Frequent deletion of chromosome 3 in malignant sporadic pancreatic endocrine tumors.

Pancreatic endocrine tumors (PETs) arise from neuroendocrine cells in and around the pancreas. As loss of heterozygosity (LOH) of chromosome 3 has been reported in sporadic PETs, we examined 16 sporadic PETs for LOH of 10 polymorphic DNA markers spanning both arms of chromosome 3. LOH was demonstrated in 4 of 8 (50%) sporadic PETs with hepatic metastasis, but in none of 8 sporadic PETs without hepatic involvement. The smallest common-deleted region (SCDR) mapped to 3q27-qter. Analysis of this data with the status of markers on chromosomes 1, 11, and MEN1 mutations in these 16 sporadic PETs revealed that chromosome 3q loss may be a late event in sporadic PET tumorigenesis. These data, combined with reports from other investigators, indicate that chromosome 3q27-qter may contain a tumor suppressor gene that's important in the tumorigenesis of sporadic PETs.

Menin localizes to chromatin through an ATR-CHK1 mediated pathway after UV-induced DNA damage.

BACKGROUND: Menin is the tumor suppressor protein product of the gene identified in MEN1 syndrome. Evidence suggests menin binds DNA and interacts with proteins implicated in DNA damage pathways. The canonical cellular response to UV-induced DNA damage involves activation of the ataxia-telangiectasia-mutated and Rad3-related (ATR) kinase pathway. MATERIALS AND METHODS: HEK293 cells were irradiated in a UV chamber. Menin's cellular location before and after UV irradiation was investigated by extracting four separate cellular components--a soluble, two chromatin and a nuclear matrix. To block the ATR pathway, we treated with 5 microM of caffeine for 1 h before irradiation. The ATR pathway was further investigated by transiently transfecting HEK293 cells with two mammalian CHK1 expression constructs--full length CHK1 and truncated active CHK1. RESULTS: A 24-h post UV-irradiation time course was studied and demonstrated menin concentration in the chromatin peaked at 4 h. At 4 h post-irradiation, menin concentration in the chromatin increased in a dose dependent manner and demonstrated a 2.8-fold maximal increase. HEK293 cells were pretreated with caffeine, an inhibitor of the ATR. Caffeine decreased menin localization to the chromatin after UV. Constitutively active CHK1 (1-365) transfection increased chromatin-bound menin, mimicking UV irradiation. CONCLUSIONS: Menin localizes to the chromatin after UV irradiation. Caffeine blocks menin localization to the chromatin after UV-irradiation. Over expressing active CHK1 (1-365) increased chromatin-bound menin, similar to UV. The data suggest menin localization to chromatin after UV irradiation is the result of an ATR-CHK1 dependent pathway.

Deletion of chromosome 1, but not mutation of MEN-1, predicts prognosis in sporadic pancreatic endocrine tumors.

Pancreatic endocrine tumors (PETs) may be sporadic or inherited in the multiple endocrine neoplasia type 1 (MEN-1) syndrome. The inherited form is caused by mutations of the MEN-1 gene, which functions as a tumor suppressor gene and maps to chromosome 11q13. These tumors tend to have a better prognosis than their sporadic counterparts, which often have mutations of the MEN-1 gene. Previous molecular analyses of sporadic PETs suggest a high frequency of loss of heterozygosity (LOH) at chromosome 1 as well as mutation of MEN-1. In this study we correlate abnormalities of MEN-1 and chromosome 1 LOH with the biological behavior of sporadic PETs. Loss of heterozygosity for markers at chromosome 11q13 and mutation of MEN-1 were equally frequent in tumors with or without liver metastases. Mutation of MEN-1 is more frequent in gastrinomas than in non-gastrinomas. Loss of heterozygosity for markers on chromosome 1 is more frequent in PETs with liver metastases. These results suggest a molecular tumor model in which there is a dichotomy in the development of benign and malignant PETs.