Two novel mutations and a new STK11/LKB1 gene isoform in Peutz-Jeghers patients

An atypical presentation of a pathogenic STK11 gene variant in siblings not fulfilling the clinical diagnostic criteria for Peutz-Jeghers Syndrome

OBJECTIVES

To report an atypical presentation of a pathogenic STK11 gene variant in siblings not fulfilling the clinical diagnostic criteria for Peutz-Jeghers Syndrome (PJS).

CASE PRESENTATION

Two siblings presented with prepubertal gynaecomastia and bilateral macro-orchidism, without mucocutaneous pigmentation or gastrointestinal symptoms. There was no family history of PJS. Sibling 1 had unilateral gynaecomastia. Sibling 2 had bilateral gynaecomastia, advanced bone age and bilateral testicular microlithiasis, not indicative of a large-cell calcifying Sertoli cell tumour. Genetics revealed a paternally inherited heterozygous pathogenic STK11 variant (910C>T) in both siblings. The diagnosis was confirmed following the identification of multiple intestinal polyps in their father.

CONCLUSIONS

Prepubertal gynaecomastia and prepubertal macro-orchidism (testicular enlargement without virilisation), always warrant endocrinological investigation, with PJS being an important differential diagnosis. Children may not fulfil the clinical criteria for a diagnosis of PJS at presentation. Genetic testing and gastroenterological investigation of parents may aid diagnosis.

Implications of Splicing Alterations in the Onset and Phenotypic Variability of a Family with Subclinical Manifestation of Peutz-Jeghers Syndrome: Bioinformatic and Molecular Evidence

Peutz–Jeghers Syndrome (PJS) is an autosomal dominant pre-cancerous disorder caused in 80–90% of cases by germline mutations in the tumor suppressor gene STK11. We performed a genetic test of the STK11 gene in two Italian young sisters suspected of PJS, since they showed pathognomonic café au lait spots in absence of other symptoms and familiarity. Sequencing of all exons of STK11 gene and other 8 genes, suggested to be involved in hamartomatous syndromes, (PTEN, BMPR1A, SDHB, SDHD, SMAD4, AKT1, ENG, PIK3CA) led to the identification in both the probands of a novel germline silent mutation named c.597 G>A, hitting the last nucleotide of exon 4. Interestingly, genetic testing of the two probands’ parents showed that their unaffected father was carrier of this mutation. Moreover, he carried a second intronic substitution named c.465-51 T>C (rs2075606) which was not inherited by his daughters. We also observed that all the family members carrying the c.597 G>A mutation presented an aberrant splice variant of STK11 mRNA lacking exon 4. Furthermore, in silico analysis of c.465-51 T>C substitution showed that it may activate an Enhancer Splicing Element. Finally, qRT-PCR analysis of STK11 expression levels showed a slight downregulation of the wild type allele in the father and a 2-fold downregulation in the probands compared to the unaffected mother. Our results have led the hypothesis that the c.465-51 T>C intronic variant, which segregates with the wild type allele, could increase the splicing effectiveness of STK11 wild-type allele and compensate the side effect of the c.597 G>A splicing mutation, being responsible for the phenotypic variability observed within this family. This finding highlight the importance of RNA analysis in genetic testing, remarking that silent DNA variant can often be splicing variant involved in disease onset and progression. The identification of these variants has a crucial role to ensure an appropriate follow-up and cancer prevention in at-risk individuals.

Molecular cloning, polymorphism, and expression analysis of the LKB1/STK11 gene and its association with non-specific digestive disorder in rabbits

Liver kinase B1 (LKB1, also called STK11) encodes a serine/threonine kinase mutated in Peutz-Jeghers cancer syndrome characterized by gastrointestinal polyposis. Although LKB1 plays an important role in regulating energy homeostasis, cell growth, and metabolism via activation of adenosine monophosphate (AMP)-activated protein kinase (AMPK), nothing is known about its molecular characteristics and possible involvement in non-specific digestive disorder (NSDD) of rabbits. In the present study, we first cloned the coding sequence (CDS) of rabbit LKB1, which consisted of 1317 bp encoding 438 amino acids (AAs) and contained a highly conserved S_TKc kinase domain. Its deduced AA sequence showed 87.93-91.10% similarities with that of other species. In order to determine its involvement in NSDD, a NSDD rabbit model was built by a dietary fiber deficiency. The polymorphic site of LKB1 was then investigated in both healthy and NSDD groups using directing sequencing. Our results suggested that a synonymous variant site (840 c. G > C, CCC→CCG) existed in its S_TKc domain, which was associated with susceptibility to NSDD. Furthermore, qPCR was utilized to examine the mRNA levels of LKB1 and its downstream targets (i.e., PRKAA2, mTOR and NF-kβ) in several intestinal-related tissues from both healthy and NSDD groups. Significant changes in their expression levels between two groups indicated that impaired LKB1 signaling contributed to the intestinal abnormality in NSDD rabbits. Taken together, it could be concluded that LKB1 might be a potential candidate gene affecting the occurrence of rabbit NSDD. This information may serve as a basis for further investigations on rabbit digestive diseases.

Dissecting the role of polarity regulators in cancer through the use of mouse models

Loss of cell polarity and tissue architecture is a hallmark of aggressive epithelial cancers. In addition to serving as an initial barrier to tumorigenesis, evidence in the literature has pointed towards a highly conserved role for many polarity regulators during tumor formation and progression. Here, we review recent developments in the field that have been driven by genetically engineered mouse models that establish the tumor suppressive and context dependent oncogenic function of cell polarity regulators in vivo. These studies emphasize the complexity of the polarity network during cancer formation and progression, and reveal the need to interpret polarity protein function in a cell-type and tissue specific manner. They also highlight how aberrant polarity signaling could provide a novel route for therapeutic intervention to improve our management of malignancies in the clinic.

Downregulation of LKB1 suppresses Stat3 activity to promote the proliferation of esophageal carcinoma cells

The tumor suppressor liver kinase B1 (LKB1) encodes a serine/threonine kinase. The defect in LKB1 is the primary cause of Peutz-Jeghers syndrome (PJS). Inactivation of LKB1 by mutations or loss of LKB1 expression is associated with ovarian, lung and pancreatic cancer; however, the correlation between LKB1 and esophageal carcinoma remains unknown. Thus, quantitative PCR was performed to determine the clinical significance of LKB1 expression in 60 cases of esophageal cancer and its adjacent normal epithelium. LKB1 expression was observed to significantly downregulate the accompanying cancer progression, which was verified at the protein level by western blot analysis. Furthermore, the phosphorylated signal transducer and activator of transcription 3 (Stat3) level is reversibly associated with LKB1 expression. To determine the function of LKB1 in esophageal cancer, LKB1 expression is induced in TE1 esophageal cancer cells. The results show that LKB1 overexpression suppresses the proliferation of TE1 cells, downregulates the expression of cyclin D1 and Myc and represses Stat3 phosphorylation. Suppression of cell proliferation and cyclin D1 expression by LKB1 is fully inhibited by constitutively active Stat3C coexpression, suggesting that LKB1 inhibits esophageal cancer cell proliferation through suppression of Stat3 transaction. In conclusion, downregulation of LKB1 expression suppresses Stat3 activity that may promote tumor growth during esophageal cancer progression.

One novel deletion and one splicing mutation of the LKB1 gene in two Chinese patients with Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is an uncommon autosomal dominant inherited disease, characterized by the occurrence of gastrointestinal hamartomatous polyps and pigmentation of the lips, buccal mucosa, and digits. Patients with PJS have a significant risk for developing tumors in multiple organs. Germline mutation of the LKB1 gene, which encodes a serine/threonine kinase that acts as a tumor suppressor, has been identified as a cause of PJS. The current study included two Chinese PJS probands and their available family members, as well as 200 unrelated healthy controls for comparison. Genomic DNA was extracted from the peripheral blood of these subjects. The nine coding exons and flanking introns of the LKB1 gene in the two probands and their family members were amplified by polymerase chain reaction (PCR) and then directly sequenced. Mutations identified in the patients were checked in the 200 healthy controls by PCR and denaturing high-performance liquid chromatography. Total RNA was extracted from the patient who was found to have a dubious splice site mutation and his available family members. Reverse transcription PCR was performed to identify the abnormal splicing caused by the splice site mutation. Two types of mutations were detected in the two PJS families. One type was a previously unreported 30-base-pair deletion in exon 4, and the other was an intron mutation that affected splicing. None of the 200 controls had either of these two types of mutations. The results provide support that mutation of the LKB1 gene is a cause of PJS, and expand the spectrum of LKB1 gene mutations.

Signal-dependent regulation of gene expression as a target for cancer treatment: inhibiting p38alpha in colorectal tumors

In the last year, several evidences indicated that pharmacological manipulation of relevant signaling pathways could selectively affect gene expression to influence cell fate. These findings render of extreme importance the elucidation of how external stimuli are transduced to mediate chromatin modifications, resulting in a permissive or repressive environment for gene expression. These signaling cascades activate or repress the function of chromatin binding proteins that represent attractive pharmacological targets for human diseases. Actually, the closer the target is to chromatin, the more the transcriptional effect will be selective. Recent studies suggest that pharmacological manipulation of signaling pathways to modulate cell fate is indeed possible and that chromatin-associated kinases could represent an optimal target. The p38 MAPK is the prototype of this class of enzymes and its central role in the transcription process is evolutionary conserved. In this review we will focus on the possibility to inhibit p38alpha in colorectal cancer to arrest tumor progression and induce autophagic cell death.

LKB1-dependent signaling pathways

This review focuses on remarkable recent findings concerning the mechanism by which the LKB1 protein kinase that is mutated in Peutz-Jeghers cancer syndrome operates as a tumor suppressor. We discuss evidence that the cellular localization and activity of LKB1 is controlled through its interaction with a catalytically inactive protein resembling a protein kinase, termed STRAD, and an armadillo repeat-containing protein, named mouse protein 25 (MO25). The data suggest that LKB1 functions as a tumor suppressor by not only inhibiting proliferation, but also by exerting profound effects on cell polarity and, most unexpectedly, on the ability of a cell to detect and respond to low cellular energy levels. Genetic and biochemical findings indicate that LKB1 exerts its effects by phosphorylating and activating 14 protein kinases, all related to the AMP-activated protein kinase. The work described in this review shows how a study of an obscure cancer syndrome can uncover new and important regulatory pathways, relevant to the understanding of multiple human diseases.

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.

Ganglioglioma arising in a Peutz-Jeghers patient: a case report with molecular implications

The Peutz-Jeghers syndrome (PJS), an autosomal dominant disorder caused by inactivating germline mutations in the serine-threonine kinase gene LKB1, is characterized by mucocutaneous pigmentation, multiple gastrointestinal hamartomatous polyps, and by an increased risk for developing tumors involving several different organs. To date, no brain tumors have been described in PJS patients. In this report, we describe a case of ganglioglioma in a 22-year-old PJS patient. Single-strand conformation polymorphism-Heteroduplex analysis evidenced an abnormal pattern in exon 6 of the LKB1 gene. Sequencing revealed a 821delTinsAC mutation creating a termination codon 29 nucleotides downstream (p.Asn274fsX11). RNA studies showed an out-of-frame LKB1 isoform derived from the wild type allele and generated by exon 4 skipping. Since the LKB1 gene is expressed in the fetal and adult brain, our data would suggest its likely involvement in the pathogenesis of a subset of gangliogliomas.

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 in the humanLKB1/STK11gene

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.

An LKB1 AT-AC intron mutation causes Peutz-Jeghers syndrome via splicing at noncanonical cryptic splice sites

Peutz-Jeghers syndrome (PJS) is an autosomal dominant disorder associated with gastrointestinal polyposis and an increased cancer risk. PJS is caused by germline mutations in the tumor suppressor gene LKB1. One such mutation, IVS2+1A>G, alters the second intron 5' splice site, which has sequence features of a U12-type AT-AC intron. We report that in patients, LKB1 RNA splicing occurs from the mutated 5' splice site to several cryptic, noncanonical 3' splice sites immediately adjacent to the normal 3' splice site. In vitro splicing analysis demonstrates that this aberrant splicing is mediated by the U12-dependent spliceosome. The results indicate that the minor spliceosome can use a variety of 3' splice site sequences to pair to a given 5' splice site, albeit with tight constraints for maintaining the 3' splice site position. The unusual splicing defect associated with this PJS-causing mutation uncovers differences in splice-site recognition between the major and minor pre-mRNA splicing pathways.

Cardiac work up in primary renal hypokalaemia-hypomagnesaemia (Gitelman syndrome)

BACKGROUND

Potassium and magnesium depletion prolongs the duration of the action potential of the cardiomyocyte, which predisposes to ventricular arrhythmias. In addition, potassium or magnesium depletion might impair cardiac performance and facilitate coronary artery thrombosis.

METHODS

Continuous 24-h ambulatory electrocardiographic monitoring, treadmill exercise testing and echocardiography were assessed in 21 patients (11 female and 10 male subjects, aged 5.9-39, median 19 years) with primary renal hypokalaemia-hypomagnesaemia.

RESULTS

The QT interval corrected for heart rate was normal (between 379 and 430 ms) in 10 and slightly to moderately prolonged in the remaining 11 patients (between 446 and 509 ms). Plasma potassium, magnesium and bicarbonate were similar in patients with normal and in those with prolonged QT interval. Continuous ambulatory electrocardiography over 24 h and exercise testing did not detect significant abnormalities of cardiac rhythm or features suggestive of myocardial ischaemia. Finally, echocardiographic and Doppler assessment failed to reveal any abnormalities in myocardial morphology and function.

CONCLUSION

The QT interval is often prolonged in primary renal hypokalaemia-hypomagnesaemia, confirming that potassium and magnesium depletion tends to prolong the duration of the action potential of the cardiomyocyte. The results of continuous ambulatory electrocardiography, exercise testing and echocardiography are reassuring. Nonetheless, we assume that dangerous cardiac arrhythmias may occur in patients with very severe hypokalaemia, during medication with drugs that prolong the QT interval or in the context of short-term non-adherence to the recommended regimen of care.

Mapping of a translocation breakpoint in a Peutz-Jeghers hamartoma to the putative PJS locus at 19q13.4 and mutation analysis of candidate genes in polyp andSTK11-negative PJS cases

Germ-line mutations in the serine-threonine kinase gene STK11 (LKB1) cause Peutz-Jeghers syndrome (PJS), a rare autosomal dominantly inherited disease, characterized by hamartomatous polyposis and mucocutaneous pigmentation. STK11 mutations only account for about half of PJS cases, and a second disease locus has been proposed at chromosome segment 19q13.4 on the basis of genetic linkage analysis in one family. We identified a t(11;19)(q13;q13.4) in a PJS polyp arising from the small bowel in a female infant age 6 days. Because the breakpoint in 19q13.4 may disrupt the putative PJS disease gene mapping to this region, we mapped the breakpoint and analyzed DNA from the case and a series of STK11-negative PJS cases. Using two-color interphase fluorescence in situ hybridization, the breakpoint region was refined to a 0.5-Mb region within 19q13.4. Eight candidate genes mapping to the breakpoint region--U2AF2, EPN1, NALP4, NALP11, NALP5, ZNF444, PTPRH, and KIAA1811--were screened for mutations in germ-line and polyp DNA from the case and from 15 PJS cases that did not harbor germ-line STK11 mutations. No pathogenic mutations in the candidate genes were identified. This report provides further evidence of the existence of a second PJS disease locus at 19q13.4 and excludes involvement of eight candidate genes.

MO25alpha/beta interact with STRADalpha/beta enhancing their ability to bind, activate and localize LKB1 in the cytoplasm

Mutations in the LKB1 protein kinase result in the inherited Peutz Jeghers cancer syndrome. LKB1 has been implicated in regulating cell proliferation and polarity although little is known about how this enzyme is regulated. We recently showed that LKB1 is activated through its interaction with STRADalpha, a catalytically deficient pseudokinase. Here we show that endogenous LKB1-STRADalpha complex is associated with a protein of unknown function, termed MO25alpha, through the interaction of MO25alpha with the last three residues of STRADalpha. MO25alpha and STRADalpha anchor LKB1 in the cytoplasm, excluding it from the nucleus. Moreover, MO25alpha enhances the formation of the LKB1-STRADalpha complex in vivo, stimulating the catalytic activity of LKB1 approximately 10-fold. We demonstrate that the related STRADbeta and MO25beta isoforms are also able to stabilize LKB1 in an active complex and that it is possible to isolate complexes of LKB1 bound to STRAD and MO25 isoforms, in which the subunits are present in equimolar amounts. Our results indicate that MO25 may function as a scaffolding component of the LKB1-STRAD complex and plays a crucial role in regulating LKB1 activity and cellular localization.

Complexes between the LKB1 tumor suppressor, STRAD alpha/beta and MO25 alpha/beta are upstream kinases in the AMP-activated protein kinase cascade

Background

The AMP-activated protein kinase (AMPK) cascade is a sensor of cellular energy charge that acts as a 'metabolic master switch' and inhibits cell proliferation. Activation requires phosphorylation of Thr172 of AMPK within the activation loop by upstream kinases (AMPKKs) that have not been identified. Recently, we identified three related protein kinases acting upstream of the yeast homolog of AMPK. Although they do not have obvious mammalian homologs, they are related to LKB1, a tumor suppressor that is mutated in the human Peutz-Jeghers cancer syndrome. We recently showed that LKB1 exists as a complex with two accessory subunits, STRADα/β and MO25α/β.

Results

We report the following observations. First, two AMPKK activities purified from rat liver contain LKB1, STRADα and MO25α, and can be immunoprecipitated using anti-LKB1 antibodies. Second, both endogenous and recombinant complexes of LKB1, STRADα/β and MO25α/β activate AMPK via phosphorylation of Thr172. Third, catalytically active LKB1, STRADα or STRADβ and MO25α or MO25β are required for full activity. Fourth, the AMPK-activating drugs AICA riboside and phenformin do not activate AMPK in HeLa cells (which lack LKB1), but activation can be restored by stably expressing wild-type, but not catalytically inactive, LKB1. Fifth, AICA riboside and phenformin fail to activate AMPK in immortalized fibroblasts from LKB1-knockout mouse embryos.

Conclusions

These results provide the first description of a physiological substrate for the LKB1 tumor suppressor and suggest that it functions as an upstream regulator of AMPK. Our findings indicate that the tumors in Peutz-Jeghers syndrome could result from deficient activation of AMPK as a consequence of LKB1 inactivation.

Eruptive melanotic macules and papules associated with adenocarcinoma

BACKGROUND

Malignancies may be associated with paraneoplastic cutaneous manifestations, including pigmentary disorders.

METHODS

The clinical findings were reviewed. Skin and tumor tissue samples were examined by routine histology, immunohistochemistry, and in one case also by electron microscopy.

RESULTS

Two patients developed diffuse melanotic macules and papules associated with visceral adenocarcinoma. One patient was a 64-year-old man with advanced carcinoma of the distal esophagus. The other was a 62-year-old man with metastatic pulmonary adenocarcinoma. The detection of the primary tumor in both patients was preceded by the rapid onset of melanotic macules and papules in the anogenital region and in one patient also around both nipples. The pigmented lesions were histologically characterized by a lentiginous melanocytic proliferation of large and heavily pigmented melanocytes associated with hyperpigmentation of adjacent keratinocytes. Both patients had been misdiagnosed as having epidermotropic metastatic malignant melanoma. None of them had prior, concurrent, or subsequent cutaneous or extracutaneous invasive melanoma. Both patients died of metastatic adenocarcinoma.

CONCLUSION

Eruptive melanotic macules and papules represent an under-recognized paraneoplastic syndrome. The cases illustrate a diagnostic pitfall for clinicians and pathologists unaware of this phenomenon.

LKB1, a protein kinase regulating cell proliferation and polarity

LKB1 is a serine-threonine protein kinase mutated in patients with an autosomal dominantly inherited cancer syndrome predisposing to multiple benign and malignant tumours, termed Peutz-Jeghers syndrome. Since its discovery in 1998, much research has focused on identification and characterisation of its cellular roles and analysing how LKB1 might be regulated. In this review we discuss exciting recent advances indicating that LKB1 functions as a tumour suppressor perhaps by controlling cell polarity. We also outline the current understanding of the molecular mechanisms by which LKB1 is regulated in vivo, through interaction with other proteins as well as by protein phosphorylation and prenylation.

Loss of Stk11/Lkb1 expression in pancreatic and biliary neoplasms

We have documented previously somatic mutations of STK11/LKB11, the gene responsible for Peutz-Jeghers syndrome (PJS), in a small proportion of sporadic pancreatic adenocarcinomas, intraductal papillary mucinous neoplasms (IPMNs), and biliary adenocarcinomas. In this report, we characterize the expression of Stk11, the protein product of the STK11 gene, in a larger series of pancreatic and biliary neoplasms. First, the specificity of the Stk11 antibody was established in 23 neoplasms (22 IPMNs and 1 biliary adenocarcinoma) with known STK11 gene status. Complete absence of labeling was seen in the neoplastic cells of 3 of the 3 (100%) cases with previously documented biallelic inactivation of the STK11 gene, whereas 16 of the 20 (80%) IPMNs, presumably with at least one wild-type STK11 gene, retained Stk11 expression in the neoplastic cells. The marked decrease or absence of Stk11 expression in four neoplasms with wild-type STK11 suggests that additional mechanisms may account for the lack of Stk11 expression. Subsequently, to further evaluate Stk11 expression in pancreatic and biliary neoplasms, tissue microarrays (TMAs) were constructed from a series of nearly 100 ductal adenocarcinomas and biliary neoplasms. Stk11 expression was lost in 4 of the 56 (7%) pancreatic adenocarcinomas and 1 of the 38 (2.6%) biliary cancers by immunohistochemistry; the absence of labeling was confirmed by repeated immunohistochemical labeling of complete tissue sections for the same cases. Thus, Stk11 expression is abrogated in a small proportion of pancreatic and biliary neoplasms. The inactivation of Stk11 in 27% (6/22) of IPMNs versus 7% (4/56) of pancreatic adenocarcinomas suggests genetic disparities in the pathogenesis of these closely related neoplasms. Immunohistochemical analysis for Stk11 expression may be a valid surrogate for genetic analysis of STK11 gene mutations in cancers.