Anaplastic Lymphoma Kinase
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Anaplastic lymphoma kinase (ALK) also known as ALK tyrosine kinase receptor or CD246 (
cluster of differentiation The cluster of differentiation (also known as cluster of designation or classification determinant and often abbreviated as CD) is a protocol used for the identification and investigation of cell surface molecules providing targets for immunophe ...
246) is an
enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
that in humans is encoded by the ''ALK''
gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
.


Identification

Anaplastic lymphoma kinase (ALK) was originally discovered in 1994 in anaplastic large-cell lymphoma (ALCL) cells. ALCL is caused by a (2;5)(p23:q35)
chromosomal translocation In genetics, chromosome translocation is a phenomenon that results in unusual rearrangement of chromosomes. This includes "balanced" and "unbalanced" translocation, with three main types: "reciprocal", "nonreciprocal" and "Robertsonian" transloc ...
that generates the fusion protein NPM-ALK, in which the
kinase In biochemistry, a kinase () is an enzyme that catalyzes the transfer of phosphate groups from high-energy, phosphate-donating molecules to specific substrates. This process is known as phosphorylation, where the high-energy ATP molecule don ...
domain of ALK is fused to the amino-terminal part of the nucleophosmin (NPM) protein. Dimerization of NPM constitutively activates the ALK kinase domain. The full-length protein ALK was identified in 1997 by two groups. The deduced
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...
sequences revealed that ALK was a novel
receptor tyrosine kinase Receptor tyrosine kinases (RTKs) are the high-affinity cell surface receptors for many polypeptide growth factors, cytokines, and hormones. Of the 90 unique tyrosine kinase genes identified in the human genome, 58 encode receptor tyrosine kinas ...
(RTK), having an
extracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...
ligand-binding domain, a transmembrane domain, and an
intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...
tyrosine kinase domain. While the tyrosine kinase domain of human ALK shares a high degree of similarity with that of the insulin receptor, its extracellular domain is unique among the RTK family in containing two MAM domains ( meprin, A5 protein and receptor protein tyrosine phosphatase mu), an LDLa domain ( low-density lipoprotein receptor class A) and a
glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid. Glycine is one of the proteinogenic amino acids. It is encoded by all the codons starting with GG (G ...
-rich region. Based on overall homology, ALK is closely related to the leukocyte receptor tyrosine kinase (LTK) and, together with the insulin receptor, forms a subgroup in the RTK superfamily. The human ''ALK'' gene encodes a protein 1,620 amino acids long with a
molecular weight A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
of 180 kDa. Since the original discovery of the receptor in mammals, several orthologs of ALK have been identified: dAlk in the fruit fly (''
Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (an insect of the Order (biology), order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly", "pomace fly" ...
'') in 2001, scd-2 in the
nematode The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (h ...
(''
Caenorhabditis elegans ''Caenorhabditis elegans'' () is a free-living transparent nematode about 1 mm in length that lives in temperate soil environments. It is the type species of its genus. The name is a Hybrid word, blend of the Greek ''caeno-'' (recent), ''r ...
'') in 2004, and DrAlk in the
zebrafish The zebrafish (''Danio rerio'') is a species of freshwater ray-finned fish belonging to the family Danionidae of the order Cypriniformes. Native to South Asia, it is a popular aquarium fish, frequently sold under the trade name zebra danio (an ...
(''
Danio rerio The zebrafish (''Danio rerio'') is a species of freshwater ray-finned fish belonging to the family Danionidae of the order Cypriniformes. Native to South Asia, it is a popular aquarium fish, frequently sold under the trade name zebra danio (a ...
'') in 2013. The
ligands In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's ...
of the human ALK/LTK receptors were identified in 2014: ALKAL1 (FAM150A, AUGβ) and ALKAL2 (FAM150B, AUGα), two small secreted
peptide Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty am ...
s that strongly activate ALK signaling. In invertebrates, ALK-activating ligands are Jelly belly (Jeb) in ''Drosophila'', and hesitation behaviour 1 (HEN-1) in ''C. elegans''. No such ligands have been reported yet in zebrafish or other
vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...
s.


Mechanism

Following binding of the ligand, the full-length receptor ALK dimerizes, changes conformation, and autoactivates its own
kinase In biochemistry, a kinase () is an enzyme that catalyzes the transfer of phosphate groups from high-energy, phosphate-donating molecules to specific substrates. This process is known as phosphorylation, where the high-energy ATP molecule don ...
domain, which in turn phosphorylates other ALK receptors in ''trans'' on specific
tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a conditionally essential amino acid with a polar side group. The word "tyrosine" is ...
amino acid residues. ALK phosphorylated residues serve as
binding site In biochemistry and molecular biology, a binding site is a region on a macromolecule such as a protein that binds to another molecule with specificity. The binding partner of the macromolecule is often referred to as a ligand. Ligands may includ ...
s for the recruitment of several adaptor and other cellular proteins, such as
GRB2 Growth factor receptor-bound protein 2, also known as Grb2, is an adaptor protein involved in signal transduction/ cell communication. In humans, the GRB2 protein is encoded by the ''GRB2'' gene. The protein encoded by this gene binds recepto ...
, IRS1, Shc, Src, FRS2, PTPN11/Shp2, PLCγ,
PI3K Phosphoinositide 3-kinases (PI3Ks), also called phosphatidylinositol 3-kinases, are a family of enzymes involved in cellular functions such as cell growth, proliferation, differentiation, motility, survival and intracellular trafficking, which i ...
, and NF1. Other reported downstream ALK targets include
FOXO3 Forkhead box O3, also known as FOXO3 or FOXO3a, is a human protein encoded by the ''FOXO3'' gene. Function FOXO3 belongs to the O subclass of the forkhead family of transcription factors which are characterized by a distinct fork head DNA- ...
a, CDKN1B(p27Kip1), cyclin D2, NIPA, RAC1, CDC42, BCAR1(p130Cas), SHP1, and PIKFYVE. Phosphorylated ALK activates multiple downstream
signal transduction Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a biochemical cascade, series of molecular events. Proteins responsible for detecting stimuli are generally termed receptor (biology), rece ...
pathways, including MAPK-ERK, PI3K-AKT, PLCγ, CRKL-C3G, and JAK-STAT.


Function

The receptor ALK plays a pivotal role in cellular communication and in the normal development and function of the nervous system. This observation is based on the extensive expression of ALK
messenger RNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein. mRNA is created during the ...
(mRNA) throughout the nervous system during mouse
embryogenesis An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male ...
. ''
In vitro ''In vitro'' (meaning ''in glass'', or ''in the glass'') Research, studies are performed with Cell (biology), cells or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in ...
'' functional studies have demonstrated that ALK activation promotes
neuron A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...
al differentiation of PC12 or neuroblastoma cell lines. ALK is critical for
embryonic development In developmental biology, animal embryonic development, also known as animal embryogenesis, is the developmental stage of an animal embryo. Embryonic development starts with the fertilization of an egg cell (ovum) by a sperm, sperm cell (spermat ...
in ''
Drosophila ''Drosophila'' (), from Ancient Greek δρόσος (''drósos''), meaning "dew", and φίλος (''phílos''), meaning "loving", is a genus of fly, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or p ...
''. Flies lacking the receptor die due to failure of founder cell specification in embryonic visceral muscle. However, while ALK
knockout mice A knockout mouse, or knock-out mouse, is a genetically modified mouse (''Mus musculus'') in which researchers have inactivated, or " knocked out", an existing gene by replacing it or disrupting it with an artificial piece of DNA. They are importan ...
exhibit defects in
neurogenesis Neurogenesis is the process by which nervous system cells, the neurons, are produced by neural stem cells (NSCs). This occurs in all species of animals except the porifera (sponges) and placozoans. Types of NSCs include neuroepithelial cells ( ...
and
testosterone Testosterone is the primary male sex hormone and androgen in Male, males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testicles and prostate, as well as promoting se ...
production, they remain viable, suggesting that ALK is not critical to their developmental processes. ALK regulates
retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...
l axon targeting, growth and size,
synapse In the nervous system, a synapse is a structure that allows a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or a target effector cell. Synapses can be classified as either chemical or electrical, depending o ...
development at the
neuromuscular junction A neuromuscular junction (or myoneural junction) is a chemical synapse between a motor neuron and a muscle fiber. It allows the motor neuron to transmit a signal to the muscle fiber, causing muscle contraction. Muscles require innervation to ...
, behavioral responses to
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...
, and
sleep Sleep is a state of reduced mental and physical activity in which consciousness is altered and certain Sensory nervous system, sensory activity is inhibited. During sleep, there is a marked decrease in muscle activity and interactions with th ...
. It restricts and constrains
learning Learning is the process of acquiring new understanding, knowledge, behaviors, skills, value (personal and cultural), values, Attitude (psychology), attitudes, and preferences. The ability to learn is possessed by humans, non-human animals, and ...
and
long-term memory Long-term memory (LTM) is the stage of the Atkinson–Shiffrin memory model in which informative knowledge is held indefinitely. It is defined in contrast to sensory memory, the initial stage, and short-term or working memory, the second stage ...
and small-molecule inhibitors of the ALK receptor can improve learning, long-term memory, and extend healthy lifespan. ALK is also a candidate thinness gene, as its genetic deletion leads to resistance to diet- and
leptin Leptin (from Ancient Greek, Greek λεπτός ''leptos'', "thin" or "light" or "small"), also known as obese protein, is a protein hormone predominantly made by adipocytes (cells of adipose tissue). Its primary role is likely to regulate long ...
-mutation-induced
obesity Obesity is a medical condition, considered by multiple organizations to be a disease, in which excess Adipose tissue, body fat has accumulated to such an extent that it can potentially have negative effects on health. People are classifi ...
.In 2020, a genome-wide association study (GWAS) was published of 47,102 people in the Estonian Genome Center of the University of Tartu (EGCUT) Biobank which compared the DNA of healthy thin individuals in the lowest 6th percentile of body mass index to the DNA of normal-weight individuals. This study identified a number of genetic variations of the ALK gene that were associated with thinness. As a next step, experiments in mice and Drosophila fruit flies showed that mice in which the ALK gene was knocked out had the similar activity and diet levels as normal mice, but had lower body fat and weight from early age into adulthood. This implies that inhibition of this kinase, already of interest as a chemotherapy for cancers associated with this gene, might be a way to prevent weight gain.


Pathology

The ALK gene can be oncogenic in three ways – by forming a fusion gene with any of several other genes, by gaining additional gene copies or with mutations of the actual DNA code for the gene itself.


Anaplastic large-cell lymphoma

The 2;5 chromosomal translocation is associated with approximately 60% of anaplastic large-cell lymphomas (ALCLs), type ALK-positive anaplastic large cell lymphoma and very rare cases of ALCL type primary cutaneous anaplastic large cell lymphoma. The translocation creates a fusion gene consisting of the ALK (anaplastic lymphoma kinase) gene and the nucleophosmin (NPM) gene: the 3' half of ALK, derived from chromosome 2 and coding for the catalytic domain, is fused to the 5' portion of NPM from chromosome 5. The product of the NPM-ALK fusion gene is oncogenic. In a smaller fraction of ALCL patients, the 3' half of ALK is fused to the 5' sequence of TPM3 gene, encoding for tropomyosin 3. In rare cases, ALK is fused to other 5' fusion partners, such as TFG, ATIC, CLTC1, TPM4, MSN, ALO17, MYH9.


Adenocarcinoma of the lung

The EML4-ALK fusion gene is responsible for approximately 3-5% of non-small-cell lung cancer (NSCLC). The vast majority of cases are adenocarcinomas. Patients with this ALK rearrangement have the following clinicopathologic characteristics: Young age at diagnosis (median 50 years), female gender, nonsmoker/light smoker, adenocarcinoma histology with specific morphologic patterns such as cribriform and solid signet ring, expression of thyroid transcription factor 1, tendency to metastasize to pleura or pericardium, frequently with more metastases than other molecular types, and predominantly metastases to the central nervous system. The standard test used to detect this gene in tumor samples is fluorescence in situ hybridization (FISH) by a US FDA approved kit. Recently Roche Ventana obtained approval in China and European Union countries to test this mutation by immunohistochemistry. Other techniques like reverse-transcriptase PCR (RT-PCR) can also be used to detect lung cancers with an ALK gene fusion but not recommended. ALK lung cancers are found in patients of all ages, although on average these patients tend to be younger. ALK lung cancers are more common in light cigarette smokers or nonsmokers, but a significant number of patients with this disease are current or former cigarette smokers. EML4-ALK-rearrangement in NSCLC is exclusive and not found in EGFR- or KRAS-mutated tumors.


Gene rearrangements and overexpression in other tumours

*Familial cases of neuroblastoma * Inflammatory myofibroblastic tumor * Adult and pediatric renal cell carcinomas * Esophageal squamous cell carcinoma *
Breast cancer Breast cancer is a cancer that develops from breast tissue. Signs of breast cancer may include a Breast lump, lump in the breast, a change in breast shape, dimpling of the skin, Milk-rejection sign, milk rejection, fluid coming from the nipp ...
, notably the inflammatory subtype * Colonic adenocarcinoma * Glioblastoma multiforme * Anaplastic thyroid cancer


ALK inhibitors

* Xalkori ( crizotinib), produced by Pfizer, was approved by the FDA for treatment of late stage lung cancer on August 26, 2011. Early results of an initial Phase I trial with 82 patients with ALK induced lung cancer showed an overall response rate of 57%, a disease control rate at 8 weeks of 87% and progression free survival at 6 months of 72%. In patients affected by relapsed or refractory ALK+ Anaplastic Large Cell Lymphoma, crizotinib produced objective response rates ranging from 65% to 90% and 3 year progression free survival rates of 60-75%. No relapse of the lymphoma was ever observed after the initial 100 days of treatment. Treatment must be continued indefinitely at present. * Ceritinib was approved by the FDA in April 2014 for the treatment of patients with anaplastic lymphoma kinase (ALK)-positive metastatic non-small cell lung cancer (NSCLC) who have progressed on or are intolerant to crizotinib. * Entrectinib (RXDX-101) is a selective tyrosine kinase inhibitor developed by Ignyta, Inc., with specificity, at low nanomolar concentrations, for all of three Trk proteins (encoded by the three ''NTRK'' genes, respectively) as well as the ROS1, and ALK receptor tyrosine kinases. An open label, multicenter, global phase 2 clinical trial calle
STARTRK-2
is currently underway to test the drug in patients with ROS1/ NTRK/ALK gene rearrangements.


See also

*
Cluster of differentiation The cluster of differentiation (also known as cluster of designation or classification determinant and often abbreviated as CD) is a protocol used for the identification and investigation of cell surface molecules providing targets for immunophe ...


Notes and references


Notes


References


Further reading

* * * * * * * * * *


External links

*
ALK Correlations, Experiments, Publications and Clinical Trials

GeneReviews/NCBI/NIH/UW entry on ALK-Related Neuroblastoma Susceptibility

OMIM entries on ALK-Related Neuroblastoma Susceptibility
* {{Portal bar, Biology, border=no Clusters of differentiation Tyrosine kinase receptors