The Single‐Stranded DNA‐ and RNA‐Binding Proteins Pur α and Pur β Link BC1 RNA to Microtubules Through Binding to the Dendrite‐Targeting RNA Motifs

Abstract

Neural BC1 RNA is distributed in neuronal dendrites as RNA-protein complexes (BC1 RNPs) containing Translin. In this study, we demonstrated that the single-stranded DNA-and RNA-binding protein pur ␣ and its isoform, pur ␤, which have been implicated in control of DNA replication and transcription, linked BC1 RNA to microtubules (MTs). The binding site was within the 5Ј proximal region of BC1 RNA containing putative dendrite-targeting RNA motifs rich in G and U residues, suggesting that in the cytoplasm of neurons, these nuclear factors are involved in the BC1 RNA transport along dendritic MTs. The pur proteins were not components of BC1 RNP but appeared to associate with MTs in brain cells. Therefore, it is suggested that they may transiently interact with the RNP during transport. In this respect, the interaction of pur proteins with BC1 RNA could be regulated by the Translin present within the RNP, because the binding mode of these two classes of proteins (pur proteins and Translin) to the dendrite-targeting RNA motifs was mutually exclusive. As the motifs are well conserved in microtubule-associated protein 2a/b mRNA as well, the pur proteins may also play a role(s) in the dendritic transport of a subset of mRNAs. Key Words: BC1 RNABrain-Neuronal dendrite -Pur ␣ and pur ␤ proteinsMicrotubule-binding protein-RNA transport. J. Neurochem. 75, 1781Neurochem. 75, -1790Neurochem. 75, (2000.Neural BC1 RNA is expressed selectively in rodent brain (Sutcliffe et al., 1982;Anzai et al., 1986) and is distributed in neuronal dendrites (Tiedge et al., 1991) in the form of ribonucleoprotein particles (RNPs) (Kobayashi et al., 1991;Cheng et al., 1996). In a previous study, we demonstrated the presence of two copies of y-, h-element homologous sequences in BC1 RNA [nucleotides (nt) 1-22 and 47-76] (see Fig. 1) (Muramatsu et al., 1998), and we detected two RNA-binding proteins using the radiolabeled 3Ј distal y-, h-elements (nt 47-76) as a probe, which co-purified with BC1 RNP (Kobayashi et al., 1998;Muramatsu et al., 1998). One of these proteins was mouse Translin and the other was a 37-kDa protein. In addition to these observations, we demonstrated the dendritic distribution of Translin protein in hippocampal neurons in primary culture (Kobayashi et al., 1998), suggesting that Translin is involved in the dendritic translocation of BC1 RNP. Recently, Translin was also detected in dendrites of a subset of neurons of the mouse brain (Wu et al., 1999). Wu et al. (1997) reported that testis/brain RNA-binding protein (TB-RBP), which was originally identified as a y-, h-element-binding protein (Kwon and Hecht, 1991), is the mouse homologue of Translin. They also reported that TB-RBP has translational repressor activity (Kwon and Hecht, 1993) and links a subset of mRNAs to microtubules (MTs) in vitro through binding to their y-, h-sequence elements (Han et al., 1995a). These observations in turn suggested that dendritic MTs are also involved in the process of BC1 RNP transport and that this RNP may have regulatory roles...

Identification of a Rice RNA- and Microtubule-binding Protein as the Multifunctional Protein, a Peroxisomal Enzyme Involved in the β-Oxidation of Fatty Acids

“…These proteins appear to mediate the translocation and anchoring of specific RNAs and, similar to rice MFP (Fig. 6B), were shown to simultaneously bind microtubules and RNAs in co-sedimentation assays (56,57). In plant cells, the direct interaction of a class of RNAbinding proteins to microtubules has revealed a potentially novel mechanism of RNA trafficking.…”

Pur .ALPHA. Protein Implicated in Dendritic RNA Transport Interacts with Ribosomes in Neuronal Cytoplasm.

“…Nevertheless, it seems unlikely that BC1 RNA is the sole target of these proteins, as the nucleotide sequences bound by pur proteins, which contain GGN repeats, 1,2) are relatively simple and have been found in several RNAs. 2,9,10,13,14) These observations suggest that pur proteins may also link other dendritic RNAs including rRNA to MTs. Therefore, it is necessary to define the target RNA that is specifically bound by these proteins in vivo, particularly in neuronal cytoplasm, and to analyze the subcellular localization of the pur proteins.…”

“…9) The pur-binding site is within the 5Ј-proximal region of BC1 RNA which contains putative dendrite-targeting RNA motifs, 9,10) suggesting that in the cytoplasm of neurons these nuclear proteins are involved in the process of BC1 RNA transport along dendritic MTs. The expression of pur proteins is developmentally regulated, 8) and mimics the time course of BC1 RNA expression in the postnatal brain.…”

Dysregulation of Gene Expression in the 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine-Lesioned Mouse Substantia Nigra

“…Reduction of Pur-␣, a multifunctional RNA-and DNA-binding protein, is expected to manifest effects on proliferation, transcription, translation, and targeting of proteins to various subcellular compartments. Pur-␣ binds dendritic targeting motifs and aids in their attachment to microtubules Ohashi et al, 2000). Pur-␣ through binding of the retinoblastoma protein inhibits cell cycle progression (Itoh et al, 1998;Stacey et al, 1999;Darbinian et al, 2001).…”