Mutations and allelic deletions of the MEN1 gene are associated with a subset of sporadic endocrine pancreatic and neuroendocrine tumors and not restricted to foregut neoplasms

Abstract

Endocrine pancreatic tumors (EPT) and neuroendocrine tumors (NET) occur sporadically and rarely in association with multiple endocrine neoplasia type 1 (MEN1). We analyzed the frequency of allelic deletions and mutations of the recently identified MEN1 gene in 53 sporadic tumors including 30 EPT and 23 NET (carcinoids) of different locations and types. Allelic deletion of the MEN1 locus was identified in 18/49 (36.7%) tumors (13/30, 43.3% in EPT and 5/19, 26.3% in NET) and mutations of the MEN1 gene were present in 8/52 (15.3%) tumors (4/30 (13.3%) EPT and 4/22 (18.1%) NET). The somatic mutations were clustered in the 5' region of the coding sequence and most frequently encompassed missense mutations. All tumors with mutations exhibited a loss of the other allele and a wild-type sequence of the MEN1 gene in nontumorous DNA. In one additional patient with a NET of the lung and no clinical signs or history of MEN1, a 5178-9G-->A splice donor site mutation in intron 4 was identified in both the tumor and blood DNA, indicating the presence of a thus far unknown MEN1 syndrome. In most tumor groups the frequency of allelic deletions at 11q13 was 2 to 3 times higher than the frequency of identified MEN1 gene mutations. Some tumor types, including rare forms of EPT and NET of the duodenum and small intestine, exhibited mutations more frequently than other types. Furthermore, somatic mutations were not restricted to foregut tumors but were also detectable in a midgut tumor (15.2% versus 16.6%). Our data indicate that somatic MEN1 gene mutations contribute to a subset of sporadic EPT and NET, including midgut tumors. Because the frequency of mutations varies significantly among the investigated tumor subgroups and allelic deletions are 2 to 3 times more frequently observed, factors other than MEN1 gene inactivation, including other tumor-suppressor genes on 11q13, may also be involved in the tumorigenesis of these neoplasms.

Figure 1.

Loss of heterozygosity analysis, PCR-SSCP analysis, and sequence analysis of the MEN1 gene in a sporadic neuroendocrine tumor of the lung (Cd1). Note that only one of the MEN1 genes (green spots, arrows) is detectable in the majority of tumor cells when compared with the chromosomes 11 (red dots) and that one allele of the three 11q13 markers is lost in the tumor DNA (T) when compared to normal tissue (N). The PCR-SSCP of exon 3 shows a band shift (line 4, red arrowheads) in the tumor DNA caused by a D172V missense mutation. In the sporadic endocrine pancreatic tumor P149 the LOH-FISH analysis shows only one signal of chromosome 11 (red) and the MEN1 locus (green), indicating the loss of one chromosome 11 in the majority of tumor cells. PCR-SSCP analysis reveals a band shift in exon 2 (line 3, red arrowheads) caused by an A50F missense mutation.