Excessive urokinase-type plasminogen activator activity in the euglobulin fraction of patients with Alzheimer-type dementia

Impacts of aging and amyloid-β deposition on plasminogen activators and plasminogen activator inhibitor-1 in the Tg2576 mouse model of Alzheimer's disease

Plasminogen activators (PAs), which convert plasminogen into the fibrinolytic protease plasmin, may initiate the degradation of amyloid-β (Aβ) to suppress the amyloid pathogenesis. In that way, tissue plasminogen activator (tPA)-mediated plasmin activation could maintain a low level of Aβ deposition to delay the pathogenesis of Alzheimer's disease (AD). In a previous study, we reported that tPA/plasmin proteolytic activity is attenuated throughout the brain during aging or with Aβ accumulation but clustered intense around the amyloid plaques in AD brain. The present study demonstrates that the altered proteolytic activity primarily results from the competition between the expressions of tPA and plasminogen activator inhibitor-1 (PAI-1) in the brains of Tg2576 Aβ-transgenic mice, as revealed by immunohistochemistry and immunoblot assays. Compared with that in the brains of younger Tg2576 mice, tPA protein is generally reduced throughout the brain in older Tg2576 mice but elevated near amyloid plaques. In contrary, PAI-1 expression increases during aging or Aβ deposition with its clusters surrounding amyloid plaques. No significant alteration in the expression of urokinase plasminogen activator (uPA) is detected. These results suggest reciprocal feedback influences between tPA, PAI-1 and Aβ during aging and amyloid pathogenesis in AD brain; tPA-mediated plasmin activity is declined throughout the brain causing Aβ deposition during aging, and the Aβ deposits locally attract the cluster of tPA and/or PAI-1 around their deposits to competitively determine tPA/plasmin-mediated Aβ proteolysis.

Turnover of protein phosphorylation evolving under stabilizing selection

Most proteins are regulated by posttranslational modifications and changes in these modifications contribute to evolutionary changes as well as to human diseases. Phosphorylation of serines, threonines, and tyrosines are the most common modifications identified to date in eukaryotic proteomes. While the mode of action and the function of most phosphorylation sites remain unknown, functional studies have shown that phosphorylation affects protein stability, localization and ability to interact. Two broad modes of action have been described for protein phosphorylation. The first mode corresponds to the canonical and qualitative view whereby single phosphorylation sites act as molecular switches that either turn on or off specific protein functions through direct or allosteric effects. The second mode is more akin to a rheostat than a switch. In this case, a group of phosphorylation sites in a given protein region contributes collectively to the modification of the protein, irrespective of the precise position of individual sites, through an aggregate property. Here we discuss these two types of regulation and examine how they affect the rate and patterns of protein phosphorylation evolution. We describe how the evolution of clusters of phosphorylation sites can be studied under the framework of complex traits evolution and stabilizing selection.

Increased expression and activity of urokinase-type plasminogen activator during epileptogenesis

Our recent large-scale molecular profiling study revealed a sevenfold upregulation in the expression of urokinase-type plasminogen activator (uPA) during epileptogenesis. uPA is a member of the plasminogen activation system, which is a major contributor to the reorganization of neuronal circuits after trauma. Here, we investigated the expression and activity of uPA in normal and epileptogenic rat hippocampus to test a hypothesis that the expression of uPA is altered in brain areas that undergo epilepsy-related circuitry reorganization. Epileptogenesis was triggered by inducing status epilepticus (SE) with electrical stimulation of the amygdala in rats. Continuous video-electroencephalogram recordings were used to monitor the development of SE and the occurrence of spontaneous seizures. Animals were killed at 1, 4 or 14 days after SE, and brains were processed for immunohistochemistry or protein extraction. Confocal microscopy analysis of double-immunolabelled preparations indicated that SE triggered an increased expression of uPA in hippocampal astrocytes, neurons, white matter and blood vessels. Zymography revealed that the expression of uPA protein is associated with increased levels of enzymatically active uPA during epileptogenesis. uPA expression and enzymatic activity peaked within 1-4 days after SE, that is, before the occurrence of spontaneous seizures, and remained elevated for at least 2 weeks. These data suggest that uPA is involved in the reorganization of neuronal tissue during the epileptogenic process.

Reduction of mouse mammary tumor formation and metastasis by lovastatin, an inhibitor of the mevalonate pathway of cholesterol synthesis

Lovastatin, a fungal antibiotic used in the treatment of hypercholesterolemia, is an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, the key regulatory enzyme in the mevalonate pathway of cholesterol synthesis. We examined the antitumor properties of lovastatin on the F3II sarcomatoid mammary carcinoma, a highly invasive and metastatic murine tumor model. Female BALB/c inbred mice were inoculated subcutaneously with F3II tumor cells and injected i.p. daily with 10 mg/kg body weight of lovastatin or administered p.o. at a level corresponding to the human dosage of 1-2 mg/kg/day. Treatment significantly prolonged tumor latency and reduced tumor formation and metastatic dissemination to the lungs from established mammary tumors. In vitro, antitumor properties of lovastatin were strongly associated with inhibition of tumor cell attachment and migration. These actions were prevented by addition of mevalonate but not by equivalent concentrations of farnesyl pyrophosphate. In accordance, Western blot assays showed that lovastatin effects did not appear to be related to modifications in Ras oncoproteins in our model. The present data indicate that lovastatin could be an antitumor agent with potentially useful clinical applications in breast cancer.