Germline mutations of the LKB1 (STK11) gene in Peutz-Jeghers patients

Germline mutations of the LKB1 (STK11) serine/threonine kinase gene (chromosome 19p13.3) cause Peutz-Jeghers syndrome, which is characterised by hamartomas of the gastrointestinal tract and typical pigmentation. Peutz-Jeghers syndrome carries an overall risk of cancer that may be up to 20 times that of the general population. Here, we report the results of a screen for germline LKB1 mutations by DNA sequencing in 12 Peutz-Jeghers patients (three sporadic and nine familial cases). Mutations were found in seven (58%) cases, in exons 1, 2, 4, 6, and 9. Five of these mutations, two of which are identical, are predicted to lead to a truncated protein (three frameshifts, two nonsense changes). A further mutation is an in frame deletion of 6 bp, resulting in a deletion of lysine and asparagine; the second of these amino acids is conserved between species. The seventh mutation is a missense change in exon 2, converting lysine to arginine, affecting non-conserved amino acids and of uncertain functional significance. Despite the fact that Peutz-Jeghers syndrome is usually an early onset disease with characteristic clinical features, predictive and diagnostic testing for LKB1 mutations will be useful for selected patients in both familial and non-familial contexts.     

STK11/LKB1 Peutz-Jeghers Gene Inactivation in Intraductal Papillary-Mucinous Neoplasms of the Pancreas

Despite the growing awareness of intraductal papillary-mucinous neoplasms (IPMNs) of the pancreas among clinicians, the molecular features of IPMNs have not been well characterized. Previous reports suggest that inactivation of the STK11/LKB1, a tumor-suppressor gene responsible for Peutz-Jeghers syndrome (PJS), plays a role in the pathogenesis of gastrointestinal hamartomas as well as several cancers, including pancreatic adenocarcinoma. Using polymerase chain reaction amplification of five microsatellite markers from the 19p13.3 region harboring the STK11/LKB1 gene, we analyzed DNA from 22 IPMNs for loss of heterozygosity (LOH). LOH at 19p13.3 was identified in 2 of 2 (100%) IPMNs from patients with PJS and 5 of 20 (25%) from patients lacking features of PJS (7 of 22, 32% overall). Sequencing analysis of the STK11/LKB1 gene in these IPMNs with LOH revealed a germline mutation in one IPMN that arose in a patient with PJS and a somatic mutation in 1 of the 20 sporadic IPMNs. None of the 22 IPMNs showed hypermethylation of the STK11/LKB1 gene. These results suggest that the STK11/LKB1 gene is involved in the pathogenesis of some IPMNs.     

Mutations in the human LKB1/STK11 gene

The human LKB gene (official HUGO symbol, STK11) encodes a serine/threonine protein kinase that is defective in patients with Peutz-Jeghers syndrome (PJS). PJS is an autosomal dominantly inherited syndrome characterized by hamartomatous polyposis of the gastrointestinal tract and mucocutaneous pigmentation. To date, 145 different germline LKB1 mutations have been reported. The majority of the mutations lead to a truncated protein product. One mutational hotspot has been observed. A 1-bp deletion and a 1-bp insertion at the mononucleotide repeat (C6 repeat, c.837-c.842) between the codons 279-281 have been found in six and seven unrelated PJS families, respectively. However, these mutations account only for approximately 7% of all mutations identified in the PJS families (13/193). A review of the literature provides a total of 40 different somatic LKB1 mutations in 41 sporadic tumors and seven cancer cell lines. Mutations occur particularly in lung and colorectal cancer. Most of the somatic LKB1 mutations result in truncation of the protein. A mutational hotspot seems to be a C6 repeat accounting for 12.5% of all somatic mutations (6/48). These results are concordant with the germline mutation spectrum. However, the proportion of the missense mutations seems to be higher among the somatic mutations (45%) than among the germline mutations (21%), and only seven of the mutations are exactly the same in both of the mutation types.     

LKB1／STK11研究进展

LKB1 STK1 1基因是PJS患者的主要致病基因 ,为一种肿瘤抑制基因 ,编码一种功能未知的丝氨酸 苏氨酸蛋白激酶。LKB1基因的失活性表达以低频率事件广泛存在于全身多种肿瘤中 ,并在细胞生长抑制和p53依赖性细胞凋亡 ,以及胚胎和血管发育中具有重要作用     

De novo germline mutation in the serine-threonine kinase STK11/LKB1 gene associated with Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is an autosomal dominant disease, characterized phenotypically by mucocutaneous pigmentation and hamartomatous polyposis. Affected patients are at an increased risk of developing gastrointestinal and other malignancies. Mutations in the STK11/LKB1 (LKB1) gene, which encodes for a serine-threonine kinase, have been identified as a genetic cause of PJS. Molecular analysis of the LKB1 gene in a simplex case of PJS revealed a substitution of cytosine (C) for guanine (G) at codon 246 in exon 6, resulting in the Tyr246X mutation. The nucleotide substitution leads to a premature stop codon at the 246 residue, predicting a truncated protein and presumed loss of kinase activity. Analysis of DNA from both parents of the PJS patient did not show this mutation, which is therefore a de novo mutation. We isolated DNA from microdissected gastrointestinal hamartomatous polyps in the PJS patient and investigated the loss of heterozygosity (LOH) at the LKB1 locus by real-time fluorescence polymerase chain reaction genotyping using a fluorescent resonance energy transfer technique. The results suggest a different mechanism from LOH in the formation of hamartomatous polyps.     

Functional analysis of LKB1/STK11 mutants and two aberrant isoforms found in Peutz-Jeghers Syndrome patients

Peutz-Jeghers Syndrome (PJS) is thought to be caused by mutations occurring in the widely expressed serine/threonine protein kinase named LKB1/STK11. Recent work has led to the identification of four mutants (R304W, I177N, K175-D176del, L263fsX286) and two novel aberrant LKB1/STK11 cDNA isoforms (r291-464del, r485-1283del) in a group of PJS Italian patients. Three of the four mutations only change 1 or 2 amino acids in the LKB1/STK11 catalytic domain. Here we demonstrate that all six LKB1/STK11 variants analysed are completely inactive in vitro as they were unable to autophosphorylate at Thr336, the major LKB1/STK11 autophosphorylation site, and to phosphorylate the p53 tumour suppressor protein. We also show that 5 out of the 6 variants are entirely localised in the nucleus in contrast to the wild type LKB1/STK11, which is detected in both the nucleus and cytoplasm. Finally we demonstrate that all 6 LKB1/STK11 variants, in contrast to wild type LKB1/STK11, are unable to suppress the growth of melanoma G361 cells. Taken together, these results demonstrate that the LKB1 mutations investigated in this study lead to the loss of serine/threonine kinase activity and are therefore likely to be the primary cause of PJS development in the patients that they were isolated from.     

Peutz-Jeghers families unlinked to STK11/LKB1 gene mutations are highly predisposed to primitive biliary adenocarcinoma

INTRODUCTION—Germline mutations of the STK11/LKB1 tumour suppressor gene (19p13.3) are responsible for Peutz-Jeghers syndrome (PJS), a rare genetic disorder, which is dominantly inherited. In addition to the typical hamartomatous gastrointestinal polyps and perioral pigmented lesions, PJS is also associated with the development of tumours in various sites. No specific follow up has yet been evaluated for gene carriers. Furthermore, genetic heterogeneity has been reported, which makes genetic counselling difficult.
METHODS—We report here the analysis of the STK11/LKB1 locus in a series of 34 PJS families, combining the search for mutations and rearrangements in the coding sequence, allele specific expression tests, and linkage studies.
RESULTS—Germline deleterious mutation of the STK11/LKB1 gene were identified in 70% of cases. The hypothesis of a second PJS locus was reinforced and PJS families could be divided into two groups on the basis of the presence or absence of an identified STK11/LKB1 alteration. Analysis of clinical data indicates that the cancer associated risk is markedly different in the two groups. PJS patients with no identified STK11/LKB1 mutation are at major risk for proximal biliary adenocarcinoma, an infrequent tumour in the general population.
CONCLUSION—Up to 30% of PJS patients are caused by mutation in an unidentified gene that confers high susceptibility to cancer development.


Keywords: Peutz-Jeghers disease; genetic heterogeneity; cancer predisposition; risk estimation     

Germline mutation screening of the STK11/LKB1 gene in familial breast cancer with LOH on 19p

The recently cloned STK11/LKB1 on chromosome 19p has been shown to be a new tumor suppressor gene. Mutations in the LKB1/STK11 gene on chromosome 19p account for most cases of Peutz-Jeghers syndrome (PJS), in which intestinal hamartomas are associated with elevated risks of several cancer types, including breast cancer. A previous study revealed that familial breast cancer is associated with loss of heterozygosity (LOH) on 19p. To establish whether germline mutations of STK11/LKB1 account for familial breast cancer, 22 patients from 14 breast cancer families with LOH on 19p and one PJS family were selected for screening for germline mutations of LKB1/STK11. A combination of polymerase chain reaction (PCR)-heteroduplex, single-strand conformational polymorphism (SSCP) analyses, Southern blot analysis and direct sequencing were used for mutation detection. No mutations were identified. Germline mutations of LKB1/STK11 did not contribute to breast cancer in these families.     

Mutation analysis of the STK11/LKB1 gene and clinical characteristics of an Australian series of Peutz-Jeghers syndrome patients

Peutz-Jeghers syndrome (PJS) is a rare cancer predisposition, which is characterized by the presence of hamartomatous polyposis and mucocutaneous pigmentation. A significant proportion of both familial and sporadic forms of this disorder are associated with mutations in the STK11 (serine/threonine kinase 11)/LKB1 gene. In this report we present a series of Australian PJS cases, which suggest that mutations in the STK11 gene do not account for many families or patients without a family history. The most likely explanation is either the presence of another susceptibility gene or genetic mosaicism in the non-familial patients.     

Somatic mutations in the STK11/LKB1 gene are uncommon in rare gynecological tumor types associated with Peutz-Jegher's syndrome

Peutz-Jegher's syndrome (PJS) is a rare autosomal dominant disorder characterized by mucocutaneous pigmentation, hamartomatous polyposis, and predisposition to benign and malignant tumors of the gastrointestinal tract, breast, ovary, uterine cervix, and testis. Germline-inactivating mutations in one allele of the STK11/LKB1 gene at chromosome 19p13.3 have been found in most PJS patients. Although ovarian sex cord tumors with annular tubules (SCTATs) and minimal deviation adenocarcinomas (MDAs) of the uterine cervix are very rare in the general population, both tumor types occur with increased frequency in women with PJS. An earlier report indicated that the 19p13.3 region containing the STK11 gene was affected by loss of heterozygosity (LOH) in nearly 50% of MDAs of the uterine cervix. We investigated the role of STK11 mutations and LOH of the 19p13.3 region in two PJS-associated SCTATs and in five SCTATs and eight MDAs of the uterine cervix, which occurred in patients lacking features of PJS (referred to here as "sporadic" cases). Germline mutations in the STK11 gene, accompanied by LOH of markers near the wild-type STK11 allele, were found in the two PJS-associated SCTATs. Somatic mutations in the coding region of STK11 were not found in any of the sporadic SCTATs or MDAs studied, although LOH of the 19p13.3 region was seen in three of eight MDAs. Our findings indicate that STK11, like other tumor suppressor genes, is affected by biallelic inactivation in gynecological tumors of PJS patients. In addition, although LOH of the 19p13.3 region was seen in sporadic MDAs, somatic STK11 mutations are rare. A yet-to-be-defined tumor suppressor gene in the 19p13.3 region may be the specific target of inactivation in these tumors.     

Novel mutations in the LKB1/STK11 gene in Dutch Peutz‐Jeghers families

The Peutz‐Jeghers syndrome (PJS) is a rare hereditary disorder in which gastrointestinal hamartomatous polyposis, mucocutaneous pigmentation, and a predisposition for developing cancer are transmitted in an autosomal dominant fashion. The recently identified LKB1/STK11 gene located at chromosome 19p13.3 is mutated in a number of PJS pedigrees. We performed mutation analysis in 19, predominantly Dutch, PJS families. In 12 of these families, we identified LKB1/STK11 mutations, none of which has been described before. These 12 novel LKB1/STK11 mutations consist of one nonsense mutation, three frameshift deletions, three frameshift insertions, two acceptor splice site mutations, and three missense mutations. In addition, we detected four polymorphisms in LKB1/STK11. In the remaining seven PJS families, we found no apparent abnormalities of the LKB1/STK11 gene, which could reflect the existence of locus heterogeneity in PJS. None of the mutations occurred in more than one family, and a number were demonstrated to have arisen de novo. The diverse array of mutations found, the apparent high mutation rate, as well as the existence of a possible second PJS locus, renders diagnostic or predictive genetic testing in individual patients difficult, although future identification of additional mutations or even gene(s) will help in increasing the yield of direct mutation analysis. Hum Mutat 13:476–481, 1999. © 1999 Wiley‐Liss, Inc.     

In situ analysis of LKB1/STK11 mRNA expression in human normal tissues and tumours

The LKB1/STK11 serine/threonine kinase is mutated in Peutz-Jeghers' syndrome and acts as a tumour suppressor. Using northern blotting and RT-PCR, LKB1 has been reported to be expressed widely in human adult tissues, although in Xenopus the expression of its homologue, XEEK1, is apparently restricted to early embryogenesis. In situ hybridization has been used to detect and localize LKB1 mRNA in a variety of adult and fetal tissues and tumours. The results show that LKB1 expression is widespread, but predominant in epithelia and in the seminiferous tubules of the testis. Expression is higher in fetal than in adult tissues. Expression also appears to be higher in many malignant tumours than in normal tissues or benign lesions, although some cancers have lost LKB1 expression, quite possibly as part of the process of tumourigenesis. These data are consistent with a widespread functional role for LKB1 in tissues of most types, and with a role for LKB1 in the pathogenesis of some sporadic cancers. LKB1 expression may primarily be related to the rate of cell replication.     

STK11/LKB1 germline mutations are not identified in most Peutz–Jeghers syndrome patients

Germline mutations of the STK11 gene mapped to chromosome 19p13.3 are responsible for Peutz Jeghers syndrome (PJS), a dominant disorder associated with characteristic gastrointestinal hamartomatous polyps and a predisposition to various cancers. We conducted a detailed investigation of germline STK11 alterations by protein truncation test and genomic DNA sequence analysis in ten unrelated PJS families. We identified a novel truncating deletion spanning STK11 exons 2-7 in a single patient and several known polymorphisms. Loss of heterozygosity studies in PJS polyps of four of these patients identified an allelic deletion of D19S886 in another patient. Our results suggest that STK11 mutations account for only a proportion of PJS cases.     

High proportion of large genomic STK11 deletions in Peutz-Jeghers syndrome

Germline mutations in the STK11 gene have been identified in 10-70% of patients with Peutz-Jeghers syndrome (PJS), an autosomal-dominant hamartomatous polyposis syndrome. A second locus was assumed in a large proportion of PJS patients. To date, STK11 alterations comprise mainly point mutations; only a small number of large deletions have been reported. We performed a mutation analysis for the STK11 gene in 71 patients. Of these, 56 met the clinical criteria for PJS and 12 were presumed to have PJS because of mucocutaneous pigmentation only or bowel problems due to isolated PJS polyps. No clinical information was available for the remaining three patients. By direct sequencing of the coding region of the STK11 gene, we identified point mutations in 37 of 71 patients (52%). We examined the remaining 34 patients by means of the multiplex ligation-dependent probe amplification (MLPA) method, and detected deletions in 17 patients. In four patients the deletion extended over all 10 exons, and in eight patients only the promoter region and exon 1 were deleted. The remaining deletions encompassed exons 2-10 (in two patients), exons 2-3, exons 4-5, or exon 8. When only patients who met the clinical criteria for PJS are considered, the overall mutation detection rate increases to 94% (64% point mutations and 30% large deletions). No mutation was identified in any of the 12 presumed cases. In conclusion, we found that approximately one-third of the patients who met the clinical PJS criteria exhibited large genomic deletions that were readily detectable by MLPA. Screening for point mutations and large deletions by direct sequencing or MLPA, respectively, increased the mutation detection rate in the STK11 gene up to 94%. There may be still other mutations in the STK11 gene that are not detectable by the methods applied here. Therefore, it is questionable whether a second PJS locus exists at all.     

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

Germline mutations in LKB1 have been reported to underlie familial Peutz-Jeghers syndrome (PJS) with intestinal hamartomatous polyps and an elevated risk of various neoplasms. To investigate the prevalence of LKB1 germline mutations in PJS more generally, we studied samples from 33 unrelated PJS patients including eight non-familial sporadic patients, 20 familial patients and five patients with unknown family history. Nineteen germline mutations were identified, 12 (60%) in familial and four (50%) in sporadic cases. LKB1 mutations were not detected in 14 (42%) patients, indicating that the existence of additional minor PJS loci cannot be excluded. LKB1 is predicted to encode a serine/threonine kinase. To demonstrate the putative Lkb1 kinase function and to study the consequences of LKB1 mutations in PJS and sporadic tumors, we have analyzed the kinase activity of wild-type and mutant Lkb1 proteins. Interestingly, while most of the small deletions or missense mutations resulted in loss-of-function alleles, one missense mutation (G163D) previously identified in a sporadic testicular tumor demonstrated severely impaired but detectable kinase activity.      

Mutations in STK11 gene in Czech Peutz-Jeghers patients

Background  

Peutz-Jeghers syndrome (PJS) is an autosomal dominant hereditary disease characterized by mucocutaneous pigmentation and gastrointestinal hamartomatous polyposis. The germline mutations in the serine/threonine kinase 11 (STK11) gene have been shown to be associated with the disease. Individuals with PJS are at increased risk for development of various neoplasms. The aim of the present study was to characterize the genotype and phenotype of Czech patients with PJS.     

Lack of STK11 gene expression in homozygous twins with Peutz-Jeghers syndrome

Clinical features of Peutz-Jeghers syndrome (PJS), an autosomal dominant disorder, include clusters of melanotic spots on the lips and limbs, polyposis of the gastrointestinal (GI) tract, and propensity to develop neoplasms of the GI tract, ovaries, testes, and other sites. We report twin sisters with PJS who were found to be homozygous, based on analyses of 9 DNA markers containing short tandem repeats (STR). Aberrant expression of a putative tumor suppressor gene, STK11, which encodes a serine threonine kinase, has been suggested as the etiologic factor in PJS. In both of the twin sisters with PJS, mRNA analyses by RT-PCR demonstrated a complete lack of STK11 gene expression. These results provide direct evidence that STK11 gene expression is abnormal in PJS. Detecting abnormal expression of the STK11 gene may serve as a molecular approach to the diagnosis of PJS and may facilitate genotype-phenotype correlations in PJS patients.