K252B

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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