Signaling Pathways- different effects on the same pathway.

The growth and division of cells is highly regulated so they don’t get out of control in either the positive direction (tumor formation) or the negative direction (too few cells). This control is exerted by a number of external ‘growth factors’ which bind to signaling receptors on cells. Consider a cell that responds to fibroblast growth factor (FGF) through a receptor tyrosine kinase (RTK). Its response is to divide and grow faster. But the cell also responds to another signal molecule, ‘X’, that binds to and activates a GPCR that stimulates adenylyl cyclase. Signaler X has the opposite effects; ie, downregulation of whatever FGF upregulated.

Assume that both FGF and X signaling impinges on the MAP-kinase pathway.

Propose signaling pathways that could account for these observations. That is, explain how FGF and X can have opposite effects on the same MAP-K pathway.
Answer