Epidermal growth factor receptor

The epidermal growth factor receptor (EGFR; ErbB-1; HER1 in humans) is the cell-surface receptor for members of the is_associated_with::epidermal growth factor family (EGF-family) of is_associated_with::extracellular protein ligands.

The epidermal growth factor receptor is a member of the ErbB family of receptors, a subfamily of four closely related is_associated_with::receptor tyrosine kinases: EGFR (ErbB-1), HER2/c-neu (ErbB-2), Her 3 (ErbB-3) and is_associated_with::Her 4 (ErbB-4). Mutations affecting EGFR expression or activity could result in is_associated_with::cancer.

Epidermal growth factor and its receptor was discovered by Stanley Cohen of is_associated_with::Vanderbilt University. Cohen shared the 1986 is_associated_with::Nobel Prize in Medicine with is_associated_with::Rita Levi-Montalcini for their discovery of is_associated_with::growth factors.

Function
Epidermal growth factor receptor (EGFR) exists on the cell surface and is activated by binding of its specific is_associated_with::ligands, including is_associated_with::epidermal growth factor and transforming growth factor α (TGFα) (note, a full list of the ligands able to activate EGFR and other members of the ErbB family is given in the ErbB article). ErbB2 has no known direct activating ligand, and may be in an activated state constitutively or become active upon heterodimerization with other family members such as EGFR. Upon activation by its growth factor ligands, EGFR undergoes a transition from an inactive monomeric form to an active homodimer – although there is some evidence that preformed inactive dimers may also exist before ligand binding. In addition to forming homodimers after ligand binding, EGFR may pair with another member of the ErbB receptor family, such as ErbB2/Her2/neu, to create an activated heterodimer. There is also evidence to suggest that clusters of activated EGFRs form, although it remains unclear whether this clustering is important for activation itself or occurs subsequent to activation of individual dimers.

EGFR dimerization stimulates its intrinsic intracellular protein-tyrosine kinase activity. As a result, autophosphorylation of several is_associated_with::tyrosine (Y) residues in the C-terminal domain of EGFR occurs. These include Y992, Y1045, Y1068, Y1148 and Y1173, as shown in the diagram to the left. This autophosphorylation elicits downstream activation and signaling by several other proteins that associate with the phosphorylated tyrosines through their own phosphotyrosine-binding is_associated_with::SH2 domains. These downstream signaling proteins initiate several is_associated_with::signal transduction cascades, principally the MAPK, Akt and is_associated_with::JNK pathways, leading to DNA synthesis and cell proliferation. Such proteins modulate phenotypes such as is_associated_with::cell migration, is_associated_with::adhesion, and proliferation. Activation of the receptor is important for the innate immune response in human skin. The kinase domain of EGFR can also cross-phosphorylate tyrosine residues of other receptors it is aggregated with, and can itself be activated in that manner.

Cancer
is_associated_with::Mutations that lead to EGFR overexpression (known as upregulation) or overactivity have been associated with a number of is_associated_with::cancers, including is_associated_with::lung cancer, is_associated_with::anal cancers and is_associated_with::glioblastoma multiforme. These somatic mutations involving EGFR lead to its constant activation, which produces uncontrolled cell division. In glioblastoma a more or less specific mutation of EGFR, called EGFRvIII is often observed. Mutations, amplifications or misregulations of EGFR or family members are implicated in about 30% of all epithelial cancers.

Inflammatory disease
Aberrant EGFR signaling has been implicated in psoriasis, eczema and atherosclerosis. However, its exact roles in these conditions are ill-defined.

Monogenic disease
A single child displaying multi-organ epithelial inflammation was found to have a homozygous loss of function mutation in the EGFR gene. The pathogenicity of the EGFR mutation was supported by in vitro experiments and functional analysis of a skin biopsy. His severe phenotype reflects many previous research findings into EGFR function. His clinical features included a papulopustular rash, dry skin, chronic diarrhea, abnormalities of hair growth, breathing difficulties and electrolyte imbalances.

Cancer treatment
The identification of EGFR as an is_associated_with::oncogene has led to the development of anticancer therapeutics directed against EGFR (called "is_associated_with::EGFR inhibitors"), including is_associated_with::gefitinib, is_associated_with::erlotinib, is_associated_with::afatinib, brigatinib and is_associated_with::icotinib for lung cancer, and is_associated_with::cetuximab for is_associated_with::colon cancer.

Many therapeutic approaches are aimed at the EGFR. Cetuximab and is_associated_with::panitumumab are examples of monoclonal antibody inhibitors. However the former is of the is_associated_with::IgG1 type, the latter of the is_associated_with::IgG2 type; consequences on is_associated_with::antibody-dependent cellular cytotoxicity can be quite different. Other monoclonals in clinical development are is_associated_with::zalutumumab, is_associated_with::nimotuzumab, and is_associated_with::matuzumab. The monoclonal antibodies block the extracellular ligand binding domain. With the binding site blocked, signal molecules can no longer attach there and activate the tyrosine kinase.

Another method is using small molecules to inhibit the EGFR tyrosine kinase, which is on the cytoplasmic side of the receptor. Without kinase activity, EGFR is unable to activate itself, which is a prerequisite for binding of downstream adaptor proteins. Ostensibly by halting the signaling cascade in cells that rely on this pathway for growth, tumor proliferation and migration is diminished. is_associated_with::Gefitinib, is_associated_with::erlotinib, brigatinib and is_associated_with::lapatinib (mixed EGFR and ERBB2 inhibitor) are examples of small molecule is_associated_with::kinase inhibitors.

is_associated_with::CimaVax-EGF, an active is_associated_with::vaccine targeting EGF as the major is_associated_with::ligand of EGF, uses a different approach, raising is_associated_with::antibodies against EGF itself, thereby denying EGFR-dependent cancers of a proliferative stimulus; it is in use as a cancer therapy against is_associated_with::non-small-cell lung carcinoma (the most common form of lung cancer) in Cuba, and is undergoing further trials for possible licensing in Japan, Europe, and the United States.

There are several quantitative methods available that use protein phosphorylation detection to identify EGFR family inhibitors.

New drugs such as is_associated_with::gefitinib, is_associated_with::erlotinib and brigatinib directly target the EGFR. Patients have been divided into EGFR-positive and EGFR-negative, based upon whether a tissue test shows a mutation. EGFR-positive patients have shown a 60% response rate, which exceeds the response rate for conventional chemotherapy.

However, many patients develop resistance. Two primary sources of resistance are the T790M Mutation and MET oncogene. However, as of 2010 there was no consensus of an accepted approach to combat resistance nor FDA approval of a specific combination. Clinical trial phase II results reported for brigatinib targeting the T790M mutation, and brigatinib received Breakthrough Therapy designation status by FDA in Feb. 2015.

The most common is_associated_with::adverse effect of EGFR inhibitors, found in more than 90% of patients, is a is_associated_with::papulopustular rash that spreads across the face and torso; the rash's presence is correlated with the drug's antitumor effect. In 10% to 15% of patients the effects can be serious and require treatment.

Some tests are aiming at predicting benefit from EGFR treatment, as is_associated_with::Veristrat.

Laboratory research using genetically engineered stem cells to target EGFR in mice was reported in 2014 to show promise.

Interactions
Epidermal growth factor receptor has been shown to interact with:


 * AR,
 * is_associated_with::ARF4,
 * CAV1,
 * CAV3,
 * CBL,
 * CBLB,
 * is_associated_with::CBLC,
 * is_associated_with::CDC25A,
 * CRK,
 * CTNNB1,
 * DCN,
 * EGF,
 * is_associated_with::GRB14,
 * is_associated_with::Grb2,
 * JAK2,
 * is_associated_with::MUC1,
 * is_associated_with::NCK1,
 * is_associated_with::NCK2
 * is_associated_with::PKC alpha,
 * is_associated_with::PLCG1,
 * is_associated_with::PLSCR1,
 * is_associated_with::PTPN1,
 * is_associated_with::PTPN11,
 * is_associated_with::PTPN6,
 * is_associated_with::PTPRK,
 * is_associated_with::SH2D3A,
 * is_associated_with::SH3KBP1,
 * is_associated_with::SHC1,
 * is_associated_with::SOS1,
 * Src,
 * is_associated_with::STAT1,
 * is_associated_with::STAT3,
 * is_associated_with::STAT5A,
 * UBC, and
 * WAS.