We have previously examined the specificities of 28 commercially available compounds, reported to be relatively selective inhibitors of particular serine/threonine-specific protein kinases [Davies, Reddy, Caivano and Cohen (2000) Biochem. J. 351, 95—105]. In the present study, we have extended this analysis to a further 14 compounds. Of these, indirubin-3′-monoxime, SP 600125, KT 5823 and ML-9 were found to inhibit a number of protein kinases and conclusions drawn from their use in cell-based assays are likely to be erroneous. Kenpaullone, Alsterpaullone, Purvalanol, Roscovitine, pyrazolopyrimidine 1 (PP1), PP2 and ML-7 were more specific, but still inhibited two or more protein kinases with similar potency. Our results suggest that the combined use of Roscovitine and Kenpaullone may be useful for identifying substrates and physiological roles of cyclin-dependent protein kinases, whereas the combined use of Kenpaullone and LiCl may be useful for identifying substrates and physiological roles of glycogen synthase kinase 3. The combined use of SU 6656 and either PP1 or PP2 may be useful for identifying substrates of Src family members. Epigallocatechin 3-gallate, one of the main polyphenolic constituents of tea, inhibited two of the 28 protein kinases in the panel, dual-specificity, tyrosine-phosphorylated and regulated kinase 1A (DYRK1A; IC50 = 0.33μM) and p38-regulated/activated kinase (PRAK; IC50 = 1.0μM).

Abbreviations used: AMPK, AMP-activated protein kinase; CDK, cyclin-dependent protein kinase; CK, casein kinase; CSK, C-terminal Src kinase; DYRK, dual-specificity, tyrosine-phosphorylated and regulated kinase; EGCG, epigallocatechin 3-gallate; ERK, extracellular-signal-regulated kinase; GSK3, glycogen synthase kinase 3; GST, glutathione S-transferase; JNK, c-Jun N-terminal kinase; LCK, lymphocyte kinase; MAPK, mitogen-activated protein kinase; MLCK, myosin light chain kinase; MSK1, mitogen- and stress-activated protein kinase 1; PHK, phosphorylase kinase; PKA, cAMP-dependent protein kinase; PKC, protein kinase C; PKG, cGMP-dependent protein kinase; PP, pyrazolopyrimidine; PRAK, p38-regulated/activated kinase; ROCK-II, Rho-dependent protein kinase II; RSK1, ribosomal S6 kinase 1; SAPK, stress-activated protein kinase; SGK, serum- and glucocorticoid-induced kinase; S6K1, p70 ribosomal protein S6 kinase.

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Author notes


These authors contributed equally to this work.