Abstract
Zinc-finger protein 36 (Zfp36) family RNA-binding proteins, such as tristetraprolin (TTP/Zfp36), butyrate response factor (BRF)-1/Zfp36L1, and BRF-2/Zfp36L2, regulate the expression of cytokine/chemokine mRNA with AU-rich elements. In traumatic brain injury (TBI), reactive astrocytes produce various cytokines and chemokines that induce neuroinflammation. However, despite their importance in neuroinflammation, little is known about the regulation of cytokine and chemokine production by the Zfp36 family proteins in astrocytes. Endothelin-1 (ET-1), which promotes the conversion to reactive astrocytes, stimulates astrocytic cytokine and chemokine production. In the present study, we examined the effects of ET-1 on Zfp36 family protein expression in astrocytes and the roles of these proteins in cytokine/chemokine production. ET-1 (100 nM) increased the expression of TTP and BRF-1 in cultured astrocytes. In a mouse model of TBI, expression of TTP and BRF-1 increased, which was reduced by intracerebroventricular administration of BQ788, an ET(B) antagonist. Immunohistochemical analyses showed that TTP and BRF-1 were present in reactive astrocytes. Knockdown of TTP by siRNA enhanced the production of ET-induced CCL2 and IL-6 in cultured astrocytes, while BRF-1 knockdown enhanced the CCL2, CXCL1, and CX3CL1 production. RNA immunoprecipitation/PCR analyses showed that ET-1 stimulated TTP binding to CCL2 and IL-6 mRNAs, and BRF-1 binding to CCL2, CXCL1, and CX3CL1 mRNAs. These results suggest that ET-1 stimulates the induction of TTP and BRF-1 in astrocytes and that the production of some astrocytic chemokine/cytokine is negatively regulated by the increments in TTP and BRF-1 production.