The naturally occurring PKC inhibitor sphingosine and tumor promoter phorbol ester potentially induce tyrosine phosphorylation/activation of oncogenic proline-directed protein kinase FA/GSK-3alpha in a common signalling pathway

A role for sphingosine kinase 1 in dextran sulfate sodium-induced colitis

The bioactive lipid sphingosine-1-phosphate (S1P) is emerging as an important mediator of immune and inflammatory responses. S1P formation is catalyzed by sphingosine kinase (SK), of which the SK1 isoenzyme is activated by tumor necrosis alpha (TNF-alpha). SK1 has been shown to be required for mediating TNF-alpha inflammatory responses in cells, including induction of cyclooxygenase 2 (COX-2). Because TNF-alpha and COX-2 are increased in patients with inflammatory bowel disease (IBD), we investigated the role of SK1 in a murine model of colitis. SK1(-/-) mice treated with dextran sulfate sodium (DSS) had significantly less blood loss, weight loss, colon shortening, colon histological damage, and splenomegaly than did wild-type (WT) mice. In addition, SK1(-/-) mice had no systemic inflammatory response. Moreover, WT but not SK1(-/-) mice treated with dextran sulfate sodium had significant increases in blood S1P levels, colon SK1 message and activity, and colon neutrophilic infiltrate. Unlike WT mice, SK1(-/-) mice failed to show colonic COX-2 induction despite an exaggerated TNF-alpha response; thus implicating for the first time SK1 in TNF-alpha-mediated COX-2 induction in vivo. Inhibition of SK1 may prove to be a valuable therapeutic target by inhibiting systemic and local inflammation in IBD.

Corticotropin-releasing factor receptors differentially regulate stress-induced tau phosphorylation

Hyperphosphorylation of the microtubule-associated protein tau is a key event in the development of Alzheimer's disease (AD) neuropathology. Acute stress can induce hippocampal tau phosphorylation (tau-P) in rodents, but the mechanisms and pathogenic relevance of this response are unclear. Here, we find that hippocampal tau-P elicited by an acute emotional stressor, restraint, was not affected by preventing the stress-induced rise in glucocorticoids but was blocked by genetic or pharmacologic disruption of signaling through the type 1 corticotropin-releasing factor receptor (CRFR1). Conversely, these responses were exaggerated in CRFR2-deficient mice. Parallel CRFR dependence was seen in the stress-induced activation of specific tau kinases. Repeated stress exposure elicited cumulative effects on tau-P and its sequestration in an insoluble, and potentially pathogenic, form. These findings support differential regulatory roles for CRFRs in an AD-relevant form of neuronal plasticity and may link datasets documenting alterations in the CRF signaling system in AD and implicating chronic stress as a risk factor in age-related neurological disorders.

Predicting the phosphorylation sites using hidden Markov models and machine learning methods

Accurately predicting phosphorylation sites in proteins is an important issue in postgenomics, for which how to efficiently extract the most predictive features from amino acid sequences for modeling is still challenging. Although both the distributed encoding method and the bio-basis function method work well, they still have some limits in use. The distributed encoding method is unable to code the biological content in sequences efficiently, whereas the bio-basis function method is a nonparametric method, which is often computationally expensive. As hidden Markov models (HMMs) can be used to generate one model for one cluster of aligned protein sequences, the aim in this study is to use HMMs to extract features from amino acid sequences, where sequence clusters are determined using available biological knowledge. In this novel method, HMMs are first constructed using functional sequences only. Both functional and nonfunctional training sequences are then inputted into the trained HMMs to generate functional and nonfunctional feature vectors. From this, a machine learning algorithm is used to construct a classifier based on these feature vectors. It is found in this work that (1) this method provides much better prediction accuracy than the use of HMMs only for prediction, and (2) the support vector machines (SVMs) algorithm outperforms decision trees and neural network algorithms when they are constructed on the features extracted using the trained HMMs.

Role of tau protein in both physiological and pathological conditions

The morphology of a neuron is determined by its cytoskeletal scaffolding. Thus proteins that associate with the principal cytoskeletal components such as the microtubules have a strong influence on both the morphology and physiology of neurons. Tau is a microtubule-associated protein that stabilizes neuronal microtubules under normal physiological conditions. However, in certain pathological situations, tau protein may undergo modifications, mainly through phosphorylation, that can result in the generation of aberrant aggregates that are toxic to neurons. This process occurs in a number of neurological disorders collectively known as tauopathies, the most commonly recognized of which is Alzheimer's disease. The purpose of this review is to define the role of tau protein under normal physiological conditions and to highlight the role of the protein in different tauopathies.