14-3-3θ facilitates plasma membrane delivery and function of mechanosensitive connexin 43 hemichannels

Intracellular signaling in osteocytes activated by mechanical loading is important for bone formation and remodeling. These signaling events are mediated by small modulators released from Cx43 hemichannels (HC). We have recently shown that integrin alpha 5 senses the mechanical stimulation and induces the opening of Cx43 HC; however, the underlying mechanism is unknown. Here, we show that both Cx43 and integrin alpha 5 interact with 14-3-3 theta, and this interaction is required for the opening of Cx43 HC upon mechanical stress. The absence of 14-3-3 theta prevented the interaction between Cx43 and integrin alpha 5, and blocked HC opening. Furthermore, it decreased the transport of Cx43 and integrin alpha 5 from the Golgi apparatus to the plasma membrane. Mechanical loading promoted the movement of Cx43 to the surface which was associated not only with an increase in 14-3-3 theta levels but also its interaction with Cx43 and integrin alpha 5. This stimulatory effect on forward transport by mechanical loading was attenuated in the absence of 14-3-3 theta and the majority of the Cx43 accumulated in the Golgi. Disruption of the Golgi by brefeldin A reduced the association of Cx43 and integrin alpha 5 with 14-3-3 theta, further suggesting that the interaction is likely to occur in the Golgi. Together, these results define a previously unidentified, scaffolding role of 14-3-3 theta in assisting the delivery of Cx43 and integrin alpha 5 to the plasma membrane for the formation of mechanosensitive HC in osteocytes.