K252b is an indolocarbazole isolated from the actinomycete Nocardiopsis, first described as an inhibitor of protein kinase C. However, as this compound does not freely pass through the cell membrane, it is used to inhibit extracellular kinases (ectokinases) of cells in culture. K252b inhibits receptor-mediated degranulation from basophil-like RBL-2H3 cells (IC50 = 0.5 μg/ml) and human basophils. This extracellular inhibitor is also used in comparison studies with the closely related, cell-permeable inhibitor K252a, particularly in studies of neuronal differentiation.
K252A is a staurosporine analogue isolated from a Nocardiopsis strain as a potent inhibitor of protein kinase C. K252A exhibits potent antitumour activity but shows no antimicrobial activity in vitro, or in vivo toxicity in rodents. While K252A is a potent inhibitor of Ca2+/calmodulin kinase II, it is also active against other kinases, notably myosin light chain kinase, cAMP-dependent protein kinase (PKA), protein kinase C (PKC) and cGMP-dependent protein kinase (PKG).
K 252b, is an antibiotics, and a known protein tyrosine kinase inhibitor. It has been also shown to inhibit the trophic activity of brain-derived neurotrophic factor on dopaminergic (DAergic) neurons and nerve growth factor on basal forebrain cholinergic neurons.
1) Kase et al. (1987), K252 compounds, novel and potent inhibitors of protein kinase C and cyclic nucleotide-dependent protein kinases; Biochem. Biophys. Res. Commun., 142 436
2) Makino et al. (2012), Inhibition of uterine sarcoma cell growth through suppression of endogenous tyrosine kinase B signaling; PLoS One, 7 e41049
