Merck UK - Calbiochem - Inhibitors: Phosphorylation/Dephosphorylation

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		Technical Information

		Calbiochem Information

		Inhibitor Resource

		Phosphorylation Dephosphorylation

		AKT
		AMPK
		Aurora Kinase
		Cam Kinase
		Casein Kinase
		Checkpoint Kinase
		Cyclin-dependent Kinase
		DNA-Dependent Protein Kinase
		Glycogen Synthase Kinase
		c-Jun N-Terminal Kinase
		IP3 Kinase & TGF-b Receptor I Kinase
		MAP Kinase
		MLCK
		PI 3 Kinase
		Protein Kinase A
		Protein Kinase C
		Protein Kinase G
		Protein Phosphatase
		Protein Tyrosine Kinase
		Raf Kinase
		Rho Kinase
		Sphingosine Kinase

Phosphorylation/Dephosphorylation: MAP Kinase Inhibitors

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Table 1� | Inhibitors | Related Products | Related Resources

The mitogen-activated protein (MAP) kinases are a group of evolutionarily conserved protein serine/threonine kinases that are activated in response to a variety of extracellular stimuli and mediate signal transduction from the cell surface to the nucleus. They regulate several physiological and pathological cellular phenomena, including inflammation, apoptotic cell death, oncogenic transformation, tumor cell invasion, and metastasis. MAP kinases, in combination with several other signaling pathways, can differentially alter the phosphorylation status of transcription factors in a pattern unique to a given external signal. Although MAP kinases are expressed in all cell types, they regulate very specific biological responses that differ from cell type to cell type. Four major types of MAP kinase cascades have been reported in mammalian cells that respond synergistically to different upstream signals. MAP kinases are part of a three-tiered phospho-relay cascade consisting of MAP kinase, a MAP kinase kinase (MEK) and a MAP kinase kinase kinase (MEKK). Controlled regulation of these cascades is involved in cell proliferation and differentiation, whereas unregulated activation of these MAP kinases can result in oncogenesis. The most widely studied cascade is that of ERK1/ERK2 MAP kinases. In the cell, one highly active form of ERK1 or ERK2 (dual phosphorylated) exists, which exhibits over 1000-fold greater activity than the unphosphorylated form. At any one time, there may be three low activity forms of ERKs: one unphosphorylated enzyme, and two singly phosphorylated forms that contain phosphate either at a tyrosine or a threonine residue.

The JNK/SAPK cascade is activated following exposure to UV radiation, heat shock, or inflammatory cytokines. The activation of these MAP kinases is mediated by Rac and cdc42, two small G-proteins. Activated cdc42 binds to PAK protein kinase and activates it. Activated PAK⁶⁵ can activate MEKK, which in turn phosphorylates SEK/JNKK and activates it. The active SEK/JNKK phosphorylates JNK/SAPK (at the TPY motif). The sites of activating phosphorylation are conserved between ERK and JNK, however, these sites are located within distinct dual specificity phosphorylation motifs (TPY for JNK and TEY for ERK).

The p38 kinase, another member of the MAP kinase family, bears similarity to the yeast MAPK, Hog-1. It is activated in response to inflammatory cytokines, endotoxins, and osmotic stress. It shares about 50% homology with the ERKs. The upstream steps in its activation of this cascade are not well defined. However, downstream activation of p38 occurs following its phosphorylation (at the TGY motif) by MKK3, a dual specificity kinase. Following its activation, p38 translocates to the nucleus and phosphoryates ATF-2. Another known target of p38 is MAPKAPK2 that is involved in the phosphorylation and activation of heat-shock proteins.

The fourth and least studied mammalian MAP kinase pathway is big MAP kinase 1 (BMK1), also known as extracellular signal regulated kinase 5 (ERK5). BMK1 is activated in response to growth factors and stress. Activation of the BMK1 signaling pathway has not only been implicated in normal cell survival, cell proliferation, cell differentiation, but also in pathological states such as carcinogenesis, cardiac hypertrophy, and atherosclerosis. BMK1 can be activated following exposure EGF, BDNF, NGF, VEGF, FGF-2, phorbol esters, and oxidative stress. The signaling molecules in the ERK5 cascade include MEKK2/3, MEK5, and ERK5. Since BMK1 is the only known substrate of MEK5, all effects of MEK5 have been attributed to its ability to activate BMK1. Thus far, myocyte enhancer factor 2 (MEF-2), Ets-domain transcription factor (Sap1a), Bad, and serum- and glucocorticoid-inducible kinase (SGK) have been identified as substrates for BMK1.

Although different MAP kinase cascades show a high degree of specificity and functional separation, some degree of cross-talk is observed between different pathways. Another important observation is that when mammalian cells are treated with mitogenic agents, ERKs are significantly activated whereas JNK/SAPK are not affected. Conversely, cells exposed to stress activate the JNK/SAPK pathway without altering the activity of ERKs. At the transcription level, even though ATF-2 is phosphorylated and activated by all three MAP kinases, and c-Jun and Elk-1 are phosphorylated by ERKs and JNK/SAPK, all these pathways result in transcriptional activity that is unique for a particular external stress.

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Selected, Cell-Permeable Inhibitors of MAP Kinase and MAP Kinase Kinase (MEK)

Product	Cat. No.	MW	Comments
Apigenin	178278	270.2	A plant flavonoid that acts as a potent inhibitor of p42/p44 MAP kinase.
ERK Activation Inhibitor I, Cell-Permeable	328000	1757.3	A cell-permeable, stearated 13-amino acid peptide corresponding to the N-terminus of MEK1 that acts as a specific inhibitor of ERK activation. Selectively binds to ERK2 and prevents its interaction with MEK (IC₅₀ = 2.5 mM).
ERK Activation Inhibitor II, Cell-Permeable	328005	3146.8	A cell-permeable, 13-amino acid peptide corresponding to the N-terminus of MEK1 that is fused to the HIV-TAT membrane translocating peptide (MTP) sequence via a glycine linker. Acts as a specific inhibitor of ERK activation that binds to ERK2 and prevents its interaction with MEK (IC₅₀ = 210 nM).
Hsp25 Kinase Inhibitor	385880	1396.7	A potent and selective inhibitor of mammalian HSP25 kinase (also known as mitogen-activated protein kinase activated protein kinase-2. Inhibition is competitive with respect to the substrate peptide (K_i = 8.1 mM) and non-competitively with respect to ATP (K_i = 134 mM).
5-Iodotubercidin	407900	392.2	A potent and competitive inhibitor of ERK2 (K_i = 530 nM) that also inhibits adenosine kinase (K_i = 30 nM).
MEK1/2 Inhibitor	444939	335.4	A cell-permeable, selective inhibitor of MEK1 (IC₅₀ = 180 nM) and MEK2 (IC₅₀ = 220 nM). Inhibits ERK1, MKK3/p38, MKK4, JNK, and PKC activities only at higher concentrations (IC₅₀ > 10 mM).
MEK Inhibitor I	444937	374.5	A potent and selective inhibitor of MEK (IC₅₀ = 12 nM). Exhibits superior potency, solubility, and stability compared to U0126 (Cat. No. 662005).
MEK Inhibitor II	444938	289.7	A cell-permeable, potent, and selective inhibitor of MEK (IC₅₀ = 380 nM for MEK1).
InSolution™ ML 3163	475800	423.5	A potent and specific p38 MAP kinase inhibitor (IC₅₀ = 4 mM) that occupies the ATP binding site of p38 MAP kinase. ML 3163 combines the structural features of SKF-86002 (Cat. No. 567305) and SB 203580 (Cat. No. 559389).
p38 MAP Kinase Inhibitor	506126	365.8	A potent p38 MAP kinase inhibitor (IC₅₀ = 35 nM).
p38 MAP Kinase Inhibitor III	506121	404.5	A cell-permeable, potent, selective, and ATP-competitive inhibitor of p38 MAP kinase (IC₅₀ = 380 nM for p38a).
MK2a Inhibitor	475863	349.4	Selectively inhibits the phosphorylation of MK2a (K_iapp = 330 nM) by p38a in a non-ATP-competitive manner. Does not affect the kinase activity of p38a towards other substrates.
PD 98059	513000	267.3	A potent and selective MEK inhibitor. It selectively blocks the activation of MEK, thus preventing its phosphorylation by cRaf or MEK kinase (IC₅₀ = 2-7 mM).
PD 169316	513030	360.3	A potent and selective p38 MAP kinase inhibitor (IC₅₀ = 89 nM).
Protein Kinase Inhibitor, DMAP	476493	163.2	A puromycin analog that acts as a protein kinase inhibitor. Reported to inhibit a number of TNF-a-induced effects, including CAP kinase activation, JNK activity, and suppression of Jun-b expression.
SB 202190	559388	331.3	A potent and selective inhibitor of p38 MAP kinase b (p38b) (IC₅₀ = 16 nM in vitro). See also Cat. No. 559397.
SB 202190, Hydrochloride	559393	367.8	A water-soluble form of SB 202190 (Cat. No. 559388).
SB 202474	559387	279.3	A negative control for SB 202190 (Cat. No. 559388) and SB 203580 (Cat. No. 559389).
SB 202474, Dihydrochloride	559407	352.3	A water-soluble form of SB 202474 (Cat. No. 559387).
SB 203580	559389	377.4	A potent and selective inhibitor of p38 MAP kinase (IC₅₀ = 34 nM in vitro and 600 nM in cells). See also Cat. No. 559398.
SB 203580, Hydrochloride	559395	413.9	A water-soluble form of SB 203580 (Cat. No. 559389).
SB 203580, Sulfone	559399	393.4	The sulfone analog of SB 203580 (Cat. No. 559389). Potently inhibits MAP kinase (IC₅₀ = 30 nM).
SB 203580, Iodo-	559400	485.3	A highly specific and potent inhibitor of p38 MAP kinase, similar to SB 203580 (Cat. No. 559389). Useful for the identification of inhibitor binding sites of p38 MAP kinase.
SB 220025	559396	338.4	A potent and specific inhibitor of human p38 MAP kinase (IC₅₀ = 60 nM). Displays 2000-fold greater selectivity for p38 MAPK over ERK (p42/p44 MAP kinase).
SB 239063	559404	368.4	A potent, cell-permeable inhibitor of p38a and b forms (IC₅₀ = 44 nM) of MAP kinase.
SC 68376	565625	236.3	A potent and selective inhibitor of p38 MAP kinase (IC₅₀ = 2-5 mM).
SKF-86002	567305	297.4	A cytokine-suppressive anti-inflammatory drug that blocks p38 MAP kinase activation.
U0124	662006	226.3	A useful negative control for MEK inhibitors U0125 (Cat. No. 662008) and U0126 (Cat. No. 662005).
U0125	662008	350.5	A potent and specific inhibitor of MEK1 and MEK2. About 10-fold less potent than U0126 (Cat. No. 662005).
U0126	662005	380.5	A potent and specific inhibitor of MEK1 (IC₅₀ = 72 nM) and MEK2 (IC₅₀ = 58 nM).