Hu Antigen R (HuR) is a Positive Regulator of RNA Binding Proteins TDP-43 and FUS/TLS: Implications for Amyotrophic Lateral Sclerosis [RNA]

September 19th, 2014 by Lu, L., Zheng, L., Si, Y., Luo, W., Dujardin, G., Kwan, T., Potochick, N. R., Thompson, S. R., Schneider, D. A., King, P. H.

Posttranscriptional gene regulation is governed by a network of RNA-binding proteins (RBP) that interact with regulatory elements in the mRNA to modulate multiple molecular processes including splicing, RNA transport, RNA stability and translation. Mounting evidence indicates that there is a hierarchy within this network, whereby certain RBPs cross-regulate other RBPs to coordinate gene expression. HuR, an RNA-binding protein which we previously linked to aberrant VEGF mRNA metabolism in models of SOD1-associated ALS, has been identified as high up in this hierarchy, serving as a regulator of RNA regulators. Here, we investigated the role of HuR in regulating two RBPs, TDP-43 and FUS/TLS, that have genetically been linked to ALS. We found that HuR promotes the expression of both RBPs in primary astrocytes and U251 cells under normal and stressed (hypoxic) conditions. For TDP-43, we found that HuR binds to the 3′ untranslated region (UTR) and regulates its expression through translational efficiency rather than RNA stability. With HuR knockdown, there was a shift of TDP-43 and FUS mRNAs away from polysomes consistent with translational silencing. TDP-43 splicing function was attenuated upon HuR knockdown which could be rescued by ectopic TDP-43 lacking the 3′ UTR regulatory elements. Finally, conditioned medium from astrocytes in which HuR or TDP-43 was knocked down produced significant motor neuron and cortical neuron toxicity in vitro. These findings indicate that HuR regulates TDP-43 and FUS/TLS expression and that loss of HuR-mediated RNA processing in astrocytes can alter the molecular and cellular landscape to produce a toxic phenotype.