A frequent activated smoothened mutation in sporadic basal cell carcinomas

Basal-cell carcinomas (BCCs) are the most common cancer in Caucasians. It has been reported that the patched gene is inactivated in 30-40% sporadic BCCs and 20% sporadic medulloblastomas via loss of heterozygosity and nonsense mutations. Recently, two activating smoothened mutations have been found in the sporadic basal cell carcinomas. One, at base pair 1604 (G-to-T transversion) of exon 9, changes codon 535 from tryptophan to leucine, and the other, at base pair 1685 (G-to-A transition) of exon 10, changes codon 562 from arginine to glutamine (Xie et al., 1998). In our study, 1604G-->T was found in 20 out of 97 (20.6%) sporadic BCCs. The high prevalence indicates that 1604G is the mutation hot spot in our tumor samples. This mutation was detected in all three histological subtypes of BCCs, suggesting that smoothened mutation is an early event during the development of the tumor. Our finding of a high smoothened mutation rate, together with high frequent patched gene mutations reported recently, indicates that activation of the hedgehog signal transduction pathway is the most common and early event in the development of sporadic BCCs. Additionally, to determine whether smoothened, like patched, is also involved in the carcinogenesis of medulloblastomas, we screened medulloblastoma samples for these two mutations by restriction analysis. We have found the 1604G-->T mutation in 1 out of 21 medulloblastomas. This result confirmed smoothened gene involvement in the carcinogenesis of medulloblastoma.     

Resident attrition from family practice residencies: United States versus international medical graduates

BACKGROUND: Attrition of residents from family practice residency programs may cause significant problems for faculty, residents, and patients. The objective of this study was to determine international medical graduates' attrition rate from family practice residencies, compared with US medical school graduates. METHODS: Surveys were sent to all family practice residency program directors asking them to calculate their attrition rate for a 10-year period. RESULTS: The overall response rate was 56.6%, but interpretable responses were received from 45% of all civilian, continental US family practice residencies. Responding programs did not differ from all family practice programs with respect to program overall. Of those residents leaving, 63% did so to enter other specialties. The attrition rate was 18.5% for international graduates, compared with 7.8% for US graduates (P < .0001). International graduates enrolled outside of the National Resident Matching Program (NRMP) were most likely to leave programs before completion. CONCLUSIONS: Attrition rates from family practice residency programs are higher for international medical graduates than for US graduates. International graduates enrolled outside of the NRMP were most likely to leave a program.     

Endocytosis and recycling of neurokinin 1 receptors in enteric neurons

Neurotransmission depends on the availability of transmitter and on the presence of functional, high-affinity receptors at the plasma membrane that are capable of binding ligand. The pathway, mechanism and function of endocytosis and recycling of the substance P or neurokinin 1 receptor in enteric neurons were studied using fluorescent substance P, receptor antibodies and confocal microscopy. In both the soma and neurites, substance P induced rapid, clathrin-mediated internalization of the neurokinin 1 receptor into early endosomes, which also contained the transferrin receptor. After 4-8 h, there was a return in surface neurokinin 1 receptor immunoreactivity in the soma, which was not prevented by cycloheximide, and was thus independent of new protein synthesis. This return was prevented by acidotropic agents, therefore required endosomal acidification. This suggests that the neurokinin 1 receptor recycles in the soma. In contrast, in neurites, substance P and the neurokinin 1 receptor remained in endosomes and recycling was not detected. Neurons of the myenteric plexus were heavily innervated by substance P-containing nerve fibers, and K(+)-stimulated release of endogenous substance P from cultured neurons induced internalization of the neurokinin 1-receptor. Therefore, endogenous substance P may induce endocytosis of the neurokinin 1 receptor. In the soma, endocytosis and recycling correlated with loss and recovery of functional binding sites for substance P. suggesting that this process contributes to the regulation of peptidergic neurotransmission. Thus, ligand-induced endocytosis of the neurokinin 1 receptor in myenteric neurons is associated with a loss of surface receptors and functional binding sites. Since release of endogenous substance P induces neurokinin 1 receptor internalization, and neurokinin 1 receptor neurons are innervated by substance P-containing fibers, endocytosis of neuropeptide receptors may regulate neurotransmission.     

Metabolic fate of S-(-)-pulegone in rat

1. S-(-)-pulegone was administered orally to rat (250 mg/kg) and the nature of the urinary metabolites was investigated. Eleven metabolites, namely S-(-)-menthofuran, piperitone, piperitenone, p-cresol, 5-hydroxypulegone, 4-methylcyclohexenone, 3-methylcyclohexanone, isopulegone, pulegol, 7-hydroxypiperitone and benzoic acid, have been isolated from rat urine. It is assumed that menthofuran, isopulegone and 4-methylcyclohexenone retain the stereochemistry of the parent compound, whereas in other metabolites the stereochemistry at the asymmetric centres is not known. 2. The relative amounts of various major metabolites present in the total urine extracts from the R-(+) and S-(-)-pulegone-treated rat were established by glc analyses. Urine samples of rats treated with R-(+)-pulegone contained higher levels of p-cresol and piperitenone than in similar experiment carried out with S-(-)-pulegone, whereas the levels of unmetabolized pulegone, piperitone and benzoic acid were considerably higher in the urine of rat treated with S-(-)-pulegone than in a corresponding experiment with R-(+)-pulegone. 3. Phenobarbital-induced rat liver microsomes converted S-(-)-pulegone to S-(-)-menthofuran (VII) and piperitenone (III) in the presence of NADPH and O2. The levels of VII and III were significantly higher in similar experiments carried out with R-(+)-pulegone. 4. Based on these studies, metabolic pathways for the biotransformation of S-(-)-pulegone in rat have been proposed and possible reasons for the observed difference in the toxicity mediated by these two enantiomers are discussed.     

The plant cell cycle in context

Biological scientists are eagerly confronting the challenge of understanding the regulatory mechanisms that control the cell division cycle in eukaryotes. New information will have major implications for the treatment of growth-related diseases and cancer in animals. In plants, cell division has a key role in root and shoot growth as well as in the development of vegetative storage organs and reproductive tissues such as flowers and seeds. Many of the strategies for crop improvement, especially those aimed at increasing yield, involve the manipulation of cell division. This review describes, in some detail, the current status of our understanding of the regulation of cell division in eukaryotes and especially in plants. It also features an outline of some preliminary attempts to exploit transgenesis for manipulation of plant cell division.