Daniel Lindberg

Genetic alterations on 3p, 11q13, and 18q in nonfamilial and MEN 1-associated pancreatic endocrine tumors.

Pancreatic endocrine tumors occur sporadically and as part of the multiple endocrine neoplasia type 1 (MEN 1) and von Hippel‐Lindau (VHL) syndromes. The MEN1 locus on 11q13 and a candidate tumor suppressor locus on 3p are known to be hemi‐ or homozygously mutated in a subset of these tumors. Chromosome arm 18q harbors the SMAD4/DPC4 tumor suppressor gene that is frequently deleted and inactivated in tumors of the exocrine pancreas. We have analyzed 22 nonfamilial and 16 MEN 1‐associated pancreatic endocrine tumors for loss of heterozygosity (LOH) at 3p, 11q13, and 18q. LOH at 3p was revealed in 45% and 36% of tumors from 31 patients with nonfamilial and MEN 1‐associated disease, respectively. The corresponding proportions for 11q13 were 55% and 91%, and for 18q 27% and 25%, respectively. A striking relation between LOH at 11q13 and 3p and a malignant phenotype was found for the nonfamilial tumors. None of the six benign tumors (all of them insulinomas) had allelic loss at 3p or 11q13, whereas 92% (P < 0.01) of the malignant tumors (including malignant insulinomas) had such deletions. Besides the 11q13 abnormality, more than half of the MEN 1‐associated tumors had additional genetic lesions affecting 3p or 18q. LOH analysis of several tumors from two MEN 1 patients suggested different clonal origin of the lesions. Sequencing of the SMAD4/DPC4 gene did not identify mutations in coding regions or at exon/intron boundaries in tumors with LOH at 18q. The data indicate involvement of tumor suppressor genes on 3p and 18q, in addition to the MEN1 gene at 11q13, in the tumorigenesis of both nonfamilial and MEN 1‐associated pancreatic endocrine tumors. Genes Chromosomes Cancer 26:258–264, 1999.

Stabilizing mutation of CTNNB1/beta-catenin and protein accumulation analyzed in a large series of parathyroid tumors of Swedish patients.

BackgroundAberrant accumulation of β-catenin plays an important role in a variety of human neoplasms. We recently reported accumulation of β-catenin in parathyroid adenomas from patients with primary hyperparathyroidism (pHPT). In CTNNB1 exon 3, we detected a stabilizing mutation (S37A) in 3 out of 20 analyzed adenomas. The aim of the present study was to determine the frequency and zygosity of mutations in CTNNB1 exon 3, and β-catenin accumulation in a large series of parathyroid adenomas of Swedish patients.ResultsThe mutation S37A (TCT > GCT) was detected by direct DNA sequencing of PCR fragments in 6 out of 104 sporadic parathyroid adenomas (5.8%). Taking our previous study into account, a total of 9 out of 124 (7.3%) adenomas displayed the same mutation. The mutations were homozygous by DNA sequencing, restriction enzyme cleavage, and gene copy number determination using the GeneChip 500 K Mapping Array Set. All tumors analyzed by immunohistochemistry, including those with mutation, displayed aberrant β-catenin accumulation. Western blotting revealed a slightly higher expression level of β-catenin and nonphosphorylated active β-catenin in tumors with mutation compared to those without. Presence of the mutation was not related to distinct clinical characteristics.ConclusionAberrant accumulation of β-catenin is very common in parathyroid tumors, and is caused by stabilizing homozygous mutation in 7.3% of Swedish pHPT patients.

Evaluation of CDKN2C/p18, CDKN1B/p27 and CDKN2B/p15 mRNA expression, and CpG methylation status in sporadic and MEN1-associated pancreatic endocrine tumours

Objective  Menin, encoded by the multiple endocrine neoplasia type 1 (MEN1) gene at 11q13, enhances transcription of the cyclin‐dependent kinase inhibitors (CDIs), CDKN2C (p18) and CDKN1B (p27) in mouse pancreatic islets, and inactivation of menin reduced CDKN2B (p15) expression in this mouse model. Here, we have compared the relative mRNA expression level and CpG methylation status of p18, p27 and p15 in 18 pancreatic endocrine tumours (PETs) with or without MEN1 gene mutations.

Cyclin-Dependent Kinase 4 (CDK4) Expression in Pancreatic Endocrine Tumors

Background/Aims: Pancreatic endocrine tumors (PETs) occur sporadically, in association with the multiple endocrine neoplasia type 1 (MEN1) and the von Hippel-Lindau syndromes. CDK4 is central to the cell cycle control in pancreatic β cells, and we have assessed whether CDK4 expression is deregulated in 18 human sporadic or familial PETs. Methods: Real-time quantitative PCR, immunohistochemistry, DNA sequencing, and Western blot analysis were used. Results: CDK4 mRNA was expressed in all PETs within the range of the arbitrary control. CDK4 protein was absent in normal pancreatic islets but distinctly expressed in all PETs as determined by immunohistochemistry. CDK4 expression was confirmed by Western blot analysis. No significant differences of CDK4 expression were observed between the groups of benign and malignant PETs or between tumors with or without MEN1 gene mutations. CDK4 expression was not due to gene amplification, and no mutations were identified in coding exons and RNA splice sites. c-Myc is known to be overexpressed in PETs and directly augments CDK4 expression in other cell types. Analysis of consecutive tissue sections for CDK4 and c-Myc showed overlapping homo- or heterogeneous immunostaining in all 18 PETs. Conclusion: We conclude that CDK4 and c-Myc is generally expressed in benign and malignant PETs, and regardless of MEN1 mutational status. Targeting of CDK4 may present an alternative to traditional chemotherapy of PETs in the future.

Mutational analyses of WNT7A and HDAC11 as candidate tumour suppressor genes in sporadic malignant pancreatic endocrine tumours.

Objective  We and others have reported loss of heterozygosity (LOH) on chromosome 3p25 in sporadic malignant pancreatic endocrine tumours (PETs). A common region of deletion on chromosome 3p25 contains numerous genes, including VHL and PPARγ, that have been excluded previously as candidate tumour suppressor genes by DNA sequencing analysis. We have analysed whether WNT7A or HDAC11 was biallelically inactivated in a group of well‐characterized PETs.