Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P43146 (tumour suppressor)
 5,935 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Germline mutations in the LKB1/STK11 tumour suppressor gene cause Peutz-Jeghers syndrome (PJS), a rare dominant disorder. In addition to typical hamartomatous gastrointestinal polyps and pigmented perioral lesions, PJS is associated with an increased risk of tumours at multiple sites. Follow-up information on carriers is limited and genetic heterogeneity makes counselling and management in PJS difficult. Here we report the analysis of the LKB1/STK11 locus in a series of 33 PJS families, and estimation of cancer risks in carriers and noncarriers. Germline mutations of LKB1/STK11 were identified in 52% of cases. This observation reinforces the hypothesis of a second PJS locus. In carriers of LKB1/STK11 mutations, the risk of cancer was markedly elevated. The risk of developing any cancer in carriers by age 65 years was 47% (95% CI: 27-73%) with elevated risks of both gastrointestinal and breast cancer. PJS with germline mutations in LKB1/STK11 are at a very high relative and absolute risk of multiple gastrointestinal and nongastrointestinal cancers. To obtain precise estimates of risk associated with PJS requires further studies of genotype-phenotype especially with respect to LKB1/STK11 negative cases, as this group is likely to be heterogeneous.
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PMID:Further observations on LKB1/STK11 status and cancer risk in Peutz-Jeghers syndrome. 1286 22

The tumour suppressor gene, LKB1/STK11, has been mapped to chromosome 19p13, a region showing frequent allelic loss in various human cancers, including hepatocellular carcinoma (HCC). Additionally, LKB1 physically associates with p53 and regulates p53-dependent apoptotic pathways. To investigate whether genetic alterations of LKB1 could be involved in the tumorigenesis of HCC, we analysed the genetic alterations of the LKB1 and p53 genes in seven dysplastic nodules and 80 HCCs. We found one LKB1 missense mutation, CCG-->CTG (Pro-->Leu) at codon 281 within the kinase domain. We also found allelic loss in six of 27 (22%) informative HCC cases and all of them were HBV-positive cases. In addition, we detected seven missense, one nonsense and one silent mutations (nine of 80, 11%) of p53 in HCCs only. These results suggest that genetic alterations of the LKB1 or p53 genes may play an important role in tumour development or progression of a sub-set of HCCs, and may also provide alternative mechanisms to protect the HCC cell from p53-dependent apoptosis.
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PMID:Genetic analysis of the LKB1/STK11 gene in hepatocellular carcinomas. 1468 97

Peutz-Jeghers syndrome (PJS, MIM175200) is an autosomal-dominant inherited disorder characterised by multiple gastrointestinal hamartomatous polyps, melanin spots of the oral mucosa and digits, and an increased risk for various neoplasms. The PJS results from germline alterations of the STK11/LKB1 tumour suppressor gene, located on 19p13.3, and encoding a serine/threonine kinase. The detection of STK11 germline mutations, in only 50-70% of PJS families, has suggested a genetic heterogeneity of the disease. We report the case of a family with typical features of PJS, including gastrointestinal hamartomatous, breast cancers and melanin spots of the oral mucosa. Quantitative multiplex PCR of short fluorescent fragments (QMPSF) of the 19p13 region allowed us to identify an approximately 250 kb heterozygous deletion removing entirely the STK11 locus. This report, which constitutes the first description of a complete germline deletion of STK11, shows that the presence of such large genomic deletions should be considered in PJS families without detectable point mutations of STK11.
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PMID:Complete germline deletion of the STK11 gene in a family with Peutz-Jeghers syndrome. 1497 Aug 44

We recently demonstrated that the LKB1 tumour suppressor kinase, in complex with the pseudokinase STRAD and the scaffolding protein MO25, phosphorylates and activates AMP-activated protein kinase (AMPK). A total of 12 human kinases (NUAK1, NUAK2, BRSK1, BRSK2, QIK, QSK, SIK, MARK1, MARK2, MARK3, MARK4 and MELK) are related to AMPK. Here we demonstrate that LKB1 can phosphorylate the T-loop of all the members of this subfamily, apart from MELK, increasing their activity >50-fold. LKB1 catalytic activity and the presence of MO25 and STRAD are required for activation. Mutation of the T-loop Thr phosphorylated by LKB1 to Ala prevented activation, while mutation to glutamate produced active forms of many of the AMPK-related kinases. Activities of endogenous NUAK2, QIK, QSK, SIK, MARK1, MARK2/3 and MARK4 were markedly reduced in LKB1-deficient cells. Neither LKB1 activity nor that of AMPK-related kinases was stimulated by phenformin or AICAR, which activate AMPK. Our results show that LKB1 functions as a master upstream protein kinase, regulating AMPK-related kinases as well as AMPK. Between them, these kinases may mediate the physiological effects of LKB1, including its tumour suppressor function.
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PMID:LKB1 is a master kinase that activates 13 kinases of the AMPK subfamily, including MARK/PAR-1. 1497 52

LKB1, the product of a tumour suppressor gene, is a serine/threonine kinase that coordinates disparate cellular processes. Recent data have revealed novel functions for LKB1, providing new insight into the regulation of cell polarity and energy-generating metabolism.
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PMID:LKB1 kinase: master and commander of metabolism and polarity. 1518 63

The AMP-activated protein kinase (AMPK) cascade is a sensor of cellular energy status. Whenever the cellular ATP:ADP ratio falls, owing to a stress that inhibits ATP production or increases ATP consumption, this is amplified by adenylate kinase into a much larger increase in the AMP:ATP ratio. AMP activates the system by binding to two tandem domains on the gamma subunits of AMPK, and this is antagonized by high concentrations of ATP. AMP binding causes activation by a sensitive mechanism involving phosphorylation of AMPK by the tumour suppressor LKB1. Once activated, AMPK switches on catabolic pathways that generate ATP while switching off ATP-consuming processes. As well as acting at the level of the individual cell, the system also regulates food intake and energy expenditure at the whole body level, in particular by mediating the effects of hormones and cytokines such as leptin, adiponectin and ghrelin. A particularly interesting downstream target recently identified is TSC2 (tuberin). The LKB1-->AMPK-->TSC2 pathway negatively regulates the target of rapamycin (TOR), and this appears to be responsible for limiting protein synthesis and cell growth, and protecting against apoptosis, during cellular stresses such as glucose starvation.
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PMID:The AMP-activated protein kinase pathway--new players upstream and downstream. 1550 64

Mutations in the LKB1 tumour suppressor threonine kinase cause the inherited Peutz-Jeghers cancer syndrome and are also observed in some sporadic cancers. Recent work indicates that LKB1 exerts effects on metabolism, polarity and proliferation by phosphorylating and activating protein kinases belonging to the AMPK subfamily. In vivo, LKB1 forms a complex with STRAD, an inactive pseudokinase, and MO25, an armadillo repeat scaffolding-like protein. Binding of LKB1 to STRAD-MO25 activates LKB1 and re-localises it from the nucleus to the cytoplasm. To learn more about the inherent properties of the LKB1-STRAD-MO25 complex, we first investigated the activity of 34 point mutants of LKB1 found in human cancers and their ability to interact with STRAD and MO25. Interestingly, 12 of these mutants failed to interact with STRAD-MO25. Performing mutagenesis analysis, we defined two binding sites located on opposite surfaces of MO25alpha, which are required for the assembly of MO25alpha into a complex with STRADalpha and LKB1. In addition, we demonstrate that LKB1 does not require phosphorylation of its own T-loop to be activated by STRADalpha-MO25alpha, and discuss the possibility that this unusual mechanism of regulation arises from LKB1 functioning as an upstream kinase. Finally, we establish that STRADalpha, despite being catalytically inactive, is still capable of binding ATP with high affinity, but that this is not required for activation of LKB1. Taken together, our findings reinforce the functional importance of the binding of LKB1 to STRAD, and provide a greater understanding of the mechanism by which LKB1 is regulated and activated through its interaction with STRAD and MO25.
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PMID:Analysis of the LKB1-STRAD-MO25 complex. 1556 63

Mutations in the lkb1 gene are found in Peutz-Jeghers syndrome (PJS), with loss of heterozygosity or somatic mutations at the lkb1 locus, suggesting the gene product, the serine/threonine kinase LKB1, may function as a tumour suppressor. Patients with PJS are at a greater risk of developing cancers of epithelial tissue origin. It is widely accepted that the presence of hamartomatous polyps in PJS does not in itself lead to the development of malignancy. The signalling mechanisms that lead to these PJS related malignancies are not well understood. However, it is evident from the recent literature that LKB1 is a multitasking kinase, with unlimited potential in orchestrating cell activity. Thus far, LKB1 has been found to play a role in chromatin remodelling, cell cycle arrest, Wnt signalling, cell polarity, and energy metabolism, all of which may require the tumour suppressor function of this kinase and/or its catalytic activity.
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PMID:LKB1, the multitasking tumour suppressor kinase. 1562 75

Recent work has shown that the LKB1 tumour suppressor protein kinase phosphorylates and activates protein kinases belonging to the AMP activated kinase (AMPK) subfamily. In this study, we identify the sucrose non-fermenting protein (SNF1)-related kinase (SNRK), a largely unstudied AMPK subfamily member, as a novel substrate for LKB1. We demonstrate that LKB1 activates SNRK by phosphorylating the T-loop residue (Thr173), and that the LKB1 regulatory subunits STRAD and MO25 are required for LKB1 to activate SNRK. We find that SNRK is not active when expressed in HeLa cells that lack expression of LKB1, and its activity is restored by expression of wild type LKB1, but not catalytically deficient LKB1. We also present evidence that two other AMPK-related kinases more distantly related to AMPK than SNRK, namely NIM1 and testis-specific serine/threonine kinase-1 (TSSK1) are not substrates for LKB1. Tissue distribution analysis indicates that SNRK protein is mainly expressed in testis, similar to TSSK isoforms, whereas NIM1 is more widely expressed. These results provide evidence that SNRK could mediate some of the physiological effects of LKB1.
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PMID:Identification of the sucrose non-fermenting related kinase SNRK, as a novel LKB1 substrate. 1573 51

Recent studies indicate that the LKB1 tumour suppressor protein kinase is the major "upstream" activator of the energy sensor AMP-activated protein kinase (AMPK). We have used mice in which LKB1 is expressed at only approximately 10% of the normal levels in muscle and most other tissues, or that lack LKB1 entirely in skeletal muscle. Muscle expressing only 10% of the normal level of LKB1 had significantly reduced phosphorylation and activation of AMPKalpha2. In LKB1-lacking muscle, the basal activity of the AMPKalpha2 isoform was greatly reduced and was not increased by the AMP-mimetic agent, 5-aminoimidazole-4-carboxamide riboside (AICAR), by the antidiabetic drug phenformin, or by muscle contraction. Moreover, phosphorylation of acetyl CoA carboxylase-2, a downstream target of AMPK, was profoundly reduced. Glucose uptake stimulated by AICAR or muscle contraction, but not by insulin, was inhibited in the absence of LKB1. Contraction increased the AMP:ATP ratio to a greater extent in LKB1-deficient muscles than in LKB1-expressing muscles. These studies establish the importance of LKB1 in regulating AMPK activity and cellular energy levels in response to contraction and phenformin.
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PMID:Deficiency of LKB1 in skeletal muscle prevents AMPK activation and glucose uptake during contraction. 1588 49


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