Heat shock-mediated regulation of IκB-α at the post-transcriptional level by HuR

Abstract

Heat shock treatment induces tolerance to subsequent thermal stress and abrogates the response to alternative stimuli, including LPS and cytokines in vitro and in vivo. One of the mechanisms responsible for this phenomenon is inhibition of the nuclear factor-κB (NF-κB) pathway via NF-κB inhibitor proteins (IκB-α). However, the underlying mechanisms involved in the effect of heat shock treatment on IκB-α expression remain unclear. In the present study, the effect of heat shock treatment on the production of IκB-α and the possible mechanisms involved were investigated. The results revealed a significant increase in the half-lives of IκB-α mRNA and proteins in RAW264.7 macrophages following heat shock treatment and IκB-α transcription levels also increased. In addition, RNA pull-down and RNA immunoprecipitation studies showed that the RNA-binding protein, HuR, may specifically bind to the IκB-α mRNA 3'UTR upon heat shock treatment. Overexpression of HuR in 3T3 cells caused an alteration in IκB-α protein expression leading to a change in NF-κB expression, however, IκB-α mRNA expression levels were unchanged. The relocalization of HuR from the nucleus to the cytoplasm was observed following 1 h heat shock treatment and HuR was colocalized with the G3BP1 protein, the main content of stress granules. The results indicate that following heat shock treatment, HuR translocates from the nucleus to the cytoplasm, forming stress granules and regulating the translation of IκB-α mRNA without affecting the half-life.