LMTK3 | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Aliases | LMTK3 , LMR3, PPP1R101, TYKLM3, lemur tyrosine kinase 3 | ||||||||||||||||||||||||||||||||||||||||||||||||||
External IDs | MGI: 3039582 HomoloGene: 79449 GeneCards: LMTK3 | ||||||||||||||||||||||||||||||||||||||||||||||||||
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Lemur tail kinase 3 is a protein that in humans is encoded by the LMTK3 gene. [5] [6]
LMTK3 is often overexpressed in human cancers where it promotes tumour growth, invasion and metastasis and therapy resistance. [5] It was first identified in 2011 through a kinase screen of regulators of ERα by Giamas et al. [7] who found that it promotes upregulation of ERα through PKC inhibition and inhibits ERα degradation through direct phosphorylation of ERα. Numerous other studies have linked LMTK3 to cancer in glioblastoma, [8] non-small cell lung cancer, [9] thyroid malignancies [10] and bladder cancer, [11] among others. A small molecule inhibitor, C28, has now been developed for LMTK3 which shows potent anti-cancer activity in vitro and in vivo.
The most well-characterised physiological role of LMTK3 is in the central nervous system. LMTK3 is expressed in the cerebral cortex, striatum, cerebellum, hippocampus, olfactory bulb and tubercle. [12] LMTK3 knockout mice are more hyperactive and show less signs of anxiety than wild-type counterparts. In addition, the mice showed lower levels of depression-like behaviour in forced swim tests and tail suspension assays. [13] LMTK3 knockout mice also have cognitive impairments and show behaviour related to schizophrenia and bipolar disorder. This may be due to impairment in GluA1 trafficking in neurons. [14] These studies show that LMTK3 plays an important role in the central nervous system.
LMTK3 is implicated in a number of human cancers as an oncogene as well as a potential predictive or prognostic biomarker. [5] The most well-known role of LMTK3 is in ERα signalling. In 2011, Giamas et al. showed that LMTK3 is a potent regulator of ERα through a kinome-wide siRNA screen. [7] By examining the effect of depletion of different genes of the expression of an ERα-regulated gene, they showed that LMTK3 knockdown significantly reduces ERα activity. LMTK3 phosphorylates ERα, increasing stability and protecting ERα from proteasomal degradation. LMTK3 also inhibits PKC, reducing AKT activity and therefore allowing accumulation of FoxO3 in cells, lifting inhibition of ESR1 transcription, causing an increase in ERα expression. An in vivo model also showed that LMTK3 siRNA reduces tumour growth in mice injected with MCF7 ER+ cells. Later analyses of clinical data show that LMTK3 is predictive and prognostic in breast cancer. High nuclear and cytoplasmic staining in breast cancer cells for LMTK3 is associated with poor clinical outcomes . [15]
LMTK3 is also associated with endocrine resistance in breast cancer. [16] Stebbing et al. showed that LMTK3 regulates a number of genes involved in tamoxifen resistance. LMTK3 overexpression also promotes chemotherapy resistance in breast cancer cells. [17]
Later, another study by Giamas' group revealed that LMTK3 is strongly associated with cell invasiveness and metastasis through regulation of integrin subunits. [18] LMTK3 acts through GRB2, inducing RAS activation and CDC42 activation, leading to increased ITGA5 and ITGB1 expression through the transcription factor, serum response factor (SRF). The group also showed that LMTK3 has nuclear roles where is facilitates the interaction between KAP1 (Krüppel-associated box domain-associated protein 1) and a KAP1 phosphatase, PP1α (protein phosphatase 1α). [19] This results in trimethylation of Histone H3 lysine 9 (H3K9me3) at tumour suppressor-like genes, resulting in silencing and a downregulation of tumour suppressors in breast cancer.
Giamas' group discovered the small molecule inhibitor, C28 in 2020 which is a potent, selective inhibitor of LMTK3. [20] C28 is an orally available and highly selective ATP-competitive inhibitor of LMTK3. Data from the NCI-60 cell line panel and experiments in xenografts show that the drug is an effective inhibitor of breast cancer growth in vivo. LMTK3 is an HSP90-CDC37 client protein which requires this interaction for folding and stability. C28 is a competitive inhibitor of LMTK3 that also deprives LMTK3 of HSP90, promoting instability and degradation of LMTK3. More recently, another compound, C36 has been characterised as a selective inhibitor of LMTK3 with apoptosis-promoting properties in breast cancer cells. [21]
Tumor necrosis factor is an adipokine and a cytokine. TNF is a member of the TNF superfamily, which consists of various transmembrane proteins with a homologous TNF domain.
Estrogen receptors (ERs) are a group of proteins found inside cells. They are receptors that are activated by the hormone estrogen (17β-estradiol). Two classes of ER exist: nuclear estrogen receptors, which are members of the nuclear receptor family of intracellular receptors, and membrane estrogen receptors (mERs), which are mostly G protein-coupled receptors. This article refers to the former (ER).
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Estrogen receptor beta (ERβ) also known as NR3A2 is one of two main types of estrogen receptor—a nuclear receptor which is activated by the sex hormone estrogen. In humans ERβ is encoded by the ESR2 gene.
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Serine/threonine kinase 11 (STK11) also known as liver kinase B1 (LKB1) or renal carcinoma antigen NY-REN-19 is a protein kinase that in humans is encoded by the STK11 gene.
RhoC is a small signaling G protein, and is a member of the Rac subfamily of the family Rho family of GTPases. It is encoded by the gene RHOC.
Activated CDC42 kinase 1, also known as ACK1, is an enzyme that in humans is encoded by the TNK2 gene. TNK2 gene encodes a non-receptor tyrosine kinase, ACK1, that binds to multiple receptor tyrosine kinases e.g. EGFR, MERTK, AXL, HER2 and insulin receptor (IR). ACK1 also interacts with Cdc42Hs in its GTP-bound form and inhibits both the intrinsic and GTPase-activating protein (GAP)-stimulated GTPase activity of Cdc42Hs. This binding is mediated by a unique sequence of 47 amino acids C-terminal to an SH3 domain. The protein may be involved in a regulatory mechanism that sustains the GTP-bound active form of Cdc42Hs and which is directly linked to a tyrosine phosphorylation signal transduction pathway. Several alternatively spliced transcript variants have been identified from this gene, but the full-length nature of only two transcript variants has been determined.
Cyclin-dependent kinase 4 inhibitor D is an enzyme that in humans is encoded by the CDKN2D gene.
Large tumor suppressor kinase 1 (LATS1) is an enzyme that in humans is encoded by the LATS1 gene.
Serine/threonine-protein kinase PAK 5 is an enzyme that in humans is encoded by the PAK5 gene.
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Protein CIP2A also known as cancerous inhibitor of PP2A (CIP2A) is a protein that in humans is encoded by the KIAA1524 gene.
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.
Forkhead box protein A1 (FOXA1), also known as hepatocyte nuclear factor 3-alpha (HNF-3A), is a protein that in humans is encoded by the FOXA1 gene.