The capsaicin receptor, also known as 'transient receptor potential vanilloid receptor subtype 1' (TRPV1, VR1), is an ion channel subunit expressed in primary afferent nociceptors, which plays a critical role in pain transduction and thermal hyperalgesia. Increases in nociceptor TRPV1 mRNA and protein are associated with tissue injury-inflammation. As little is understood about what controls TRPV1 RNA transcription in nociceptors, we functionally characterized the upstream portion of the rat TRPV1 gene. Two functional rTRPV1 promoter regions and their transcription initiation sites were identified. Although both promoter regions directed transcriptional activity in nerve growth factor (NGF) treated rat sensory neurons, the upstream Core promoter was the most active in cultures enriched in sensory neurons. Because NGF is a key modulator of inflammatory pain, we examined the effect of NGF on rTRPV1 transcription in PC12 cells. NGF positively regulated transcriptional activity of both rTRPV1 promoter regions in PC12 cells. We propose that the upstream regulatory region of the rTRPV1 gene is composed of a dual promoter system that is regulated by NGF. These findings support the hypothesis that NGF produced under conditions of tissue injury and/or inflammation directs an increase of TRPV1 expression in nociceptors in part through a transcriptiondependent mechanism. Keywords: capsaicin receptor, gene, nociceptor, pain, vanilloid receptor subtype 1. . One consideration has been that the threshold of TRPV1 (nociceptor) activation can be lowered or that the channel is directly activated following exposure of nociceptors to locally released inflammatory mediators including nerve growth factor (NGF). Notably, the action of NGF on nociceptors has been extensively investigated and found to direct both early and long-term increases of capsaicin receptor-mediated responses (Koltzenburg 1999;Bonnington and McNaughton 2003;Petruska and Mendell 2004). The induction by NGF of rapid sensitization of nociceptive sensory neurons to painful thermal stimuli has been reported Woolf et al. 1994;McMahon et al. 1995;Nicholas et al. 1999;Shu and Mendell 1999). Mechanisms have been proposed to explain this early NGF effect on TRPV1, which includes the release of TRPV1 from PIP 2 inhibition (Chuang et al. 2001). In addition, it has been proposed that the long-term (daysweeks) development of thermal hyperalgesia is dependent on increased expression of TRPV1 in nociceptors as the driving component of this pathophysiologic state (Hudson et al. 2001;Fukuoka et al. 2002;Amaya et al. 2003Amaya et al. , 2004Luo et al. 2004). However, the mechanism(s) responsible for an Received May 22, 2006; revised manuscript received September 21, 2006; accepted September 29, 2006. Address correspondence and reprint requests to Mark Schumacher, Department of Anesthesia and Perioperative Care, University of California, San Francisco, 513 Parnassus Ave (0427), Rm S436, San Francisco, CA 94143-0427, USA. E-mail: schumacm@anesthesia.ucsf.eduAbbreviations us...

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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 approximately 4.3-kb cDNA was isolated and sequence analysis inferred a approximately 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.

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