RhoB is a small GTP-binding protein that is involved in apoptotic signal 
transduction. We have cloned the mouse RhoB mRNA including a 1377 nucleotide 
3'-untranslated region (UTR) that contains six AU-rich elements (AREs) as well 
as several uridine-rich stretches. There is 94% homology overall between the 
mouse and rat RhoB genes and 92% homology between the mouse and a putative human 
clone. Ultraviolet light (UVL) induces RhoB production through regulated changes 
in gene transcription and mRNA stabilization although the latter mechanism is 
unknown. We observed that UVL increased the half-life of RhoB mRNA from 63 min 
to 3.3 h in NIH/3T3 cells and from 87 min to 2.7 h in normal human keratinocyte 
cells. In vitro mobility shift assays demonstrated that HuR bound the 3'-UTR of 
RhoB at three distinct locations (nucleotides 1342-1696, 1765-1920 and 
1897-1977) suggesting a regulatory role for this RNA-binding protein. HuR 
immunoprecipitations were positive for RhoB mRNA indicating an in vivo 
association, and Western blot analysis and immunofluorescence demonstrated that 
HuR rapidly partitions from the nucleus to the cytoplasm after UVL. Therefore, 
we propose a model in which UVL induces stress-activated signal transduction 
leading to nuclear/cytoplasmic shuttling of HuR and subsequent stabilization of 
RhoB mRNA.