Mutations and impaired function of LKB1 in familial and non-familial Peutz-Jeghers syndrome and a sporadic testicular cancer

LKB1 biology: assessing the therapeutic relevancy of LKB1 inhibitors

Liver Kinase B1 (LKB1), encoded by Serine-Threonine Kinase 11 (STK11), is a master kinase that regulates cell migration, polarity, proliferation, and metabolism through downstream adenosine monophosphate-activated protein kinase (AMPK) and AMPK-related kinase signalling. Since genetic screens identified STK11 mutations in Peutz-Jeghers Syndrome, STK11 mutants have been implicated in tumourigenesis labelling it as a tumour suppressor. In support of this, several compounds reduce tumour burden through upregulating LKB1 signalling, and LKB1-AMPK agonists are cytotoxic to tumour cells. However, in certain contexts, its role in cancer is paradoxical as LKB1 promotes tumour cell survival by mediating resistance against metabolic and oxidative stressors. LKB1 deficiency has also enhanced the selectivity and cytotoxicity of several cancer therapies. Taken together, there is a need to develop LKB1-specific pharmacological compounds, but prior to developing LKB1 inhibitors, further work is needed to understand LKB1 activity and regulation. However, investigating LKB1 activity is strenuous as cell/tissue type, mutations to the LKB1 signalling pathway, STE-20-related kinase adaptor protein (STRAD) binding, Mouse protein 25-STRAD binding, splicing variants, nucleocytoplasmic shuttling, post-translational modifications, and kinase conformation impact the functional status of LKB1. For these reasons, guidelines to standardize experimental strategies to study LKB1 activity, associate proteins, spliced isoforms, post-translational modifications, and regulation are of upmost importance to the development of LKB1-specific therapies. Therefore, to assess the therapeutic relevancy of LKB1 inhibitors, this review summarizes the importance of LKB1 in cell physiology, highlights contributors to LKB1 activation, and outlines the benefits and risks associated with targeting LKB1.

Familial syndromes associated with testicular and paratesticular neoplasms: a comprehensive review

A syndromic association between a subset of testicular/paratesticular neoplasms is well established. Such examples include Carney complex and large cell calcifying Sertoli cell tumor, Peutz-Jeghers syndrome and intratubular large cell hyalinizing Sertoli cell neoplasia, and VHL syndrome and clear cell papillary cystadenoma of the epididymis.However, recent studies proposed potential novel links between some testicular and paratesticular neoplasms with certain tumor syndromes. While more studies are still needed to solidify these associations, recent research suggests that a subset of Leydig cell tumors may arise in patients with hereditary leiomyomatosis and renal cell carcinoma syndrome or that some seminomas may occur in Lynch syndrome patients. Additionally, an association between testicular sex cord stromal tumors and paratesticular sarcomas with Familial adenomatous polyposis syndrome and DICER1 syndrome, respectively, has been proposed as well. This review provides a comprehensive overview of the intricate relationship between familial syndromes and associated testicular and paratesticular tumors, shedding light on their clinicopathological and molecular characteristics.

Posttranslational regulation of liver kinase B1 (LKB1) in human cancer

Liver kinase B1 (LKB1) is a serine-threonine kinase that participates in multiple cellular and biological processes, including energy metabolism, cell polarity, cell proliferation, cell migration, and many others. LKB1 is initially identified as a germline-mutated causative gene in Peutz-Jeghers syndrome (PJS) and is commonly regarded as a tumor suppressor due to frequent inactivation in a variety of cancers. LKB1 directly binds and activates its downstream kinases including the AMP-activated protein kinase (AMPK) and AMPK-related kinases by phosphorylation, which has been intensively investigated for the past decades. An increasing number of studies has uncovered the posttranslational modifications (PTMs) of LKB1 and consequent changes in its localization, activity, and interaction with substrates. The alteration in LKB1 function as a consequence of genetic mutations and aberrant upstream signaling regulation leads to tumor development and progression. Here, we review current knowledge about the mechanism of LKB1 in cancer and the contributions of PTMs, such as phosphorylation, ubiquitination, SUMOylation, acetylation, prenylation, and others, to the regulation of LKB1 function, offering new insights into the therapeutic strategies in cancer.

The Tumor Suppressor Kinase LKB1: Metabolic Nexus

Liver kinase B1 (LKB1) is a multitasking tumor suppressor kinase that is implicated in multiple malignancies such as lung, gastrointestinal, pancreatic, and breast. LKB1 was first identified as the gene responsible for Peutz-Jeghers syndrome (PJS) characterized by hamartomatous polyps and oral mucotaneous pigmentation. LKB1 functions to activate AMP-activated protein kinase (AMPK) during energy stress to shift metabolic processes from active anabolic pathways to active catabolic pathways to generate ATP. Genetic loss or inactivation of LKB1 promotes metabolic reprogramming and metabolic adaptations of cancer cells that fuel increased growth and division rates. As a result, LKB1 loss is associated with increased aggressiveness and treatment options for patients with LKB1 mutant tumors are limited. Recently, there has been new insights into the role LKB1 has on metabolic regulation and the identification of potential vulnerabilities in LKB1 mutant tumors. In this review, we discuss the tumor suppressive role of LKB1 and the impact LKB1 loss has on metabolic reprograming in cancer cells, with a focus on lung cancer. We also discuss potential therapeutic avenues to treat malignancies associated with LKB1 loss by targeting aberrant metabolic pathways associated with LKB1 loss.

Deleterious mis-splicing of STK11 caused by a novel single-nucleotide substitution in the 3' polypyrimidine tract of intron five

Background

Pathogenic variants in STK11, also designated as LKB1, cause Peutz–Jeghers syndrome, which is a rare autosomal dominant disorder characterized by mucocutaneous pigmentation changes, polyposis, and a high risk of cancer.

Methods

A male meeting the clinical diagnostic criteria for Peutz–Jeghers syndrome underwent next‐generation sequencing. To validate the predicted splicing impact of a detected STK11 variant, we performed RNA‐Seq on mRNA extracted from patient‐derived Epstein‐Barr virus‐transformed lymphocytes treated with cycloheximide to inhibit nonsense‐mediated decay ex vivo.

Results

Blood testing identified a novel single‐nucleotide substitution, NM_000455.4:c.735‐10C>A, at the end of the 3′ polypyrimidine tract of intron five in STK11. RNA‐Seq confirmed a predicted eight base pair insertion in the mRNA transcript. Following inhibition of nonsense‐mediated decay, the out‐of‐frame insertion was detected in 50% of all RNA‐Seq reads. This confirmed a strong, deleterious splicing impact of the variant.

Conclusion

We characterized a novel likely pathogenic germline variant in intron five of STK11 associated with Peutz–Jeghers syndrome. The study highlights RNA‐Seq as a useful supplement in hereditary cancer predisposition testing.

Approaches to functionally validate candidate genetic variants involved in colorectal cancer predisposition

Most next generation sequencing (NGS) studies identified candidate genetic variants predisposing to colorectal cancer (CRC) but do not tackle its functional interpretation to unequivocally recognize a new hereditary CRC gene. Besides, germline variants in already established hereditary CRC-predisposing genes or somatic variants share the same need when trying to categorize those with relevant significance. Functional genomics approaches have an important role in identifying the causal links between genetic architecture and phenotypes, in order to decipher cellular function in health and disease. Therefore, functional interpretation of identified genetic variants by NGS platforms is now essential. Available approaches nowadays include bioinformatics, cell and molecular biology and animal models. Recent advances, such as the CRISPR-Cas9, ZFN and TALEN systems, have been already used as a powerful tool with this objective. However, the use of cell lines is of limited value due to the CRC heterogeneity and its close interaction with microenvironment. Access to tridimensional cultures or organoids and xenograft models that mimic the in vivo tissue architecture could revolutionize functional analysis. This review will focus on the application of state-of-the-art functional studies to better tackle new genes involved in germline predisposition to this neoplasm.

Controlling the master-upstream regulation of the tumor suppressor LKB1

The tumor suppressor LKB1 is an essential serine/threonine kinase, which regulates various cellular processes such as cell metabolism, cell proliferation, cell polarity, and cell migration. Germline mutations in the STK11 gene (encoding LKB1) are the cause of the Peutz-Jeghers syndrome, which is characterized by benign polyps in the intestine and a higher risk for the patients to develop intestinal and extraintestinal tumors. Moreover, mutations and misregulation of LKB1 have been reported to occur in most types of tumors and are among the most common aberrations in lung cancer. LKB1 activates several downstream kinases of the AMPK family by direct phosphorylation in the T-loop. In particular the activation of AMPK upon energetic stress has been intensively analyzed in various diseases, including cancer to induce a metabolic switch from anabolism towards catabolism to regulate energy homeostasis and cell survival. In contrast, the regulation of LKB1 itself has long been only poorly understood. Only in the last years, several proteins and posttranslational modifications of LKB1 have been analyzed to control its localization, activity and recognition of substrates. Here, we summarize the current knowledge about the upstream regulation of LKB1, which is important for the understanding of the pathogenesis of many types of tumors.

Two novel STK11 missense mutations induce phosphorylation of S6K and promote cell proliferation in Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is a rare hereditary disease caused by mutations in serine threonine kinase 11 (STK11) and characterized by an increased risk of developing cancer. Inactivation of STK11 has been associated with the mammalian target of rapamycin (mTOR) pathway. Hyperactivation and phosphorylation of the key downstream target genes ribosomal protein S6 kinase 1 (S6K1) and S6 promote protein synthesis and cell proliferation. To better understand the effects of STK11 dysfunction in the pathogenesis of PJS, genomic DNA samples from 21 patients with PJS from 11 unrelated families were investigated for STK11 mutations in the present study. The results revealed 6 point mutations and 2 large deletions in 8 (72.7%, 8/11) of the unrelated families. Notably, 3 novel mutations were identified, which included 2 missense mutations [c.88G>A (p.Asp30Asn) and c.869T>C (p.Leu290Pro)]. Subsequent immunohistochemical analysis revealed staining for phosphorylated-S6 protein in colonic hamartoma and breast benign tumor tissues from patients with PJS carrying the two respective missense mutations. Additionally, the novel missense STK11 mutants induced phosphorylation of S6K1 and S6, determined using western blot analysis, and promoted the proliferation of HeLa and SW1116 cells, determined using Cell Counting Kit-8 and colony formation assays. Collectively, these findings extend the STK11 mutation spectrum and confirm the pathogenicity of two novel missense mutations. This study represents a valuable insight into the molecular mechanisms implicated in the pathogenesis of PJS.

Clinical manifestations and STK11 germline mutations in Taiwanese patients with Peutz-Jeghers syndrome

BACKGROUNDS

Clinical manifestations and molecular basis of Taiwanese patients with Peutz-Jeghers syndrome (PJS) were investigated to add the knowledge of phenotype and genotype of the disease.

METHODS

Based on the Pathology Data Bank and the Colorectal Cancer Register, we collected their clinical data. The entire coding sequence of the STK11 gene was amplified and analyzed by sequencing using the genomic DNA.

RESULTS

Fifteen patients diagnosed with PJS from 11 unrelated families were collected until 2015. The median age at the onset of symptoms was 19 years with intussusception as the most frequent presenting symptom. Ten patients developing 11 cancers at various anatomical sites, including two cases of sinonasal cancer, two lung cancers, two breast cancers, two rectal cancers, two gynecological cancers and one small bowel cancer. Five of the deceased patients had died of cancers. The median age of diagnosis of first cancer in the probands was 32 years. Seventy patients (7 of 10) diagnosed before age of 40. Mutations found in eight families included five novel mutations (exon 6, c.843 ins G; exon 8, c.2065 delete A; exon 8, c.G923A, nonsense; exon 6, c.748dupA; and mTOR c.5107dupA) and three previously reported mutations. The other three PJS families without detectable STK11 mutations did not develop malignancies so far.

CONCLUSION

This is the first comprehensive study of patients with Peutz-Jeghers syndrome in the Taiwanese. We have demonstrated that the phenotype of Peutz-Jeghers syndrome varies greatly among the patients. Patients with detectable STK11 mutations have very high risk of developing cancers.

Post-translational regulation contributes to the loss of LKB1 expression through SIRT1 deacetylase in osteosarcomas

Background:

The most prevalent form of bone cancer is osteosarcoma (OS), which is associated with poor prognosis in case of metastases formation. Mice harbouring liver kinase B1 (LKB1^+/−) develop osteoblastoma-like tumours. Therefore, we asked whether loss of LKB1 gene has a role in the pathogenesis of human OS.

Methods:

Osteosarcomas (n=259) were screened for LKB1 and sirtuin 1 (SIRT1) protein expression using immunohistochemistry and western blot. Those cases were also screened for LKB1 genetic alterations by next-generation sequencing, Sanger sequencing, restriction fragment length polymorphism and fluorescence in situ hybridisation approaches. We studied LKB1 protein degradation through SIRT1 expression. MicroRNA expression investigations were also conducted to identify the microRNAs involved in the SIRT1/LKB1 pathway.

Results:

Forty-one per cent (106 out of 259) OS had lost LKB1 protein expression with no evident genetic anomalies. We obtained evidence that SIRT1 impairs LKB1 protein stability, and that SIRT1 depletion leads to accumulation of LKB1 in OS cell lines resulting in growth arrest. Further investigations revealed the role of miR-204 in the regulation of SIRT1 expression, which impairs LKB1 stability.

Conclusions:

We demonstrated the involvement of sequential regulation of miR-204/SIRT1/LKB1 in OS cases and showed a mechanism for the loss of expression of LKB1 tumour suppressor in this malignancy.

Correlation between genotype and phenotype in three families with Peutz-Jeghers Syndrome

Peutz-Jeghers syndrome (PJS) is a hereditary disorder characterized by mucocutaneous pigmentations, gastrointestinal (GI) polyposis and an increased risk of certain malignancies. Little is known about the causative genes of PJS, or their association with the clinical phenotypes of PJS. The present study reports the results of clinical and genetic analysis of three Chinese families with PJS. In addition, the medical histories and clinical manifestations of these families were compared. DNA was collected from the blood samples of patients with PJS and controls. Serine/threonine kinase 11 (STK11), olfactory receptor family 4 subfamily C member 45 (OR4C45) and zonadhesin (ZAN) were amplified by polymerase chain reaction, and analyzed by sequencing and cloning. Two PJS-affected members of one family had a de novo single base deletion (NM_000455.4:c.842delC) in the STK11 gene, and their clinical presentations reflected the quantity of mutant STK11 copies in a dose-dependent manner. No pathogenic variants of OR4C45 or ZAN were found in the patients with PJS, although a new single nucleotide polymorphism (NM_003386.2:c.5768delG) of ZAN was identified. The results of the current study identified that a STK11 mutation dose-dependent genotype-phenotype relationship exists in patients with PJS. In addition, an early onset and high severity of oral pigmentations in PJS was indicative of serious GI phenotypes. These findings may aid the diagnosis and treatment of PJS.

First report of somatic mosaicism for mutations in STK11 in four patients with Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is an autosomal dominant cancer predisposition syndrome characterised by gastrointestinal polyposis and mucocutaneous pigmentation. Mutations in STK11, a serine-threonine protein kinase, have been associated with PJS in up to 100 % of published series. The hypothesis that a further genetic locus for PJS exists is controversial. No mutations in any other genes have been described in association with PJS. To date, no instances of somatic mosaicism for STK11 have been described. DNA extracted from peripheral lymphocytes and buccal cells was screened by sequence analysis for mutations in STK11. Dosage analysis was undertaken by multiplex ligation-dependent probe amplification (MLPA). Four patients have been shown to have mosaicism in STK11: two had mosaic deletions of specific exons (2-3 and 3-10) of the STK11 gene; one had a mosaic nonsense mutation in exon 5; and one had a mosaic frameshift mutation in exon 8. This report details the first four reported cases of somatic mosaicism for STK11 associated with PJS. This shows that techniques in addition to direct sequencing such as MLPA must be used to assess for large scale genomic deletions in patients meeting clinical diagnostic criteria for PJS. This also adds further weight to the hypothesis of a single genetic locus for PJS.

[Hereditary predisposition to cancers of the digestive tract, breast, gynecological and gonadal: focus on the Peutz-Jeghers]

Peutz-Jeghers syndrome (PJS) is a rare autosomal dominant disease due to mutations in the tumor suppressor gene STK11. PJS is characterized by periorificial hyperpigmented macules (lentiginosis) and hamartomatous polyposis. Polyps can be located anywhere in the gastrointestinal tract, but are preferably observed in the small bowel (70-90%), the colon (50%) and the stomach (25%). They tend to be cancerous in a particular sequence hamartoma-dysplasia-cancer. The diagnosis is often made in the first or second decade following the appearance of lentigines or upon the occurrence of complications due to polyps (obstruction, intussusception, occult bleeding responsible for anemia). Furthermore PJS is associated with a significant increase in cancer risk (relative risk of 89% over the life according to the most recent series). Digestive cancers are the more frequent with cumulative incidences of 55% for gastro-intestinal cancer (39% for colorectal cancer, 13% for small bowel cancer and between 11 and 36% for pancreatic cancer, respectively). There is also an increased risk of non digestive cancers. In particular the risk of breast cancer is similar to that of patients carrying deleterious BRCA1 or BRCA2 mutations (cumulative incidence of 45%). Gynecological and gonadal tumors are frequent as well and can be more (adenoma malignum) or less aggressive (ovarian sex cord tumors with annular tubules and testicular tumors with calcified Sertoli cells). Finally the frequency of lung cancer is moderately increased. Recommendations for screening and management based on retrospective series in the literature have led to various strategies. The aim of this paper is to summarize the clinical and molecular diagnostic criteria of PJS as well as recommendations on screening strategies, management and monitoring.

Recent progress on liver kinase B1 (LKB1): expression, regulation, downstream signaling and cancer suppressive function

Liver kinase B1 (LKB1), known as a serine/threonine kinase, has been identified as a critical cancer suppressor in many cancer cells. It is a master upstream kinase of 13 AMP-activated protein kinase (AMPK)-related protein kinases, and possesses versatile biological functions. LKB1 gene is mutated in many cancers, and its protein can form different protein complexes with different cellular localizations in various cell types. The expression of LKB1 can be regulated through epigenetic modification, transcriptional regulation and post-translational modification. LKB1 dowcnstream pathways mainly include AMPK, microtubule affinity regulating kinase (MARK), salt-inducible kinase (SIK), sucrose non-fermenting protein-related kinase (SNRK) and brain selective kinase (BRSK) signalings, etc. This review, therefore, mainly discusses recent studies about the expression, regulation, downstream signaling and cancer suppressive function of LKB1, which can be helpful for better understanding of this molecular and its significance in cancers.

Liver kinase B1 enhances chemoresistance to gemcitabine in breast cancer MDA-MB-231 cells

Liver kinase B1 (LKB1) is a well-known tumor suppressor gene in a variety of human cancers, including breast cancer. However, its role in gemcitabine resistance is unclear. Since gemcitabine in combination with other chemotherapeutic reagents is the first-line treatment in advanced breast cancer, the aim of the present study was to determine the effect of ectopic expression of LKB1 on chemosensitivity to gemcitabine in the breast cancer MDA-MB-231 cell line. Increasing the expression of LKB1 was found to directly correlate with gemcitabine chemoresistance. Although LKB1 suppressed the cell proliferation rate and clonogenicity in the absence of gemcitabine, it increased the median inhibitory concentration of gemcitabine and clonogenicity of cells in the presence of gemcitabine. Mechanistic analysis indicated that LKB1 was able to protect cells from DNA damage caused by gemcitabine. Furthermore, it was found that LKB1 induced a significant upregulation of cytidine deaminase expression, an important enzyme that accelerates gemcitabine catabolization. Overall, dual characteristics of LKB1 were identified: Suppressing cell growth in normal conditions and enhancing chemoresisitance to gemcitabine, possibly by accelerating degradation of gemcitabine, and protecting cells from DNA damage caused by gemcitabine.

STK11 domain XI mutations: candidate genetic drivers leading to the development of dysplastic polyps in Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is a rare hereditary disorder resulting from mutations in serine/threonine kinase 11 (STK11) and characterized by gastrointestinal (GI) hamartomatous polyps, mucocutaneous pigmentation, and an increased risk for specific cancers. Little is known about the genetic implications of specific STK11 mutations with regard to their role in dysplastic and malignant transformation of GI polyps. Peripheral blood genomic DNA samples from 116 Chinese PJS patients from 52 unrelated families were investigated for STK11 mutations. Genotype-phenotype correlations were investigated. The mutation detection rate was 67.3% (51.9% point mutations, 15.4% large deletions). Fourteen out of the 25 point mutations identified were novel. Nearly one-third of all mutations, 8/27 (29.6%), were in exon 7, the shortest out of the nine exons. Strikingly, mutations affecting protein kinase domain XI, encoded in part by exon 7, correlated with a 90% (9/10) incidence of GI polyp dysplasia. In contrast, only two out of 17 (11.8%) nondomain XI mutations were linked to polyp dysplasia (P = 0.0001). The extent of the association between dysplasia and the development of GI-related cancers is currently unknown but our results highlight a novel STK11 genotype-phenotype association as the basis for future genetic counseling and basic research studies.

Identification of patients at risk for hereditary colorectal cancer

Diagnosis of hereditary colorectal cancer syndromes requires clinical suspicion and knowledge of such syndromes. Lynch syndrome is the most common cause of hereditary colorectal cancer. Other less common causes include familial adenomatous polyposis (FAP), Peutz-Jeghers syndrome (PJS), juvenile polyposis syndrome, and others. There have been a growing number of clinical and molecular tools used to screen and test at risk individuals. Screening tools include diagnostic clinical criteria, family history, genetic prediction models, and tumor testing. Patients who are high risk based on screening should be referred for genetic testing.

N-methylnitrosourea aggravates gastrointestinal polyposis in Lkb1+/- mice

Peutz-Jeghers patients develop hamartomatous polyps and carcinomas of the gastrointestinal tract. Cyclooxygenase-2 accelerates polyp growth in Lkb1 (+/-) mice modelling Peutz-Jeghers polyposis. In this study, we aimed to evaluate the effect of the mutagenic carcinogen N-methylnitrosourea (MNU) on gastrointestinal tumourigenesis in Lkb1 (+/-) mice and to investigate the role of cyclooxygenase-2 on the tumourigenesis. We treated 40 Lkb1 (+/-) and 51 wild-type mice with MNU, 10 mice from both groups received the cyclooxygenase-2 inhibitor celecoxib. Carcinogen-treated Lkb1 (+/-) mice displayed worse survival (60%) than treated wild-type (100%, P = 0.028) or untreated Lkb1 (+/-) mice (92%, P = 0.045). Also, the gastrointestinal tumour burden was almost 10-fold higher in carcinogen-treated (2181 mm(3)) than in untreated (237 mm(3), P = 0.00045) Lkb1 (+/-) mice. Celecoxib was much less efficient in reducing tumourigenesis in MNU-treated mice (by 23%; 1686 mm(3)) than in untreated mice (76%; 58 mm(3)). Surprisingly, the increase in tumour burden in MNU-treated mice was not accompanied by consistent histological changes, with only a single focus of epithelial dysplasia noted. This study suggests that MNU promotes Peutz-Jeghers polyposis independently from the acceleration by cyclooxygenase-2.

Hamartomatous polyposis syndromes

Hamartomas are tumour-like malformations, consisting of disorganized normal tissues, typical of the site of tumour manifestation. Familial manifestation of hamartomatous polyps can be noted in juvenile polyposis syndrome (JPS), Peutz-Jeghers’ syndrome (PJS), hereditary mixed polyposis syndrome (HMPS) and PTEN hamartoma tumour syndrome (PHTS). All the aforementioned syndromes are inherited in an autosomal dominant manner and form a rather heterogenous group both in respect to the number and localization of polyps and the risk of cancer development in the alimentary tract and other organs. Individual syndromes of hamartomatous polyposis frequently manifest similar symptoms, particularly during the early stage of the diseases when in several cases their clinical pictures do not allow for differential diagnosis. The correct diagnosis of the disease using molecular methods allows treatment to be implemented earlier and therefore more effectively since it is followed by a strict monitoring of organs that manifest a predisposition for neoplastic transformation.

Unusually early presentation of small-bowel adenocarcinoma in a patient with Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is an autosomal dominant cancer predisposition syndrome characterized by melanotic macules and hamartomatous polyps. Small-bowel surveillance in the pediatric PJS population is not designed to identify small-bowel malignancy, which is thought to arise in adulthood. A 13-year-old boy presented with lead-point intussusception, requiring emergent surgical resection. A mucinous adenocarcinoma was found arising from high-grade dysplasia within a polyp. On the basis of these findings and mucosal pigmentation, he was diagnosed with PJS. DNA sequencing revealed a heterozygous c.921-1G>T STK11 mutation. This case is the earliest onset of small-bowel carcinoma in PJS, an observation relevant to surveillance guidelines.

Targeting LKB1 signaling in cancer

The serine/threonine kinase LKB1 is a master kinase involved in cellular responses such as energy metabolism, cell polarity and cell growth. LKB1 regulates these crucial cellular responses mainly via AMPK/mTOR signaling. Germ-line mutations in LKB1 are associated with the predisposition of the Peutz-Jeghers syndrome in which patients develop gastrointestinal hamartomas and have an enormously increased risk for developing gastrointestinal, breast and gynecological cancers. In addition, somatic inactivation of LKB1 has been associated with sporadic cancers such as lung cancer. The exact mechanisms of LKB1-mediated tumor suppression remain so far unidentified; however, the inability to activate AMPK and the resulting mTOR hyperactivation has been detected in PJS-associated lesions. Therefore, targeting LKB1 in cancer is now mainly focusing on the activation of AMPK and inactivation of mTOR. Preclinical in vitro and in vivo studies show encouraging results regarding these approaches, which have even progressed to the initiation of a few clinical trials. In this review, we describe the functions, regulation and downstream signaling of LKB1, and its role in hereditary and sporadic cancers. In addition, we provide an overview of several AMPK activators, mTOR inhibitors and additional mechanisms to target LKB1 signaling, and describe the effect of these compounds on cancer cells. Overall, we will explain the current strategies attempting to find a way of treating LKB1-associated cancer.

The LKB1 tumor suppressor controls spindle orientation and localization of activated AMPK in mitotic epithelial cells

Orientation of mitotic spindles plays an integral role in determining the relative positions of daughter cells in a tissue. LKB1 is a tumor suppressor that controls cell polarity, metabolism, and microtubule stability. Here, we show that germline LKB1 mutation in mice impairs spindle orientation in cells of the upper gastrointestinal tract and causes dramatic mislocalization of the LKB1 substrate AMPK in mitotic cells. RNAi of LKB1 causes spindle misorientation in three-dimensional MDCK cell cysts. Maintaining proper spindle orientation, possibly mediated by effects on the downstream kinase AMPK, could be an important tumor suppressor function of LKB1.

Altered LKB1/AMPK/TSC1/TSC2/mTOR signaling causes disruption of Sertoli cell polarity and spermatogenesis

Male patients with Peutz-Jeghers syndrome (PJS) have defective spermatogenesis and are at increased risk of developing Sertoli cell tumors. Mutations in the Liver Kinase B1 (LKB1/STK11) gene are associated with the pathogenesis of PJS and have been identified in non-PJS patients with sporadic testicular cancers. The mechanisms controlled by LKB1 signaling in Sertoli cell functions and testicular biology have not been described. We have conditionally deleted the Lkb1 gene (Lkb1(cko)) in somatic testicular cells to define the molecular mechanisms involved in the development of the testicular phenotype observed in PJS patients. Focal vacuolization in some of the seminiferous tubules was observed in 4-week-old mutant testes but germ cell development appeared to be normal. However, similar to PJS patients, we observed progressive germ cell loss and Sertoli cell only tubules in Lkb1(cko) testes from mice older than 10 weeks, accompanied by defects in Sertoli cell polarity and testicular junctional complexes and decreased activation of the MAP/microtubule affinity regulating and focal adhesion kinases. Suppression of AMP kinase and activation of mammalian target of rapamycin (mTOR) signaling were also observed in Lkb1(cko) testes. Loss of Tsc1 or Tsc2 copies the progressive Lkb1(cko) phenotype, suggesting that dysregulated activation of mTOR contributes to the pathogenesis of the Lkb1(cko) testicular phenotype. Pten(cko) mice had a normal testicular phenotype, which could be explained by the comparative lack of mTOR activation detected. These studies describe the importance of LKB1 signaling in testicular biology and the possible molecular mechanisms driving the pathogenesis of the testicular defects observed in PJS patients.

The role of LKB1 in lung cancer

In humans, the LKB1 gene is located on the short arm of chromosome 19, which is frequently deleted in lung tumors. Unlike most cancers of sporadic origin, in non-small cell lung cancer (NSCLC) nearly half of the tumors harbor somatic and homozygous inactivating mutations in LKB1. In NSCLC, LKB1 inactivation strongly predominates in adenocarcinomas from smokers and coexists with mutations at other important cancer genes, including KRAS and TP53. Remarkably, LKB1 alterations frequently occur simultaneously with inactivation at another important tumor suppressor gene, BRG1 (also called SMARCA4), which is also located on chromosome 19p. The present review considers the frequency and pattern of LKB1 mutations in lung cancer and the distinct biological pathways in which the LKB1 protein is involved in the development of this type of cancer. Finally, the possible clinical applications in cancer management, especially in lung cancer treatment, associated with the presence of absence of LKB1 are discussed.

Lower gastrointestinal tract cancer predisposition syndromes

Although inherited predisposition to colorectal cancer (CRC) has been suspected for more than 100 years, definitive proof of Mendelian syndromes had to await maturation of molecular genetic technologies. Since the l980s, the genetics of several clinically distinct entities has been revealed. Five disorders that share a hereditary predisposition to CRC are reviewed in this article.

Liver kinase B1 (LKB1) in the pathogenesis of epithelial cancers

LKB1 acts as a master kinase, with its major protein targets being the family of AMPKs. Through activation of multiple signaling pathways, LKB1's main physiologic functions involve regulating cellular growth, metabolism, and polarity. Germline mutations in LKB1 result in Peutz-Jeghers Syndrome, a rare cancer susceptibility syndrome. In addition, multiple LKB1 mutations have been identified in sporadic cancers, especially those of the lung. Recent studies from a variety of murine models have helped characterize LKB1's role in the pathogenesis of epithelial cancers. In some tumor types, LKB1 might function chiefly to suppress cell growth or invasion, while in other cases, it may serve to prevent metastasis. Moreover, molecular signatures of individual tumors likely influence LKB1's operational role, as multiple studies have shown that LKB1 can synergize with other tumor suppressors and/or oncogenes to accelerate tumorigenesis. To date, LKB1 has been considered mainly a tumor suppressor; however, some studies have suggested its potential oncogenic role, mainly through the suppression of apoptosis. In short, LKB1 is a tissue and context-specific kinase. This review aims to summarize our current understanding of its role in the pathogenesis of epithelial cancers.

Liver kinase B1 (LKB1) in the pathogenesis of UVB-induced murine basal cell carcinoma

LKB1, a known tumor suppressor, is mutated in Peutz-Jeghers Syndrome (PJS). It is responsible for the enhanced cancer risk in patients with PJS. Dysregulation of LKB1-dependent signaling also occurs in various epithelial cancers. UVB alters the expression of LKB1, though its role in the pathogenesis of skin cancer is unknown. Here we describe upregulation of LKB1 expression in UVB-induced murine basal cell carcinoma (BCC) and in human skin tumor keratinocytes. AMP-kinase and acetyl Co-A carboxylase, the downstream LKB1 targets, are also enhanced in this neoplasm. In addition, p-Akt, a kinase which inactivates GSK3β by its phosphorylation, is enhanced in BCCs. Consistently, an accumulation of p-GSK3β and an increase in activated nuclear β-catenin are found. mTOR signaling, which is also inhibited by LKB1, remains upregulated in BCCs. However, a marked decrease in the expression of sestrins, which function as potent negative regulators of mTOR is observed. Metformin, a known chemical inducer of this pathway, was found effective in immortalized HaCaT keratinocytes, but failed to activate the LKB1-dependent signaling in human carcinoma A431 cells. Thus, our data show that the LKB1/AMPK axis fails to regulate mTOR pathway, and a complex regulatory mechanism exists for the persistent mTOR activation in murine BCCs.

Clinical and genetic analysis of Peutz-Jeghers syndrome patients in Taiwan

BACKGROUND/PURPOSE

Peutz-Jeghers syndrome (PJS) is an autosomal dominant inherited disorder that is characterized by intestinal hamartomatous polyps and mucocutaneous pigmentation. Recently, germline mutations in the LKB1 gene have been reported to underlie PJS. The gene that encodes this serine/threonine kinase is located at chromosome 19p13.3. The aim of this study was to investigate the clinical and genetic characteristics of PJS patients in Taiwan.

METHODS

We searched the patient database of the National Taiwan University Hospital, a tertiary medical center in Taiwan, between January 1990 and November 2005. Patients' clinical information, demographic data, endoscopic pictures, and outcome were reviewed and analyzed. After obtaining informed consent, DNA and RNA were extracted from peripheral blood mononuclear cells and the LKB1 gene was sequenced.

RESULTS

A total of 14 unrelated patients who fulfilled the diagnostic criteria of PJS were included, and seven of them had genetic analysis performed. Mucocutaneous pigmentation was the most frequent presentation. Hamartomas occur most commonly in the small intestine (86%). Frequent abdominal complications include intussusception and gastrointestinal bleeding. Four germline mutations were found (57.1%). Three resulted in stop codons at codon 60, 162 (novel mutation), and 308. The fourth mutation was a missense mutation at codon 239 (novel mutation).

CONCLUSION

Compared with other countries, PJS patients in Taiwan tended to have more extensive polyps in the gastrointestinal tract, with intussusception being the most common abdominal symptom. Mutations in the LKB1 gene were identified in 57% of the probands in Taiwan.

Breakpoint determination of 15 large deletions in Peutz-Jeghers subjects

The Peutz-Jeghers Syndrome (PJS) is an autosomal dominant polyposis disorder with increased risk of multiple cancers. STK11/LKB1 (hereafter named STK11) germline mutations account for the large majority of PJS cases whereas large deletions account for about 30% of the cases. We report here the first thorough molecular characterization of 15 large deletions identified in a cohort of 51 clinically well-characterized PJS patients. The deletions were identified by MLPA analysis and characterized by custom CGH-array and quantitative PCR to define their boundaries. The deletions, ranging from 2.9 to 180 kb, removed one or more loci contiguous to the STK11 gene in six patients, while partial STK11 gene deletions were present in the remaining nine cases. By means of DNA sequencing, we were able to precisely characterize the breakpoints in each case. Of the 30 breakpoints, 16 were located in Alu elements, revealing non-allelic homologous recombination (NAHR) as the putative mechanism for the deletions of the STK11 gene, which lays in a region with high Alu density. In the remaining cases, other mechanisms could be hypothesized, such as microhomology-mediated end-joining (MMEJ) or non-homologous end-joining (NHEJ). In conclusion we here demonstrated the non-random occurrence of large deletions associated with PJS. All our patients had a classical PJS phenotype, which shows that haploinsufficiency for SBNO2, C19orf26, ATP5D, MIDN, C19orf23, CIRBP, C19orf24,and EFNA2, does not apparently affect their clinical phenotype.

Medical management update: Peutz Jeghers syndrome

Peutz Jeghers syndrome (PJS) is an autosomal dominant disease characterized by hamartomatous polyposis and distinct mucocutaneous pigmentation. PJS is associated with an increased risk for several cancers and other complications such as small intestine intussusception, short bowel syndrome, and anemia. Medical management mainly consists of treatment of the polyps and surveillance. This medical management update will review clinical concepts, therapeutic advances, and emphasize features of PJS important to the oral health care provider.

Carney complex and lentiginosis

Initially described as the 'complex of myxomas, spotty skin pigmentation and endocrine overactivity,' Carney complex (CNC) is known as an autosomal dominant multiple neoplasia syndrome involving skin and cardiac myxomas, pigmented skin lesions and endocrine tumors. Pigmented cutaneous manifestations in CNC are important diagnostically because they can be used for the early detection of the disease and, thus, the prevention of life-threatening complications of CNC related to heart myxomas and endocrine abnormalities. Specific for the disease skin lesions are present in more than half of the CNC patients. A major challenge is to distinguish pigmented skin lesions associated with CNC from other skin pathology, and thus accurately estimate the risk of cancer in affected patients; curiously, patients with CNC do not appear to have predisposition to skin cancers whereas this is not the case with other genetic syndromes associated with melanotic and other cutaneous lesions. In this paper, we review the current knowledge on cutaneous pathology associated with CNC and the most recent data on the molecular basis of the disease.

Identification of the serine 307 of LKB1 as a novel phosphorylation site essential for its nucleocytoplasmic transport and endothelial cell angiogenesis

LKB1, a master kinase that controls at least 13 downstream protein kinases including the AMP-activated protein kinase (AMPK), resides mainly in the nucleus. A key step in LKB1 activation is its export from the nucleus to the cytoplasm. Here, we identified S307 of LKB1 as a putative novel phosphorylation site which is essential for its nucleocytoplasmic transport. In a cell-free system, recombinant PKC-zeta phosphorylates LKB1 at S307. AMPK-activating agents stimulate PKC-zeta activity and LKB1 phosphorylation at S307 in endothelial cells, hepatocytes, skeletal muscle cells, and vascular smooth muscle cells. Like the kinase-dead LKB1 D194A mutant (mutation of Asp194 to Ala), the constitutively nucleus-localized LKB1 SL26 mutant and the LKB1 S307A mutant (Ser307 to Ala) exhibit a decreased association with STRAD alpha. Interestingly, the PKC-zeta consensus sequence surrounding LKB1 S307 is disrupted in the LKB1 SL26 mutant, thus providing a likely molecular explanation for this mutation causing LKB1 dysfunction. In addition, LKB1 nucleocytoplasmic transport and AMPK activation in response to peroxynitrite are markedly reduced by pharmacological inhibition of CRM1, which normally facilitates nuclear export of LKB1-STRAD complexes. In comparison to the LKB1 wild type, the S307A mutant complexes show reduced association with CRM1. Finally, adenoviral overexpression of wild-type LKB1 suppresses, while the LKB1 S307A mutant increases, tube formation and hydrogen peroxide-enhanced apoptosis in cultured endothelial cells. Taken together, our results suggest that, in multiple cell types the signaling pathways engaged by several physiological stimuli converge upon PKC-zeta-dependent LKB1 phosphorylation at S307, which directs the nucleocytoplasmic transport of LKB1 and consequent AMPK activation.

LKB1 catalytic activity contributes to estrogen receptor alpha signaling

The tumor suppressor serine-threonine kinase LKB1 is mutated in Peutz-Jeghers syndrome (PJS) and in epithelial cancers, including hormone-sensitive organs such as breast, ovaries, testes, and prostate. Clinical studies in breast cancer patients show low LKB1 expression is related to poor prognosis, whereas in PJS, the risk of breast cancer is similar to the risk from germline mutations in breast cancer (BRCA) 1/BRCA2. In this study, we investigate the role of LKB1 in estrogen receptor alpha (ERalpha) signaling. We demonstrate for the first time that LKB1 binds to ERalpha in the cell nucleus in which it is recruited to the promoter of ERalpha-responsive genes. Furthermore, LKB1 catalytic activity enhances ERalpha transactivation compared with LKB1 catalytically deficient mutants. The significance of our discovery is that we demonstrate for the first time a novel functional link between LKB1 and ERalpha. Our discovery places LKB1 in a coactivator role for ERalpha signaling, broadening the scientific scope of this tumor suppressor kinase and laying the groundwork for the use of LKB1 as a target for the development of new therapies against breast cancer.

The molecular mechanisms that underlie the tumor suppressor function of LKB1

Germline mutations of the LKB1 tumor suppressor gene result in Peutz-Jeghers syndrome (PJS) characterized by intestinal hamartomas and increased incidence of epithelial cancers. Inactivating mutations in LKB1 have also been found in certain sporadic human cancers and with particularly high frequency in lung cancer. LKB1 has now been demonstrated to play a crucial role in pulmonary tumorigenesis, controlling initiation, differentiation, and metastasis. Recent evidences showed that LKB1 is a multitasking kinase, with great potential in orchestrating cell activity. Thus far, LKB1 has been found to play a role in cell polarity, energy metabolism, apoptosis, cell cycle arrest, and cell proliferation, all of which may require the tumor suppressor function of this kinase and/or its catalytic activity. This review focuses on remarkable recent findings concerning the molecular mechanism by which the LKB1 protein kinase operates as a tumor suppressor and discusses the rational treatment strategies to individuals suffering from PJS and other common disorders related to LKB1 signaling.

LKB1 gene mutations in Japanese lung cancer patients

Mutation of the LKB1 gene (also known as STK11) is regarded as a cause of Peutz-Jeghers syndrome. In Caucasian patients, LKB1 somatic mutations occur in approximately one-third of lung adenocarcinomas. The aim of the present study was to examine the LKB1 gene in Japanese patients with lung cancer and to evaluate its clinical and pathological implications. We sequenced the LKB1 gene in 22 lung cancer cell lines and 100 Japanese patients with lung cancer (including 81 adenocarcinomas, 14 squamous cell carcinomas and five other histological types) who had undergone curative pulmonary resection. We also determined expression levels of the LKB1 gene by quantitative real-time reverse transcription-polymerase chain reaction and correlated these results with the clinical and pathological features of patients. Among the 22 cell lines, four had mutations and three of these were in adenocarcinoma cells. Of 100 primary lung cancers, only three had LKB1 gene mutations (3%). All of them were male smokers with adenocarcinomas. Hence, when confined to this subset of patients, the mutation frequency was 9% (3/33). No significant correlation was observed between the expression level of LKB1 and patient clinicopathological features. In conclusion, LKB1 gene mutations were relatively rare in Japanese patients with lung cancer compared with Caucasian patients. LKB1 gene mutations appear to be frequent in male, smoking patients of Caucasian origin, in contrast to EGFR or HER2 mutations that are frequent in non-smoking, female patients of Asian origin.

Do sporadic Peutz-Jeghers polyps exist? Experience of a large teaching hospital

Most types of sporadic gastrointestinal (GI) polyps vastly outnumber their syndromic counterparts. In contrast, the incidence of sporadic Peutz-Jeghers polyps (PJP) is unknown. We examined all potential PJP seen at our hospital over a 22-year (y) period to assess the incidence of sporadic PJP. The pathology database of a large hospital was searched for "Peutz-Jeghers polyp(s)," yielding 121 polyps from 38 patients. The polyps were reviewed by 3 pathologists to confirm the diagnosis. Clinical information to confirm or refute a diagnosis of Peutz-Jeghers syndrome (PJS) was collected. Of the 102 polyps included after histologic review, 94 polyps arose in patients meeting the World Health Organization criteria for PJS. These PJS polyps were eliminated from further analysis. Clinical information was obtained for the remaining 8 patients with potential "sporadic" PJP (1 to 50 y; mean=14 y; median=4 y). Of the 8 potential sporadic PJP, only 3 polyps from 3 patients had unequivocal PJP histologic features, all from the small intestine. All 3 patients had clinical histories suggesting syndromic PJP although they did not meet World Health Organization criteria, that is, 2 developed pancreatic cancer, 1 had bilateral "ovarian cystic masses" and a glomus tympanicum tumor, and 1 had strong family history of GI malignancies. The 5 remaining patients each had a colonic polyp with features suggestive, but not definitely diagnostic of, PJP. In these cases, prolapse lesions could not be excluded. One patient had a history of high-grade dysplasia in a tubulovillous adenoma in the colon at 53 years, but no family cancer history. Another had a family GI cancer history. Another had a history of pituitary adenoma at age 39, and the last had ductal breast carcinoma diagnosed 4 years before the discovery of the polyp. Our findings suggest that if sporadic PJP exist, they are extremely rare. Moreover, our data suggest that individuals with a single PJP may have a cumulative lifetime risk of cancer similar to those with the syndrome.

Molecular and clinical characteristics in 46 families affected with Peutz-Jeghers syndrome

Germline mutations of the tumor suppressor gene LKB1/STK11 are responsible for the Peutz-Jeghers syndrome (PJS), an autosomal-dominant disorder characterized by mucocutaneous pigmentation, hamartomatous polyps, and an increased risk of associated malignancies. In this study, we assessed the presence of pathogenic mutations in the LKB1/STK11 gene in 46 unrelated PJS families, and also carried genotype-phenotype correlation in regard of the development of cancer in 170 PJS patients belonging to these families. All LKB1/STK11 variants detected with single-strand conformational polymorphism were confirmed by direct sequencing, and those without LKB1/STK11 mutation were further submitted to Southern blot analysis for detection of deletions/rearrangements. Statistical analysis for genotype-phenotype correlation was performed. In 59% (27/46) of unrelated PJS cases, pathogenic mutations in the LKB1/STK11 gene, including 9 novel mutations, were identified. The new mutations were 2 splice site deletion-insertions, 2 missenses, 1 nonsense, and 4 abnormal splice sites. Genotype-phenotype analysis did not yield any significant differences between patients carrying mutations in LKB1/STK11 versus those without mutations, even with respect to primary biliary adenocarcinoma. This study presents the molecular characterization and cancer occurrence of a large cohort of PJS patients, increases the mutational spectrum of LKB1/STK11 allelic variants worldwide, and provides a new insight useful for clinical diagnosis and genetic counseling of PJS families.

Intratubular large cell hyalinizing sertoli cell neoplasia of the testis: a report of 8 cases of a distinctive lesion of the Peutz-Jeghers syndrome

We report the clinical and pathologic features of 8 boys with Peutz-Jeghers syndrome who had distinctive testicular lesions. The patients were 4 to 13 years of age (mean, 6.5 y), and all had gynecomastia, which was the presenting feature in 7. Physical examination demonstrated bilateral testicular enlargement in the absence of a discrete mass. Advanced bone age and elevated serum estradiol were demonstrated in 3 and 4 cases, respectively. Testicular biopsy, performed in all cases, usually showed no gross abnormality, but on microscopic examination there were patchily distributed clusters of expanded seminiferous tubules that contained large Sertoli cells with vacuolated to eosinophilic cytoplasm admixed with globular deposits of basement membrane that extended from a thickened peritubular basement membrane. Small, focal calcifications occurred in 3 cases; no invasive tumor was present in any of the cases. Follow-up was available in 5 patients after biopsy, and none showed evidence of progression at 10 months to 5 years (median, 4 y). Review of the previously reported cases of testicular lesions in Peutz-Jeghers patients verified a low frequency of invasive tumors (27%) and no known case with metastasis. The testicular lesions seen in patients with Peutz-Jeghers syndrome mostly represent multifocal intratubular neoplasia of large Sertoli cells with unique morphology distinct from other lesions such as the large cell calcifying Sertoli cell tumor and sex cord tumor with annular tubules. The process usually remains confined to the tubules for prolonged intervals (years), but it may occasionally progress to invasive large cell Sertoli cell tumors with or without associated calcification. This indolent course justifies management by careful follow-up, including ultrasound examination, rather than orchiectomy in the majority of cases. Orchiectomy is indicated when there is evidence of an invasive tumor and may be necessary to control hormonal manifestations.

A role for LKB1 gene in human cancer beyond the Peutz-Jeghers syndrome

Germline LKB1 mutations are responsible for Peutz-Jeghers syndrome (PJS). Tumors at several locations frequently arise in these patients, confirming that LKB1 is linked to cancer predisposition and is therefore a bona fide tumor-suppressor gene. In humans, the LKB1 gene is located in the short arm of chromosome 19, which is frequently deleted in many tumors of sporadic origin. However, LKB1 alterations in tumors other than those of PJS are rarely reported. Notably, this is not the case for non-small-cell lung cancer, where nearly half of the tumors harbor somatic and homozygous inactivating mutations in LKB1. The present review considers the frequency and pattern of LKB1 gene mutations in sporadic cancers of various origins, and the role of the encoded protein in cancer development.

Mitochondrial membrane permeabilization in cell death

Irrespective of the morphological features of end-stage cell death (that may be apoptotic, necrotic, autophagic, or mitotic), mitochondrial membrane permeabilization (MMP) is frequently the decisive event that delimits the frontier between survival and death. Thus mitochondrial membranes constitute the battleground on which opposing signals combat to seal the cell's fate. Local players that determine the propensity to MMP include the pro- and antiapoptotic members of the Bcl-2 family, proteins from the mitochondrialpermeability transition pore complex, as well as a plethora of interacting partners including mitochondrial lipids. Intermediate metabolites, redox processes, sphingolipids, ion gradients, transcription factors, as well as kinases and phosphatases link lethal and vital signals emanating from distinct subcellular compartments to mitochondria. Thus mitochondria integrate a variety of proapoptotic signals. Once MMP has been induced, it causes the release of catabolic hydrolases and activators of such enzymes (including those of caspases) from mitochondria. These catabolic enzymes as well as the cessation of the bioenergetic and redox functions of mitochondria finally lead to cell death, meaning that mitochondria coordinate the late stage of cellular demise. Pathological cell death induced by ischemia/reperfusion, intoxication with xenobiotics, neurodegenerative diseases, or viral infection also relies on MMP as a critical event. The inhibition of MMP constitutes an important strategy for the pharmaceutical prevention of unwarranted cell death. Conversely, induction of MMP in tumor cells constitutes the goal of anticancer chemotherapy.

Enhanced expression of LKB1 in breast cancer cells attenuates angiogenesis, invasion, and metastatic potential

LKB1 (also known as STK11) is a recently identified tumor suppressor gene whose mutation can lead to Peutz-Jeghers syndrome, which is characterized by gastrointestinal polyps and cancers of different organ systems. Approximately 30% of sporadic breast cancer samples express low levels of LKB1. This suggests that the LKB1 gene may be related to the tumorigenesis of breast cancer. We reintroduced LKB1 into MDA-MB-435 breast cancer cells that lack the LKB1 gene to investigate how overexpression of LKB1 affects tumor invasiveness and metastasis. Overexpression of the LKB1 protein in breast cancer cells resulted in significant inhibition of in vitro invasion. In vivo, LKB1 expression reduced tumor growth in the mammary fat pad, microvessel density, and lung metastasis. LKB1 overexpression was associated with down-regulation of matrix metalloproteinase-2, matrix metalloproteinase-9, vascular endothelial growth factor, and basic fibroblast growth factor mRNA and protein levels. Overexpression of the LKB1 protein in human breast cancer is significantly associated with a decrease in microvessel density. Our results indicate that LKB1 plays a negative regulatory role in human breast cancer, a finding that may lead to a new therapeutic strategy.

STK11 status and intussusception risk in Peutz-Jeghers syndrome

BACKGROUND

Peutz-Jeghers syndrome (PJS) is caused by germline STK11 mutations and characterised by gastrointestinal polyposis. Although small bowel intussusception is a recognised complication of PJS, risk varies between patients.

OBJECTIVE

To analyse the time to onset of intussusception in a large series of PJS probands.

METHODS

STK11 mutation status was evaluated in 225 PJS probands and medical histories of the patients reviewed.

RESULTS

135 (60%) of the probands possessed a germline STK11 mutation; 109 (48%) probands had a history of intussusception at a median age of 15.0 years but with wide variability (range 3.7 to 45.4 years). Median time to onset of intussusception was not significantly different between those with identified mutations and those with no mutation detected, at 14.7 years and 16.4 years, respectively (log-rank test of difference, chi(2) = 0.58, with 1df; p = 0.45). Similarly no differences were observed between patient groups on the basis of the type or site of STK11 mutation.

CONCLUSIONS

The risk of intussusception in PJS is not influenced by STK11 mutation status.

An updated mutation spectrum in an Australian series of PJS patients provides further evidence for only one gene locus

The genetic predisposition Peutz-Jeghers Syndrome (PJS) has been shown to be associated with mutations in the serine threonine kinase 11 (STK11) gene but only a proportion of probands have been shown to harbour changes in the gene. The remaining patients were proposed to be either associated with a second PJS gene or they harboured more cryptic mutations within the STK11 gene itself. With the introduction of the multiplex ligation probe amplification (MLPA) assay, large sequence losses or gains can be more readily identified. In this report we have screened 33 PJS patients from unrelated families, employing a combination of denaturing high-performance liquid chromatography, direct DNA sequencing and the MLPA assay to identify deleterious changes in the STK11 gene. The results revealed that 24 (73%) of patients diagnosed with PJS-harboured pathogenic mutations in the STK11 gene, including 10 (36%) with exonic or whole-gene deletions. No phenotypic differences were identified in patients harbouring large deletions in the STK11 gene compared to patients harbouring missense or nonsense mutations. Mutation analysis in PJS should include techniques such as MLPA to identify large exonic or whole-gene deletions and rearrangements. The high proportion of families with identifiable mutations in the STK11 gene using this range of techniques suggests that most, if not all PJS, is attributable to mutations in the STK11 gene, perhaps including as yet undiscovered changes in promoter or enhancer sequences or other cryptic changes.

The LKB1 tumor suppressor kinase in human disease

Inactivating germline mutations in the LKB1 gene underlie Peutz-Jeghers syndrome characterized by hamartomatous polyps and an elevated risk for cancer. Recent studies suggest the involvement of LKB1 also in more common human disorders including diabetes and in a significant fraction of lung adenocarcinomas. These observations have increased the interest towards signaling pathways of this tumor suppressor kinase. The recent breakthroughs in understanding the molecular functions of the LKB1 indicate its contribution as a regulator of cell polarity, energy metabolism and cell proliferation. Here we review how the substrates and cellular functions of LKB1 may be linked to Peutz-Jeghers syndrome and other diseases, and discuss how some of the molecular changes associated with altered LKB1 signaling might be used in therapeutic approaches.

Frequency and spectrum of cancers in the Peutz-Jeghers syndrome

BACKGROUND

Although an increased cancer risk in Peutz-Jeghers syndrome is established, data on the spectrum of tumors associated with the disease and the influence of germ-line STK11/LKB1 (serine/threonine kinase) mutation status are limited.

EXPERIMENTAL DESIGN

We analyzed the incidence of cancer in 419 individuals with Peutz-Jeghers syndrome, and 297 had documented STK11/LKB1 mutations.

RESULTS

Ninety-six cancers were found among individuals with Peutz-Jeghers syndrome. The risk for developing cancer at ages 20, 30, 40, 50, 60, and 70 years was 2%, 5%, 17%, 31%, 60%, and 85%, respectively. The most common cancers represented in this analysis were gastrointestinal in origin, gastroesophageal, small bowel, colorectal, and pancreatic, and the risk for these cancers at ages 30, 40, 50, and 60 years was 1%, 9%, 15%, and 33%, respectively. In women with Peutz-Jeghers syndrome, the risk of breast cancer was substantially increased, being 8% and 31% at ages 40 and 60 years, respectively. Kaplan-Meier analysis showed that cancer risks were similar in Peutz-Jeghers syndrome patients with identified STK11/LKB1 mutations and those with no detectable mutation (log-rank test of difference chi2 = 0.62; 1 df; P = 0.43). Furthermore, the type or site of STK11/LKB1 mutation did not significantly influence cancer risk.

CONCLUSIONS

The results from our study provide quantitative information on the spectrum of cancers and risks of specific cancer types associated with Peutz-Jeghers syndrome.

LKB1 exonic and whole gene deletions are a common cause of Peutz-Jeghers syndrome

BACKGROUND

LKB1/STK11 germline mutations cause Peutz-Jeghers syndrome (PJS). The existence of a second PJS locus is controversial, the evidence in its favour being families unlinked to LKB1 and the low frequency of LKB1 mutations found using conventional methods in several studies. Exonic and whole gene deletion or duplication events cannot be detected by routine mutation screening methods.

OBJECTIVE

To seek evidence for LKB1 germline deletions or duplications by screening patients meeting clinical criteria for PJS but without detected mutations on conventional screening.

METHODS

From an original cohort of 76 patients, 48 were found to have a germline mutation by direct sequencing; the remaining 28 were examined using multiplex ligation dependent probe amplification (MLPA) analysis to detect LKB1 copy number changes.

RESULTS

Deletions were found in 11 of the 28 patients (39%)--that is, 14% of all PJS patients (11/76). Five patients had whole gene deletions, two had the promoter and exon 1 deleted, and in one patient exon 8 was deleted. Other deletions events involved: loss of exons 2-10; deletion of the promoter and exons 1-3; and loss of part of the promoter. No duplications were detected. Nine samples with deletions were sequenced at reported single nucleotide polymorphisms to exclude heterozygosity; homozygosity was found in all cases. No MLPA copy number changes were detected in 22 healthy individuals.

CONCLUSIONS

These results lessen the possibility of a second PJS locus, as the detection rate of germline mutations in PJS patients was about 80% (59/76). It is suggested that MLPA, or a suitable alternative, should be used for routine genetic testing of PJS patients in clinical practice.