Isolation of an mRNA binding protein homologue that is expressed in nociceptors

The peripheral detection of painful stimuli requires the activation of small-diameter primary afferent neurons known as nociceptors. We have exploited two features of nociceptor biology, expression of the high affinity receptor for nerve growth factor (TrkA) and sensitivity to capsaicin, to isolate novel proteins using a differential display cloning scheme. A resulting ∼4.3-kb cDNA was isolated and sequence analysis inferred a ∼157-kDa protein containing a signal/mitochondrial targeting peptide sequence. Due to its molecular weight and significant amino acid identity with 'human leucine-rich protein 130' [leucine-rich pentatricopeptide motif containing (LRPPRC)], we termed the cDNA candidate leucine-rich protein 157 (rLRP157). Western blot analysis of HEK293 cells over-expressing the candidate cDNA showed a single protein product of similar size to that found in rat dorsal root ganglion as well as in other neuronal tissues and cell lines. Although expressed in a wide variety of tissues, in situ hybridization and immunohistochemistry in dorsal root ganglion revealed that rLRP157 expression was restricted to the small-diameter neurons. Sequence identity with previously characterized mRNA binding proteins and its subcellular localization in sensory neurons suggest that rLRP157 is associated with mitochondrial function. Moreover, the genetic basis of French-Canadian Leigh syndrome, which confers a loss of mitochondrial cytochrome c oxidase and is characterized by neurodegeneration, was recently mapped to a mutation in the LRPPRC gene. Taken together with its expression in small-diameter sensory neurons, we hypothesize that rLRP157, the rat orthologue of the human LRPPRC, may play a role in the modulation of peripheral pain transduction and serve as a novel marker for nociceptor subtypes.