GPER1 and breast cancer: For example, in ER− breast cancer cells, GPR30 activates the tyrosine kinase SRC through the Gβγ subunit, which stimulates the autophosphorylation of EGFR to initiate MAP-kinase ERK1/2 and phosphatidylinositol 3 kinase (PI3K) signaling, ultimately inducing proliferation [36, 37].