Rho and Rac, but not ROCK, are required for secretion of human and mouse eosinophil‐associated RNases

Summary Background Eosinophil‐associated RNases (EARs) are stored preformed in eosinophil cytoplasmic secretory granules and have a key role in eosinophil effector functions in host defence and inflammatory disorders. However, the secretion mechanisms of EARs are poorly understood. Objective Our study aimed to understand the involvement of cytoskeleton machinery in EAR secretion. Methods Fresh human and mouse eosinophils were stimulated with CCL11, and the secretion of enzymatically active EARs was detected using an RNase activity assay. The involvement of cytoskeletal elements or microtubules was probed using specific inhibitors. Results We found that dynamic polymerization of microtubules and cytoskeletal elements, such as Rho and Rac, is required for chemokine‐mediated EAR secretion from human and mouse eosinophils. However, inhibition of ROCK (Rho‐associated protein kinase) increased EAR secretion in human and mouse eosinophils even in the absence of chemokine stimulation, suggesting ROCK negatively regulates EAR secretion. Conclusions Collectively, these data suggest a cytoskeleton‐dependent mechanism of EAR secretion from eosinophils, findings that are pertinent to host defence, allergy and other eosinophil‐associated diseases.