MAPK

MAPK
Name	Mitogen-activated protein kinase
Uniprot	P36888
Organism	Homo sapiens
Length	360

MAPK Mitogen-activated protein kinase (MAPK) denotes a family of serine/threonine protein kinases central to transducing extracellular signals to intracellular responses. MAPK pathways link receptors such as Epidermal growth factor receptor, Toll-like receptor 4, G protein-coupled receptor, and Integrin alpha-5 to nuclear effectors including c-Fos, c-Jun, and Elk-1. Discovered through studies involving Janeway, Goodman (biochemistry), and laboratories at Cold Spring Harbor Laboratory, MAPKs are studied across model organisms from Saccharomyces cerevisiae to Mus musculus.

Introduction

MAPK families were characterized in classical genetic and biochemical screens alongside work at Max Planck Institute and European Molecular Biology Laboratory. Early signaling frameworks integrated concepts from Signal transduction research conducted by groups at Harvard Medical School, Stanford University School of Medicine, and Massachusetts Institute of Technology. MAPKs mediate responses to mitogens, stressors, and developmental cues mapped in studies using Drosophila melanogaster, Caenorhabditis elegans, and human cell lines from HeLa and HEK293.

Nomenclature and Isoforms

The MAPK superfamily comprises distinct subgroups: extracellular signal-regulated kinases (ERK1/2), c-Jun N-terminal kinases (JNK1/2/3), p38 MAPKs (p38α/β/γ/δ), and ERK5. Canonical human isoforms include proteins encoded by genes such as MAPK1, MAPK3, MAPK8, MAPK9, MAPK10, MAPK14, MAPK11, MAPK12, and MAPK13. Isoform diversity arises from alternative splicing described in publications from Nature, Cell, and Science. Comparative genomics studies at Broad Institute and Wellcome Sanger Institute traced paralogs across vertebrates and invertebrates, including genes annotated in Ensembl and GenBank.

Structure and Activation Mechanism

MAPKs share a bilobed kinase fold elucidated by crystallography performed at facilities such as Diamond Light Source and Argonne National Laboratory. The activation loop contains the conserved TXY motif phosphorylated by MAPK kinases (MKKs) like MEK1, MKK4, and MKK3. Structural transitions upon dual phosphorylation were resolved in studies by groups at European Synchrotron Radiation Facility and described in reviews from EMBO Journal and Trends in Biochemical Sciences. Upstream activation involves MAPKK kinases (MAP3Ks) including RAF1, TAK1, ASK1, and MEKK1, which receive input from adaptors such as GRB2, TIRAP, and MyD88.

Signaling Pathways and Cascades

Classical MAPK cascades operate in tiers: MAP3K → MAP2K → MAPK. The ERK pathway links Receptor tyrosine kinase signaling through SOS1 and RAS to RAF1 and MEK1/2 leading to ERK activation. The JNK pathway integrates stress signals via MAP3K7 (TAK1) and scaffold proteins like JIP1, whereas p38 cascades involve upstream kinases such as MKK6 and sensors including TLR4 and TNF receptor 1. Cross-talk with pathways regulated by PI3K, AKT1, mTOR, NF-κB, and STAT3 modulates outcomes in processes studied at institutions like NIH and Salk Institute.

Cellular Functions and Physiological Roles

Activated MAPKs regulate proliferation, differentiation, apoptosis, migration, and immune responses by phosphorylating substrates including transcription factors (ATF2, FOXO3, SP1), cytoskeletal regulators (Cofilin, Cortactin), and metabolic enzymes such as Glycogen synthase kinase 3 beta. ERK controls cell cycle progression via targets like Cyclin D1 and CDK4, while JNK influences apoptosis through BCL2 family modulation. p38 MAPKs are central to inflammation and cytokine production involving Interleukin 6 and Tumor necrosis factor. Roles in development are documented in studies of Xenopus laevis and Zebrafish embryogenesis.

Regulation and Modulation

MAPK activity is tightly regulated by scaffolds (e.g., KSR1, JIP3), phosphatases including dual-specificity phosphatases (DUSP1, DUSP6), and feedback loops involving Sprouty proteins. Ubiquitination by E3 ligases such as FBXW7 and regulation by microRNAs characterized at Johns Hopkins University add layers of control. Spatial regulation occurs via anchoring to organelles like the Golgi apparatus and Mitochondrion, and temporal control is achieved through oscillatory inputs recorded in single-cell studies at MIT.

Role in Disease and Therapeutics

Aberrant MAPK signaling underlies cancers driven by oncogenes such as mutated KRAS, BRAF, and amplified EGFR. Targeted therapies include inhibitors developed by companies like Novartis and Roche—for example, RAF inhibitors and MEK inhibitors evaluated in clinical trials at MD Anderson Cancer Center and Memorial Sloan Kettering Cancer Center. Resistance mechanisms involve feedback activation of PI3K and secondary mutations cataloged by COSMIC. MAPKs are implicated in neurodegenerative disorders studied at Karolinska Institutet and University College London, inflammatory diseases researched at Imperial College London, and cardiovascular pathology examined at Cleveland Clinic. Small-molecule inhibitors, antisense oligonucleotides, and biologics targeting upstream receptors remain active areas of translational research funded by Wellcome Trust and European Commission.

Category:Protein kinases