Juvenile hemangiomas are the most common tumors of infancy, occurring in as many as 10% of all births. These benign vascular lesions enlarge rapidly during the first year of life by hyperplasia of endothelial cells and attendant pericytes and then spontaneously involute over a period of years, leaving loose fibrofatty tissue. Several hypotheses have been put forth concerning hemangiogenesis, including the possibility that the tumor is the result of somatic mutation in one or more components of critical vascular growth-regulatory pathways. To test this hypothesis, we obtained 15 proliferative-phase hemangiomas after surgical resection and dissected them to enrich for the lesional (endothelial and pericytic) components of each specimen. To determine whether hemangiomas represent a clonal expansion from a single progenitor cell, we assayed X-inactivation patterns for each lesion by using the polymorphic X-linked human androgen receptor gene. Twelve of 14 informative hemangiomas showed a significant degree of allelic loss after methylation-based and transcription-based polymerase chain reaction clonality assays, suggesting a nonrandom X-inactivation pattern and, thus, a monoclonal origin. We then sequenced genes encoding the receptors of the vascular endothelial growth factors (VEGFs) as candidates for potential somatic mutation. Mutations were found in two of the 15 hemangioma specimens: a missense mutation (P1147S) in the kinase domain of the VEGFR2 (FLK1/KDR) gene in one specimen and a missense mutation (P954S) in the kinase insert of the VEGFR3 (FLT4) gene in another specimen. In each case, the mutation was detected in tumor tissue but not in adjacent normal tissue. These results suggest that one potential mechanism involved in hemangioma formation is the alteration of the VEGF signaling pathway in endothelial and/or pericytic cells.
AMPK (AMP-activated protein kinase) is a key sensor of energy status within the cell. Activated by an increase in the AMP/ATP ratio, AMPK acts to limit cellular energy depletion by down-regulating selective ATP-dependent processes. The purpose of the present study was to determine the role of AMPK in regulating intestinal glucose transport. [3H]3-O-methyl glucose fluxes were measured in murine jejunum in the presence and absence of the AMPK activators AICAR (5-aminoimidazole-4-carboxamide riboside) and metformin and the p38 inhibitor, SB203580. To differentiate between a sodium-coupled (SGLT1) and diffusive (GLUT2) route of entry, fluxes were measured in the presence of the SGLT1 and GLUT2 inhibitors phloridzin and phloretin. Glucose transporter mRNA levels were measured by reverse transcriptase-PCR, and localization by Western blotting. Surface-expressed GLUT2 was assessed by luminal biotinylation. Activation of p38 mitogen-activated protein kinase was analysed by Western blotting. We found that treatment of jejunal tissue with AICAR resulted in enhanced net glucose uptake and was associated with phosphorylation of p38 mitogen-activated protein kinase. Inhibition of p38 abrogated the stimulation of AICAR-stimulated glucose uptake. Phloretin abolished the AICAR-mediated increase in glucose flux, whereas phloridzin had no effect, suggesting the involvement of GLUT2. In addition, AICAR decreased total protein levels of SGLT1, concurrently increasing levels of GLUT2 in the brush-border membrane. The anti-diabetic drug metformin, a known activator of AMPK, also induced the localization of GLUT2 to the luminal surface. We conclude that the activation of AMPK results in an up-regulation of non-energy requiring glucose uptake by GLUT2 and a concurrent down-regulation of sodium-dependent glucose transport.
Probiotics have been shown to reduce the incidence of colon cancer in animal models. The mechanisms responsible for this activity are poorly defined. Conjugated linoleic acids (CLA) are a group of isomers of linoleic acid (LA) possessing anti-inflammatory and anticarcinogenic properties, which can be produced from LA by certain bacterial strains. In this study, the ability of probiotic bacteria to exert anticarcinogenic effects through the production of CLA was assessed. Incubation of probiotic bacteria (VSL3, Lactobacillus acidophilus, L. bulgaricus, L. casei, L. plantarum, Bifidobacterium breve, B. infantis, B. longum, and Streptococcus thermophilus) in the presence of LA yielded CLA production as measured by gas chromatography. Conditioned medium, containing probiotic-produced CLA, reduced viability and induced apoptosis of HT-29 and Caco-2 cells, as assessed by MTT assay and DNA laddering, respectively. Western blotting demonstrated an increased expression of PPARgamma in cells treated with conditioned medium compared with LA alone. Incubation of murine feces with LA after administering VSL3 yielded 100-fold more CLA than feces collected prior to VSL3 feeding. This study supports a role for supplemental probiotics as a strategy both for attenuating inflammation and for preventing colon cancer.
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