the brain and blood vessels do not have a receptor for vasopressin.
C) Vasopressin binds to the same exact receptor in different tissues, but causes a different conformational change to the receptor in each tissue.
D) Vasopressin can be released at different times to result in different effects.

Answer 3

Vasopressin can bind to, and act on, different receptor subtypes, leading to different cellular responses in different tissues.

Question 4

You have identified a molecule, molecule X, that can bind to the ATP binding site of a specific protein kinase, and prevent ATP binding. You are conducting a kinase assay using this protein kinase and a known substrate of this kinase, and have set up the reaction using the proper conditions and co-factors to allow for optimal protein kinase activity. If you add molecule X to the reaction, what do you predict will be the outcome?

A) More phosphorylation of the substrate will be seen in the presence of molecule X.
B) The substrate will be phosphorylated normally in the presence of molecule X.
C) Less phosphorylation of the substrate will be seen in the presence of molecule X.

Question 5

You are interested in developing an inhibitor for the estrogen receptor. You have identified a molecule that is small and hydrophilic. In a test tube, this inhibitor binds tightly to the estrogen receptor, and inhibits the interaction of the receptor with estrogen. Do you think that this molecule will be an effective inhibitor of the estrogen receptor in cells?

A) Yes, because it is small.
B) No, because it will need to bind to the DNA-binding domain to act as an inhibitor.
C) No, because it is hydrophilic.
D) Yes, because it can prevent estrogen binding.

Question 6

Tamoxifen is a drug that is used to treat breast cancer. It inhibits the activities of the estrogen receptor in breast epithelial cells, which are the cells that are relevant to breast cancer. One of the concerns that scientists had during the development of Tamoxifen as a therapy for breast cancer was that other cell types require estrogen signaling for their function. For example, it is known that cells in bone tissue require estrogen signaling. As a result, there was a concern that use of Tamoxifen would lead to bone loss in patients. In reality, however, researchers were surprised to find that Tamoxifen actually led to an increase in bone density in breast cancer patients. At the same time, Tamoxifen did inhibit the activity of the estrogen receptor in breast epithelial cells in these patients. What is the best explanation for this finding?

A) The estrogen receptor is bound to different coactivators in different tissues.
B) Tamoxifen binds different parts of the estrogen receptor in different tissues.
C) Tamoxifen can only enter certain cell types.
D) Bone cells make use of a different type of estrogen receptor that does not bind to Tamoxifen.

Question 7

You are having lunch with an elderly friend when suddenly he begins to experience chest pain and tightness. He reaches into his pocket, gets out one of his nitroglycerin tablets and quickly takes it. After the episode passes, your friend asks you how the nitroglycerin helps his angina. You explain that nitroglycerin gets converted by cells to nitric oxide (NO) causing the smooth muscle cells of the blood vessel to relax and increase blood flow to the heart. He pushes you for a more detailed explanation, so you explain further that:

A) NO inhibits guanylyl cyclase, which allows the build up of cGMP, which acts as an intracellular messenger in a pathway leading to smooth muscle relaxation.
B) NO activates guanylyl cyclase, which catalyzes the synthesis of cGMP, which acts as an intracellular messenger in a pathway leading to smooth muscle relaxation.
C) NO activates cGMP, which catalyzes the synthesis of guanylyl cyclase, which acts as an intracellular messenger in a pathway leading to smooth muscle relaxation.
D) NO activates a protein kinase which catalyzes the synthesis of cGMP, which acts as an intracellular messenger in a pathway leading to smooth muscle relaxation.

Question 8

What is the mechanism by which binding of testosterone to the testosterone receptor leads to upregulated gene transcription?

A) Binding of testosterone to the testosterone receptor leads to the activation of a G protein that stimulates the activation of enzymes that promote gene transcription.
B) Binding of testosterone to the testosterone receptor leads to the opening of an ion channel that leads to an increase in calcium in the cytoplasm. The increased calcium levels activate calmodulin, which can go on to activate other proteins that promote gene transcription.
C) Binding of testosterone to the testosterone receptor leads to a conformational change that allows the receptor to enter the nucleus where it can bind to DNA and promote gene transcription.
D) Binding of testosterone to the testosterone receptor activates guanylyl cyclase, and the resulting cGMP promotes gene transcription.
E) Binding of testosterone to the testosterone receptor leads to the increase in second messengers that activate a kinase cascade, ultimately leading to the activation of transcription factors that promote gene transcription.

Question 9

How are receptor tyrosine kinases and steroid hormone receptors similar?

A) Both have a DNA-binding domain.
B) Both have a site for binding ligand.
C) Both are activated by autophosphorylation.
D) Both are transmembrane proteins with a single transmembrane domain.

Question 10

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, 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.
B) 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.
C) 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.
D) 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.

Question 11

Your research project involves the characterization of a particular signal transduction pathway. Specifically, you have been studying a receptor tyrosine kinase and protein X, which initiates downstream events. You are certain that protein X is part of the signal transduction pathway, but have been unable to identify a direct protein-protein interaction between the receptor tyrosine kinase and the protein X. What should you do next in your attempt to identify a link between the receptor tyrosine kinase and protein X?

A) Try to identify proteins that act downstream of protein X.
B) Try to identify an adapter protein that can interact with both the receptor and protein X.
C) Try to identify a coactivator protein.
D) Confirm the interaction between the receptor tyrosine kinase and its ligand.

Question 12

Many receptor tyrosine kinase (RTK) pathways lead to the activation of Ras. To activate Ras, it is necessary to recruit a guanine nucleotide exchange factor to the plasma membrane, because Ras is a membrane associated protein. Guanine nucleotide exchange factors, such as SOS, stimulate the exchange of GDP for GTP. However, SOS cannot bind directly to most RTKs. The protein Grb2 has a domain that can bind to phosphorylated tyrosines, and another domain that can bind to SOS. Therefore, Grb2 can bind to active RTKs and recruit SOS to the plasma membrane. Grb2 is an example of what kind of signaling molecule?

A) Scaffold
B) Adapter protein
C) Second messenger
D) Enzyme