The lipid raft proteins flotillins/reggies interact with Gαq and are involved in Gq-mediated p38 mitogen-activated protein kinase activation through tyrosine kinase

The heterotrimeric G protein α q subunit (Gαq) mediates a variety of cell functions by activating the effector molecule phospholipase Cβ. Gαq activity is regulated by G protein βγ subunits, G protein-coupled receptors, RGS proteins, and Ric-8. In this study, we identified the lipid raft resident proteins, flotillin-1/reggie-2 and flotillin-2/reggie-1, as Gαq-binding proteins. The interactions of Gαq and flotillins were independent of the nucleotide-binding state of Gαq, and the N-terminal portion of flotillins was critical for the interaction. A short interfering RNA-mediated knockdown of flotillins, particularly flotillin-2, attenuated the UTP-induced activation of p38 mitogen-activated protein kinase (MAPK) but not that of ERK1/2. The activation of p38 MAPK was inhibited by the Src family tyrosine kinase inhibitor PP2 and the cholesterol-depleting agent methyl-β-cyclodextrin, which is generally used for the disruption of lipid rafts. In contrast, the activation of ERK1/2 was not inhibited by these compounds. These lines of evidence suggested that a Gq-coupled receptor activates specifically p38 MAPK through lipid rafts and Src kinase activation, in which flotillins positively modulate the Gq signaling.