Functional activation of the neuronal K+-Cl- co-transporter KCC2 (also known as SLC12A5) is a prerequisite for shifting GABAA responses from depolarizing to hyperpolarizing during development. Here, we introduce transforming growth factor beta 2 (TGF-beta 2) as a new regulator of KCC2 membrane trafficking and functional activation. TGF-beta 2 controls membrane trafficking, surface expression and activity of KCC2 in developing and mature mouse primary hippocampal neurons, as determined by immunoblotting, immunofluorescence, biotinylation of surface proteins and KCC2-mediated Cl- extrusion. We also identify the signaling pathway from TGF-beta 2 to cAMP-response-element-binding protein (CREB) and Ras-associated binding protein 11b (Rab11b) as the underlying mechanism for TGF-beta 2-mediated KCC2 trafficking and functional activation. TGF-beta 2 increases colocalization and interaction of KCC2 with Rab11b, as determined by 3D stimulated emission depletion (STED) microscopy and co-immunoprecipitation, respectively, induces CREB phosphorylation, and enhances Rab11b gene expression. Loss of function of either CREB1 or Rab11b suppressed TGF-beta 2-dependent KCC2 trafficking, surface expression and functionality. Thus, TGF-beta 2 is a new regulatory factor for KCC2 functional activation and membrane trafficking, and a putative indispensable molecular determinant for the developmental shift of GABAergic transmission.Peer reviewe
