Identification of sex hormone binding globulin-interacting proteins in the brain using phage display screening.

The present study reports the identification of human sex hormone binding globulin (SHBG)-interacting proteins in the brain using a phage display-based screening technology. Phage display is a system in which a foreign protein is displayed on the surface of a bacteriophage as a fusion protein with one of the coat proteins of the bacteriophage. T7 phage clones expressing normal human brain proteins (human normal brain phage-display cDNA expression library) were screened using SHBG as bait. The bound phage clones were then identified by DNA sequencing and by BLAST search analysis. Of the twenty binding proteins analyzed, three were found to be membrane-associated proteins: synaptosomal associated protein 25 (SNAP25), Thy-1 cell surface antigen and zonadhesin. Further studies will determine if the interactions of SHBG with these proteins have any role in the internalization and cell signaling events or whether they contribute to steroid delivery to specific cells.

Mycobacterium avium binds to mouse intestinal mucus aldolase.

SETTING: Mycobacterium avium complex (MAC) is known to colonize the gastrointestinal tract of human immunodeficiency virus (HIV) infected patients before causing bacteremia and disseminated disease. However, the mechanism involved in the gastrointestinal colonization is not known. OBJECTIVE: To identify putative intestinal mucus receptors which serve as anchor for MAC colonization. DESIGN: C57BL/6 mouse intestinal mucus was subjected to single and two-dimensional electrophoresis and blotted on nitrocellulose membranes. MAC specific mucus proteins were identified by probing the mucus western blots with biotinylated proteins derived from M.avium strain 101 (MAC101). RESULTS: Biotinylated MAC 101 proteins recognized a 39 kDa intestinal mucus glycoprotein. The protein displaying an isoelectric point (pI) of 9.0, was found to be periodate sensitive but resistant to sialidase, heparinase I and chondroitinase ABC. The internal amino acid sequence of the 39 kDa protein displayed homology with fructose-1-6-bisphosphate aldolase B (aldolase). The proclivity between MAC adhesins and aldolase was confirmed by probing rabbit muscle aldolase with MAC proteins. Furthermore, both 25 and 31 kDa MAC adhesins, superoxide dismutase and heparin binding protein, respectively, were found to bind to aldolase. CONCLUSIONS: MAC binds to intestinal mucus aldolase, conceivably facilitating intestinal colonization of the organism.

UDP-glucuronosyltransferase in the rat olfactory bulb: identification of the UGT1A6 isoform and age-related changes in 1-naphthol glucuronidation.

Xenobiotic glucuronidation represents a major metabolic protection of the brain against chemical aggressions at blood-brain interfaces. We previously observed that glucuronidation of 1-naphthol was very effective in olfactory bulb, which is a pathway for the entry of foreign molecules into the brain. In this work, we showed that 1-naphthol glucuronidation varied according to age. It was very high at birth, then decreased markedly in 3-month-old rats and increased again significantly during aging. By Western blot and reverse transcription-polymerase chain reaction (RT-PCR), we demonstrated the presence in the olfactory bulb of the UDP-glucuronosyltransferase (UGT) 1A6 isoform, which catalyzes the glucuronidation of phenols, such as 1-naphthol. Quantitative RT-PCR indicated that the mRNA levels encoding UGT1A6 did not significantly change according to age, thus suggesting that other differently regulated UGT isoforms were present and would account for the variations of 1-naphthol glucuronidation observed.

Identification of the uridine diphosphate glucuronosyltransferase isoform UGT1A6 in rat brain and in primary cultures of neurons and astrocytes.

The expression of a phenol uridine diphosphate glucuronosyltransferase (UGT) was investigated in rat brain homogenate and in primary cultures of astrocytes and neurons, by means of model substrates (1-naphthol and 4-methylumbelliferone) assays, Western blot analysis and reverse transcription-polymerase chain reaction (RT-PCR) experiments. Glucuronidation of these substances occurred in cerebral cell or brain homogenates, although to different extents. The specific activity was the highest in astrocytes, with values more than 10- and 100-fold those found in neurons or total brain, respectively. Using antibodies able to recognize several rat liver UGT isoforms, only one protein with an apparent molecular mass of 54 kDa was detected in astrocyte and neuron homogenates and brain microsomes. RT-PCR experiments run with primers specifically designed for the rat liver UGT1A6 revealed amplificons of the expected sizes in accordance with the presence of UGT1A6 mRNA. The nucleotide sequence of the 330-base pair product was 100% homologous to that of exon 1 of rat liver isoform UGT1A6. In conclusion, this work allowed us to identify for the first time a constitutive cerebral UGT isoform identical to rat liver UGT1A6, which glucuronidates planar phenolic substances in cultured astrocytes, neurons, and the entire brain.

Uridine diphosphate-glucuronosyltransferase activities in rat brain microsomes.

The glucuronidation capacity of rat brain microsomes was investigated using a series of chemically related phenolic compounds and fatty acids which are usually glucuronidated in vivo. Most of the phenols assayed were glucuronidated, but no glucuronide formation was detected for stearic and alpha-linolenic acids, 4-methylphenol, bilirubin, morphine, dopamine and serotonin. The activity of uridine diphosphate-glucuronosyltransferase (UGT) towards 1-naphthol represented 0.28% of that obtained with liver microsomes. The inhibitory effects on the formation of 1-naphthol glucuronide of some endogenous and exogenous substances were investigated. The results suggest that only the isoform of UGT conjugating 1-naphthol is present in rat brain.