See diagram below: a MAPK pathway is SOLELY responsible for mediating two opposi

Question

See diagram below: a MAPK pathway is SOLELY responsible for mediating two opposing signals in the same cell: a mitogen, which stimulates cell growth, and a myogen, which promotes myogenic differentiation. MAPK1 (not MAPK2) directly activates gene expression that leads to growth and differentiation in response to mitogen and myogen, respectively. (a) What may be the difference in MAPK1 activation between these two pathways? (4 pts) (b) How is this difference achieved? [Your answers should not involve any protein other than those shown in the diagram.]

Explanation / Answer

Part a) It can be clearly seen from the image and the information that MAPK1 is involved in either cell growth or myogenesis in the same cell at the same time. This discrete phenomenon of regulation of different cellular functions might be attributed to the differential transcriptional control of MAPK1 in the nucleus of this cell. It is very well known that every cellular protein is regulated by a specific gene in the nuclear genome. Every gene also requires a specific transcription factor or activator for modulating of gene expression. Thus, it is highly likely that MAPK1 might be involved in regulating the gene expression of these two genes at transcriptional levels. Further, it can also be stated and inferred from the image that involvement of different secondary signalling molecules might be actively involved in modulating the nature of function of MAPK1. It is very well known that phosphorylation and activation of MAPK1 plays a crucial functional role in modulating gene function and it can be seen from the image that both of these pathways involve different secondary signalling molecules, thus making it very likely that in order to conduct these two functions, the MAPK1 might have undergone differential phosphorylation at different amino acid residues.

Part b) Since different cellular signals are involved in these pathways, it is very likely that both these signalling events might have differentially phosphorylated MAPK1 at different amino acid residues (such as different serine or threonine residues) and this might have contributed to differential transriptional responses of MAPK1 in the same cell.

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