I've been doing a lot of research recently on the melatonin cell signaling pathway for an extra credit project at school. I've included an image in this post, which is a diagram of the MT1 pathway. It seems to be a fairly standard GPCR sequence. I can identify all of the elements depicted in the diagram, but unfortunately I don't understand why some of these elements are present at all.
The portion of this pathway that stands out to me the most is the presence of a Prostaglandin F receptor (FP) as well as the presence of Prostaglandin F2-alpha (PGF2α). From the research that I have done, I've gathered that PGF2α is a prostaglandin found naturally in the body that can been used as an abortifacient in medical applications. I have not found any research that covers exactly why these two elements are present in the MT1 pathway.
Here's what I know: the Gi beta-gamma complex (Gβγi) and the Gq alpha subunit (Gαq) both activate Phospholipase C (PLC), which in this reaction causes the hydrolysis of PIP2 to create IP3 and DAG. My current hypothesis is that FP carries PGF2α into the cell, and PGF2α helps to activate PLC in some way. Unfortunately, I haven't been able to find any information online supporting this. Has anybody done any research regarding this topic, and if so can you provide any insight? I really, really appreciate it.