ABSTRACT
Akt activation has been associated with proliferation, differentiation, survival and death of epithelial cells. Phosphorylation of Thr308 of Akt by phosphoinositide-dependent kinase 1 (PDK1) is critical for optimal stimulation of its kinase activity. However, the mechanism(s) regulating this process remain elusive. Here, we report that 14-3-3 proteins control Akt Thr308 phosphorylation during intestinal inflammation. Mechanistically, we found that IFNγ and TNFα treatment induce degradation of the PDK1 inhibitor, 14-3-3η, in intestinal epithelial cells. This mechanism requires association of 14-3-3ζ with raptor in a process that triggers autophagy and leads to 14-3-3η degradation. Notably, inhibition of 14-3-3 function by the chemical inhibitor BV02 induces uncontrolled Akt activation, nuclear Akt accumulation and ultimately intestinal epithelial cell death. Our results suggest that 14-3-3 proteins control Akt activation and regulate its biological functions, thereby providing a new mechanistic link between cell survival and apoptosis of intestinal epithelial cells during inflammation.
Subject(s)
14-3-3 Proteins/metabolism , Proto-Oncogene Proteins c-akt/metabolism , 14-3-3 Proteins/antagonists & inhibitors , 3-Phosphoinositide-Dependent Protein Kinases/antagonists & inhibitors , 3-Phosphoinositide-Dependent Protein Kinases/metabolism , Animals , Apoptosis/drug effects , Autophagy/drug effects , Benzamides/pharmacology , Cell Line , Colitis/chemically induced , Colitis/metabolism , Colitis/pathology , Epithelial Cells/cytology , Epithelial Cells/metabolism , Interferon-gamma/pharmacology , Intestinal Mucosa/cytology , Male , Mice , Mice, Inbred C57BL , Microscopy, Fluorescence , Phosphorylation/drug effects , Protein Kinase Inhibitors/pharmacology , Protein Subunits/antagonists & inhibitors , Protein Subunits/metabolism , Proto-Oncogene Proteins c-akt/antagonists & inhibitors , Pyrazoles/pharmacology , Signal Transduction/drug effects , Threonine/metabolismABSTRACT
Peroxidase from turnip roots (TP) was isolated followed by modification with methoxypolyethylene glycol (MPEG). The catalytic activity of the modified TP (MTP) on ABTS increased 2.5 times after 80 min of reaction. MTP showed a KM similar value to that of TP, but a significantly greater kcat for ABTS oxidation, in aqueous buffer. Chemical modification produced an enhanced stability in organic solvents and increased thermal stability of about 4 times that of TP, in aqueous buffer at 70 degrees C. Circular dichroism showed that MPEG modification decreased TP alpha-helical structure from 26 to 16% and increased beta-turns from 26 to 34%, resulting in an enhanced conformational stability. The temperature at the midpoint of thermal denaturation (melting temperature) increased from 57 to 63 degrees C after modification. MTP was immobilized in alginate beads (IMTP) and tested for oxidative polymerization of concentrated phenolic synthetic solutions, achieving 17 effective contact cycles removing >65% phenols. IMTP may be useful for the development of an enzymatic process for wastewater effluent treatment.
