Abstract
Gα(q) is a critical mediator of cell and tissue responses to G(q)-coupled receptor stimulation. Canonically, active Gα(q) regulates PLCβ and RhoGEFs. To identify novel Gα(q) signaling partners, we performed a proximity labeling proteomic screen in HEK293A cells using TurboID-tagged Gα(q). Top Gα(q)((Q209L)) enriched proteins included known Gα(q) interactors (PLCβs, RhoGEFs, and GRK2), supporting the validity of this approach. Also highly enriched were several nuclear proteins including SMARCD3, a component of the SWI/SNF chromatin remodeling complex, and BCAS2, a component of the spliceosome. Luciferase complementation experiments show that Gα(q) selectively interacts with BCAS2 and SMARCD3 in an activation-dependent manner, and pulldown experiments with purified components demonstrate direct interaction of Gα(q) and SMARCD3. We also show that a small but significant portion of Gα(q) is present in the nucleus, and this is increased following GPCR activation or introduction of an activating mutation. Proximity ligation assays indicate that Gα(q)((Q209L)) engages SMARCD3 in the nucleus. These data suggest that Gα(q) engages downstream targets in the nucleus and could therefore directly regulate nuclear processes.