Elp2, a 4‐phenylbutyrate Inducible Elongator Component, Modulates Hsp70 Expression

Abstract

Sodium 4‐Phenylbutyrate (4PBA) improves the aberrant trafficking of ΔF508‐CFTR in Cystic Fibrosis (CF) epithelial cells, at least in part by increasing expression of Hsp70 (stress‐induced 70 kDa heat shock protein). To identify other 4PBA‐regulated proteins that may improve ΔF508 trafficking, we performed differential display RT‐PCR on mRNA from IB3‐1 CF bronchiolar epithelial cells treated for 0–24 h with 1 mM 4PBA. StIP‐1, a STAT‐3 (signal transducer and activator of transcription‐3) interacting protein, had transiently increased expression. StIP‐1 is identical to Elongator protein 2 (Elp2). Elongator is a multimeric complex that facilitates mRNA transcription by RNA polymerase II, and is suggested to regulate Hsp70 expression. To investigate regulation of Hsp70 by Elp2, we transfected T84 colonic epithelial cells with small interfering RNAs (siRNA) targeting Elp2. Such depletion of Elp2 reduced Hsp70 protein expression by ~50%. Elp2 is also necessary for activation of STAT‐3 in response to IL‐6, and the Hsp70 promoter contains a functional STAT‐response element. We therefore tested whether 4PBA caused activation of STAT‐3 and altered nuclear protein binding to the STAT response element of the Hsp70 promoter. In IB3‐1 cells, 4PBA caused transient activation of STAT‐3 and increased binding of nuclear proteins to the STAT‐3 element of the Hsp70 promoter. These data suggest a mechanism by which 4PBA, through increased Elp2 expression, would increase Hsp70 expression and promote ΔF508‐CFTR trafficking.