Kaplan Qbank question - Contact Inhibition

[beatlemaniac]

Hi everyone,

I'm a bit confused by the explanation Kaplan offered for this Qbank question; maybe someone can clarify this for me.

"All of the following genes can cause contact inhibition when coupled with an overactive promoter EXCEPT:"
A - The gene for a protein involved in signal transduction
B - The gene for a protein that functions as a cytoplasmic growth factor receptor
C - The gene for a protein that promotes apoptosis.
D - The gene for a protein that turns on transcription of a growth factor.

The answer given is C, and the explanation states that contact inhibition results from over-expression of cellular proteins that promote cell growth. This seems pretty backwards to me, since freedom from contact inhibition is a feature of cancer, and cancer results from overactive cell growth. Thoughts?

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[gettheleadout]

The fact that contact inhibition fails in cancer is irrelevant to the consideration of its normal mechanisms. A normal cell wouldn't experience contact inhibition if it overproduced apoptotic signals/factors. All the other choices represent means by which normal cells *would* experience contact inhibition. If something negated its effects, cancer could develop, but that's a separate issue and not what the question is asking.


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[beatlemaniac]

The fact that contact inhibition fails in cancer is irrelevant to the consideration of its normal mechanisms. A normal cell wouldn't experience contact inhibition if it overproduced apoptotic signals/factors. All the other choices represent means by which normal cells *would* experience contact inhibition. If something negated its effects, cancer could develop, but that's a separate issue and not what the question is asking.


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So would the growth factor/growth factor receptor over-expression cause the cells to divide more, thus causing them to populate the plate to the point where they experience contact inhibition?

Whereas the apoptosis would prevent them from ever reaching this point?
(i.e. none of them really have to do with the mechanism of contact inhibition, but rather whether or not the cells ever reach the point where contact inhibition would be relevant?)

 

[gettheleadout]

So would the growth factor/growth factor receptor over-expression cause the cells to divide more, thus causing them to populate the plate to the point where they experience contact inhibition?

Whereas the apoptosis would prevent them from ever reaching this point?
(i.e. none of them really have to do with the mechanism of contact inhibition, but rather whether or not the cells ever reach the point where contact inhibition would be relevant?)

Yep! That's exactly the way I interpreted it.


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