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

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.

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.