A researcher studying a signaling pathway (L -> R -> A -> B) has identified a no

Question

A researcher studying a signaling pathway (L -> R -> A -> B) has identified a novel protein “Y” that interacts with A. L is an extracellular signal; R is the receptor for L; A and B are both Ser/Thr kinases. The researcher went on to make the following observations:

(1) Y also interacts with B; Y can bind A and B at the same time.

(2) Y does not have any enzymatic activity.

(3) Overexpression of Y in two different types of cells, HeLa and HEK293, leads to different effects on the activity of B in the presence or absence of the signal L (see figure below).

(a) What is the function of Y in this signaling pathway?

(b) What is the difference in the composition of this pathway (e.g., stoichiometry of components) between HeLa and HEK293 cells that would explain the data?

(c) Please explain all the data in Fig. A and B based on your answers to a and b. (8 pts) [Your answers should not involve any protein other than L, R, A, B, Y. You do not need to know what HeLa and HEK293 cells are.]

HeLa cells HEK293 cells a 100 2000 50 100 Y overexpression Y overexpression (Notice that Y axis has relative values and different scales in the two graphs.)

Explanation / Answer

A) The function of Y in these two pathways are separate. In the HeLa cells, in graph A, there is an increase of the B kinase activity in the presence of Y protein over expression, both in the presence and absence of L. Therefore, in graph A, it is acting as a positive regulator.

In graph B, with HEK293 cells, in the absence of L, there is no difference in B kinase activity. But, when L is present, there is a reduction in B kinase activity, in case of an over expressed Y. Thus, here, in the presence of L, Y acts as a negative regulator, decreasing the expression of B kinase activity.

B) HeLa cells are an immortal cell line that is derived from the cer-vical cancer cell line, whereas the HEK293 cells are derived from the embryonic kidney cells.

C) The function of Y is of a positive regulator. In the HeLa cells, in graph A, there is an increase of the B kinase activity in the presence of Y protein over expression, both in the presence and absence of L. As both L and Y are not expressed, the B kinase activity is very less with slight increase in the activity in the presence of L. There is a more than double increase in the expression of L and an even higher increase when there is over expression of Y in the presence of L.

In graph B, with HEK293 cells, in the absence of L, there is no excessive increase in B kinase activity. But, when L is present, there is a 100% increase in B kinase activity. In case of an over expressed Y, in the presence of L, Y acts as a negative regulator, decreasing the expression of B kinase activity. There is no increase at all with Y alone in the absence of L, but in the presence of L and Y together, there is a significant decrease in B kinase activity.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.