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Regulation of HuR structure and function by Dihydrotanshinone-I

ABSTRACT: The Human antigen R protein (HuR) is a RNA-binding protein that recognizes U/AU-rich elements in diverse RNAs through two RNA-recognition motifs, RRM1 and RRM2, and post-transcriptionally regulates the fate of target RNAs. The natural product Dihydrotanshinone-I (DHTS) prevents the association of HuR and target RNAs in vitro and in cultured cells by interfering with the binding of HuR to RNA. Here, we report the structural determinants of the interaction between DHTS and HuR and the impact of DHTS on HuR binding to target mRNAs transcriptome-wide. NMR titration and Molecular Dynamic simulation identified the residues within RRM1 and RRM2 responsible for the interaction between DHTS and HuR. RNA Electromobility Shifts and Alpha Screen Assays showed that DHTS interacts with HuR through the same binding regions as target RNAs, stabilizing HuR in a locked conformation that hampers RNAs binding competitively. HuR ribonucleoprotein immunoprecipitation followed by microarray (RIP-chip) analysis showed that DHTS treatment of HeLa cells paradoxically enriched HuR binding to mRNAs with longer 3’UTR and with higher density of U/AU-rich elements, suggesting that DHTS inhibits the association of HuR to weaker target mRNAs. In vivo, DHTS potently inhibited xenograft tumor growth in a HuR-dependent model without systemic toxicity.

ORGANISM(S): Homo sapiens

PROVIDER: GSE94360 | GEO | 2017/12/20

SECONDARY ACCESSION(S): PRJNA369472

REPOSITORIES: GEO

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Project description:HuR is a regulator of mRNA turnover or translation of inflammatory genes through binding to adenylate-uridylate-rich elements (ARE) and related motifs present in the 3’untranslated region (UTR) of mRNAs. We aimed to identify HuR targets in the human airway epithelial cell line BEAS-2B challenged with TNFa plus IFNg, a strong stimulus for inflammatory epithelial responses. Ribonucleoprotein (RNP) complexes from resting and cytokine-treated cells were immunoprecipitated (IP) using anti-HuR and isotype-control antibody, and eluted mRNAs were reverse-transcribed and hybridized to an inflammatory-focused gene array. The chemokines CCL2, CCL8, CXCL1 and CXCL2 ranked highest among 27 signaling and inflammatory genes significantly enriched in the HuR RNP-IP from stimulated cells over the control IP. Among these, 20 displayed published HuR binding motifs. Association of HuR with the four endogenous chemokine mRNAs was validated by single-gene RNP-IP, and shown to be 3’UTR-dependent by biotin pull-down assay. Cytokine treatment increased mRNA stability only for CCL2 and CCL8, and transient silencing and overexpression of HuR affected only CCL2 and CCL8 expression in primary and transformed epithelial cells. Cytokine-induced CCL2 mRNA was predominantly cytoplasmic; conversely, CXCL1 mRNA remained mostly nuclear and unaffected, as CXCL2, by changes in HuR levels. Increase in cytoplasmic HuR and HuR target expression partially relied on the inhibition of AMP-dependent kinase, a negative regulator of HuR nucleocytoplasmic shuttling. We postulate that HuR critically regulates the epithelial response, by associating with multiple adenylate-uridylate-rich elements (ARE)-bearing, functionally related inflammatory transcripts. On the basis of genome-wide studies probing the relationship between RNA-binding proteins and the functional profile of their associated transcripts, we combined the specific HuR immunoprecipitation of RNPs and the genome-scale microarray to profile the target mRNAs of HuR in the human airway epithelial cell line BEAS-2B challenged with very strong inflammatory stimulation, TNFa plus IFNG. The array platform we used is the Human Autoimmune and Inflammatory Response Gene Array (SuperArray Bioscience, Frederick, MD). To validate the association of HuR and its target mRNAs, we planned to apply biotin pull-down assay. HuR overexpression and knockdown assays were also planned to further verify the association of HuR and its target mRNAs. Overall, we did three biological replicates for the IP array experiments, which include both IgG1 control IP and HuR IP arrays.

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Regulation of HuR structure and function by Dihydrotanshinone-I

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