Diacylglycerol kinase η colocalizes and interacts with apoptosis signal-regulating kinase 3 in response to osmotic shock

Diacylglycerol kinase (DGK) eta translocates from the cytoplasm to punctate vehicles via osmotic shock. Apoptosis signal-regulating kinase (ASK) 3 (MAP kinase kinase kinase (MAPKKK) 15) is also reported to respond to osmotic shock. Therefore, in the present study, we examined the subcellular localization of DGK eta and ASK3 expressed in COS-7 cells under osmotic stress. We found that DGK eta was almost completely colocalized with ASK3 in punctate structures in response to osmotic shock. In contrast, DGK delta, which is closely related to DGK eta structurally, was not colocalized with ASK3, and DGK eta failed to colocalize with another MAPKKK, C-Raf, even under osmotic stress. The structures in which DGK eta and ASK3 localized were not stained with stress granule makers. Notably, DGK eta strongly interacted with ASK3 in an osmotic shock-dependent manner. These results indicate that DGK eta and ASK3 undergo osmotic shock-dependent colocalization and associate with each other in specialized structures.