J J Keller

Academisch Medisch Centrum Universiteit van Amsterdam, Amsterdam, North Holland, Netherlands

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Publications (15)82.68 Total impact

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    ABSTRACT: LKB1/STK11 germline inactivations are identified in the majority (66-94%) of Peutz-Jeghers syndrome (PJS) patients. Therefore, defects in other genes or so far unidentified ways of LKB1 inactivation may cause PJS. The genes encoding the MARK proteins, homologues of the Par1 polarity protein that associates with Par4/Lkb1, were analyzed in this study because of their link to LKB1 and cell polarity. The genetic defect underlying PJS was determined through analysis of both LKB1 and all four MARK genes. LKB1 point mutations and small deletions were identified in 18 of 23 PJS families using direct sequencing and multiplex ligation-dependent probe amplification analysis identified exon deletions in 3 of 23 families. In total, 91% of the studied families showed LKB1 inactivation. Furthermore, a MARK1, MARK2, MARK3 and MARK4 mutation analysis and an MARK4 quantitative multiplex polymerase chain reaction analysis to identify exon deletions on another eight PJS families without identified LKB1 germline mutation did not identify mutations in the MARK genes. LKB1 defects are the major cause of PJS and genes of the MARK family do not represent alternative PJS genes. Other mechanisms of inactivation of LKB1 may cause PJS in the remaining families.
    Clinical Genetics 01/2008; 72(6):568-73. · 3.94 Impact Factor
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    Gut 11/2007; 56(10):1475-6. · 10.73 Impact Factor
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    ABSTRACT: Patients with familial adenomatous polyposis (FAP) develop multiple premalignant colorectal adenomas. Untreated, one or more of these polyps will progress to colorectal carcinoma in middle-aged adults. Extra-intestinal manifestations of FAP are frequently observed and this combination has been called Gardner's syndrome. Oral and maxillofacial symptoms of FAP include an increased risk of jaw osteomas, odontomas and supernumerary or unerupted teeth. Early diagnosis of FAP is crucial and may be life saving. As oral signs usually precede gastrointestinal symptoms, the dentist may play an important role in the diagnosis of FAP.
    Oral Diseases 08/2007; 13(4):360-5. · 2.38 Impact Factor
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    ABSTRACT: 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. To analyse the time to onset of intussusception in a large series of PJS probands. STK11 mutation status was evaluated in 225 PJS probands and medical histories of the patients reviewed. 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. The risk of intussusception in PJS is not influenced by STK11 mutation status.
    Journal of Medical Genetics 09/2006; 43(8):e41. · 5.70 Impact Factor
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    ABSTRACT: LKB1 is a tumour suppressor gene that is associated with Peutz-Jeghers syndrome (PJS), a rare autosomal dominant cancer predisposition syndrome. However, germline mutations in the LKB1 gene are found in only about 60% of patients with PJS, suggesting the existence of a second PJS gene. The STRAD gene, encoding an LKB1 interacting protein that activates LKB1, which subsequently leads to polarisation of cells, is an interesting candidate for a second PJS gene and a potential tumour suppressor gene in sporadic carcinomas. The involvement of STRAD in 42 PJS associated tumours (sporadic lung, colon, gastric, and ovarian adenocarcinomas) was studied using loss of heterozygosity (LOH) analysis of eight microsatellite markers on chromosome 17, including TP53, BRCA1, and STRAD markers. Loss of the marker near the STRAD locus was seen in 13 of 29 informative cases, including all gastric adenocarcinomas. Specific LOH of the STRAD marker was found in four of 29 informative cases. For these patients all exons and exon-intron boundaries of the STRAD gene were sequenced, but no somatic mutations were identified. Furthermore, no germline STRAD mutations were found in 10 patients with PJS and family members without LKB1 germline mutation. Despite the frequent occurrence of LOH in the STRAD region, these results indicate that inactivation of the STRAD gene is not essential in the sporadic adenocarcinomas studied, although it is possible that STRAD may be inactivated in different ways. In addition, no evidence was found for the hypothesis that STRAD is a second PJS susceptibility gene.
    Journal of Clinical Pathology 11/2005; · 2.44 Impact Factor
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    M A Wijn, J J Keller, H S Brand
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    ABSTRACT: Patients suffering from familial adenomatosis polyposis develop multiple pre-malignant gastrointestinal polyps and are at high risk of developing colon cancer. In addition extra-intestinal manifestations are observed frequently. The combination of extra-intestinal manifestations and familial adenomatosis polyposis is named Gardner's syndrome. An early diagnosis of this disease is important because it could mean a better prognosis for the patient. This review describes the oral and maxillofacial symptoms of FAP, and its potential implications for dental treatment.
    Nederlands tijdschrift voor tandheelkunde 10/2005; 112(9):340-4.
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    Gut 08/2005; 54(7):1034-43. · 10.73 Impact Factor
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    M. A. Wijn, J. J. Keller, H. S. Brand
    01/2005;
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    ABSTRACT: Nonsteroidal anti-inflammatory drugs (NSAIDs) have chemopreventive potential against colorectal carcinomas (CRCs). Inhibition of cyclooxygenase (COX)-2 underlies part of this effect, although COX-2-independent mechanisms may also exist. Nonsteroidal anti-inflammatory drugs appear to inhibit the initial stages of the adenoma-carcinoma sequence, suggesting a link to the APC/beta-catenin/TCF pathway (Wnt-signalling pathway). Therefore, the effect of the NSAID sulindac on nuclear (nonphosphorylated) beta-catenin and beta-catenin/TCF-mediated transcription was investigated. Nuclear beta-catenin expression was assessed in pretreatment colorectal adenomas and in adenomas after treatment with sulindac from five patients with familial adenomatous polyposis (FAP). Also, the effect of sulindac sulphide on beta-catenin/TCF-mediated transcription was studied. Adenomas of FAP patients collected after treatment with sulindac for up to 6 months showed less nuclear beta-catenin expression compared to pretreatment adenomas of the same patients. Sulindac sulphide abrogated beta-catenin/TCF-mediated transcription in the CRC cell lines DLD1 and SW480, and decreased the levels of nonphosphorylated beta-catenin. As a result, the protein levels of the positively regulated TCF targets Met and cyclin D1 were downregulated after sulindac treatment. This study provides in vivo and in vitro evidence that nuclear beta-catenin localisation and beta-catenin/TCF-regulated transcription of target genes can be inhibited by sulindac. The inhibition of Wnt-signalling provides an explanation for the COX-2-independent mechanism of chemoprevention by NSAIDs.
    British Journal of Cancer 02/2004; 90(1):224-9. · 5.08 Impact Factor
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    ABSTRACT: Sulindac causes the reduction of adenomas in familial adenomatous polyposis (FAP) patients, but complete regression is unusual, and breakthrough of colorectal carcinoma during sulindac treatment has been described. The molecular features related to sulindac resistance are unknown. Therefore, we investigated molecular alterations in adenomas from FAP patients with complete adenoma regression on sulindac (responsive patients) and from FAP patients with sulindac-resistant adenomas (resistant patients). Fourteen baseline adenomas (removed before sulindac treatment) from six responsive patients were studied. Also, 9 baseline adenomas and 34 resistant adenomas (removed during sulindac treatment) from three resistant patients were analyzed. Using immunohistochemistry, we evaluated the expression of beta-catenin, cyclooxygenase-2 (Cox-2), p53, Bcl-2, and Bax. K-ras codon 12 mutations, loss of heterozygosity at 5q (APC locus), and microsatellite instability were studied with PCR-based techniques. There were no significant differences between baseline adenomas from sulindac-responsive and -resistant patients (P > 0.05). There was less loss of membranous beta-catenin staining and less nuclear beta-catenin accumulation in resistant adenomas compared with baseline adenomas from the same (sulindac-resistant) patients (P < 0.01) or baseline adenomas from responsive patients (P < 0.01). Epithelial Cox-2 expression was less, though not significant, in resistant adenomas compared with baseline adenomas from resistant patients, but was significantly less in baseline adenomas from responsive patients (P < 0.01). K-ras mutations were found in 8 of 34 resistant adenomas (24%) and in none of the baseline adenomas (P < 0.05). Stromal Cox-2 expression, staining of p53 and Bcl-2, and loss of heterozygosity at 5q were comparable in both groups. Loss of Bax staining and microsatellite instability were not found in any adenoma. Sulindac-resistant adenomas display less alteration in beta-catenin staining and less epithelial Cox-2 expression when compared with adenomas removed before sulindac treatment. K-ras mutations may contribute to sulindac-resistance. Continued research is needed to investigate molecular alterations related to sulindac resistance.
    Clinical Cancer Research 12/2001; 7(12):4000-7. · 7.84 Impact Factor
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    ABSTRACT: To investigate whether mutations in the STK11/LKB1 gene and genes implicated in the colorectal adenoma-carcinoma sequence are involved in Peutz-Jeghers syndrome (PJS) related tumorigenesis. Thirty nine polyps and five carcinomas from 17 patients (from 13 families) with PJS were analysed for loss of heterozygosity (LOH) at 19p13.3 (STK11/LKB1 gene locus), 5q21 (APC gene locus), 18q21-22 (Smad4 and Smad2 gene locus), and 17p13 (p53 gene locus), and evaluated for immunohistochemical staining of p53. In addition, mutational analysis of K-ras codon 12, APC, and p53 and immunohistochemistry for Smad4 expression were performed on all carcinomas. LOH at 19p was seen in 15 of the 39 polyps and in all carcinomas (n = 5). Interestingly, six of the seven polyps from patients with cancer had LOH, compared with nine of the 31 polyps from the remaining patients (p = 0.01). In one polyp from a patient without a germline STK11/LKB1 mutation, no LOH at 19p or at three alternative PJS candidate loci (19q, 6p, and 6q) was found. No LOH at 5q was observed. However, mutational analysis revealed an APC mutation in four of the five carcinomas. LOH at 17p was not seen in polyps or carcinomas; immunohistochemistry showed expression of p53 in one carcinoma and focal expression in three polyps. At subsequent sequence analysis, no p53 mutation was found. One carcinoma had an activating K-ras codon 12 mutation and another carcinoma showed 18q LOH; however, no loss of Smad4 expression was seen. These results provide further evidence that STK11/LKB1 acts as a tumour suppressor gene, and may be involved in the early stages of PJS tumorigenesis. Further research is needed to see whether LOH in PJS polyps could be used as a biomarker to predict cancer. Differences in molecular genetic alterations noted between the adenoma-carcinoma sequence and PJS related tumours suggest the presence of a distinct pathway of carcinogenesis.
    Journal of Clinical Pathology 03/2001; 54(2):126-31. · 2.44 Impact Factor
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    ABSTRACT: Sebaceous gland carcinomas (SGCs) are rare malignant skin tumors occurring sporadically or as a phenotypic feature of the Muir-Torre syndrome (MTS). A subset of patients with MTS have a variant of the hereditary nonpolyposis colorectal cancer syndrome caused by mutations in mismatch repair (MMR) genes, which lead to microsatellite instability (MSI). We evaluated the value of MSI and loss of expression of the MMR genes, hMLH-1 and hMSH-2, as a marker to identify and distinguish MTS from sporadic SGC. Using a nationwide pathology report database system, we identified patients with the MTS phenotype. SGCs from 10 MTS patients and the colorectal carcinomas from 3 additional MTS patients were collected. In addition, SGCs from eight patients without a history of visceral neoplasm were collected. MSI was detected in 9 of 13 MTS-associated tumors (69%) versus 0 of 8 sporadic SGCs (P = 0.002). Except for the age of onset of colorectal carcinoma [58 years in the MSI-positive group versus 69.8 years in the MSI-negative group (P = 0.17)], no differences were seen between the MSI-negative and the MSI-positive MTS patients. Loss of expression of hMLH-1 (n = 4) or hMSH-2 (n = 4) was found in MSI-positive patients only. MSI and loss of expression of MMR genes can be used as markers for MTS in patients with SGC. Consequently, MSI and loss of MMR gene expression in a patient presenting with SGC as the initial malignancy have important consequences for the patient and family. There are at least two variants of MTS with different molecular genetic mechanisms because 31% of the patients with the MTS phenotype had no MSI.
    Clinical Cancer Research 06/2000; 6(5):1784-9. · 7.84 Impact Factor
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    ABSTRACT: Sulindac regresses colorectal adenomas in patients with familial adenomatous polyposis (FAP), although the mechanism of polyp regression is unclear. To determine whether differences occur in alteration of rectal epithelial apoptotic index and expression of apoptosis related proteins in FAP patients treated with sulindac compared with placebo. Twenty one FAP patients; 12 had not undergone colectomy. Patients with FAP were treated with sulindac 150 mg orally twice a day for three months (n=10) or placebo (n=11). Colorectal polyp number was determined and biopsies of the normal rectal mucosa were performed before and after three months of treatment. Response to treatment and alteration of the apoptotic ratio (index in base of crypt divided by index in surface epithelium) were evaluated. Bcl-2, bax, p21/WAF-1, and p53 proteins were assessed semiquantitatively by immunohistochemistry. Significant decreases in polyp number and in the apoptotic ratio were seen in patients treated with sulindac compared with controls. The mean percentage change in polyp number from baseline was -46% in the sulindac group and +13% in the placebo group (p=0.005). Mean percentage change in the apoptotic ratio was -8% and +25% in the sulindac and placebo treated patients, respectively (p=0.004). No differences in expression or compartmentalisation of apoptosis related proteins were noted between treatment groups. Sulindac regression of colorectal adenomas is accompanied by alteration of the rectal epithelial apoptotic ratio with relative increase in apoptosis in surface cells compared with the deeper crypt. The utility of the apoptotic ratio as an intermediate biomarker for colorectal tumorigenesis deserves further study.
    Gut 01/2000; 45(6):822-8. · 10.73 Impact Factor
  • Gastroenterology 01/1998; 114. · 12.82 Impact Factor

Publication Stats

403 Citations
82.68 Total Impact Points

Institutions

  • 2001–2008
    • Academisch Medisch Centrum Universiteit van Amsterdam
      • Department of Pathology
      Amsterdam, North Holland, Netherlands
  • 2005–2007
    • Academisch Centrum Tandheelkunde Amsterdam
      Amsterdamo, North Holland, Netherlands
    • Johns Hopkins University
      • Department of Pathology
      Baltimore, MD, United States