Notch inhibition in Kaposi's sarcoma tumor cells leads to mitotic catastrophe through nuclear factor-kappaB signaling

Kaposi's sarcoma (KS) is the most common neoplasm in untreated AIDS patients and accounts for significant morbidity and mortality worldwide. We have recently reported that Notch signaling (which plays an important role in cell proliferation, apoptosis, and oncogenesis) is constitutively activated in KS tumor cells. Blockade of this activity using gamma-secretase inhibitors resulted in apoptosis of SLK cells, a KS tumor cell line; however, this apoptosis was preceded by a prolonged G(2)-M cell cycle arrest. This result led us to hypothesize that the cells were undergoing mitotic catastrophe, an abnormal mitosis that leads to eventual cell death. Here, we show that Notch inhibition in KS tumor cells using gamma-secretase inhibitors or Notch-1 small interfering RNA resulted in G(2)-M cell cycle arrest and mitotic catastrophe characterized by the presence of micronucleated cells and an increased mitotic index. Interestingly, Notch inhibition led to a sustained increase in nuclear cyclin B1, a novel observation suggesting that Notch signaling can modulate expression of this critical cell cycle protein. Further analysis showed the induction of cyclin B1 was due, at least in part, to increased nuclear factor-kappaB (NF-kappaB) activity, which was also required for the G(2)-M growth arrest after Notch inhibition. Taken together, these studies suggest that Notch inhibition can initiate aberrant mitosis by inducing NF-kappaB activity that inappropriately increases cyclin B1 resulting in cell death via mitotic catastrophe.     

Persistence of abnormal gastrointestinal motility after operation for Hirschsprung's disease

OBJECTIVE: Recent studies in patients with Hirschsprung's disease (HD) suggest that morphological abnormalities of the intramural intestinal plexuses are not restricted to the colon. In this report, symptoms and objective tests of gastrointestinal (GI) motor dysfunction were determined long after operative treatment to see whether evidence of a more widespread and relevant motility disturbance could be detected. METHODS: Twenty-one children were available for study an average of 6.6 yr after surgery for HD. All of these patients underwent evaluation of bowel frequency per week, total GI transit time (TGTT), and a scintigraphic gastric emptying test using solid food; anorectal manometry and segmental colonic transit times were performed in a subset of patients. Results were compared with findings in appropriately matched controls. RESULTS: Frequency of defecation per week in patients with HD after surgery was not different from that in control children, but TGTT was significantly longer (p < 0.01). Percentage retention of gastric isotope at 60 min exceeded the normal range in 12 of 21 (57.1%) patients, and colonic transit was abnormal in all six children studied. Symptoms persisted in two-thirds of patients postoperatively, and transit abnormalities were more common in the symptomatic subset (p = 0.026). CONCLUSIONS: Our data show that, in a subset of patients with HD, GI motor dysfunction persists long after surgical correction. The heterogeny of basic defects responsible for HD could provide the substrate for these motor abnormalities that, in turn, seem at least partially responsible for continuation of the symptomatic state.     

Methylglyoxal impairs endothelial insulin sensitivity both in vitro and in vivo

Aims/hypothesis

Insulin exerts a direct action on vascular cells, thereby affecting the outcome and progression of diabetic vascular complications. However, the mechanism through which insulin signalling is impaired in the endothelium of diabetic individuals remains unclear. In this work, we have evaluated the role of the AGE precursor methylglyoxal (MGO) in generating endothelial insulin resistance both in cells and in animal models.

Methods

Time course experiments were performed on mouse aortic endothelial cells (MAECs) incubated with 500 μmol/l MGO. The glyoxalase-1 inhibitor S-p-bromobenzylglutathione-cyclopentyl-diester (SpBrBzGSHCp2) was used to increase the endogenous levels of MGO. For the in vivo study, an MGO solution was administrated i.p. to C57BL/6 mice for 7 weeks.

Results

MGO prevented the insulin-dependent activation of the IRS1/protein kinase Akt/endothelial nitric oxide synthase (eNOS) pathway, thereby blunting nitric oxide (NO) production, while extracellular signal-regulated kinase (ERK1/2) activation and endothelin-1 (ET-1) release were increased by MGO in MAECs. Similar results were obtained in MAECs treated with SpBrBzGSHCp2. In MGO- and SpBrBzGSHCp2-exposed cells, inhibition of ERK1/2 decreased IRS1 phosphorylation on S616 and rescued insulin-dependent Akt activation and NO generation, indicating that MGO inhibition of the IRS1/Akt/eNOS pathway is mediated, at least in part, by ERK1/2. Chronic administration of MGO to C57BL/6 mice impaired whole-body insulin sensitivity and induced endothelial insulin resistance.

Conclusions/interpretation

MGO impairs the action of insulin on the endothelium both in vitro and in vivo, at least in part through an ERK1/2-mediated mechanism. These findings may be instrumental in developing novel strategies for preserving endothelial function in diabetes.     

Use of primers selective for vancomycin resistance genes to determine van genotype in enterococci and to study gene organization in VanA isolates.

Vancomycin resistance in enterococci is an emerging therapeutic problem. Resistance is not always detected by standard microbiological methods. Oligonucleotide primers for PCR were designed to target amplification of defined regions of genes of the vanA cluster, as well as vanB and vanC1. These primers correctly identified 30 vancomycin-resistant isolates tested (17 VanA, 7 VanB, and 6 Enterococcus gallinarum). No amplification was observed with Enterococcus casseliflavus or vancomycin-susceptible strains. Using PCR and Southern blotting, we found that all 17 VanA isolates had orf-1, orf-2, vanR, vanS, vanH, vanA, and vanY genes in the same sequence and that the intergenic distances in the vanR-vanA segments were the same. The described methods should be applicable to the rapid detection of the different vancomycin resistance genotypes in enterococci.