Question

How can the MAP kinase pathway be activated by a G protein-coupled receptor (GPCR) instead of an RTK?

Answer 1

By simulating the activity of adenylyl cyclase via Gα subunit.

Step-by-step explanation:

GPCR or G Protein Coupled Receptor is embedded in plasma membrane and made of seven segments. Inside the cell, it is coupled with G protein. G protein is a heterotrimeric protein made of α,β and γ subunits. The α subunit is attached to GDP in inactive state and βγ subunits exist as dimer. When a ligand attaches to the receptor, GDP is exchanged for GTP and the α unit dissociates from βγ dimer activating the signalling pathway.

The α unit separates from βγ dimer and activates adenylyl cyclase. Adenylyl cyclase leads to production of cAMP and cAMP activates cAMP dependent protein kinase( PKA). PKA activates RAP1 which can inhibit or activate MAPK cascade depending on the requirement of the cell.

Answer 2

MAP kinase pathway can be activated through PIP2 signaling which is an important G protein-coupled receptor (GPCR) signalling which gets activated during the condition of inflammation, stress, hypersensitivity etc.

Step-by-step explanation:

In the signalling, PIP2 is which is a substrate present on the inner leaflet of plasma membrane is broken down into 2 secondary messengers named as DAG & IP3. DAG further activates Protein kinase C (PKC). PKC is a component of MAP kinase pathway which is responsible for gene expression.

Here it may be noted that once activated, PKC not only activates MAP kinase pathway but also activates other one more signaling like NF-kB signaling (Nuclear factor -Kapa B) signaling.