Caveolin-1 alters Ca²⁺ signal duration through specific interaction with the G_q family of G proteins

Caveolae are membrane domains having caveolin-1 (Cav1) as their main structural component. Here, we determined whether Cav1 affects Ca²⁺ signaling through the G_q-phospholipase-C (PLC) pathway using Fischer rat thyroid cells that lack Cav1 (FRTcav^-) and a sister line that forms caveolae-like domains due to stable transfection with Cav1 (FRTcav⁺). In the resting state, we found that eCFP-G and G_q-eYFP are similarly associated in both cell lines by Forster resonance energy transfer (FRET). Upon stimulation, the amount of FRET between G_q-eYFP and eCFP-G remains high in FRTcav^- cells, but decreases almost completely in FRTcav⁺ cells, suggesting that Cav1 is increasing the separation between G_q-G subunits. In FRTcav^- cells overexpressing PLC, a rapid recovery of Ca²⁺ is observed after stimulation. However, FRTcav⁺ cells show a sustained level of elevated Ca²⁺. FRET and colocalization show specific interactions between G_q and Cav1 that increase upon stimulation. Fluorescence correlation spectroscopy studies show that the mobility of G_q-eGFP is unaffected by activation in either cell type. The mobility of eGFP-G remains slow in FRTcav^- cells but increases in FRTcav⁺ cells. Together, our data suggest that, upon stimulation, G_q(GTP) switches from having strong interactions with G to Cav1, thereby releasing G. This prolongs the recombination time for the heterotrimer, thus causing a sustained Ca²⁺ signal.