Consider the following RTK-initiated signaling pathway: Ligand rightarrow RTK ri
ID: 80326 • Letter: C
Question
Consider the following RTK-initiated signaling pathway: Ligand rightarrow RTK rightarrow Sos rightarrow Ras rightarrow Raf rightarrow MEK rightarrow ERK rightarrow Transcription factor rightarrow Gene transcription You design the following protocol to test the function of two drugs: You have two cell lines, one wild-type and the other carrying a mutation in Raff that makes it permanently active. For both cell lines, you expose different cultures to the following experimental conditions: Add vehicle (no ligand or inhibitor, negative control) Add ligand only Add ligand + Sos inhibitor Add ligand + MEK inhibitor After exposure, you measure whether gene expression is high or low. In the following table, please predict whether gene transcription will be high or low in each of the experimental conditions. Which conditions would have different results for wild-type and the mutant cell line? Please explain why the Ral mutation would affect gene expression in these conditions. Which conditions would have similar results for wild-type and the mutant cell line? Please explain why the Ral mutation would not affect gene expression in these conditions.Explanation / Answer
Hi,
Cell line
vehicle
Ligand only
Ligand+SOS inhibitor
Ligand + MEK inhibitor
Wild-type
Low expression
High expression
Low expression
Low expression
Mutant RAS activated
High expression
High expression
High expression
Low expression
But in the mutant, the Raf is always active, so even if vehicles is used, the Ras continues to activate the MEK and continue the gene expression. Similarly when ligand + Sos inhibitor is used, in wild type the Sos inhibitor will block the signal created by binding of ligand. This lowers the gene expression. But in the mutant, as Sos is upstream of Raf, the inhibition of sos has no effect of Raf activity. The gene expression continues at high pace.
When the Ligand + MEK inhibitor is used gene expression in both wild and mutant decreases. This is because the MEK inhibitor will not allow the signal to pass through the MEK. In wild type, it is straight forward that when MEK is blocked no gene expression can take place. In the mutant, even though the Raf is always active, the MEK is situated downstream of Raf. So even Raf is sending signals to MEK, the MEK inhibitor is blocking MEK expression, thereby reducing the gene expression.
Cell line
vehicle
Ligand only
Ligand+SOS inhibitor
Ligand + MEK inhibitor
Wild-type
Low expression
High expression
Low expression
Low expression
Mutant RAS activated
High expression
High expression
High expression
Low expression
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