Drosophila pain sensitization and modulation unveiled by a novel pain model and analgesic drugs.

In mammals, pain is regulated by the combination of an ascending stimulating and descending inhibitory pain pathway. It remains an intriguing question whether such pain pathways are of ancient origin and conserved in invertebrates. Here we report a new Drosophila pain model and use it to elucidate the pain pathways present in flies. The model employs transgenic flies expressing the human capsaicin receptor TRPV1 in sensory nociceptor neurons, which innervate the whole fly body, including the mouth. Upon capsaicin sipping, the flies abruptly displayed pain-related behaviors such as running away, scurrying around, rubbing vigorously, and pulling at their mouth parts, suggesting that capsaicin stimulated nociceptors in the mouth via activating TRPV1. When reared on capsaicin-containing food, the animals died of starvation, demonstrating the degree of pain experienced. This death rate was reduced by treatment both with NSAIDs and gabapentin, analgesics that inhibit the sensitized ascending pain pathway, and with antidepressants, GABAergic agonists, and morphine, analgesics that strengthen the descending inhibitory pathway. Our results suggest Drosophila to possess intricate pain sensitization and modulation mechanisms similar to mammals, and we propose that this simple, non-invasive feeding assay has utility for high-throughput evaluation and screening of analgesic compounds.

Identification of CED-3 substrates by a yeast-based screening method.

Identifying cellular substrates repertoire of individual proteases will facilitate our understanding of their physiological and pathological roles. In this article, we employed a yeast-based screening method to isolate CED-3 substrates. This method uses a transcription factor anchored to the plasma membrane by fusion to a library of cellular protein sequences. When a fusion protein is cleaved by CED-3, the transcription factor is released from the plasma membrane and enters the nucleus where it turns on the expression of reporter genes. We identified seven candidate clones by screening a genomic library using this method. Of these seven clones, two were cleaved by purified CED-3 in vitro. Therefore, the method described here may be generally used for genomewide screening to isolate potential substrates of specific proteases.

A novel method for multiplex genotyping in a single reactor using GTPlex-PyroSeq: genotyping HPV as a prototype.

Herein, we describe a novel multiplex genotyping method, GTPlex-PyroSeq. This method consists of two phases: multiplex PCR followed by a single reaction of pyrosequencing. This study demonstrates how GTPlex-PyroSeq can be adapted for the determination of multiple human papillomavirus (HPV) genotypes. A biotinylated consensus primer, GP6+, and 15 high-risk HPV type-specific primers are used for multiplex PCR. Each type-specific primer has a 5'-tag unique ID sequence connected to a pyrosequencing primer binding region. The unique ID sequence is composed of three parts: i) a single nucleotide ID representing a specific genotype; ii) a sign post; and iii) an end mark. This design allows multiple genotype determination under an ID sequence-dependent nucleotide dispensation order during pyrosequencing. Following initial studies using HPV plasmids and cell lines, we evaluated the clinical utility and effectiveness by comparing our assay with direct sequencing and HPV DNA chip analysis of 80 samples from high-risk, HPV-positive patients. We found in single-type infections, 100% concordance with direct sequencing (70 of 80 perfect matches) and 97.5% concordance with HPV DNA chip data (50 of 80 perfect matches). Additionally, our system was superior to direct sequencing in detection of multiple infections (12 of 80), with a limit of detection of 100 copies. The scalability of this multiplex system, with its open-platform design and ability to use various sample types, makes the GTPlex applicable for use in multiple settings.

Detection of site-specific proteolysis in secretory pathways.

We report here a genetic assay suitable for detecting site-specific proteolysis in secretory pathways. The yeast enzyme invertase is linked to the truncated lumenal region of the yeast Golgi membrane protein STE13 via a protease substrate domain in a Saccharomyces cerevisiae strain lacking invertase. When the substrate is cleaved by a specific protease, the invertase moiety is released into the periplasmic space where it degrades sucrose to glucose and fructose. Therefore, site-specific proteolysis can be detected by monitoring the growth of yeast cells on selective media containing sucrose as the sole carbon source. We confirmed the validity of this assay with yeast Kex2 and human TMPRSS2 proteases. Our data suggest that this in vivo assay is an efficient method for the determination of substrate specificity and mutational analysis of secreted or membrane proteases.

Structure-based virtual screening and biological evaluation of potent and selective ADAM12 inhibitors.

We describe a series of potent and selective inhibitors of ADAM12 that were discovered using computational screening of a focused virtual library. The initial structure-based virtual screening selected 64 compounds from a 3D database of 67,062 molecules. Being evaluated by a cell-based ADAM12 activity assay, compounds 5, 11, 14, 16 were further identified as the potent and selective inhibitors of ADAM12 with low nanomolar IC50 values. The mechanism underlying the potency and selectivity of a representative compound, 5, was investigated through molecular docking studies.

Cell-based assay for beta-secretase activity.

The cerebral deposition of amyloid beta-peptide (Abeta) is a major factor in the etiology of Alzheimer's disease. beta-Secretase (BACE) initiates the generation of Abeta by cleaving the amyloid precursor protein at the beta-site and is therefore a prime target for therapeutic intervention. Here we report a cell-based method suitable for monitoring BACE activity and the efficacy of protease inhibitors. A fusion protein containing the amino-terminal transmembrane domain of Golgi alpha-mannosidase II, a Drosophila Golgi integral membrane protein, linked to human alkaline phosphatase (AP) by a short beta-site sequence, was expressed in Drosophila S2 cells. While the uncleaved fusion protein was retained in the Golgi apparatus, cleavage of the beta-site by BACE resulted in the release of AP to the culture medium, where it was easily detected and quantified. Three peptidomimetic inhibitors (LB83190, LB83192, LB83202) were tested for their efficacy with this cell-based assay. While LB83190 and LB83192 effectively blocked BACE activity, LB83202, a carboxylated derivative of LB83192, did not. This is consistent with the inability of LB83202 to permeate the cell membrane. The present cell-based assay could provide a convenient tool for high-throughput screening of substances that can interfere with BACE in living cells.