Classical mitogen-activated protein kinase (MAPK) pathway activation begins at the cell membrane, where small GTPases and various protein kinases phosphorylate and activate MAPKKKs. Subsequently, MAPKKKs directly phosphorylate MAPKKs, which, once activated, phosphorylate MAPKs. Activated MAPKs interact with and phosphorylate numerous cytoplasmic substrates and ultimately modulate transcription factors that drive context-specific gene expression. This, in turn, results in various biological responses, for example osmotic shock, cell cycle progression, or induction of interferon production [8].

There are at least three distinct MAPK signaling modules which mediate extracellular signals into the nucleus to turn on the responsive genes in mammalian cells. These include ERK, JNK, and p38 kinase.

The MAPK signaling pathway is essential in regulating many cellular processes including inflammation, cell stress response, cell differentiation, cell division, cell proliferation, metabolism, motility and apoptosis. The role of the MAPK pathway in cancer, immune disorders and neurodegenerative diseases has been well recognized. Thermo Scientific™ has a wide range of products to help with MAPK research.

Key MAPK Pathway Targets

MAPK interacts with major pathway targets:

The ERK kinase family consists of ERK 1 and 2. They are activated in response to several growth factors and mitogens. The activation of ERK begins with the phosphorylation of MEK, followed by the phosphorylation of the theronine and tyrosine residues. After ERK has been activated it moves to the cytoplasm and nucleus to phosphorylate other proteins. These proteins are responsible for cell regulation, growth, differentiation, and mitosis [1, 2, 5].

The JNK kinase family consists of JNK1, JNK2, and JNK3. JNK1 and 2 are present in all tissues; however, JNK3 is only located in the brain, heart and testes. JNK is activated in response to cytokines, growth factors, pathogens, stess, etc. JNK is linked to the transformation of oncogene and growth factor pathways. Irregularities in JNK activity have been linked to cancer, diabetes, inflammatory disorders and neurodegenerative disorders. ERK to JNK cross-activation has been seen. JNK is the final facilitator for ERK to stimulate cell proliferation [2, 3, 5].

The kinase p38, is activated in response to a variety of extracellular stimuli including osmotic shock, inflammatory cytokines, lipopolysaccharides (LPS), anisomycin, UV light and growth factors. The activation of p38 is mediated by several upstream kinases including MAP kinase kinase 3 (MKK3), MAP kinase kinase 6 (MKK6) and MAP kinase kinase 4 (MKK4, also known as SEK1 and JNKK1). These kinases phosphorylate p38 at threonine 180 and tyrosine 182, resulting in p38 activation. p38 is linked to asthma, autoimmunity, and inflammation [4].

Although MAPK signaling cascades are depicted as simple linear, unidirectional groups of protein kinases, the pathway is highly complex. A large degree of cross-talk within the MAPK cascades and other signaling networks exists. For example, interactions between mediators of the MAPK, PI3K networks, NFκB and JAK-STAT pathways are well documented [7].


regulation of gene expression

Mammalian MAPK Signaling Cascades. An array of proteins comprise the 4 major MAPK cascades that include ERK, p38, JNK, and ERK5. Growth factor-initiated signaling is associated with the ERK pathway, whereas the JNK, p38, and ERK5 pathways are activated by cytokines, environmental stress (including osmotic shock and ionizing radiation) and other stimuli [6].



Thermo Scientific™ offers antibodies, ELISAs, Luminex® multiplex assays and growth factors for key targets in the MAPK signaling pathway.

Featured below is immunohistochemistry and flow cytometry data using Thermo Scientific™ products.


Immunohistochemistry analysis of MAPK12 showing positive staining in the nucleus and cytoplasm of paraffin-treated Human breast carcinoma (right) compared with a negative control in the absence of primary antibody (left). To expose target proteins, antigen retrieval method was performed using 10mM sodium citrate (pH 6.0), microwaved for 8-15 minutes. Following antigen retrieval, tissues were blocked in 3% H2O2-methanol for 15 minutes at room temperature, washed with ddH2O and PBS, and then probed with a MAPK12 monoclonal antibody (Product # MA1-100) diluted by 3% BSA-PBS at a dilution of 1:20 overnight at 4°C in a humidified chamber. Tissues were washed extensively with PBST and detection was performed using an HRP-conjugated secondary antibody followed by colorimetric detection using a DAB kit. Tissues were counterstained with hematoxylin and dehydrated with ethanol and xylene to prep for mounting.


Flow cytometry analysis of phospho-p38 MAPK (pThr180/Tyr182) on Jurkat cells, either left untreated (blue histogram) or treated with anisomycin (green histogram). Cells were harvested, fixed with formaldehyde for 10 minutes at 37°C, permeabilized with ice-cold methanol at a final concentration of 90% for 30 minutes on ice, and incubated with a phospho-p38 MAPK (pThr180/Tyr182) monoclonal antibody (Product # MA5-15182) or nonspecific rabbit monoclonal antibody control (red histogram) at a 1:25 dilution for 1 hour at room temperature. For flow analysis, 30-minute incubation with a fluorescently-conjugated anti-rabbit IgG secondary antibody was performed and data were acquired on a flow cytometer.


  1. Seger, R. et al. (1995) The MAPK signaling cascade. FASEB J. 9: 726-735.
  2. Zhang, W. et al (2002) MAPK signal pathways in the regulation of cell proliferation in mammalian cells. Cell Research. 12: 9-18.
  3. Bubici, C. et al. (2014) JNK signaling in cancer: in need of new, smarter therapeutic targets. British Journal of Pharmacology. 171: 24-37.
  4. Johnson, G. et al. (2002) Mitogen-activated protein kinase pathways mediate by ERK, JNK, and p38 protein kinases. Science. 298.
  5. Fey, D. et al (2012) Crosstalk and signaling switched in mitogen-activated protein kinases cascades. Frontiers in Physiology 3: 1-21.
  6. Roberts, P.J. et al (2007) Targeting the Raf-MEK-ERK-mitogen activated protein kinase cascade for treatment of cancer. Oncogene 26(22): 3291-3310.
  7. Carracedo P. et al (2008) The PTEN-PI3K pathway: of feedbacks and cross-talks. Oncogene 27(41): 5527-5541.
  8. Cargnello M. et al (2011) Activation and function of the MAPKs and their substrates, the MAPK-activated protein kinases. Microbiol Mol Biol Rev 75(1): 50-83.

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