Kh Domains on Brain Polyribosomes: FMRP and Nova in Translational Regulation
The regulation of protein synthesis is an important aspect of the control of gene expression in neurons and is thought to contribute to neurologic diseases such as Fragile X mental retardation syndrome. We demonstrate that several neuronal RNA-binding proteins implicated in human disease are associated with brain polyribosomes, namely the Nova and Hu paraneoplastic antigens and the Fragile X mental retardation protein. We use microarray analysis of polyribosomal mRNAs in knockout mouse models of these diseases to identify target mRNAs and analyze the translational profiles of mice lacking Nova-1 or FMRP. The KH2 and RGG box RNA-binding domains of FMRP bind specific RNA motifs that form kissing complex and G-quartet structures, respectively. We find that the association of FMRP with polyribosomes in both mouse brain and human neuroblastoma cells is abrogated by competition with kissing complex RNA, but not by high-affinity G-quartet RNA. In addition, the polyribosome associations of FMRP-interacting proteins FXR1 and FXR2, are specifically abrogated by competition with this kissing complex RNA. FXR1 and FXR2 also bind kissing complex RNA via KH2, and they are competed off polyribosomes by kissing complex RNA even in the absence of FMRP. Kissing complex RNA does not disrupt heterodimerization between FMRP and FXR1 or FXR2. We conclude that the mental retardation associated with the I304N mutation, and likely the Fragile-X syndrome more generally, may relate to a crucial role for RNAs harbouring the kissing complex motif as targets for FMRP translational regulation.
protein synthesis, FMRP, polyribosomes, kissing complex RNA, RNA-binding proteins, Fragile X syndrome, Life Sciences
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