Mitogen-activated protein kinase 6 is an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

that in humans is encoded by the ''MAPK6''

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

. The protein encoded by this gene is a member of the Ser/Thr

protein kinase A protein kinase is a kinase which selectively modifies other proteins by covalently adding phosphates to them (phosphorylation) as opposed to kinases which modify lipids, carbohydrates, or other molecules. Phosphorylation usually results in a fu ...

family, and is most closely related to mitogen-activated protein kinases ( MAP kinases). MAP kinases, also known as extracellular signal-regulated kinases ( ERKs), are activated through protein phosphorylation cascades and act as integration points for multiple biochemical signals. This kinase is localized in the

nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: * Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...

, and has been reported to be activated in

fibroblasts A fibroblast is a type of biological cell that synthesizes the extracellular matrix and collagen, produces the structural framework ( stroma) for animal tissues, and plays a critical role in wound healing. Fibroblasts are the most common cells ...

upon treatment with serum or phorbol esters.

Discovery

ERK3/MAPK6 was initially cloned from the rat brain cDNA library by homology screening with probes ERK1 derived probe.

Gene location

In humans, MAPK 6 gene is located on the distal arm of chromosome 15 (15q21.2). It is 47.01kb long and is transcribed in the centromere to telomere orientation. It consist of 6 exons with the translation initiation codon which is located in exon2.

Structure

It is an atypical member of the mitogen activated kinases family. The molecular mass of the translated protein is approximately 100kDa, and is made up of 721 amino acid residues. It contains a typical kinase domain at the N- terminal and an extended C- terminal. The first 150 residues at c- terminal are 50% similar to ERK4 protein. At the kinase domain it exhibits about 70% similarity with the ERK4 protein. The activation loop of the phosphorylation motif contains only one phospho acceptor site (Ser-Glu-Gly). The structure is predicted by homology modelling using the crystal structure of phoshphorylated ERK2. According to the model, the structure of ERK3/MAPK6 kinase domain resembles other MAP kinases. The modelled ERK3/MAPK6 kinase domain is predicted to fold with a topology similar to other MAP kinases.

Expression

ERK3/MAPK6 is widely expressed protein however it is expressed in significantly higher amounts in skeletal muscles and brain. It is localized in cytoplasm and the nucleus of cells. ERK3/MAPK6 is a highly unstable protein and has a very little half life of less than an hour. It is degraded by ubiquitin mediated proteasomal pathway.

Function

It is very important for neonatal growth and survival. ERK3/MAPK6 forms a complex with microtubule associated protein2 (MAP2) and MAPKAPK5 which mediates the phosphorylation of MAPKAPK5 which in turn phosphorylates ERK3/MAPK6 at serine 189 residue mediating the entry into cell cycle. It also acts as a regulator for T- cell development. The catalytic activity of ERK3/MAPK6 plays an important for the proper differentiation of T-cells in the thymus. The long c- terminal is responsible for thymic differentiation.

Role in cancer

ERK3/MAPK6 interacts with and phosphorylated steroid receptor coactivator 3 (SRC-3) This coreceptor is an oncogenic protein which when overexpressed at serine 857 leads to cancer. After the phosphorylation of SRC-3 results in the upregulation of MMP activity ERK3-mediated phosphorylation at S857 was essential for interaction of SRC-3 with the ETS transcription factor PEA3, which promotes upregulation of MMP gene expression and proinvasive activity.

References

External links

MAP Kinase Resource
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