AXL receptor tyrosine kinase

Last updated
AXL
Protein AXL PDB 2c5d.png
Available structures
PDB Ortholog search: PDBe RCSB
Identifiers
Aliases AXL , AZF, AZFA, SP3, AZF1, ARK, JTK11, Tyro7, UFO, AXL receptor tyrosine kinase
External IDs OMIM: 109135 MGI: 1347244 HomoloGene: 7583 GeneCards: AXL
Orthologs
SpeciesHumanMouse
Entrez
Ensembl
UniProt
RefSeq (mRNA)

NM_001278599
NM_001699
NM_021913

NM_001190974
NM_001190975
NM_009465

RefSeq (protein)

NP_001265528
NP_001690
NP_068713

NP_001177903
NP_001177904
NP_033491

Location (UCSC) Chr 19: 41.22 – 41.26 Mb Chr 7: 25.46 – 25.49 Mb
PubMed search [3] [4]
Wikidata
View/Edit Human View/Edit Mouse

Tyrosine-protein kinase receptor UFO is an enzyme that in humans is encoded by the AXL gene. [5] [6] The gene was initially designated as UFO, in allusion to the unidentified function of this protein. [7] However, in the years since its discovery, research into AXL's expression profile and mechanism has made it an increasingly attractive target, especially for cancer therapeutics. In recent years, AXL has emerged as a key facilitator of immune escape and drug-resistance by cancer cells, leading to aggressive and metastatic cancers. [8]

Contents

AXL is a cell surface receptor tyrosine kinase, part of the TAM family of kinases including TYRO3 and MERTK.[ citation needed ]

Gene and protein structure

The Axl gene is evolutionarily conserved between vertebrate species. This gene has two different alternatively spliced transcript variants. [6]

The protein encoded by this gene is a member of the receptor tyrosine kinase subfamily. Although it is similar to other receptor tyrosine kinases, the Axl protein represents a unique structure of the extracellular region that juxtaposes IgL and FNIII repeats. [6]

The AXL protein is characterized by an extracellular structure consisting of two fibronectin type 3-like repeats and two immunoglobulin-like repeats along with its intracellular tyrosine kinase domain.

AXL is in close vicinity to the BCL3 oncogene, which is at 19q13.1-q13.2. [6]

Function

The AXL receptor transduces signals from the extracellular matrix into the cytoplasm by binding growth factors like vitamin K-dependent protein growth-arrest-specific gene 6 (GAS6). It is involved in the stimulation of cell proliferation and survival. Proteolytic cleavage of the AXL extracellular domain by the metalloproteinases ADAM10 and ADAM17 can downregulate this signalling activity. [9]

Signalling pathways activated downstream of AXL include PI3K-AKT-mTOR, MEKERK, NF-κB, and JAK/STAT. [10]

This receptor can also mediate cell aggregation by homophilic binding. [6]

AXL protein is expressed in normal tissues, particularly in bone marrow stroma and myeloid cells, and in tumour cells and tumour vasculature. [11] [12] In cancer, AXL is expressed on the tumor cells as well as adjacent immune cells including dendritic cells, macrophages, and NK cells.

Axl is an inhibitor of the innate immune response. The function of activated AXL in normal tissues includes the efficient clearance of apoptotic material and the dampening of TLR-dependent inflammatory responses and natural killer cell activity. [13]

AXL is a putative driver of diverse cellular processes that are critical for the development, growth, and spread of tumours, including proliferation, invasiveness and migration, epithelial-to-mesenchymal transition, stemness, angiogenesis, and immune modulation. [10] AXL has been implicated as a cancer driver and correlated with poor survival in numerous aggressive tumors including triple-negative breast cancer (TNBC), acute myeloid leukemia (AML), non-small-cell lung cancer (NSCLC), pancreatic cancer and ovarian cancer, among others. [14]

Clinical significance

Axl was first isolated in 1988 and identified as an oncogene in a screen for transforming genes in patients with a chronic myelogenous leukemia- that progressed to 'blast crisis'. [15] Since then, increased AXL expression has been associated with numerous cancers including lung cancer, breast cancer, pancreatic cancer, ovarian cancer, colon cancer and melanoma among others, and shown to have a strong correlation with poor survival outcomes. [12]

AXL has been shown to be a key driver of drug-resistance to targeted therapies, immuno therapies and chemotherapy in various animal models. Based on current knowledge of AXL's role in therapy resistance, future studies will help to determine whether AXL has a translational application as a biomarker for predicting therapeutic response to established drugs.

Recently, AXL has been implicated in chronic fibrotic diseases in several organs, including the liver. [16]

AXL also play an important role in Zika virus and SARS-CoV-2 infection, allowing for entry of the virus into host cells. [17] [18] This phenomenon is known to rely on phosphatidylserine incorporated in the viral envelope during egress, which then binds to AXL via the adapter GAS6. AXL mediates internalization into the endosome from which these viruses escape and initiate replication.

As a drug target

Studies have shown that AXL knockdown leads to downregulation of transcription factors required for EMT, including Slug, Twist, and Zeb1, and to increased expression of E-cadherin. [19]

Clinical studies

Cancer

Several drugs classified as "AXL inhibitors" have entered clinical trials; however, many target multiple kinase receptors in addition to AXL. The most advanced AXL selective inhibitor is bemcentinib (BGB324 or R428), an oral small molecule currently in multiple Phase II clinical trials for NSCLC, TNBC, AML and melanoma. Bemcentinib is being pursued as monotherapy and as combination therapy with existing and emerging targeted therapies, immunotherapies and chemotherapy.

A monoclonal antibody targeting AXL (YW327.6S2) and an AXL decoy receptor (GL2I.T) are currently in preclinical development. Additionally, an oral AXL inhibitor (TP-0903) is expected to enter Phase 1 clinical trial in November 2016 (in advanced solid tumours: NCT02729298).

Astellas Pharma is currently testing gilteritinib (ASP2215), a dual FLT3-AXL tyrosine kinase inhibitor in acute myeloid leukemia (AML). In 2017, gilteritinib gained FDA orphan drug status for AML. [20]

These approved drugs and ongoing and pending clinical trials highlight the potentially wide-ranging safety and efficacy of AXL inhibition. [10]

Interactions

AXL receptor tyrosine kinase has been shown to interact with TENC1. [21]

Related Research Articles

<span class="mw-page-title-main">Oncogene</span> Gene that has the potential to cause cancer

An oncogene is a gene that has the potential to cause cancer. In tumor cells, these genes are often mutated, or expressed at high levels.

<span class="mw-page-title-main">Tyrosine kinase</span> Class hi residues

A tyrosine kinase is an enzyme that can transfer a phosphate group from ATP to the tyrosine residues of specific proteins inside a cell. It functions as an "on" or "off" switch in many cellular functions.

<span class="mw-page-title-main">Philadelphia chromosome</span> Genetic abnormality in leukemia cancer cells

The Philadelphia chromosome or Philadelphia translocation (Ph) is a specific genetic abnormality in chromosome 22 of leukemia cancer cells. This chromosome is defective and unusually short because of reciprocal translocation, t(9;22)(q34;q11), of genetic material between chromosome 9 and chromosome 22, and contains a fusion gene called BCR-ABL1. This gene is the ABL1 gene of chromosome 9 juxtaposed onto the breakpoint cluster region BCR gene of chromosome 22, coding for a hybrid protein: a tyrosine kinase signaling protein that is "always on", causing the cell to divide uncontrollably by interrupting the stability of the genome and impairing various signaling pathways governing the cell cycle.

<span class="mw-page-title-main">KIT (gene)</span> Mammalian protein and protein-coding gene

Proto-oncogene c-KIT is the gene encoding the receptor tyrosine kinase protein known as tyrosine-protein kinase KIT, CD117 or mast/stem cell growth factor receptor (SCFR). Multiple transcript variants encoding different isoforms have been found for this gene. KIT was first described by the German biochemist Axel Ullrich in 1987 as the cellular homolog of the feline sarcoma viral oncogene v-kit.

<span class="mw-page-title-main">Acute myeloblastic leukemia with maturation</span> Medical condition

Acute myeloblastic leukemia with maturation (M2) is a subtype of acute myeloid leukemia (AML).

<span class="mw-page-title-main">CD135</span> Protein-coding gene in the species Homo sapiens

Cluster of differentiation antigen 135 (CD135) also known as fms like tyrosine kinase 3, receptor-type tyrosine-protein kinase FLT3, or fetal liver kinase-2 (Flk2) is a protein that in humans is encoded by the FLT3 gene. FLT3 is a cytokine receptor which belongs to the receptor tyrosine kinase class III. CD135 is the receptor for the cytokine Flt3 ligand (FLT3L).

<span class="mw-page-title-main">Fibroblast growth factor receptor 1</span> Protein-coding gene in the species Homo sapiens

Fibroblast growth factor receptor 1 (FGFR1), also known as basic fibroblast growth factor receptor 1, fms-related tyrosine kinase-2 / Pfeiffer syndrome, and CD331, is a receptor tyrosine kinase whose ligands are specific members of the fibroblast growth factor family. FGFR1 has been shown to be associated with Pfeiffer syndrome, and clonal eosinophilias.

<span class="mw-page-title-main">ETV6</span> Protein-coding gene in the species Homo sapiens

ETV6 protein is a transcription factor that in humans is encoded by the ETV6 gene. The ETV6 protein regulates the development and growth of diverse cell types, particularly those of hematological tissues. However, its gene, ETV6 frequently suffers various mutations that lead to an array of potentially lethal cancers, i.e., ETV6 is a clinically significant proto-oncogene in that it can fuse with other genes to drive the development and/or progression of certain cancers. However, ETV6 is also an anti-oncogene or tumor suppressor gene in that mutations in it that encode for a truncated and therefore inactive protein are also associated with certain types of cancers.

<span class="mw-page-title-main">PDGFRB</span> Protein-coding gene in the species Homo sapiens

Platelet-derived growth factor receptor beta is a protein that in humans is encoded by the PDGFRB gene. Mutations in PDGFRB are mainly associated with the clonal eosinophilia class of malignancies.

<span class="mw-page-title-main">GAS6</span> Human gene coding for the GAS6 protein

Growth arrest – specific 6, also known as GAS6, is a human gene coding for the GAS6 protein. It is similar to the Protein S with the same domain organization and 43% amino acid identity. It was originally found as a gene upregulated by growth arrested fibroblasts.

<span class="mw-page-title-main">Proto-oncogene tyrosine-protein kinase Src</span> Mammalian protein found in Homo sapiens

Proto-oncogene tyrosine-protein kinase Src, also known as proto-oncogene c-Src, or simply c-Src, is a non-receptor tyrosine kinase protein that in humans is encoded by the SRC gene. It belongs to a family of Src family kinases and is similar to the v-Src gene of Rous sarcoma virus. It includes an SH2 domain, an SH3 domain and a tyrosine kinase domain. Two transcript variants encoding the same protein have been found for this gene.

<span class="mw-page-title-main">Colony stimulating factor 1 receptor</span> Protein found in humans

Colony stimulating factor 1 receptor (CSF1R), also known as macrophage colony-stimulating factor receptor (M-CSFR), and CD115, is a cell-surface protein encoded by the human CSF1R gene. CSF1R is a receptor that can be activated by two ligands: colony stimulating factor 1 (CSF-1) and interleukin-34 (IL-34). CSF1R is highly expressed in myeloid cells, and CSF1R signaling is necessary for the survival, proliferation, and differentiation of many myeloid cell types in vivo and in vitro. CSF1R signaling is involved in many diseases and is targeted in therapies for cancer, neurodegeneration, and inflammatory bone diseases.

<span class="mw-page-title-main">MECOM</span> Protein-coding gene in the species Homo sapiens

MDS1 and EVI1 complex locus protein EVI1 (MECOM) also known as ecotropic virus integration site 1 protein homolog (EVI-1) or positive regulatory domain zinc finger protein 3 (PRDM3) is a protein that in humans is encoded by the MECOM gene. EVI1 was first identified as a common retroviral integration site in AKXD murine myeloid tumors. It has since been identified in a plethora of other organisms, and seems to play a relatively conserved developmental role in embryogenesis. EVI1 is a nuclear transcription factor involved in many signaling pathways for both coexpression and coactivation of cell cycle genes.

<span class="mw-page-title-main">MERTK</span> Protein-coding gene in the species Homo sapiens

Proto-oncogene tyrosine-protein kinase MER is an enzyme that in humans is encoded by the MERTK gene.

<span class="mw-page-title-main">TYRO3</span> Protein-coding gene in the species Homo sapiens

Tyrosine-protein kinase receptor TYRO3 is an enzyme that in humans is encoded by the TYRO3 gene.

<span class="mw-page-title-main">ROR1</span> Protein-coding gene in the species Homo sapiens

Tyrosine-protein kinase transmembrane receptor ROR1, also known as neurotrophic tyrosine kinase, receptor-related 1 (NTRKR1), is an enzyme that in humans is encoded by the ROR1 gene. ROR1 is a member of the receptor tyrosine kinase-like orphan receptor (ROR) family.

<span class="mw-page-title-main">Crenolanib</span> Chemical compound

Crenolanib besylate is an investigational inhibitor being developed by AROG Pharmaceuticals, LLC. The compound is currently being evaluated for safety and efficacy in clinical trials for various types of cancer, including acute myeloid leukemia (AML), gastrointestinal stromal tumor (GIST), and glioma. Crenolanib is an orally bioavailable benzimidazole that selectively and potently inhibits signaling of wild-type and mutant isoforms of class III receptor tyrosine kinases (RTK) FLT3, PDGFR α, and PDGFR β. Unlike most RTK inhibitors, crenolanib is a type I mutant-specific inhibitor that preferentially binds to phosphorylated active kinases with the ‘DFG in’ conformation motif.

<span class="mw-page-title-main">Volasertib</span> Chemical compound

Volasertib is an experimental small molecule inhibitor of the PLK1 protein being developed by Boehringer Ingelheim for use as an anti-cancer agent. Volasertib is the second in a novel class of drugs called dihydropteridinone derivatives.

Clonal hypereosinophilia, also termed primary hypereosinophilia or clonal eosinophilia, is a grouping of hematological disorders all of which are characterized by the development and growth of a pre-malignant or malignant population of eosinophils, a type of white blood cell that occupies the bone marrow, blood, and other tissues. This population consists of a clone of eosinophils, i.e. a group of genetically identical eosinophils derived from a sufficiently mutated ancestor cell.

<span class="mw-page-title-main">Bemcentinib</span> Chemical compound

Bemcentinib, also known as BGB324 or R428, is an experimental oral small molecule that is an inhibitor of AXL kinase. Bemcentinib was licensed from Rigel Pharmaceuticals by BerGenBio and currently undergoing six Phase II trials in various solid and hematological tumors as monotherapy and in combination with immunotherapy, chemotherapy, and targeted therapeutics.

References

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Further reading