STABILIZATION AND CYTOSKELETAL-ASSOCIATION OF LDL RECEPTOR MESSENGER-RNA ARE MEDIATED BY DISTINCT DOMAINS IN ITS 3' UNTRANSLATED REGION

The mRNA encoding the human low density lipoprotein (LDL) receptor is transiently stabilized after phorbol ester treatment of HepG2 cells an d has been shown to associate with components of the cytoskeleton in t his cell line (G., M., Wilson, E. A. Roberts, and R., G., Deeley, J., Lipid Res. 1997, 38: 437-446). Using an episomal expression system, fr agments of the 3' untranslated region (3'UTR) of LDL receptor mRNA wer e transcribed in fusion with the coding region of beta-globin mRNA in HepG2 cells. Analyses of the decay kinetics of these beta-globin-LDL r eceptor fusion mRNA deletion mutants showed that sequences in the prox imal 3'UTR of LDL receptor mRNA including several AU-rich elements (AR Es) were sufficient to confer short constitutive mRNA half-life in the heterologous system. Stabilization of LDL receptor mRNA in the presen ce of PMA required sequences in the distal 3'UTR, at or near three Alu -like repetitive elements. Furthermore, the 3'UTR of LDL receptor mRNA conferred cytoskeletal association on the otherwise unassociated beta -globin mRNA, by a mechanism involving at least two distinct RNA eleme nts.ir Comparisons of decay kinetics and subcellular localization of e ndogenous LDL receptor mRNA and beta-globin-LDL receptor mRNA fusions in HepG2 cells have demonstrated that several cia-acting elements in t he receptor 3'UTR contribute to post-transcriptional regulation of rec eptor expression, and provide further support for involvement of the c ytoskeleton in the regulation of LDL receptor mRNA turnover.