Viral-mediated stabilization of AU-rich element containing mRNA contributes to cell transformation

E4orf6 is one of the oncogene products of adenovirus and it also plays an important role for transportation of cellular and viral mRNA during the late phase of virus infection. We previously revealed that E4orf6 controls the fate of AU-rich element (ARE) containing mRNA by perturbing the CRM1-dependent export mechanism. Here, we show that E4orf6 stabilizes ARE-mRNA through the region required for its oncogenic activity and ubiquitin E3 ligase assembly. Cells that failed to stabilize ARE-mRNA after HuR knockdown were unable to produce colonies in soft-agar, even when E4orf6 was expressed. Furthermore, the stabilized ARE-mRNA induced the transformation of rodent immortalized cells. These findings indicate that stabilized ARE-mRNA is necessary, if not all, for the oncogenic activity of E4orf6 and has the potential to transform cells at least under a certain condition

HuR translocation to the cytoplasm of cancer cells in actin-independent manner

Human antigen R (HuR) is a RNA-binding protein, which binds to the AU-rich element (ARE) in the 3'-untranslated region (3'-UTR) of certain mRNA and is involved in the export and stabilization of ARE-mRNA. HuR constitutively relocates to the cytoplasm in many cancer cells, however the mechanism of intracellular HuR trafficking is poorly understood. To address this question, we examined the functional role of the cytoskeleton in HuR relocalization. We tested the effect of actin depolymerizing macrolide latrunculin A or myosin II ATPase activity inhibitor blebbistatin for HuR relocalization induced by the vasoactive hormone Angiotensin II in cancer and control normal cells. Western blot and confocal imaging data revealed that both inhibitors attenuated the cytoplasmic HuR in normal cells but no such alteration was observed in cancer cells. Concomitant with changes in intracellular HuR localization, both inhibitors markedly decreased the accumulation and half-lives of HuR target ARE-mRNAs in normal cells, whereas no change was observed in cancer cells. Furthermore, co-immunoprecipitation experiments with HuR proteins revealed clear physical interaction with beta-actin only in normal cells. The current study is the first to verify that cancer cells can implicate a microfilament independent HuR transport. We hypothesized that when cytoskeleton structure is impaired, cancer cells can acquire an alternative HuR trafficking strategy