Endotoxin binding on capillary endothelium and myocyte plasma membranes in perfused rat heart

This work uses a novel heart-perfusion technique to measure [3H]-lipopolysaccharide ([3H]-LPS) binding on capillary endothelium and myocyte cell membranes in Sprague-Dawley rats. Free or serum-containing Ringer-Lock buffer was infused at a rate of 1 ml/min and in the presence of 20 mM K+ and [ 3H]-LPS through an aortic cannula, and the effluent was collected through a catheter introduced into the right atrium cavity. The capillary endothelial lining was removed by CHAPS treatment to expose the cardiac myocyte surface. A physical model describing 1:1 binding stoichiometry of [3H]-LPS with its receptors is proposed and the mathematical equations derived allow for the calculation of binding constants (kn), reversal constants (k-n), dissociation constants (kd), and residency time constants (τ). The results showed that the presence of serum in the perfusate, slowed the binding of [3H]-LPS with the endothelial lining and myocytes, but increased the residency time by 3- and 50-fold, respectively. Hence, the endothelium and myofiber may contain LPS receptors that can bind more strongly with the ligand in association with sCD14-like and LBP-like molecules in rat serum. Thus it is postulated that the affinity of LPS to its receptor subtypes is not strictly and specifically dependent on the CD14 binding profile.

An essential role for p38 MAPK in cerebellar granule neuron precursor proliferation

Development of the cerebellum occurs postnatally and is marked by a rapid proliferation of cerebellar granule neuron precursors (CGNPs). CGNPs are the cells of origin for SHH-driven medulloblastoma, the most common malignant brain tumor in children. Here, we investigated the role of ERK, JNK, and p38 mitogen-activated protein kinases in CGNP proliferation. We found high levels of p38α in proliferating CGNPs. Concomitantly, members of the p38 pathway, such as ASK1, MKK3 and ATF-2, were also elevated. Inhibition of the Shh pathway or CGNP proliferation blunts p38α levels, irrespective of Shh treatment. Strikingly, p38α levels were high in vivo in the external granule layer of the postnatal cerebellum, Shh-dependent mouse medulloblastomas and human medulloblastomas of the SHH subtype. Finally, knocking down p38α by short hairpin RNA-carrying lentiviruses as well as the pharmacologically inhibiting of its kinase activity caused a marked decrease in CGNP proliferation, underscoring its requirement for Shh-dependent proliferation in CGNPs. The inhibition of p38α also caused a decrease in Gli1 and N-myc transcript levels, consistent with reduced proliferation. These findings suggest p38 inhibition as a potential way to increase the efficacy of treatments available for malignancies associated with deregulated SHH signaling, such as basal cell carcinoma and medulloblastoma.

Direct coupling of the cell cycle and cell death machinery by E2F

Unrestrained E2F activity forces S phase entry and promotes apoptosis through p53-dependent and -independent mechanisms. Here, we show that deregulation of E2F by adenovirus E1A, loss of Rb or enforced E2F-1 expression results in the accumulation of caspase proenzymes through a direct transcriptional mechanism. Increased caspase levels seem to potentiate cell death in the presence of p53-generated signals that trigger caspase activation. Our results demonstrate that mitogenic oncogenes engage a tumour suppressor network that functions at multiple levels to efficiently induce cell death. The data also underscore how cell cycle progression can be coupled to the apoptotic machinery.