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K252b (Nocardiopsis sp. alkaloid), Neurotrophic Alkaloid, Non-specific Protein Kinase Inhibitor
K252b is an alkaloid isolated from Nocardiopsis sp. soil fungi. This compound potentiates neurotrophin-3 activity in certain neurons by an unknown mechanism. In other neurons it serves as a control to K252a since it accumulates into the plasma membrane of the neuron. 1 K252b is a derivative of K252a 3–5 , less potent, cell-permeable protein kinase inhibitor.
K252b inhibits in vitro protein kinase C at 0.02uM; at concentrations of 1uM it inhibits also NGF induced pheochromocytoma PC12 cells differentiation. At 50nM in the presence of NT-3 it potentiates its activity.
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1: J Immunol. 1997 Jul 15;159(2):964-9. Links
Effect of an ectokinase inhibitor, K252b, on degranulation and Ca2+ signals of
RBL-2H3 cells and human basophils.Teshima R, Saito Y, Ikebuchi H, Rajiva De
Silva N, Morita Y, Nakanishi M, Sawada J, Kitani S.
Division of Biochemistry and Immunochemistry, National Institute of Health
Sciences, Setagaya-ku, Tokyo, Japan. rteshima@nihs.go.jp
We examined the effects of K252b, an ectoprotein kinase inhibitor of microbial
origin, on the activation process of RBL-2H3 cells by cross-linking of IgE
receptors by the endoplasmic reticulum Ca2+-ATPase inhibitor
2,5-di(tert-butyl)-1,4-hydroquinone or by the Ca2+ ionophore A23187. Analysis of
phosphorylation of ectoproteins following IgE receptor cross-linking revealed
that K252b mainly inhibited the phosphorylation of a 130-kDa protein. The
inhibitor simultaneously inhibited degranulation and the sustained increase in
the cytosolic calcium ion concentration even after addition of Ag. In contrast,
K252b did not inhibit the increase in degranulation and cytosolic calcium ion
concentration caused by stimulation with 2,5-di(tert-butyl)-1,4-hydroquinone and
A23187. Permeation of K252b into RBL-2H3 cells, assessed by fluorescence
intensity, was very low. K252b also inhibited degranulation caused by IgE
receptor cross-linking in human basophils, but did not inhibit the degranulation
caused by A23187. Thus, our findings suggest that the effects of K252b may be
mediated by outer surface-bound or -anchored K252b-sensitive molecules on
RBL-2H3 cells and human basophils, and that the phosphorylation of ectoprotein
may involve a transmembrane influx of Ca2+ by IgE receptor cross-linking.
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